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1.  Typhoid Fever in Young Children in Bangladesh: Clinical Findings, Antibiotic Susceptibility Pattern and Immune Responses 
PLoS Neglected Tropical Diseases  2015;9(4):e0003619.
Children bear a large burden of typhoid fever caused by Salmonella enterica serotype Typhi (S. Typhi) in endemic areas. However, immune responses and clinical findings in children are not well defined. Here, we describe clinical and immunological characteristics of young children with S. Typhi bacteremia, and antimicrobial susceptibility patterns of isolated strains.
As a marker of recent infection, we have previously characterized antibody-in-lymphocyte secretion (TPTest) during acute typhoid fever in adults. We similarly assessed membrane preparation (MP) IgA responses in young children at clinical presentation, and then 7-10 days and 21-28 days later. We also assessed plasma IgA, IgG and IgM responses and T cell proliferation responses to MP at these time points. We compared responses in young children (1-5 years) with those seen in older children (6-17 years), adults (18-59 years), and age-matched healthy controls.
Principal Findings
We found that, compared to age-matched controls patients in all age cohorts had significantly more MP-IgA responses in lymphocyte secretion at clinical presentation, and the values fell in all groups by late convalescence. Similarly, plasma IgA responses in patients were elevated at presentation compared to controls, with acute and convalescent IgA and IgG responses being highest in adults. T cell proliferative responses increased in all age cohorts by late convalescence. Clinical characteristics were similar in all age cohorts, although younger children were more likely to present with loss of appetite, less likely to complain of headache compared to older cohorts, and adults were more likely to have ingested antibiotics. Multi-drug resistant strains were present in approximately 15% of each age cohort, and 97% strains had resistance to nalidixic acid.
This study demonstrates that S. Typhi bacteremia is associated with comparable clinical courses, immunologic responses in various age cohorts, including in young children, and that TPTest can be used as marker of recent typhoid fever, even in young children.
Author Summary
The highest disease burden of typhoid fever caused by Salmonella enterica serotype Typhi (S. Typhi) is seen in children under five years of age in endemic areas. We investigated both mucosal and systemic immune responses in S. Typhi bacteremic young children (aged, 1 to 5 years) by measuring S. Typhi membrane preparation (MP) specific IgA response in lymphocyte culture secretion and plasma IgA, IgG and IgM responses using ELISA. We also measured T cell proliferation responses using 3H-thymidine incorporation assay. We compared the responses to S. Typhi bacteremic older children (6 to 17 years) and adults (18 to 59 years) and with age-matched healthy controls (HC). Younger children, older children and adults show comparable responses in lymphocyte secretions after onset of illness. Plasma antibody responses to MP vary between young children and other age groups. T cell proliferative responses increased in all age cohorts by late convalescence. Clinical characteristics were similar in all age cohorts. Emergence of MDR S. Typhi strains is seen in young children which does not impact on the clinical symptoms or the immune responses. The results of this study show that natural infections do induce immune response in young children as well as in adults.
PMCID: PMC4388457  PMID: 25849611
2.  High-Resolution Genotyping of the Endemic Salmonella Typhi Population during a Vi (Typhoid) Vaccination Trial in Kolkata 
Typhoid fever, caused by Salmonella enterica serovar Typhi (S. Typhi), is a major health problem especially in developing countries. Vaccines against typhoid are commonly used by travelers but less so by residents of endemic areas.
We used single nucleotide polymorphism (SNP) typing to investigate the population structure of 372 S. Typhi isolated during a typhoid disease burden study and Vi vaccine trial in Kolkata, India. Approximately sixty thousand people were enrolled for fever surveillance for 19 months prior to, and 24 months following, Vi vaccination of one third of the study population (May 2003–December 2006, vaccinations given December 2004).
Principal Findings
A diverse S. Typhi population was detected, including 21 haplotypes. The most common were of the H58 haplogroup (69%), which included all multidrug resistant isolates (defined as resistance to chloramphenicol, ampicillin and co-trimoxazole). Quinolone resistance was particularly high among H58-G isolates (97% Nalidixic acid resistant, 30% with reduced susceptibility to ciprofloxacin). Multiple typhoid fever episodes were detected in 22 households, however household clustering was not associated with specific S. Typhi haplotypes.
Typhoid fever in Kolkata is caused by a diverse population of S. Typhi, however H58 haplotypes dominate and are associated with multidrug and quinolone resistance. Vi vaccination did not obviously impact on the haplotype population structure of the S. Typhi circulating during the study period.
