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1.  Arginine deiminase pathway is far more important than urease for acid resistance and intracellular survival in Laribacter hongkongensis: a possible result of arc gene cassette duplication 
BMC Microbiology  2014;14:42.
Laribacter hongkongensis is a Gram-negative, urease-positive bacillus associated with invasive bacteremic infections in liver cirrhosis patients and fish-borne community-acquired gastroenteritis and traveler’s diarrhea. Its mechanisms of adaptation to various environmental niches and host defense evasion are largely unknown. During the process of analyzing the L. hongkongensis genome, a complete urease cassette and two adjacent arc gene cassettes were found. We hypothesize that the urease cassette and/or the arc gene cassettes are important for L. hongkongensis to survive in acidic environment and macrophages. In this study, we tested this hypothesis by constructing single, double and triple non-polar deletion mutants of the urease and two arc gene cassettes of L. hongkongensis using the conjugation-mediated gene deletion system and examining their effects in acidic environment in vitro, in macrophages and in a mouse model.
HLHK9∆ureA, HLHK9∆ureC, HLHK9∆ureD and HLHK9∆ureE all exhibited no urease activity. HLHK9∆arcA1 and HLHK9∆arcA2 both exhibited arginine deiminase (ADI) activities, but HLHK9∆arcA1/arcA2 double deletion mutant exhibited no ADI activity. At pH 2 and 3, survival of HLHK9∆arcA1/arcA2 and HLHK9∆ureA/arcA1/arcA2 were markedly decreased (p < 0.001) but that of HLHK9∆ureA was slightly decreased (p < 0.05), compared to wild type L. hongkongensis HLHK9. Survival of HLHK9∆ureA/arcA1/arcA2 and HLHK9∆arcA1/arcA2 in macrophages were also markedly decreased (p < 0.001 and p < 0.01 respectively) but that of HLHK9∆ureA was slightly decreased (p < 0.05), compared to HLHK9, although expression of arcA1, arcA2 and ureA genes were all upregulated. Using a mouse model, HLHK9∆ureA exhibited similar survival compared to HLHK9 after passing through the murine stomach, but survival of HLHK9∆arcA1/arcA2 and HLHK9∆ureA/arcA1/arcA2 were markedly reduced (p < 0.01).
In contrast to other important gastrointestinal tract pathogens, ADI pathway is far more important than urease for acid resistance and intracellular survival in L. hongkongensis. The gene duplication of the arc gene cassettes could be a result of their functional importance in L. hongkongensis.
PMCID: PMC3936950  PMID: 24533585
Laribacter hongkongensis; Acid resistance; Arginine deiminase pathway; Microbe-host interaction
2.  MrkH, a Novel c-di-GMP-Dependent Transcriptional Activator, Controls Klebsiella pneumoniae Biofilm Formation by Regulating Type 3 Fimbriae Expression 
PLoS Pathogens  2011;7(8):e1002204.
Klebsiella pneumoniae causes significant morbidity and mortality worldwide, particularly amongst hospitalized individuals. The principle mechanism for pathogenesis in hospital environments involves the formation of biofilms, primarily on implanted medical devices. In this study, we constructed a transposon mutant library in a clinical isolate, K. pneumoniae AJ218, to identify the genes and pathways implicated in biofilm formation. Three mutants severely defective in biofilm formation contained insertions within the mrkABCDF genes encoding the main structural subunit and assembly machinery for type 3 fimbriae. Two other mutants carried insertions within the yfiN and mrkJ genes, which encode GGDEF domain- and EAL domain-containing c-di-GMP turnover enzymes, respectively. The remaining two isolates contained insertions that inactivated the mrkH and mrkI genes, which encode for novel proteins with a c-di-GMP-binding PilZ domain and a LuxR-type transcriptional regulator, respectively. Biochemical and functional assays indicated that the effects of these factors on biofilm formation accompany concomitant changes in type 3 fimbriae expression. We mapped the transcriptional start site of mrkA, demonstrated that MrkH directly activates transcription of the mrkA promoter and showed that MrkH binds strongly to the mrkA regulatory region only in the presence of c-di-GMP. Furthermore, a point mutation in the putative c-di-GMP-binding domain of MrkH completely abolished its function as a transcriptional activator. In vivo analysis of the yfiN and mrkJ genes strongly indicated their c-di-GMP-specific function as diguanylate cyclase and phosphodiesterase, respectively. In addition, in vitro assays showed that purified MrkJ protein has strong c-di-GMP phosphodiesterase activity. These results demonstrate for the first time that c-di-GMP can function as an effector to stimulate the activity of a transcriptional activator, and explain how type 3 fimbriae expression is coordinated with other gene expression programs in K. pneumoniae to promote biofilm formation to implanted medical devices.
Author Summary
Biofilms are surface-associated communities of microorganisms. Biofilm-associated bacteria are protected from host defenses and antibiotics and are the cause of many infections. Klebsiella pneumoniae is primarily a hospital-acquired bacterial pathogen that causes pneumonia, urinary tract infections and septicemia. Its success is related to its ability to form biofilms on medical devices, such as catheters. In K. pneumoniae, biofilm formation is mediated by type 3 fimbriae – hair-like, protein appendages extending out from the cell surface that adhere to surfaces. This study investigated how K. pneumoniae regulates the expression of these fimbriae. We identified a protein, MrkH, which behaves as a “biofilm switch” that turns on the expression of genes responsible for producing type 3 fimbriae. MrkH works by binding to regulatory regions of DNA nearby to these genes and initiates their expression. Importantly, MrkH binds to DNA strongly only when the protein is stimulated by a small molecule, c-di-GMP. Furthermore, we identified bacterial enzymes that either produce or break down c-di-GMP to control its concentration within the cell, and thus modulate MrkH activity. Understanding the molecular basis for these processes may lead to the development of therapeutic compounds, possibly for incorporation into medical device materials to inhibit biofilm formation and pathogenesis.
PMCID: PMC3161979  PMID: 21901098
3.  Structure and functions of exopolysaccharide produced by gut commensal Lactobacillus reuteri 100-23 
The ISME Journal  2011;5(7):1115-1124.
