A major challenge to clinical therapy of Burkholderia cepacia complex (Bcc) pulmonary infections is their innate resistance to a broad range of antimicrobials, including polycationic agents such as aminoglycosides, polymyxins, and cationic peptides. To identify genetic loci associated with this phenotype, a transposon mutant library was constructed in B. multivorans ATCC 17616 and screened for increased susceptibility to polymyxin B. Compared to the parent strain, mutant 26D7 exhibited 8- and 16-fold increases in susceptibility to polymyxin B and colistin, respectively. Genetic analysis of mutant 26D7 indicated that the transposon inserted into open reading frame (ORF) Bmul_2133, part of a putative hopanoid biosynthesis gene cluster. A strain with a mutation in another ORF in this cluster, Bmul_2134, was constructed and named RMI19. Mutant RMI19 also had increased polymyxin susceptibility. Hopanoids are analogues of eukaryotic sterols involved in membrane stability and barrier function. Strains with mutations in Bmul_2133 and Bmul_2134 showed increased permeability to 1-N-phenylnaphthylamine in the presence of increasing concentrations of polymyxin, suggesting that the putative hopanoid biosynthesis genes are involved in stabilizing outer membrane permeability, contributing to polymyxin resistance. Results from a dansyl-polymyxin binding assay demonstrated that polymyxin B does not bind well to the parent or mutant strains, suggesting that Bmul_2133 and Bmul_2134 contribute to polymyxin B resistance by a mechanism that is independent of lipopolysaccharide (LPS) binding. Through this work, we propose a role for hopanoid biosynthesis as part of the multiple antimicrobial resistance phenotype in Bcc bacteria.
Bronchopulmonary dysplasia (BPD) is a common chronic lung disease and major risk factor for severe respiratory syncytial virus (RSV) infection among preterm infants. The Toll-like receptor 4 (TLR4) is involved in oxidative injury responses in the lungs. Two non-synonymous single nucleotide polymorphisms in the TLR4 gene have been associated with RSV infection in children. However, it is unclear to what extent this association is confounded by BPD or prematurity. In this study, we analyzed two population-based cohorts of preterm infants at risk for BPD as well as ethnicity-matched infants born at term, to test whether the TLR4 polymorphisms Asp299Gly (rs4986790) and Thr399Ile (rs4986791) are independently associated with BPD or premature birth. In a Canadian cohort (n = 269) composed of a majority of Caucasian preterm infants (BPD incidence of 38%), the TLR4-299 heterozygous genotype was significantly under-represented in infants without BPD (1.6% of infants versus 12% in infants with severe BPD) after adjusting for twins, ethnicity, gestational age, birth weight and gender (p = 0.014). This association was not replicated in a Finnish cohort (n = 434) of premature singletons or first-born siblings of Caucasian descent, although the incidence of BPD was substantially lower in this latter population (15%). We did not detect a significant association (>2-fold) between TLR4 genotypes and prematurity (p>0.05). We conclude that these TLR4 genotypes may have, at best, a modest influence on BPD severity in some populations of high-risk preterm infants. Further studies are warranted to clarify how clinical heterogeneity may impact genetic susceptibility to BPD.
Burkholderia cepacia complex (BCC) bacteria can cause devastating chronic infections in people with cystic fibrosis. Of particular concern is “cepacia syndrome,” a rapidly progressive and usually fatal decline in health, characterized by a necrotizing bacteremic pneumonia. An important component of defense against bloodstream infections is the bactericidal action of serum. Traditional methods to determine the capacity of bacterial isolates to resist the bactericidal effects of serum are relatively low-throughput viability assays. In this study, we developed a novel growth-based assay for serum susceptibility, which allows for high throughput analysis. We applied this assay to a range of clinical isolates of BCC as well as isolates comprising the BCC experimental strain panel. Our data demonstrate that isolates from all species of BCC examined can possess serum resistant or serum sensitive/intermediate phenotypes. Of particular clinical significance, we also found no direct link between the last saved pulmonary isolate from patients who subsequently developed “cepacia syndrome” and their capacity to resist the inhibitory effects of human serum, suggesting serum resistance cannot be used as a marker of an isolate’s capacity to escape from the lung and cause bacteremia.