Author Summary
Typhoid fever is caused by the bacterium Salmonella enterica serovar Typhi (S. Typhi) and is a major health problem especially in developing countries. Vaccines against typhoid are commonly used by travelers but less so by residents of endemic areas. We used single nucleotide polymorphism (SNP) typing to investigate the population structure of 372 S. Typhi bacteria isolated from typhoid patients during a typhoid disease burden study and Vi anti-typhoid vaccine trial in Kolkata, India. Approximately sixty thousand people were enrolled for fever surveillance for 19 months prior to, and 24 months following, vaccination of one third of the study population against typhoid (May 2003–December 2006, vaccinations given December 2004). We detected a diverse population of S. Typhi, including 21 different genetic forms (haplotypes) of the bacteria. The most common (69%) were of a haplogroup known as H58, which included all multidrug resistant isolates (bacteria resistant to the antibiotics chloramphenicol, ampicillin and co-trimoxazole). Resistance to quinolones, a class of antibiotics commonly used to treat typhoid fever, was particularly high among a subgroup of H58 (H58-G). Vi vaccination did not obviously impact on the haplotype distribution of the S. Typhi circulating during the study period.
PMCID: PMC3269425  PMID: 22303491
3.  Clinical outcomes in typhoid fever: adverse impact of infection with nalidixic acid-resistant Salmonella typhi 
Widespread use of fluoroquinolones has resulted in emergence of Salmonella typhi strains with decreased susceptibility to fluoroquinolones. These strains are identifiable by their nalidixic acid-resistance. We studied the impact of infection with nalidixic acid-resistant S. typhi (NARST) on clinical outcomes in patients with bacteriologically-confirmed typhoid fever.
Clinical and laboratory features, fever clearance time and complications were prospectively studied in patients with blood culture-proven typhoid fever, treated at a tertiary care hospital in north India, during the period from November 2001 to October 2003. Susceptibility to amoxycillin, co-trimoxazole, chloramphenicol, ciprofloxacin and ceftriaxone were tested by disc diffusion method. Minimum inhibitory concentrations (MIC) of ciprofloxacin and ceftriaxone were determined by E-test method.
During a two-year period, 60 patients (age [mean ± SD]: 15 ± 9 years; males: 40 [67%]) were studied. All isolates were sensitive to ciprofloxacin and ceftriaxone by disc diffusion and MIC breakpoints. However, 11 patients had clinical failure of fluoroquinolone therapy. Infections with NARST isolates (47 [78%]) were significantly associated with longer duration of fever at presentation (median [IQR] 10 [7-15] vs. 4 [3-6] days; P = 0.000), higher frequency of hepatomegaly (57% vs. 15%; P = 0.021), higher levels of aspartate aminotransferase (121 [66–235] vs. 73 [44–119] IU/L; P = 0.033), and increased MIC of ciprofloxacin (0.37 ± 0.21 vs. 0.17 ± 0.14 μg/mL; P = 0.005), as compared to infections with nalidixic acid-susceptible isolates. All 11 patients with complications were infected with NARST isolates. Total duration of illness was significantly longer in patients who developed complications than in patients who did not (22 [14.8–32] vs. 12 [9.3–20.3] days; P = 0.011). Duration of prior antibiotic intake had a strong positive correlation with the duration of fever at presentation (r = 0.61; P = 0.000) as well as the total duration of illness (r = 0.53; P = 0.000).
Typhoid fever caused by NARST infection is associated with poor clinical outcomes, probably due to delay in initiating appropriate antibiotic therapy. Fluoroquinolone breakpoints for S. typhi need to be redefined and fluoroquinolones should no longer be used as first-line therapy, if the prevalence of NARST is high.
PMCID: PMC1164413  PMID: 15904505
4.  Temporal Fluctuation of Multidrug Resistant Salmonella Typhi Haplotypes in the Mekong River Delta Region of Vietnam 
Typhoid fever remains a public health problem in Vietnam, with a significant burden in the Mekong River delta region. Typhoid fever is caused by the bacterial pathogen Salmonella enterica serovar Typhi (S. Typhi), which is frequently multidrug resistant with reduced susceptibility to fluoroquinolone-based drugs, the first choice for the treatment of typhoid fever. We used a GoldenGate (Illumina) assay to type 1,500 single nucleotide polymorphisms (SNPs) and analyse the genetic variation of S. Typhi isolated from 267 typhoid fever patients in the Mekong delta region participating in a randomized trial conducted between 2004 and 2005.