Lactobacillus reuteri strain 100-23 together with a Lactobacillus-free mouse model, provides a system with which the molecular traits underpinning bacterial commensalism in vertebrates can be studied. A polysaccharide was extracted from sucrose-containing liquid cultures of strain 100-23. Chemical analysis showed that this exopolysaccharide was a levan (β-2, 6-linked fructan). Mutation of the fructosyl transferase (ftf) gene resulted in loss of exopolysaccharide production. The ftf mutant was able to colonise the murine gastrointestinal tract in the absence of competition, but colonisation was impaired in competition with the wild type. Biofilm formation by the mutant on the forestomach epithelial surface was not impaired and the matrix between cells was indistinguishable from that of the wild type in electron micrographs. Colonisation of the mouse gut by the wild-type strain led to increased proportions of regulatory T cells (Foxp3+) in the spleen, whereas colonisation by the ftf mutant did not. Survival of the mutant in sucrose-containing medium was markedly reduced relative to the wild type. Comparison of the genomic ftf loci of strain 100-23 with other L. reuteri strains suggested that the ftf gene was acquired by lateral gene transfer early in the evolution of the species and subsequently diversified at accelerated rates. Levan production by L. reuteri 100-23 may represent a function acquired by the bacterial species for life in moderate to high-sucrose extra-gastrointestinal environments that has subsequently been diverted to novel uses, including immunomodulation, that aid in colonisation of the murine gut.
PMCID: PMC3146279  PMID: 21248858
Lactobacillus reuteri; exopolysaccharide; survival; regulatory T cells; evolution
4.  Protective Contributions against Invasive Streptococcus pneumoniae Pneumonia of Antibody and Th17-Cell Responses to Nasopharyngeal Colonisation 
PLoS ONE  2011;6(10):e25558.
The nasopharyngeal commensal bacteria Streptococcus pneumoniae is also a frequent cause of serious infections. Nasopharyngeal colonisation with S. pneumoniae inhibits subsequent re-colonisation by inducing Th17-cell adaptive responses, whereas vaccination prevents invasive infections by inducing antibodies to S. pneumoniae capsular polysaccharides. In contrast, protection against invasive infection after nasopharyngeal colonisation with mutant S. pneumoniae strains was associated with antibody responses to protein antigens. The role of colonisation-induced Th17-cell responses during subsequent invasive infections is unknown. Using mouse models, we show that previous colonisation with S. pneumoniae protects against subsequent lethal pneumonia mainly by preventing bacteraemia with a more modest effect on local control of infection within the lung. Previous colonisation resulted in CD4-dependent increased levels of Th17-cell cytokines during subsequent infectious challenge. However, mice depleted of CD4 cells prior to challenge remained protected against bacteraemia, whereas no protection was seen in antibody deficient mice and similar protection could be achieved through passive transfer of serum. Serum from colonised mice but not antibody deficient mice promoted phagocytosis of S. pneumoniae, and previously colonised mice were able to rapidly clear S. pneumoniae from the blood after intravenous inoculation. Thus, despite priming for a Th17-cell response during subsequent infection, the protective effects of prior colonisation in this model was not dependent on CD4 cells but on rapid clearance of bacteria from the blood by antibody-mediated phagocytosis. These data suggest that whilst nasopharyngeal colonisation induces a range of immune responses, the effective protective responses depend upon the site of subsequent infection.
PMCID: PMC3189185  PMID: 22003400
5.  The Bacterial Response Regulator ArcA Uses a Diverse Binding Site Architecture to Regulate Carbon Oxidation Globally 
PLoS Genetics  2013;9(10):e1003839.
Despite the importance of maintaining redox homeostasis for cellular viability, how cells control redox balance globally is poorly understood. Here we provide new mechanistic insight into how the balance between reduced and oxidized electron carriers is regulated at the level of gene expression by mapping the regulon of the response regulator ArcA from Escherichia coli, which responds to the quinone/quinol redox couple via its membrane-bound sensor kinase, ArcB. Our genome-wide analysis reveals that ArcA reprograms metabolism under anaerobic conditions such that carbon oxidation pathways that recycle redox carriers via respiration are transcriptionally repressed by ArcA. We propose that this strategy favors use of catabolic pathways that recycle redox carriers via fermentation akin to lactate production in mammalian cells. Unexpectedly, bioinformatic analysis of the sequences bound by ArcA in ChIP-seq revealed that most ArcA binding sites contain additional direct repeat elements beyond the two required for binding an ArcA dimer. DNase I footprinting assays suggest that non-canonical arrangements of cis-regulatory modules dictate both the length and concentration-sensitive occupancy of DNA sites. We propose that this plasticity in ArcA binding site architecture provides both an efficient means of encoding binding sites for ArcA, σ70-RNAP and perhaps other transcription factors within the same narrow sequence space and an effective mechanism for global control of carbon metabolism to maintain redox homeostasis.
Author Summary
The cofactor NAD+ plays a central role in energy conservation pathways, shuttling electrons from the oxidation of growth substrates to respiratory or fermentative pathways. To sustain catabolism and cellular ATP demand, an appropriate balance between the reduced and oxidized forms of NAD+ must be maintained. Our genome-scale analysis of the transcription factor ArcA provides insight into how this process is transcriptionally regulated in E. coli in the absence of O2. We found that ArcA mediates a previously unrealized comprehensive transcriptional repression of genes encoding proteins associated with oxidation of non-fermentable carbon sources. Through the repression of these pathways, oxidized NAD+ is effectively preserved for fermentation pathways, facilitating energy conservation and preserving a balance between the oxidized and reduced forms of NAD+ in the absence of aerobic respiration. In addition, we found that the majority of ArcA binding sites contain additional sequence elements beyond that required for binding of an ArcA dimer, providing novel insight into how ArcA and other members of the largest class of two component system-response regulators (OmpR/PhoB family) may achieve global regulation of gene expression.
PMCID: PMC3798270  PMID: 24146625
6.  Co-Infection Dynamics of a Major Food-Borne Zoonotic Pathogen in Chicken 
PLoS Pathogens  2007;3(11):e175.
A major bottleneck in understanding zoonotic pathogens has been the analysis of pathogen co-infection dynamics. We have addressed this challenge using a novel direct sequencing approach for pathogen quantification in mixed infections. The major zoonotic food-borne pathogen Campylobacter jejuni, with an important reservoir in the gastrointestinal (GI) tract of chickens, was used as a model. We investigated the co-colonisation dynamics of seven C. jejuni strains in a chicken GI infection trial. The seven strains were isolated from an epidemiological study showing multiple strain infections at the farm level. We analysed time-series data, following the Campylobacter colonisation, as well as the dominant background flora of chickens. Data were collected from the infection at day 16 until the last sampling point at day 36. Chickens with two different background floras were studied, mature (treated with Broilact, which is a product consisting of bacteria from the intestinal flora of healthy hens) and spontaneous. The two treatments resulted in completely different background floras, yet similar Campylobacter colonisation patterns were detected in both groups. This suggests that it is the chicken host and not the background flora that is important in determining the Campylobacter colonisation pattern. Our results showed that mainly two of the seven C. jejuni strains dominated the Campylobacter flora in the chickens, with a shift of the dominating strain during the infection period. We propose a model in which multiple C. jejuni strains can colonise a single host, with the dominant strains being replaced as a consequence of strain-specific immune responses. This model represents a new understanding of C. jejuni epidemiology, with future implications for the development of novel intervention strategies.