Burkholderia cepacia complex; serum; cystic fibrosis; complement; Bioscreen; cepacia syndrome
Prematurely born infants are highly vulnerable to infections and also exhibit a high susceptibility to organ damage from inflammation.
To investigate homeostatic immune control early in life, we used advanced multi-parameter flow cytometry to compare responses to multiple Toll-like receptor (TLR) ligands in single cells and mononuclear cell populations, between term and preterm neonates born before 29 weeks of gestation.
Preterm neonates showed globally attenuated TLR-stimulated IL-6, IFN-α and to a lesser extent TNF-α responses, but relative preservation of anti-inflammatory IL-10 responses in monocytes and dendritic cell subtypes. Remarkably, preterm neonates were also profoundly deficient in the common IL-12 and IL-23 cytokines p40 subunit, critical for immunity against a wide variety of microbial pathogens in mice. Consistent with an increased susceptibility to infections from the lack of IL-12/IL-23 in human newborns, significantly lower serum p40 concentrations were observed at birth in infants who developed early-onset sepsis.
This study is the first detailed analysis of multiple TLR function in neonates born at extreme prematurity. While attenuation of pro-inflammatory pathways may protect against tissue-damaging immunity early in life, this previously unrecognized p40 immune deficiency appears to considerably increase susceptibility to infection in human preterm newborns.
IL-12/23p40; cord blood; toll-like receptor; innate immunity; neonates
Background. Infants born prematurely are highly vulnerable to infections and also exhibit a high susceptibility to organ damage due to inflammation.
Methods. To investigate homeostatic immune control early in life, we used advanced multiparameter flow cytometry to compare responses to multiple Toll-like receptor (TLR) ligands in single cells and mononuclear cell populations in term neonates versus preterm neonates born before 29 weeks of gestation.
Results. Preterm neonates had globally attenuated TLR-stimulated interleukin (IL)-6, interferon-α, and, to a lesser extent, tumor necrosis factor-α responses but demonstrated relative preservation of anti-inflammatory IL10 responses in monocytes and dendritic cell subtypes. Remarkably, preterm neonates were also profoundly deficient in the common IL-12 and IL-23 cytokines' p40 subunit, which is critical for immunity against a wide variety of microbial pathogens in mice. Consistent with the increased susceptibility to infections resulting from the lack of IL-12/IL-23 in human newborns, significantly lower serum p40 concentrations were observed at birth in infants who developed early-onset sepsis.
Conclusion. To our knowledge, this study is the first detailed analysis of multiple TLR function in neonates born extremely premature. Although attenuation of proinflammatory pathways may protect against tissue-damaging immunity early in life, this previously unrecognized p40 immune deficiency appears to result in considerably increased susceptibility to infection in human preterm newborns.
Burkholderia cepacia complex (BCC) bacteria are opportunistic pathogens that can cause severe disease in cystic fibrosis (CF) patients and other immunocompromised individuals and are typically multidrug resistant. Here we observed that unlike other BCC species, most environmental and clinical Burkholderia vietnamiensis isolates were intrinsically susceptible to aminoglycosides but not to cationic antimicrobial peptides or polymyxin B. Furthermore, strains acquired aminoglycoside resistance during chronic CF infection, a phenomenon that could be induced under tobramycin or azithromycin pressure in vitro. In comparing susceptible and resistant B. vietnamiensis isolates, no gross differences in lipopolysaccharide structure were observed, all had lipid A-associated 4-amino-4-deoxy-l-arabinose residues, and all were resistant to the permeabilizing effects of aminoglycosides, a measure of drug entry via self-promoted uptake. However, susceptible isolates accumulated 5 to 6 times more gentamicin than a resistant isolate, and aminoglycoside susceptibility increased in the presence of an efflux pump inhibitor. B. vietnamiensis is therefore unusual among BCC bacteria in its susceptibility to aminoglycosides and capacity to acquire resistance. Aminoglycoside resistance appears to be due to decreased cellular accumulation as a result of active efflux.