Principal Findings
The population of S. Typhi circulating during the study was highly clonal, with 91% of isolates belonging to a single clonal complex of the S. Typhi H58 haplogroup. The patterns of disease were consistent with the presence of an endemic haplotype H58-C and a localised outbreak of S. Typhi haplotype H58-E2 in 2004. H58-E2-associated typhoid fever cases exhibited evidence of significant geo-spatial clustering along the Sông H u branch of the Mekong River. Multidrug resistance was common in the established clone H58-C but not in the outbreak clone H58-E2, however all H58 S. Typhi were nalidixic acid resistant and carried a Ser83Phe amino acid substitution in the gyrA gene.
The H58 haplogroup dominates S. Typhi populations in other endemic areas, but the population described here was more homogeneous than previously examined populations, and the dominant clonal complex (H58-C, -E1, -E2) observed in this study has not been detected outside Vietnam. IncHI1 plasmid-bearing S. Typhi H58-C was endemic during the study period whilst H58-E2, which rarely carried the plasmid, was only transient, suggesting a selective advantage for the plasmid. These data add insight into the outbreak dynamics and local molecular epidemiology of S. Typhi in southern Vietnam.
Author Summary
Typhoid fever remains a serious public health issue in some parts of Vietnam, including the Mekong delta region. Typhoid is caused by the bacterium Salmonella Typhi, which is frequently multidrug resistant and shows reduced susceptibility to fluoroquinolone-based drugs. We assayed single nucleotide variation in the genomes of S. Typhi organisms isolated from 267 patients with typhoid fever in the Mekong delta between 2004 and 2005, and identified genetically distinct S. Typhi strains. We also detected the presence of genes or mutations that confer drug resistance in those strains. We found that the vast majority of typhoid cases were caused by one of two subgroups of H58 S. Typhi, referred to as H58-C and H58-E2. The H58-E2 group appeared to cause an outbreak in 2004, affecting patients living in a small zone near the Mekong River. The other group, H58-C, was present throughout the study period and affected patients living in a broader area of the Mekong River delta. Most of the H58-C strains were resistant to multiple drugs and carried a plasmid encoding multiple resistance genes. However very few H58-E2 strains were multidrug resistant, which may explain why the strain did not persist after the initial outbreak.
PMCID: PMC3014949  PMID: 21245916
5.  Emergence of a Globally Dominant IncHI1 Plasmid Type Associated with Multiple Drug Resistant Typhoid 
Typhoid fever, caused by Salmonella enterica serovar Typhi (S. Typhi), remains a serious global health concern. Since their emergence in the mid-1970s multi-drug resistant (MDR) S. Typhi now dominate drug sensitive equivalents in many regions. MDR in S. Typhi is almost exclusively conferred by self-transmissible IncHI1 plasmids carrying a suite of antimicrobial resistance genes. We identified over 300 single nucleotide polymorphisms (SNPs) within conserved regions of the IncHI1 plasmid, and genotyped both plasmid and chromosomal SNPs in over 450 S. Typhi dating back to 1958. Prior to 1995, a variety of IncHI1 plasmid types were detected in distinct S. Typhi haplotypes. Highly similar plasmids were detected in co-circulating S. Typhi haplotypes, indicative of plasmid transfer. In contrast, from 1995 onwards, 98% of MDR S. Typhi were plasmid sequence type 6 (PST6) and S. Typhi haplotype H58, indicating recent global spread of a dominant MDR clone. To investigate whether PST6 conferred a selective advantage compared to other IncHI1 plasmids, we used a phenotyping array to compare the impact of IncHI1 PST6 and PST1 plasmids in a common S. Typhi host. The PST6 plasmid conferred the ability to grow in high salt medium (4.7% NaCl), which we demonstrate is due to the presence in PST6 of the Tn6062 transposon encoding BetU.