Author Summary
Pathogenic bacteria that can be transferred from animals to humans represent a highly potent human health hazard. Understanding the ecology of these pathogens in the animal host is of fundamental importance. A major analytical challenge, however, is the fact that individual animal hosts can be colonised by multiple strains of a given pathogen. We have addressed this challenge by developing a novel high-throughput approach for analyses of mixed strain infections. We chose Campylobacter jejuni colonisation of the chicken gastrointestinal (GI) tract as a model. C. jejuni is a major cause of food-borne disease in humans, and chickens are considered a main reservoir from which this bacterium may enter the food chain. We analysed the co-colonisation of seven C. jejuni strains in two groups of chickens with very different background GI microfloras. We found that mainly two of the C. jejuni strains colonised the chickens, with a shift in the dominant coloniser during the infection period. The C. jejuni colonisation pattern, however, was little affected by the dominating GI microflora. We propose a model where the chicken immune response is the important determinant for C. jejuni colonisation, and suggest that multiple strain colonisation could be a way of maintaining stable infections in the animal host. This new knowledge is very important for future development of novel intervention strategies to prevent C. jejuni from entering the human food chain.
PMCID: PMC2077904  PMID: 18020703
7.  Identification of Genes Induced In Vivo during Klebsiella pneumoniae CG43 Infection 
Infection and Immunity  2001;69(11):7140-7145.
A novel in vivo expression technology (IVET) was performed to identify Klebsiella pneumoniae CG43 genes that are specifically expressed during infection of BALB/c mice. The IVET employed a UDP glucose pyrophosphorylase (galU)-deficient mutant of K. pneumoniae which is incapable of utilizing galactose and synthesizing capsular polysaccharide, as demonstrated by its low virulence to BALB/c mice and a white nonmucoid colony morphology on MacConkey-galactose agar. By using a functional galU gene as the reporter, an IVE promoter could render the galU mutant virulent while maintaining the white nonmucoid colony phenotype. A total of 20 distinct sequences were obtained through the in vivo selection. Five of them have been identified previously as virulence-associated genes in other pathogens, while another five with characterized functions are involved in regulation and transportation of nutrient uptake, biosynthesis of isoprenoids, and protein folding. No known functions have been attributed to the other 10 sequences. We have also demonstrated that 2 of the 20 IVE genes turn on under iron deprivation, whereas the expression of another five genes was found to be activated in the presence of paraquat, a superoxide generator.
PMCID: PMC100105  PMID: 11598090
8.  Isolation of Genes Involved in Biofilm Formation of a Klebsiella pneumoniae Strain Causing Pyogenic Liver Abscess 
PLoS ONE  2011;6(8):e23500.
Community-acquired pyogenic liver abscess (PLA) complicated with meningitis and endophthalmitis caused by Klebsiella pneumoniae is an emerging infectious disease. To investigate the mechanisms and effects of biofilm formation of K. pneumoniae causing PLA, microtiter plate assays were used to determine the levels of biofilm formed by K. pneumoniae clinical isolates and to screen for biofilm-altered mutants from a transposon mutant library of a K. pneumoniae PLA-associated strain.
Methodology/Principal Findings
The biofilm formation of K. pneumoniae was examined by microtiter plate assay. Higher levels of biofilm formation were demonstrated by K. pneumoniae strains associated with PLA. A total of 23 biofilm-decreased mutants and 4 biofilm-increased mutants were identified. Among these mutants, a biofilm-decreased treC mutant displayed less mucoviscosity and produced less capsular polysaccharide (CPS), whereas a biofilm-increased sugE mutant displayed higher mucoviscosity and produced more CPS. The biofilm phenotypes of treC and sugE mutants also were confirmed by glass slide culture. Deletion of treC, which encodes trehalose-6-phosphate hydrolase, impaired bacterial trehalose utilization. Addition of glucose to the culture medium restored the capsule production and biofilm formation in the treC mutant. Transcriptional profile analysis suggested that the increase of CPS production in ΔsugE may reflect elevated cps gene expression (upregulated through rmpA) in combination with increased treC expression. In vivo competition assays demonstrated that the treC mutant strain was attenuated in competitiveness during intragastric infection in mice.
Genes important for biofilm formation by K. pneumoniae PLA strain were identified using an in vitro assay. Among the identified genes, treC and sugE affect biofilm formation by modulating CPS production. The importance of treC in gastrointestinal tract colonization suggests that biofilm formation contributes to the establishment and persistence of K. pneumoniae infection.
PMCID: PMC3155550  PMID: 21858144
9.  Acquisition of Pneumococci Specific Effector and Regulatory Cd4+ T Cells Localising within Human Upper Respiratory-Tract Mucosal Lymphoid Tissue 
PLoS Pathogens  2011;7(12):e1002396.
The upper respiratory tract mucosa is the location for commensal Streptococcus (S.) pneumoniae colonization and therefore represents a major site of contact between host and bacteria. The CD4+ T cell response to pneumococcus is increasingly recognised as an important mediator of immunity that protects against invasive disease, with data suggesting a critical role for Th17 cells in mucosal clearance. By assessing CD4 T cell proliferative responses we demonstrate age-related sequestration of Th1 and Th17 CD4+ T cells reactive to pneumococcal protein antigens within mucosal lymphoid tissue. CD25hi T cell depletion and utilisation of pneumococcal specific MHCII tetramers revealed the presence of antigen specific Tregs that utilised CTLA-4 and PDL-1 surface molecules to suppress these responses. The balance between mucosal effector and regulatory CD4+ T cell immunity is likely to be critical to pneumococcal commensalism and the prevention of unwanted pathology associated with carriage. However, if dysregulated, such responses may render the host more susceptible to invasive pneumococcal infection and adversely affect the successful implementation of both polysaccharide-conjugate and novel protein-based pneumococcal vaccines.
Author Summary
The S. pneumoniae bacteria is a major cause of disease (e.g. pneumonia and meningitis) particularly affecting infants. In most cases bacteria can colonise the nose without causing harm, however colonisation is thought to be a prerequisite of disease. With increasing age colonization and disease, rates gradually decrease which is likely due to the development of immunity to the pneumococcus with age. The CD4 T cells of the immune system may contribute to the defence against bacterial colonisation by producing factors that promote pneumococcal killing. Herein, we show that CD4 T cells reactive to pneumococci are found in greater numbers at the site of colonisation and gradually increase in their levels from infancy. However, at the peak of CD4 T cell responses from late teens, we detected the presence of regulatory T cells (Tregs) which suppressed anti-pneumococci CD4 T cell activity greatly. Our finding shows that pneumococcal reactive CD4 T cells selectively populate colonisation sites and increase with age as a result of ongoing bacterial exposure throughout life, inversely correlating with colonisation and disease rates. As factors that utilise CD4 T cells become increasingly advocated as potential preventative strategies against pneumococcal carriage and disease, the observed effect of Tregs must be considered.