Innate immunodeficiency has recently been reported resulting from the Q293X IRAK-4 mutation, with consequent defective TLR/IL-1R signalling. Here we report a method for the rapid allele-specific detection of this mutation and demonstrate both cell-type specificity and ligand specificity in defective IRAK-4-deficient cellular responses, indicating differential roles for this protein in human peripheral blood mononuclear cells and primary dermal fibroblasts, and in LPS, IL-1β and TNF-α signalling. We demonstrate transcriptional and post-transcriptional defects, despite NF-κB signalling and intact MyD88-independent signalling, and propose that dysfunctional Complex 1 (IRAK1/TRAF6/TAK1) signalling, as a consequence of IRAK-4-deficiency, generates specific defects in mitogen-activated protein kinase activation that could underpin this patient’s innate immunodeficiency. These studies demonstrate the importance of studying primary human cells bearing a clinically relevant mutation; they underscore the complexity of innate immune signalling and illuminate novel roles for IRAK-4 and the fundamental importance of accessory pro-inflammatory signalling to normal human innate immune responses and immunodeficiencies.
Human; Immunodeficiency diseases; Inflammation
The Gram-negative bacterium Pseudomonas aeruginosa is a common cause of chronic airway infections in individuals with the heritable disease cystic fibrosis (CF). After prolonged colonization of the CF lung, P. aeruginosa becomes highly resistant to host clearance and antibiotic treatment; therefore, understanding how this bacterium evolves during chronic infection is important for identifying beneficial adaptations that could be targeted therapeutically. To identify potential adaptive traits of P. aeruginosa during chronic infection, we carried out global transcriptomic profiling of chronological clonal isolates obtained from 3 individuals with CF. Isolates were collected sequentially over periods ranging from 3 months to 8 years, representing up to 39,000 in vivo generations. We identified 24 genes that were commonly regulated by all 3 P. aeruginosa lineages, including several genes encoding traits previously shown to be important for in vivo growth. Our results reveal that parallel evolution occurs in the CF lung and that at least a proportion of the traits identified are beneficial for P. aeruginosa chronic colonization of the CF lung.
Deadly diseases like AIDS, malaria, and tuberculosis are the result of long-term chronic infections. Pathogens that cause chronic infections adapt to the host environment, avoiding the immune response and resisting antimicrobial agents. Studies of pathogen adaptation are therefore important for understanding how the efficacy of current therapeutics may change upon prolonged infection. One notorious chronic pathogen is Pseudomonas aeruginosa, a bacterium that causes long-term infections in individuals with the heritable disease cystic fibrosis (CF). We used gene expression profiles to identify 24 genes that commonly changed expression over time in 3 P. aeruginosa lineages, indicating that these changes occur in parallel in the lungs of individuals with CF. Several of these genes have previously been shown to encode traits critical for in vivo-relevant processes, suggesting that they are likely beneficial adaptations important for chronic colonization of the CF lung.
The Burkholderia cepacia complex is an important group of pathogens in patients with cystic fibrosis (CF). Although evidence for patient-to-patient spread is clear, microbial factors facilitating transmission are poorly understood. To identify microbial clones with enhanced transmissibility, we evaluated B. cepacia complex isolates from patients with CF from throughout Canada. A total of 905 isolates from the B. cepacia complex were recovered from 447 patients in 8 of the 10 provinces; 369 (83%) of these patients had genomovar III and 43 (9.6%) had B. multivorans (genomovar II). Infection prevalence differed substantially by region (22% of patients in Ontario vs. 5% in Quebec). Results of typing by random amplified polymorphic DNA analysis or pulsed-field gel electrophoresis indicated that strains of B. cepacia complex from genomovar III are the most potentially transmissible and that the B. cepacia epidemic strain marker is a robust marker for transmissibility.