Author Summary
Typhoid fever is caused by the bacterium Salmonella enterica serovar Typhi (S. Typhi). Treatment relies on antimicrobial drugs, however many S. Typhi are multi-drug resistant (MDR), severely compromising treatment options. MDR typhoid is associated with multiple drug resistance genes, which can be transferred between S. Typhi and other bacteria via self-transmissible plasmids. We used sequence analysis to identify single nucleotide polymorphisms (SNPs) within these plasmids, and used high-resolution SNP typing to trace the subtypes (termed haplotypes) of both the S. Typhi bacteria and their MDR plasmids isolated from more than 450 typhoid patients since 1958. Among isolates collected before 1995, a variety of plasmid haplotypes and S. Typhi haplotypes were detected, indicating that MDR typhoid was caused by a diverse range of S. Typhi and MDR plasmids. In contrast, 98% of MDR S. Typhi samples isolated from 1995 were of the same S. Typhi haplotype and plasmid haplotype, indicating that the recent increase in rates of MDR typhoid is due to the global spread of a dominant S. Typhi-plasmid combination. We demonstrate this particular plasmid type contains a transposon encoding two transporter genes, enabling its S. Typhi host to grow in the presence of high salt concentrations.
PMCID: PMC3139670  PMID: 21811646
6.  Quantitation of Bacteria in Blood of Typhoid Fever Patients and Relationship between Counts and Clinical Features, Transmissibility, and Antibiotic Resistance 
Journal of Clinical Microbiology  1998;36(6):1683-1687.
Salmonella typhi was isolated from 369 and Salmonella paratyphi A was isolated from 6 of 515 Vietnamese patients with suspected enteric fever. Compared with conventional broth culture of blood, direct plating of the buffy coat had a diagnostic sensitivity of 99.5% (95% confidence interval [CI], 97.1 to 100%). Blood bacterial counts were estimated by the pour plate method. The median S. typhi count in blood was 1 CFU/ml (range, <0.3 to 387 CFU/ml), of which a mean of 63% (95% CI, 58 to 67%) were intracellular. The mean number of bacteria per infected leukocyte was 1.3 (interquartile range [IQR], 0.7 to 2.4) CFU/cell (n = 81). Children (<15 years old; n = 115) had higher median blood bacterial counts than adults (n = 262): 1.5 (range, <0.3 to 387) versus 0.6 (range, <0.3 to 17.7) CFU/ml (P = 0.008), and patients who excreted S. typhi in feces had higher bacteremias than those who did not: a median of 3 (range, <0.3 to 32) versus 1 (range, <0.3 to 68) CFU/ml (P = 0.02). Blood bacterial counts declined with increasing duration of illness (P = 0.002) and were higher in infections caused by multidrug-resistant S. typhi (1.3 [range, <0.3 to 387] CFU/ml; n = 313) than in infections caused by antibiotic-sensitive S. typhi (0.5 [range, <0.3 to 32] CFU/ml; n = 62) (P = 0.006). In a multivariate analysis this proved to be an independent association, suggesting a relationship between antibiotic resistance and virulence in S. typhi.
PMCID: PMC104900  PMID: 9620400
7.  In Vivo Expression of Salmonella enterica Serotype Typhi Genes in the Blood of Patients with Typhoid Fever in Bangladesh 
Salmonella enterica serotype Typhi is the cause of typhoid fever. It is a human-restricted pathogen, and few data exist on S. Typhi gene expression in humans.
Methodology/Principal Findings
We applied an RNA capture and amplification technique, Selective Capture of Transcribed Sequences (SCOTS), and microarray hybridization to identify S. Typhi transcripts expressed in the blood of five humans infected with S. Typhi in Bangladesh. In total, we detected the expression of mRNAs for 2,046 S. Typhi genes (44% of the S. Typhi genome) in human blood; expression of 912 genes was detected in all 5 patients, and expression of 1,100 genes was detected in 4 or more patients. Identified transcripts were associated with the virulence-associated PhoP regulon, Salmonella pathogenicity islands, the use of alternative carbon and energy sources, synthesis and transport of iron, thiamine, and biotin, and resistance to antimicrobial peptides and oxidative stress. The most highly represented group were genes currently annotated as encoding proteins designated as hypothetical, unknown, or unclassified. Of the 2,046 detected transcripts, 1,320 (29% of the S. Typhi genome) had significantly different levels of detection in human blood compared to in vitro cultures; detection of 141 transcripts was significantly different in all 5 patients, and detection of 331 transcripts varied in at least 4 patients. These mRNAs encode proteins of unknown function, those involved in energy metabolism, transport and binding, cell envelope, cellular processes, and pathogenesis. We confirmed increased expression of a subset of identified mRNAs by quantitative-PCR.
We report the first characterization of bacterial transcriptional profiles in the blood of patients with typhoid fever. S. Typhi is an important global pathogen whose restricted host range has greatly inhibited laboratory studies. Our results suggest that S. Typhi uses a largely uncharacterized genetic repertoire to survive within cells and utilize alternate energy sources during infection.