PMCID: PMC3228808  PMID: 22144893
10.  Gastric colonisation with a restricted commensal microbiota replicates the promotion of neoplastic lesions by diverse intestinal microbiota in the Helicobacter pylori INS-GAS mouse model of gastric carcinogenesis 
Gut  2013;63(1):54-63.
Gastric colonisation with intestinal flora (IF) has been shown to promote Helicobacter pylori (Hp)-associated gastric cancer. However, it is unknown if the mechanism involves colonisation with specific or diverse microbiota secondary to gastric atrophy.
Gastric colonisation with Altered Schaedler’s flora (ASF) and Hp were correlated with pathology, immune responses and mRNA expression for proinflammatory and cancer-related genes in germ-free (GF), Hp monoassociated (mHp), restricted ASF (rASF; 3 species), and specific pathogen-free (complex IF), hypergastrinemic INS-GAS mice 7 months postinfection.
Male mice cocolonised with rASFHp or IFHp developed the most severe pathology. IFHp males had the highest inflammatory responses, and 40% developed invasive gastrointestinal intraepithelial neoplasia (GIN). Notably, rASFHp colonisation was highest in males and 23% developed invasive GIN with elevated expression of inflammatory biomarkers. Lesions were less severe in females and none developed GIN. Gastritis in male rASFHp mice was accompanied by decreased Clostridum species ASF356 and Bacteroides species ASF519 colonisation and an overgrowth of Lactobacillus murinus ASF361, supporting that inflammation-driven atrophy alters the gastric niche for GI commensals. Hp colonisation also elevated expression of IL-11 and cancer-related genes, Ptger4 and Tgf-β, further supporting that Hp infection accelerates gastric cancer development in INS-GAS mice.
rASFHp colonisation was sufficient for GIN development in males, and lower GIN incidence in females was associated with lower inflammatory responses and gastric commensal and Hp colonisation. Colonisation efficiency of commensals appears more important than microbial diversity and lessens the probability that specific gastrointestinal pathogens are contributing to cancer risk.
PMCID: PMC4023484  PMID: 23812323
11.  Analysis of the role of 13 major fimbrial subunits in colonisation of the chicken intestines by Salmonella enterica serovar Enteritidis reveals a role for a novel locus 
BMC Microbiology  2008;8:228.
Salmonella enterica is a facultative intracellular pathogen of worldwide importance. Over 2,500 serovars exist and infections in humans and animals may produce a spectrum of symptoms from enteritis to typhoid depending on serovar- and host-specific factors. S. Enteritidis is the most prevalent non-typhoidal serovar isolated from humans with acute diarrhoeal illness in many countries. Human infections are frequently associated with direct or indirect contact with contaminated poultry meat or eggs owing to the ability of the organism to persist in the avian intestinal and reproductive tract. The molecular mechanisms underlying colonisation of poultry by S. Enteritidis are ill-defined. Targeted and genome-wide mutagenesis of S. Typhimurium has revealed conserved and host-specific roles for selected fimbriae in intestinal colonisation of different hosts. Here we report the first systematic analysis of each chromosomally-encoded major fimbrial subunit of S. Enteritidis in intestinal colonisation of chickens.
The repertoire, organisation and sequence of the fimbrial operons within members of S. enterica were compared. No single fimbrial locus could be correlated with the differential virulence and host range of serovars by comparison of available genome sequences. Fimbrial operons were highly conserved among serovars in respect of gene number, order and sequence, with the exception of safA. Thirteen predicted major fimbrial subunit genes were separately inactivated by lambda Red recombinase-mediated linear recombination followed by P22/int transduction. The magnitude and duration of intestinal colonisation by mutant and parent strains was measured after oral inoculation of out-bred chickens. Whilst the majority of S. Enteritidis major fimbrial subunit genes played no significant role in colonisation of the avian intestines, mutations affecting pegA in two different S. Enteritidis strains produced statistically significant attenuation. Plasmid-mediated trans-complementation partially restored the colonisation phenotype.
We describe the fimbrial gene repertoire of the predominant non-typhoidal S. enterica serovar affecting humans and the role played by each predicted major fimbrial subunit in intestinal colonisation of the primary reservoir. Our data support a role for PegA in the colonisation of poultry by S. Enteritidis and aid the design of improved vaccines.
PMCID: PMC2644700  PMID: 19091138
12.  Regulation of the Arginine Deiminase System by ArgR2 Interferes with Arginine Metabolism and Fitness of Streptococcus pneumoniae 
mBio  2014;5(6):e01858-14.
Streptococcus pneumoniae is auxotrophic for arginine, and molecular analysis of the pneumococcal genome showed that the gene encoding an arginine-ornithine antiporter (ArcD) is organized in a cluster together with the arcABC genes encoding the arginine deiminase system (ADS) of pneumococci. The ADS consists of the arginine deiminase (AD), the catabolic ornithine carbamoyltransferase (cOCT), and the carbamate kinase (CK). Pneumococcal genomes contain three ArgR-type regulators (ArgR1, ArgR2, and AhrC) that are supposed to be involved in the regulation of arginine metabolism. Here, we identified ArgR2 of TIGR4 as the regulator of the ADS and ArcD. ArgR2 binds to promoter sequences of the arc operon, and the deficiency of ArgR2 in TIGR4 abrogates expression of the ADS, including the arginine-ornithine antiporter ArcD. Intranasal infection of mice and real-time bioimaging revealed that deletion of the arcABCDT genes attenuates TIGR4. However, the acute-pneumonia model and coinfection experiments indicated that the arginine-ornithine antiporter ArcD is essential to maintain fitness, while the deficiency of ADS enzymes has a minor impact on pneumococcal fitness under in vivo conditions. Strikingly, argR2 mutant TIGR4 outcompeted the wild type in the respiratory tract, suggesting an increase in fitness and further regulatory functions of ArgR2. In contrast to TIGR4, other pneumococci, such as D39, lacking expression of ArgR2, constitutively express the ADS with a truncated nonfunctional AD. On the basis of these results, we propose that the arginine-ornithine antiporter is essential to maintain pneumococcal fitness and that the genes of the ADS cluster are positively regulated in a strain-specific manner by ArgR2.
Pneumococci are the major etiologic agents of community-acquired pneumonia, causing more than 1.5 million deaths annually worldwide. These versatile pathogens are highly adapted to the nutrients provided by the host niches encountered. Physiological fitness is of major importance for colonization of the nasopharyngeal cavity and dissemination during invasive infections. This work identifies the regulator ArgR2 as the activator of the S. pneumoniae TIGR4 ADS and the arginine-ornithine transporter ArcD, which is needed for uptake of the essential amino acid arginine. Although ArgR2 activates ArcD expression and uptake of arginine is required to maintain pneumococcal fitness, the deficiency of ArgR2 increases TIGR4 virulence under in vivo conditions, suggesting that other factors regulated by ArgR2 counterbalance the reduced uptake of arginine by ArcD. Thus, this work illustrates that the physiological homeostasis of pneumococci is complex and that ArgR2 plays a key role in maintaining bacterial fitness.