Burkholderia cepacia complex; cystic fibrosis; epidemiology; genomovar; Canada
Mycobacterium tuberculosis, the causative agent of tuberculosis, initially contacts host cells with elements of its outer cell wall, or capsule. We have shown that capsular material from the surface of M. tuberculosis competitively inhibits the nonopsonic binding of whole M. tuberculosis bacilli to macrophages in a dose-dependent manner that is not acting through a global inhibition of macrophage binding. We have further demonstrated that isolated M. tuberculosis capsular proteins mediate a major part of this inhibition. Two-dimensional polyacrylamide gel electrophoresis analysis of the capsular proteins showed the presence of a wide variety of protein species, including proportionately high levels of the Cpn60.2 (Hsp65, GroEL2) and DnaK (Hsp70) molecular chaperones. Both of these proteins were subsequently detected on the bacterial surface. To determine whether these molecular chaperones play a role in bacterial binding, recombinant Cpn60.2 and DnaK were tested for their ability to inhibit the association of M. tuberculosis bacilli with macrophages. We found that recombinant Cpn60.2 can inhibit ∼57% of bacterial association with macrophages, while DnaK was not inhibitory at comparable concentrations. Additionally, when polyclonal F(ab′)2 fragments of anti-Cpn60.2 and anti-DnaK were used to mask the surface presentation of these molecular chaperones, a binding reduction of ∼34% was seen for anti-Cpn60.2 F(ab′)2, while anti-DnaK F(ab′)2 did not significantly reduce bacterial association with macrophages. Thus, our findings suggest that while M. tuberculosis displays both surface-associated Cpn60.2 and DnaK, only Cpn60.2 demonstrates adhesin functionality with regard to macrophage interaction.
Three structural features of lipid A (addition of palmitate [C16 fatty acid], addition of aminoarabinose [positively charged amino sugar residue], and retention of 3-hydroxydecanoate [3-OH C10 fatty acid]) were determined for Pseudomonas aeruginosa isolates from patients with cystic fibrosis (CF; n = 86), from the environment (n = 13), and from patients with other conditions (n = 14). Among P. aeruginosa CF isolates, 100% had lipid A with palmitate, 24.6% with aminoarabinose, and 33.3% retained 3-hydroxydecanoate. None of the isolates from the environment or from patients with other conditions displayed these modifications. These results indicate that unique lipid A modifications occur in clinical P. aeruginosa CF isolates.
We demonstrate that all nine species of the Burkholderia cepacia complex can express the mucoid phenotype. A survey of clinical isolates showed that strains of B. cenocepacia, the most virulent species of the complex, are most frequently nonmucoid. Additionally, isolates from patients with chronic infections can convert from mucoid to nonmucoid.
Burkholderia multivorans is a prominent B. cepacia complex (BCC) species causing infection in people with cystic fibrosis. Despite infection control measures being introduced to reduce the spread of BCC there is a continued emergence of infections by B. multivorans. Our objective was to analyze a global collection of B. multivorans isolates, comparing those from environmental and clinical sources with those from reported outbreaks. Multilocus sequence typing (MLST) was performed on 107 B. multivorans isolates to provide a detailed analysis of the global population biology of this species. MLST resolved 64 B. multivorans sequence types. Twelve of these were globally distributed and associated with human infection; two of these (ST-21 and ST-375) were also composed of environmental isolates. These global lineages included strains previously linked to large outbreaks (e.g., French epidemic clone ST-16). Though few environmental isolates of B. multivorans were available for analysis, of six strains identified, three were identical to strains recovered from cystic fibrosis (CF) infection. Although the ability of B. multivorans to cause CF outbreaks is known, our report here concerning the existence of globally distributed B. multivorans CF strains is a new observation for this emerging B. cepacia complex pathogen and suggests that certain strain types may be better adapted to human infection than others. Common transmission-associated risk factors were not obviously linked to the globally distributed strains; however, the overlap in strains recovered from water environments, industrial products, and human infection suggests that environmental sources may be an important reservoir for infection with B. multivorans.
The first year of life represents a time of marked susceptibility to infections; this is particularly true for regions in sub-Saharan Africa. As innate immunity directs the adaptive immune response, the observed increased risk for infection as well as a suboptimal response to vaccination in early life may be due to less effective innate immune function. In this study, we followed a longitudinal cohort of infants born and raised in South Africa over the first year of life, employing the most comprehensive analysis of innate immune response to stimulation published to date. Our findings reveal rapid changes in innate immune development over the first year of life. This is the first report depicting dramatic differences in innate immune ontogeny between different populations in the world, with important implications for global vaccination strategies.