Author Summary
Salmonella enterica serotype Typhi is the cause of typhoid fever and infects over 21 million cases and causes 200,000 deaths each year. S. Typhi only infects humans and this has greatly limited studies of S. Typhi pathogenesis. To study bacterial gene expression in human hosts, we used Selective Capture of Transcribed Sequences (SCOTS) and array hybridization to identify S. Typhi mRNAs expressed in the blood of 5 patients with S. Typhi infection. In total, we detected the expression of 2,046 S. Typhi genes (44% of the S. Typhi genome) in human blood; of these, 1,320 (29% of the S. Typhi genome) had significantly different levels of detection in human blood compared to in vitro cultures. Our results provide insight into S. Typhi pathogenesis, identifying both previously described and novel interactions occurring between host and microbe during the natural course of human infection. Further study of these genes, especially those of unknown function, may further our understanding of S. Typhi pathogenesis and aid in vaccine, diagnostic, and/or drug target development.
PMCID: PMC3236720  PMID: 22180799
8.  High prevalence of Non–typhoid salmonella bacteraemia among febrile HIV adult patients admitted at a tertiary Hospital, North-Western Tanzania 
Bacterial blood stream infections constitute a significant public-health problem and it is an important cause of morbidity and mortality in HIV infected patients. Little is known in developing countries regarding salmonella bacteraemia among HIV patients. The purpose of this study was to determine the bacterial pathogens causing blood stream infection among febrile adults attending in a tertiary hospital North-Western, Tanzania.
A prospective cross-sectional study involving 346 consecutive, febrile adult patients admitted at Bugando Medical Centre was conducted. Demographic and other data were collected using standardized questionnaires. Blood culture was done followed by susceptibility testing using disc diffusion method. HIV testing was also performed as per Tanzania national algorithm and total white blood cell counts and CD4+ counts determined.
Of 346 febrile adult patients 33 (9.5%) had blood stream infections. The common isolates were Salmonella spp 13(39.4%), Escherichia coli 8 (24.2%), Streptococcus pneumonia 5(15.2%), Staphylococcus aureus 4(12.1%), Citrobacter spp 1(3%), Streptococcus pyogenes 1(3%) and Klebsiella pneumonia 1(3%). A total of 156 (45.1%) patients were HIV infected; of whom 12/156 (7.6%) were infected by non-typhoid Salmonella spp compared to 1/190 (0.5%) of non-HIV infected patients (RRR 11.2, p=0.029) infected with Salmonella typhi. HIV infected patients with bacteraemia had significantly lower CD4+ count than those without bacteraemia (median 28 vs. 88 cells/ml, p=0.01). Patients with salmonella bacteraemia had significantly lower median of WBC than those with non-salmonella as well as those without bacteraemia (median, 3.6 vs. 17.5 vs. 9.8x109, p=0.0001). All Salmonella spp were sensitive to ceftriaxone and imipenem, while being 84%, 69.2%, 38% and 8% resistant to chloramphenicol, ampicillin, sulphamethaxazole/trimethoprim and ciprofloxacin respectively. Predictors of mortality were HIV infection (OR 2.3, p=0.006), Glasgow coma score of less than 15 (OR 3.4, p=0.0001) and night sweats (OR 2.4, p=0.014).
Non-typhoid Salmonella spp that are highly resistant to common antibiotics are predominant cause of bacterial blood stream infection among HIV patients attending Bugando Medical Centre. Continuous surveillance and intervention strategies should be put in place to monitor and manage cases of bloodstream infections in HIV-positive patients in Mwanza, Tanzania.
PMCID: PMC3540015  PMID: 23075077
9.  Typhoid Outbreak in Songkhla, Thailand 2009–2011: Clinical Outcomes, Susceptibility Patterns, and Reliability of Serology Tests 
PLoS ONE  2014;9(11):e111768.
To determine the clinical manifestations and outcomes, the reliability of Salmonella enterica serotype Typhi (S ser. Typhi) IgM and IgG rapid tests, and the susceptibility patterns and the response to treatment during the 2009–2011 typhoid outbreak in Songkhla province in Thailand.
The medical records of children aged <15 years with S ser. Typhi bacteremia were analysed. The efficacy of the typhoid IgM and IgG rapid tests and susceptibility of the S ser. Typhi to the current main antibiotics used for typhoid (amoxicillin, ampicillin, cefotaxime, ceftriaxone, co-trimoxazole, and ciprofloxacin), were evaluated.