PMCID: PMC4278536  PMID: 25538192
13.  Nebulised amphotericin B to eradicate Candida colonisation from the respiratory tract in critically ill patients receiving selective digestive decontamination: a cohort study 
Critical Care  2013;17(5):R233.
Colonisation of the lower respiratory tract with Candida species occurs in 25% of mechanically ventilated critically ill patients, and is associated with increased morbidity. Nebulised amphotericin B has been used to eradicate Candida as part of selective decontamination of the digestive tract (SDD) protocols, but its effectiveness is unknown. We aimed to determine the effectiveness of nebulised amphotericin B in eradicating Candida respiratory tract colonisation in patients receiving SDD.
We included consecutive mechanically ventilated patients during a four-year period. Microbiological screening was performed upon admission and twice weekly thereafter according to a standardised protocol. A colonisation episode was defined as the presence of Candida species in two consecutive sputum samples taken at least one day apart. To correct for time-varying bias and possible confounding, we used a multistate approach and performed time-varying Cox regression with adjustment for age, disease severity, Candida load at baseline and concurrent corticosteroid use.
Among 1,819 patients, colonisation with Candida occurred 401 times in 363 patients; 333 of these events were included for analysis. Decolonisation occurred in 51 of 59 episodes (86%) and in 170 of 274 episodes (62%) in patients receiving and not receiving nebulised amphotericin B, respectively. Nebulised amphotericin B was associated with an increased rate of Candida eradication (crude HR 2.0; 95% CI 1.4 to 2.7, adjusted HR 2.2; 95% CI 1.6 to 3.0). Median times to decolonisation were six and nine days, respectively. The incidence rate of ventilator-associated pneumonia, length of stay and mortality did not differ between both groups.
Nebulised amphotericin B reduces the duration of Candida colonisation in the lower respiratory tracts of mechanically ventilated critically ill patients receiving SDD, but data remain lacking that this is associated with a meaningful improvement in clinical outcomes. Until more evidence becomes available, nebulised amphotericin B should not be used routinely as part of the SDD protocol.
PMCID: PMC4056077  PMID: 24119707
14.  Gastrointestinal Candida colonisation promotes sensitisation against food antigens by affecting the mucosal barrier in mice 
Gut  2006;55(7):954-960.
Backgrounds and aims
Controversy still exists as to whether gastrointestinal colonisation by Candida albicans contributes to aggravation of atopic dermatitis. We hypothesised that Candida colonisation promotes food allergy, which is known to contribute to a pathogenic response in atopic dermatitis. We tested this using a recently established murine Candida colonisation model.
Candida colonisation in the gastrointestinal tract was established by intragastric inoculation with C albicans in mice fed a synthetic diet. To investigate sensitisation against food antigen, mice were intragastrically administered with ovalbumin every other day for nine weeks, and antiovalbumin antibody titres were measured weekly. To examine gastrointestinal permeation of food antigen, plasma concentrations of ovalbumin were measured following intragastric administration of ovalbumin.
Ovalbumin specific IgG and IgE titres were higher in BALB/c mice with Candida colonisation than in normal mice. Gastrointestinal permeation of ovalbumin was enhanced by colonisation in BALB/c mice. Histological examination showed that colonisation promoted infiltration and degranulation of mast cells. Candida colonisation did not enhance ovalbumin permeation in mast cell deficient W/Wv mice but did in congenic littermate control +/+ mice. Reconstitution of mast cells in W/Wv mice by transplantation of bone marrow derived mast cells restored the ability to increase ovalbumin permeation in response to Candida colonisation.
These results suggest that gastrointestinal Candida colonisation promotes sensitisation against food antigens, at least partly due to mast cell mediated hyperpermeability in the gastrointestinal mucosa of mice.
PMCID: PMC1856330  PMID: 16423887
Candida albicans ; food allergy; atopic dermatitis; mast cells
15.  Characterization of a novel chaperone/usher fimbrial operon present on KpGI-5, a methionine tRNA gene-associated genomic island in Klebsiella pneumoniae 
BMC Microbiology  2012;12:59.
Several strain-specific Klebsiella pneumoniae virulence determinants have been described, though these have almost exclusively been linked with hypervirulent liver abscess-associated strains. Through PCR interrogation of integration hotspots, chromosome walking, island-tagging and fosmid-based marker rescue we captured and sequenced KpGI-5, a novel genomic island integrated into the met56 tRNA gene of K. pneumoniae KR116, a bloodstream isolate from a patient with pneumonia and neutropenic sepsis.
The 14.0 kb KpGI-5 island exhibited a genome-anomalous G + C content, possessed near-perfect 46 bp direct repeats, encoded a γ1-chaperone/usher fimbrial cluster (fim2) and harboured seven other predicted genes of unknown function. Transcriptional analysis demonstrated expression of three fim2 genes, and suggested that the fim2A-fim2K cluster comprised an operon. As fimbrial systems are frequently implicated in pathogenesis, we examined the role of fim2 by analysing KR2107, a streptomycin-resistant derivative of KR116, and three isogenic mutants (Δfim, Δfim2 and ΔfimΔfim2) using biofilm assays, human cell adhesion assays and pair-wise competition-based murine models of intestinal colonization, lung infection and ascending urinary tract infection. Although no statistically significant role for fim2 was demonstrable, liver and kidney CFU counts for lung and urinary tract infection models, respectively, hinted at an ordered gradation of virulence: KR2107 (most virulent), KR2107∆fim2, KR2107∆fim and KR2107∆fim∆fim2 (least virulent). Thus, despite lack of statistical evidence there was a suggestion that fim and fim2 contribute additively to virulence in these murine infection models. However, further studies would be necessary to substantiate this hypothesis.
Although fim2 was present in 13% of Klebsiella spp. strains investigated, no obvious in vitro or in vivo role for the locus was identified, although there were subtle hints of involvement in urovirulence and bacterial dissemination from the respiratory tract. Based on our findings and on parallels with other fimbrial systems, we propose that fim2 has the potential to contribute beneficially to pathogenesis and/or environmental persistence of Klebsiella strains, at least under specific yet-to-be identified conditions.
PMCID: PMC3419637  PMID: 22520965
16.  Human Nasal Challenge with Streptococcus pneumoniae Is Immunising in the Absence of Carriage 
PLoS Pathogens  2012;8(4):e1002622.