Members of the Burkholderia cepacia complex (Bcc), found in many environments, are associated with clinical infections. Examining diverse species and strains from different environments with multilocus sequence typing, we identified >20% of 381 clinical isolates as indistinguishable from those in the environment. This finding links the natural environment with the emergence of many Bcc infections.
MLST; Burkholderia cepacia complex; epidemiology; identical; genotype; environmental; clinical; global; widespread; dispatch
A single multilocus sequence typing (MLST) scheme was developed for precise characterization of the opportunistic pathogens of Burkholderia cepacia complex (BCC), a group composed of at least nine closely related species. Seven conserved housekeeping genes were selected after a comparison of five Burkholderia species, and a collection of strains was subjected to nucleotide sequence analysis using a nested PCR amplification approach for each gene. MLST differentiated all nine current BCC species and identified 114 sequence types within a collection of 119 strains. No differentiation was found between strains recovered from environmental or clinical sources. The improved resolution in strain identification offered by MLST was able to identify previously characterized epidemic strain lineages and also demonstrated the presence of four novel potential species groups within the complex. There was also evidence for recombination having an important role in the recent evolution of individual BCC species. This highly transferable, validated, MLST scheme provides a new means to assist in species identification as well as unambiguous strain discrimination of the BCC by a single approach. It is also the first MLST scheme designed at the outset to incorporate multiple species and should facilitate global epidemiological investigations of the BCC.
Differences in infection kinetics and host response between Burkholderia multivorans and Burkholderia cenocepacia were demonstrated in a pulmonary infection model in BALB/c mice. B. multivorans persisted in the lung, while B. cenocepacia was cleared. Indirect immunofluorescence and electron microscopy of B. multivorans-infected lungs localized bacteria to macrophages. Clearance of B. cenocepacia was associated with greater interleukin-1β and neutrophil responses than the responses induced by B. multivorans.
A proportion of individuals vaccinated with live attenuated Oka varicella-zoster virus (VZV) vaccine subsequently develop attenuated chicken pox and/or herpes zoster. To determine whether postvaccination varicella infections are caused by vaccine or wild-type virus, a simple method for distinguishing the vaccine strain from wild-type virus is required. We have developed a TaqMan real-time PCR assay to detect and differentiate wild-type virus from Oka vaccine strains of VZV. The assay utilized two fluorogenic, minor groove binding probes targeted to a single nucleotide polymorphism in open reading frame 62 that distinguishes the Oka vaccine from wild-type strains. VZV DNA could be genotyped and quantified within minutes of thermocycling completion due to real-time monitoring of PCR product formation and allelic discrimination analysis. The allelic discrimination assay was performed in parallel with two standard PCR-restriction fragment length polymorphism (RFLP) methods on 136 clinical and laboratory VZV strains from Canada, Australia, and Japan. The TaqMan assay exhibited a genotyping accuracy of 100% and, when compared to both PCR-RFLP methods, was 100 times more sensitive. In addition, the method was technically simpler and more rapid. The TaqMan assay also allows for high-throughput genotyping, making it ideal for epidemiologic study of the live attenuated varicella vaccine.
The purpose of this study was to determine the role of colonial morphology of Burkholderia cepacia complex (BCC) organisms in pathogenicity in a mouse model of pulmonary infection. BCC strain C1394 was rapidly cleared by leukopenic mice after intranasal challenge, whereas a spontaneous variant (C1394mp2) that was indistinguishable from the parent strain by genetic typing persisted in the lungs and differed in colonial morphology. The parent strain had a matte colonial phenotype, made scant exopolysaccharide (EPS), and was lightly piliated. The variant had a shiny phenotype, produced abundant EPS, and was heavily piliated. Matte to shiny colonial transformation was induced by growth at 42°C. Colonial morphology in the BCC strain variant was associated with persistence after pulmonary challenge and appeared to be correlated with the elaboration of putative virulence determinants.