S ser. Typhi bacteremia was found in 368 patients, and all isolated strains were susceptible to all 6 antimicrobials tested. Most of the patients were treated with ciprofloxacin for 7–14 days. The median time (IQR) of fever before treatment and duration of fever after treatment were 5 (4, 7) days and 4 (3, 5) days, respectively. Complications of ascites, lower respiratory symptoms, anemia (Hct <30%), and ileal perforation were found in 7, 7, 22, and 1 patients, respectively. None of the patients had recurrent infection or died. The sensitivities of the typhoid IgM and IgG tests were 58.3% and 25.6% respectively, and specificities were 74.1% and 50.5%, respectively.
Most of the patients were diagnosed at an early stage and treated with a good outcome. All S ser. Typhi strains were susceptible to standard first line antibiotic typhoid treatment. The typhoid IgM and IgG rapid tests had low sensitivity and moderate specificity.
PMCID: PMC4222948  PMID: 25375784
10.  Host response transcriptional profiling reveals extracellular components and ABC (ATP-binding cassette) transporters gene enrichment in typhoid fever-infected Nigerian children 
BMC Infectious Diseases  2011;11:241.
Salmonella enterica serovar Typhi (S. Typhi) is a human-specific pathogen that causes typhoid fever, and remains a global health problem especially in developing countries. Its pathogenesis is complex and host response is poorly understood. In Africa, typhoid fever can be a major cause of morbidity in young infected children. The onset of the illness is insidious and clinical diagnosis is often unreliable. Gold standard blood culture diagnostic services are limited, thus rapid, sensitive, and affordable diagnostic test is essential in poor-resourced clinical settings. Routine typhoid fever vaccination is highly recommended but currently licensed vaccines provide only 55-75% protection. Recent epidemiological studies also show the rapid emergence of multi-drug resistant S. Typhi strains. High-throughput molecular technologies, such as microarrays, can dissect the molecular mechanisms of host responses which are S. Typhi-specific to provide a comprehensive genomic component of immunological responses and suggest new insights for diagnosis and treatment.
Global transcriptional profiles of S. Typhi-infected young Nigerian children were obtained from their peripheral blood and compared with that of other bacteremic infections using Agilent gene expression microarrays. The host-response profiles of the same patients in acute vs. convalescent phases were also determined. The top 96-100 differentially-expressed genes were identified and four genes were validated by quantitative real-time PCR. Gene clusters were obtained and functional pathways were predicted by DAVID (Database for Annotation, Visualization and Integrated Discovery).
Transcriptional profiles from S. Typhi-infected children could be distinguished from those of other bacteremic infections. Enriched gene clusters included genes associated with extracellular peptides/components such as lipocalin (LCN2) and systemic immune response which is atypical in bacterial invasion. Distinct gene expression profiles can also be obtained from acute vs. convalescent phase during typhoid fever infection. We found novel down-regulation of ABC (ATP-binding cassette) transporters genes such as ABCA7, ABCC5, and ABCD4 and ATPase activity as the highest enriched pathway.
We identified unique extracellular components and ABC transporters gene enrichments in typhoid fever-infected Nigerian children, which have never been reported. These enriched gene clusters may represent novel targeted pathways to improve diagnostic, prognostic, therapeutic and next-generation vaccine strategies for typhoid fever in Africa.
PMCID: PMC3189140  PMID: 21914192
11.  Evaluation of an Electricity-free, Culture-based Approach for Detecting Typhoidal Salmonella Bacteremia during Enteric Fever in a High Burden, Resource-limited Setting 
In many rural areas at risk for enteric fever, there are few data on Salmonella enterica serotypes Typhi (S. Typhi) and Paratyphi (S. Paratyphi) incidence, due to limited laboratory capacity for microbiologic culture. Here, we describe an approach that permits recovery of the causative agents of enteric fever in such settings. This approach involves the use of an electricity-free incubator based upon use of phase-change materials. We compared this against conventional blood culture for detection of typhoidal Salmonella.