Infectious challenge of the human nasal mucosa elicits immune responses that determine the fate of the host-bacterial interaction; leading either to clearance, colonisation and/or disease. Persistent antigenic exposure from pneumococcal colonisation can induce both humoral and cellular defences that are protective against carriage and disease. We challenged healthy adults intra-nasally with live 23F or 6B Streptococcus pneumoniae in two sequential cohorts and collected nasal wash, bronchoalveolar lavage (BAL) and blood before and 6 weeks after challenge. We hypothesised that both cohorts would successfully become colonised but this did not occur except for one volunteer. The effect of bacterial challenge without colonisation in healthy adults has not been previously assessed. We measured the antigen-specific humoral and cellular immune responses in challenged but not colonised volunteers by ELISA and Flow Cytometry. Antigen-specific responses were seen in each compartment both before and after bacterial challenge for both cohorts. Antigen-specific IgG and IgA levels were significantly elevated in nasal wash 6 weeks after challenge compared to baseline. Immunoglobulin responses to pneumococci were directed towards various protein targets but not capsular polysaccharide. 23F but not 6B challenge elevated IgG anti-PspA in BAL. Serum immunoglobulins did not increase in response to challenge. In neither challenge cohort was there any alteration in the frequencies of TNF, IL-17 or IFNγ producing CD4 T cells before or after challenge in BAL or blood. We show that simple, low dose mucosal exposure with pneumococci may immunise mucosal surfaces by augmenting anti-protein immunoglobulin responses; but not capsular or cellular responses. We hypothesise that mucosal exposure alone may not replicate the systemic immunising effect of experimental or natural carriage in humans.
Author Summary
Exposure to respiratory pathogens such as Streptococcus pneumoniae (pneumococcus) is a frequent event that can result in immediate clearance, nasal colonisation or disease for the host. Human and mouse studies have shown that natural colonisation is an immunising event. Colonisation is prevalent in children but rare in human adults (<10%), suggesting that despite high pneumococcal exposure adult mucosal defences are sufficient to prevent colonisation. We exposed healthy adults to pneumococci in the nose in order to achieve colonisation and mimic a natural colonisation event. In most volunteers, however, we were not able to obtain colonisation using this protocol. In exposed but not colonised volunteers we measured antibody and cellular responses in nose, lung and blood samples. The mucosal defences elicited during acute pneumococcal exposure are poorly described but these data will shed light on the mechanisms that prevent colonisation in healthy adults and inform future vaccine design. Live bacterial exposure increases specific antibody and innate responses at mucosal surfaces such as the nose and lung. Systemic responses were not increased. These data suggest that acute bacterial exposure per se augments mucosal but not systemic defences. Natural or experimental colonisation may be required for systemic immunisation.
PMCID: PMC3320601  PMID: 22496648
17.  Physiological Roles of ArcA, Crp, and EtrA and Their Interactive Control on Aerobic and Anaerobic Respiration in Shewanella oneidensis 
PLoS ONE  2010;5(12):e15295.
In the genome of Shewanella oneidensis, genes encoding the global regulators ArcA, Crp, and EtrA have been identified. All these proteins deviate from their counterparts in E. coli significantly in terms of functionality and regulon. It is worth investigating the involvement and relationship of these global regulators in aerobic and anaerobic respiration in S. oneidensis. In this study, the impact of the transcriptional factors ArcA, Crp, and EtrA on aerobic and anaerobic respiration in S. oneidensis were assessed. While all these proteins appeared to be functional in vivo, the importance of individual proteins in these two major biological processes differed. The ArcA transcriptional factor was critical in aerobic respiration while the Crp protein was indispensible in anaerobic respiration. Using a newly developed reporter system, it was found that expression of arcA and etrA was not influenced by growth conditions but transcription of crp was induced by removal of oxygen. An analysis of the impact of each protein on transcription of the others revealed that Crp expression was independent of the other factors whereas ArcA repressed both etrA and its own transcription while EtrA also repressed arcA transcription. Transcriptional levels of arcA in the wild type, crp, and etrA strains under either aerobic or anaerobic conditions were further validated by quantitative immunoblotting with a polyclonal antibody against ArcA. This extensive survey demonstrated that all these three global regulators are functional in S. oneidensis. In addition, the reporter system constructed in this study will facilitate in vivo transcriptional analysis of targeted promoters.
PMCID: PMC3011009  PMID: 21203399
18.  Structural and Functional Analysis of the Gene Cluster Encoding the Enzymes of the Arginine Deiminase Pathway of Lactobacillus sake 
Journal of Bacteriology  1998;180(16):4154-4159.
Lactobacillus sake can use arginine via the arginine deiminase (ADI) pathway. We designed degenerate primers based on an alignment of known sequences of ornithine transcarbamoylase (OTC)-encoding genes in order to amplify the L. sake counterpart sequences by PCR. Screening a genomic library of L. sake in λEMBL3 allowed us to isolate a clone containing a 10-kb L. sake genomic DNA insert. Sequence analysis revealed that the genes involved in arginine catabolism were clustered and encoded ADI (arcA), OTC (arcB), carbamate kinase (arcC), and a putative carrier with high similarity to the arginine/ornithine antiporter of Pseudomonas aeruginosa (arcD). Additionally, a putative transaminase-encoding gene (arcT) was located in this region. The genes followed the order arcA arcB arcC arcT arcD, which differs from that found in other microorganisms. arcA, arcB, arcC, and arcD mutants were constructed, and the ADI pathway was impaired in all of them. Transcriptional studies indicated that arcA gene is subject to catabolite repression, and under the conditions used, several transcripts could be detected, suggesting the existence of different initiation sites or processing of a larger mRNA.
PMCID: PMC107411  PMID: 9696763
19.  Population structure and characterization of viridans group streptococci (VGS) isolated from the upper respiratory tract of patients in the community 
The Ulster Medical Journal  2013;82(3):164-168.