Pseudomonas aeruginosa is an important opportunistic human pathogen. Certain strains can transmigrate across epithelial cells, and their invasive phenotype is correlated with capacity to cause invasive human disease and fatal septicemia in mice. Four multidrug efflux systems have been described in P. aeruginosa, however, their contribution to virulence is unclear. To clarify the role of efflux systems in invasiveness, P. aeruginosa PAO1 wild-type (WT) and its efflux mutants were evaluated in a Madin-Darby canine kidney (MDCK) epithelial cell monolayer system and in a murine model of endogenous septicemia. All efflux mutants except a ΔmexCD-oprJ deletion demonstrated significantly reduced invasiveness compared with WT. In particular, a ΔmexAB-oprM deletion strain was compromised in its capacity to invade or transmigrate across MDCK cells, and could not kill mice, in contrast to WT which was highly invasive (P < 0.0006) and caused fatal infection (P < 0.0001). The other mutants, including ΔmexB and ΔmexXY mutants, were intermediate between WT and the ΔmexAB-oprM mutant in invasiveness and murine virulence. Invasiveness was restored to the ΔmexAB-oprM mutant by complementation with mexAB-oprM or by addition of culture supernatant from MDCK cells infected with WT. We conclude that the P. aeruginosa MexAB-OprM efflux system exports virulence determinants that contribute to bacterial virulence.
Pseudomonas aeruginosa; bacterial invasion; multidrug efflux system; outer membrane protein; endogenous bacteremia
Acyl homoserine lactone (acyl-HSL)-mediated gene regulation has been shown to influence biofilm formation in one Burkholderia cepacia cystic fibrosis isolate, but it is not known whether this relationship is a consistent feature of the several genomic species that make up the B. cepacia complex (BCC). We screened strains belonging to genomovars I to V of the BCC for biofilm formation on an abiotic surface and for acyl-HSL synthesis. We determined that organisms from each of these genomovars were capable of biofilm formation. Similarly, acyl-HSL was synthesized by organisms from each of genomovars I to V, with most isolates producing octanoyl-HSL in greatest abundance. When biofilms were grown in Luria broth, acyl-HSL synthesis and biofilm formation appeared to be associated, but these phenotypes were independent when the biofilms were grown in basal salts containing citrate. Genomovar V strains synthesized the greatest quantities of acyl-HSL, and genomovar II and III-A strains elaborated the most abundant biofilms. Quorum sensing may play a role in BCC pathogenesis, but it may not regulate biofilm formation under all growth conditions.
Cystic fibrosis patients infected with strains from different genomovars of the Burkholderia cepacia complex can experience diverse clinical outcomes. To identify genomovar-specific determinants that might be responsible for these differences, we developed a pulmonary model of infection in BALB/c mice. Mice were rendered leukopenic by administration of cyclophosphamide prior to intranasal challenge with 1.6 × 104 bacteria. Five of six genomovar II strains persisted at stable numbers in the lungs until day 16 with minimal toxicity, whereas zero of seven genomovar III strains persisted but resulted in variable toxicity. We have developed a chronic pulmonary model of B. cepacia infection which reveals differences among genomovars in terms of clinical infection outcome.
Recent taxonomic advances have demonstrated that Burkholderia cepacia is a cluster of at least seven closely related genomic species (or genomovars) collectively referred to as the B. cepacia complex, all of which may cause infections among cystic fibrosis patients and other vulnerable individuals. Thus, it is important for clinical microbiologists to be able to differentiate genomovars. Prior to this study, 361 B. cepacia complex isolates and 51 isolates easily confused with B. cepacia complex previously had been identified using a polyphasic approach, and in this study, a comparison of phenotypic and biochemical tests was carried out. It was determined that Burkholderia multivorans and Burkholderia stabilis could reliably be separated from other members of the B. cepacia complex by phenotypic methods. A combination of phenotypic and molecular tests such as recA PCR and 16S rRNA RFLP are recommended for differentiation among the genomovars of the B. cepacia complex. A biochemical reaction scheme for the identification of B. gladioli, Pandoraea species, and Ralstonia pickettii and the differentiation of these species from the B. cepacia complex is also presented.
A method for distinguishing among Pseudomonas aeruginosa strains using random amplified polymorphic DNA (RAPD) typing was evaluated for reproducibility and discriminatory power. A total of 200 isolates, blinded in triplicate, were evaluated by RAPD. All 600 samples were typeable; 197 of 200 isolates gave identical results on all three occasions, and 131 distinct RAPD types were identified.