Methodology/Principal Findings
Three hundred and four patients with undifferentiated fever attending the outpatient and emergency departments of a public hospital in the Kathmandu Valley of Nepal were recruited. Conventional blood culture was compared against an electricity-free culture approach. Blood from 66 (21.7%) patients tested positive for a Gram-negative bacterium by at least one of the two methods. Sixty-five (21.4%) patients tested blood culture positive for S. Typhi (30; 9.9%) or S. Paratyphi A (35; 11.5%). From the 65 individuals with culture-confirmed enteric fever, 55 (84.6%) were identified by the conventional blood culture and 60 (92.3%) were identified by the experimental method. Median time-to-positivity was 2 days for both procedures. The experimental approach was falsely positive due to probable skin contaminants in 2 of 239 individuals (0.8%). The percentages of positive and negative agreement for diagnosis of enteric fever were 90.9% (95% CI: 80.0%–97.0%) and 96.0% (92.7%–98.1%), respectively. After initial incubation, Salmonella isolates could be readily recovered from blood culture bottles maintained at room temperature for six months.
A simple culture approach based upon a phase-change incubator can be used to isolate agents of enteric fever. This approach could be used as a surveillance tool to assess incidence and drug resistance of the etiologic agents of enteric fever in settings without reliable local access to electricity or local diagnostic microbiology laboratories.
Author Summary
Every year, 20 million people worldwide suffer from typhoid, a bacterial infection spread by contaminated food and water, and over 200,000 die from the infection. However, few data are available on the prevalence and antimicrobial resistance profiles of the causative agents of typhoid, especially in settings without reliable access to laboratories and electricity. Here, we describe an approach that permits recovery of the causative agents of typhoid that requires no electricity, laboratory infrastructure, or specialized laboratory personnel at the site of patient contact. This approach involves the use of an electricity-free incubator, consisting of an insulated container and reusable packets filled with a chemical that upon warming in hot water or direct sun, maintains 38°C for 24 hours. We used blood culture bottles with a color indicator that signals growth of bacteria and an antibiotic that selects for Gram-negative bacteria. We validated this approach in a clinical study among individuals with fever presenting to a hospital in urban Nepal, demonstrating that the approach performed comparably to conventional blood culture for isolating the bacteria causing typhoid. Such an approach would permit an estimate of the burden of typhoid in areas where such data are lacking, which could inform control strategies.
PMCID: PMC3694822  PMID: 23853696
12.  Epidemic typhoid in Chile: analysis by molecular and conventional methods of Salmonella typhi strain diversity in epidemic (1977 and 1981) and nonepidemic (1990) years. 
Journal of Clinical Microbiology  1996;34(7):1701-1707.
From 1977 to 1986, Chile experienced an important typhoid fever epidemic, despite statistics that indicated apparently improving levels of sanitation of drinking water and sewage disposal. The lack of antibiotic resistance among the Salmonella typhi strains isolated during this period, the mild clinical presentation of the disease, and the initially low level of efficacy of the S. typhi Ty21a vaccine in the population exposed to the epidemic suggested that this epidemic might have resulted from the dissemination of S. typhi strains with unique characteristics. To investigate this hypothesis, we used conventional methods (bacteriophage typing and biotyping) and molecular methods (restriction fragment length polymorphism analysis, ribotyping, IS200 typing, and PCR amplification of the fliC-d gene) to study a population of 149 S. typhi isolates during 1977, 1981, and 1990, the years that included periods with low (when the disease was endemic) and high (when the disease was epidemic) morbidities. Our results indicate that these S. typhi isolates in Chile represent a number of highly diverse variants of the clone of S. typhi with a worldwide distribution described by Selander et al. (R. K. Selander, P. Beltran, N.H. Smith, R. Helmuth, F.A. Rubin, D.J. Kopecko, K. Ferris, B.D. Tall, A. Cravioto, and J.M. Musser, Infect. Immun. 58:2262-2275, 1990). For example, we detected 26 PstI and 10 ClaI ribotypes among 47 and 16 S. typhi strains belonging to this clone, respectively. These results suggest that the Chilean epidemic was probably produced by multiple sources of infection because of deficient sanitary conditions. These findings illustrate the usefulness of molecular methods for characterizing the potential causes of the typhoid epidemics and the possible routes of transmission of S. typhi strains in typhoid epidemics.
PMCID: PMC229098  PMID: 8784573
13.  Shifts in Geographic Distribution and Antimicrobial Resistance during a Prolonged Typhoid Fever Outbreak — Bundibugyo and Kasese Districts, Uganda, 2009–2011 
Salmonella enterica serovar Typhi is transmitted by fecally contaminated food and water and causes approximately 22 million typhoid fever infections worldwide each year. Most cases occur in developing countries, where approximately 4% of patients develop intestinal perforation (IP). In Kasese District, Uganda, a typhoid fever outbreak notable for a high IP rate began in 2008. We report that this outbreak continued through 2011, when it spread to the neighboring district of Bundibugyo.