A study was undertaken to examine the population structure of viridans group streptococci (VGS) isolated the upper respiratory tract of adult and paediatric patients within the community. VGS are common commensal bacterial inhabitants of the upper respiratory tract and valuable sentinel reporters of underlying antibiotic resistance (AR). Laboratory examination of the colonising VGS species may provide a valuable ecological description of the species isolated from the upper respiratory tract and their antibiotic susceptibility, including an estimation of the AR reservoir in this population. Freshly obtained nasal and oropharyngeal swabs from 84 patients were examined by selective conventional culture on Mitis-Salivarius agar and yielded 363 isolates of VGS. Sequence analyses of the rpnB and 16–23S rRNA ITS genes identified these isolates to belong to 10 species of VGS and included S. anginosus, S. australis, S. constellatus, S. infantis, S. mitis, S. oralis, S. parasanguinis, S. salivarius, S. sanguinis and S. vestibularis. The most frequent VGS organisms isolated was S. salivarius (282/363; 78.0%), followed by S. sanguinis (23/363; 6.3%), S. parasanguinis (21/363; 5.8%), S. mitis (18/363; 5.0%), S. anginosus (5/363; 1.4%), S. vestibularis (5/363; 1.4%), S. australis (3/363; 0.8%), S. oralis (3/363; 0.8%), S. infantis (1/363; 0.3%) and S. constellatus (1/363; 0.3%). All patients examined carried at least one VGS organism, where there were 17 combination patterns of carriage of the 10 species of VGS species isolated, where 54.2%, 37.3%, 7.2% and 1.2% of patients harboured one, two, three and four different VGS species, respectively. Antibiotic susceptibility was determined by standard disk diffusion assay testing against four classes of antibiotics, including the b-lactams [cefotaxime, cefuroxime], the tetracyclines [doxycycline], the fluoroquinolones [levofloxacin] and the macrolides [erythromycin]. Overall, there was no resistance to levofloxacin and cefuroxime, with limited resistance to cefotaxime (3.3%) and doxycycline (9.8%). Antibiotic resistance was highest in erythromycin, where 40.9% of isolates were resistant. S. vestibularis was the most antibiotic resistance of all VGS species examined (S. vestibularis v S. salivarius p=0.011), followed by S. anginosis. S. salivarius was the most antibiotic susceptible VGS species examined.
Overall, given their infrequency in causing infection, relatively few studies to date have attempted to examine their ecology in their preferred body niche, namely the upper respiratory tract. However, knowing their prevalence is becoming increasingly important in relation to their ability to exclude significant respiratory pathogens, including Streptococcus pneumoniae.
In conclusion, these data indicate that VGS colonisation of the upper respiratory tract in individuals within the community is dominated mainly with relatively antibiotic susceptible S. salivarius.
PMCID: PMC3913407  PMID: 24505152
20.  Transfer of antimicrobial resistance plasmids from Klebsiella pneumoniae to Escherichia coli in the mouse intestine 
Objectives and methods
Klebsiella pneumoniae is a nosocomial pathogen and is considered the most common Gram-negative bacterium that exhibits multiple antimicrobial resistances. In this study, the transfer of antimicrobial resistance genes from the clinical multiresistant K. pneumoniae MGH75875 isolate was assessed in vitro and in vivo in an intestinal colonization animal model. The ability to colonize and transfer was tested under different antimicrobial treatments. The frequency of the horizontal gene transfer was also examined in vitro.
The clinical isolate of K. pneumoniae colonized the intestine of mice at levels up to 109 cfu/g faeces in antimicrobial-treated mice. In mice without antimicrobial treatment, the strain quickly decreased to below the detection limit due to competitive exclusion by the indigenous mouse flora. Onset of antimicrobial treatment gave immediate rise to detectable levels of the strain in the faeces of up to 109 cfu/g faeces. The experiment clearly shows that the treatment selects resistant strains and gives advantages to colonize the gastrointestinal tract. Furthermore, high transfer frequency of different plasmids was observed during colonization of the mouse intestine. The blaSHV and blaTEM genotypes were transferred to both an indigenous recipient in the in vivo setting and to an MG1655 Escherichia coli recipient strain in vitro.
K. pneumoniae is an excellent colonizer of the intestine and is extremely promiscuous with respect to the transferability of its numerous plasmids. Antimicrobial treatment enhances the selection of resistant strains and results in an increase in the resistance gene pool, which ultimately raises the risk of spreading resistance genes.
PMCID: PMC2566516  PMID: 18703526
MGH78578; horizontal gene transfer; streptomycin-treated mice; gastrointestinal tract; indigenous flora; selective pressure
21.  Analysis of the ArcA regulon in anaerobically grown Salmonella enterica sv. Typhimurium 
BMC Microbiology  2011;11:58.
Salmonella enterica serovar Typhimurium (S. Typhimurium) is a Gram-negative pathogen that must successfully adapt to the broad fluctuations in the concentration of dissolved dioxygen encountered in the host. In Escherichia coli, ArcA (Aerobic Respiratory Control) helps the cells to sense and respond to the presence of dioxygen. The global role of ArcA in E. coli is well characterized; however, little is known about its role in anaerobically grown S. Typhimurium.
We compared the transcriptional profiles of the virulent wild-type (WT) strain (ATCC 14028s) and its isogenic arcA mutant grown under anaerobic conditions. We found that ArcA directly or indirectly regulates 392 genes (8.5% of the genome); of these, 138 genes are poorly characterized. Regulation by ArcA in S. Typhimurium is similar, but distinct from that in E. coli. Thus, genes/operons involved in core metabolic pathways (e.g., succinyl-CoA, fatty acid degradation, cytochrome oxidase complexes, flagellar biosynthesis, motility, and chemotaxis) were regulated similarly in the two organisms. However, genes/operons present in both organisms, but regulated differently by ArcA in S. Typhimurium included those coding for ethanolamine utilization, lactate transport and metabolism, and succinate dehydrogenases. Salmonella-specific genes/operons regulated by ArcA included those required for propanediol utilization, flagellar genes (mcpAC, cheV), Gifsy-1 prophage genes, and three SPI-3 genes (mgtBC, slsA, STM3784). In agreement with our microarray data, the arcA mutant was non-motile, lacked flagella, and was as virulent in mice as the WT. Additionally, we identified a set of 120 genes whose regulation was shared with the anaerobic redox regulator, Fnr.
We have identified the ArcA regulon in anaerobically grown S. Typhimurium. Our results demonstrated that in S. Typhimurium, ArcA serves as a transcriptional regulator coordinating cellular metabolism, flagella biosynthesis, and motility. Furthermore, ArcA and Fnr share in the regulation of 120 S. Typhimurium genes.
PMCID: PMC3075218  PMID: 21418628
22.  Large-Scale Identification of Virulence Genes from Streptococcus pneumoniae 
Infection and Immunity  1998;66(12):5620-5629.
Streptococcus pneumoniae is the major cause of bacterial pneumonia, and it is also responsible for otitis media and meningitis in children. Apart from the capsule, the virulence factors of this pathogen are not completely understood. Recent technical advances in the field of bacterial pathogenesis (in vivo expression technology and signature-tagged mutagenesis [STM]) have allowed a large-scale identification of virulence genes. We have adapted to S. pneumoniae the STM technique, originally used for the discovery of Salmonella genes involved in pathogenicity. A library of pneumococcal chromosomal fragments (400 to 600 bp) was constructed in a suicide plasmid vector carrying unique DNA sequence tags and a chloramphenicol resistance marker. The recent clinical isolate G54 was transformed with this library. Chloramphenicol-resistant mutants were obtained by homologous recombination, resulting in genes inactivated by insertion of the suicide vector carrying a unique tag. In a mouse pneumonia model, 1.250 candidate clones were screened; 200 of these were not recovered from the lungs were therefore considered virulence-attenuated mutants. The regions flanking the chloramphenicol gene of the attenuated mutants were amplified by inverse PCR and sequenced. The sequence analysis showed that the 200 mutants had insertions in 126 different genes that could be grouped in six classes: (i) known pneumococcal virulence genes; (ii) genes involved in metabolic pathways; (iii) genes encoding proteases; (iv) genes coding for ATP binding cassette transporters; (v) genes encoding proteins involved in DNA recombination/repair; and (vi) DNA sequences that showed similarity to hypothetical genes with unknown function. To evaluate the virulence attenuation for each mutant, all 126 clones were individually analyzed in a mouse septicemia model. Not all mutants selected in the pneumonia model were confirmed in septicemia, thus indicating the existence of virulence factors specific for pneumonia.
PMCID: PMC108710  PMID: 9826334
23.  Toward Repurposing Ciclopirox as an Antibiotic against Drug-Resistant Acinetobacter baumannii, Escherichia coli, and Klebsiella pneumoniae 
PLoS ONE  2013;8(7):e69646.
Antibiotic-resistant infections caused by gram-negative bacteria are a major healthcare concern. Repurposing drugs circumvents the time and money limitations associated with developing new antimicrobial agents needed to combat these antibiotic-resistant infections. Here we identified the off-patent antifungal agent, ciclopirox, as a candidate to repurpose for antibiotic use. To test the efficacy of ciclopirox against antibiotic-resistant pathogens, we used a curated collection of Acinetobacter baumannii, Escherichia coli, and Klebsiella pneumoniae clinical isolates that are representative of known antibiotic resistance phenotypes. We found that ciclopirox, at 5–15 µg/ml concentrations, inhibited bacterial growth regardless of the antibiotic resistance status. At these same concentrations, ciclopirox reduced growth of Pseudomonas aeruginosa clinical isolates, but some of these pathogens required higher ciclopirox concentrations to completely block growth. To determine how ciclopirox inhibits bacterial growth, we performed an overexpression screen in E. coli. This screen revealed that galE, which encodes UDP-glucose 4-epimerase, rescued bacterial growth at otherwise restrictive ciclopirox concentrations. We found that ciclopirox does not inhibit epimerization of UDP-galactose by purified E. coli GalE; however, ΔgalU, ΔgalE, ΔrfaI, or ΔrfaB mutant strains all have lower ciclopirox minimum inhibitory concentrations than the parent strain. The galU, galE, rfaI, and rfaB genes all encode enzymes that use UDP-galactose or UDP-glucose for galactose metabolism and lipopolysaccharide (LPS) biosynthesis. Indeed, we found that ciclopirox altered LPS composition of an E. coli clinical isolate. Taken together, our data demonstrate that ciclopirox affects galactose metabolism and LPS biosynthesis, two pathways important for bacterial growth and virulence. The lack of any reported fungal resistance to ciclopirox in over twenty years of use in the clinic, its excellent safety profiles, novel target(s), and efficacy, make ciclopirox a promising potential antimicrobial agent to use against multidrug-resistant problematic gram-negative pathogens.
PMCID: PMC3720592  PMID: 23936064
24.  Cloning and Sequencing of the Klebsiella pneumoniae O5 wb Gene Cluster and Its Role in Pathogenesis 
Infection and Immunity  2000;68(5):2435-2440.
One representative recombinant clone encoding Klebsiella pneumoniae O5-antigen lipopolysaccharide (LPS) was found upon screening for serum resistance in a cosmid-based genomic library of K. pneumoniae KT769 (O5:K57) introduced into Escherichia coli DH5α. A total of eight open reading frames (wbO5 gene cluster) were necessary to produce K. pneumoniae O5-antigen LPS in E. coli K-12. The enzymatic activities proposed for the wbO5 gene cluster are in agreement with the activities proposed for the biosynthesis of K. pneumoniae O5-antigen LPS. Using the complete DNA sequence of the K. pneumoniae wbO5 gene cluster, we obtained (by single or double recombination) genetically well-characterized mutants devoid only of this O5-antigen LPS. Finally, using these O5− mutants and the corresponding wild-type strains or complemented mutants with the wbO5 gene cluster (O5+ strains), we found that the presence of K. pneumoniae O5-antigen LPS is essential for some pathogenic features like serum resistance, adhesion to uroepithelial cells, and colonization (experimental infections) of the urinary tract in rats.
PMCID: PMC97443  PMID: 10768928
25.  Prevalence of Uropathogens in Diabetic Patients and Their Corresponding Resistance Pattern: Results of a Survey Conducted at Diagnostic Centers in Dhaka, Bangladesh 
Oman Medical Journal  2010;25(4):282-285.
Urinary tract infection is the second most common clinical indication for empirical antibiotic treatment in primary and secondary health care settings. The incidence of diabetes mellitus throughout the world is increasing strikingly and in the long run, it has some major effects on the genitourinary system which makes diabetic patients more liable to urinary tract infection. This study is designed to reveal the distribution of uropathogens in diabetic patients according to age and sex, and corresponding resistance patterns.
A six-month retrospective review of urine culture assay data from August 2009 to January 2010 from randomly selected 85 patients who suffered from both urinary tract infection and diabetes was conducted. Relevant information was retrieved and analyzed statistically using Microsoft® Excel 2002 software.
The study showed that females are more vulnerable to pathogenic attack than males throughout a wide age distribution. In terms of pathogenic distribution, Escherichia coli was the highest followed by Streptococcus sp., Acinetobacter, Klebsiella pneumoniae and few others. Though Meropenem showed no resistance with E. coli, Acinetobacter and Klebsiella pneumoniae, in the case of Streptococcus sp. it exhibited resistance of 25%. Amikacin exhibited only 3% resistance with E. coli, whereas no resistance with Acinetobacter and Klebsiella pneumoniae, and most interestingly showed 75% resistance with Streptococcus sp. Gentamicin exhibited no resistance with Acinetobacter while 26.9%, 50% and 87.5% resistance with E. coli, Klebsiella pneumoniae and Streptococcus sp. respectively. Hence, Nitrofurantoin exhibited less resistance 11.9% compared to 12.5% resistance with E. coli and Streptococcus sp. Nitrofurantoin was highly prone to resistance with Acinetobacter and Klebsiella pneumoniae (100%, 50% respectively). Cephalosporins (cephradine, cefixime, ceftriaxone, cefepime etc.) showed moderate resistance (avg. 50%), whereas amoxicillin and ciprofloxacin showed the highest resistance in all these cases.
Pathogens are mostly resistant to antibiotics including amoxicillin, ciprofloxacin, cephalosporins and nitrofurantoin, with few exceptions including gentamicin, amikacin and meropenem.
PMCID: PMC3191656  PMID: 22043358

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