Methodology/Principal Findings
A suspected typhoid fever case was defined as IP or symptoms of fever, abdominal pain, and ≥1 of the following: gastrointestinal disruptions, body weakness, joint pain, headache, clinically suspected IP, or non-responsiveness to antimalarial medications. Cases were identified retrospectively via medical record reviews and prospectively through laboratory-enhanced case finding. Among Kasese residents, 709 cases were identified from August 1, 2009–December 31, 2011; of these, 149 were identified during the prospective period beginning November 1, 2011. Among Bundibugyo residents, 333 cases were identified from January 1–December 31, 2011, including 128 cases identified during the prospective period beginning October 28, 2011. IP was reported for 507 (82%) and 59 (20%) of Kasese and Bundibugyo cases, respectively. Blood and stool cultures performed for 154 patients during the prospective period yielded isolates from 24 (16%) patients. Three pulsed-field gel electrophoresis pattern combinations, including one observed in a Kasese isolate in 2009, were shared among Kasese and Bundibugyo isolates. Antimicrobial susceptibility was assessed for 18 isolates; among these 15 (83%) were multidrug-resistant (MDR), compared to 5% of 2009 isolates.
Molecular and epidemiological evidence suggest that during a prolonged outbreak, typhoid spread from Kasese to Bundibugyo. MDR strains became prevalent. Lasting interventions, such as typhoid vaccination and improvements in drinking water infrastructure, should be considered to minimize the risk of prolonged outbreaks in the future.
Author Summary
Typhoid fever is an acute febrile illness caused by the bacteria Salmonella Typhi and transmitted through food and water contaminated with the feces of typhoid fever patients or carriers. We investigated typhoid fever outbreaks in two neighboring Ugandan districts, Kasese and Bundibugyo, where typhoid fever outbreaks began in 2008 and 2011, respectively. In Kasese from August 2009–December 2011, we documented 709 cases of typhoid fever. In Bundibugyo from January–December 2011, we documented 333 cases. Salmonella Typhi from Bundibugyo and Kasese had indistinguishable molecular fingerprints; laboratory and epidemiological evidence indicate that the outbreak spread from Kasese to Bundibugyo. Salmonella Typhi isolated during our investigation were resistant to more antibiotics than isolates obtained from Kasese in 2009. Drinking water in both districts was fecally contaminated and the likely vehicle for the outbreaks. Our investigation highlights that in unchecked typhoid fever outbreaks, illness can become geographically dispersed and outbreak strains can become increasingly resistant to antibiotics. Lasting interventions, including investments in drinking water infrastructure and typhoid vaccination, are needed to control these outbreaks and prevent future outbreaks.
PMCID: PMC3945727  PMID: 24603860
14.  Randomized Controlled Comparison of Ofloxacin, Azithromycin, and an Ofloxacin-Azithromycin Combination for Treatment of Multidrug-Resistant and Nalidixic Acid-Resistant Typhoid Fever▿  
Isolates of Salmonella enterica serovar Typhi that are multidrug resistant (MDR, resistant to chloramphenicol, ampicillin, and trimethoprim-sulfamethoxazole) and have reduced susceptibility to fluoroquinolones (nalidixic acid resistant, Nar) are common in Asia. The optimum treatment for infections caused by such isolates is not established. This study compared different antimicrobial regimens for the treatment of MDR/Nar typhoid fever. Vietnamese children and adults with uncomplicated typhoid fever were entered into an open randomized controlled trial. Ofloxacin (20 mg/kg of body weight/day for 7 days), azithromycin (10 mg/kg/day for 7 days), and ofloxacin (15 mg/kg/day for 7 days) combined with azithromycin (10 mg/kg/day for the first 3 days) were compared. Of the 241 enrolled patients, 187 were eligible for analysis (186 S. enterica serovar Typhi, 1 Salmonella enterica serovar Paratyphi A). Eighty-seven percent (163/187) of the patients were children; of the S. enterica serovar Typhi isolates, 88% (165/187) were MDR and 93% (173/187) were Nar. The clinical cure rate was 64% (40/63) with ofloxacin, 76% (47/62) with ofloxacin-azithromycin, and 82% (51/62) with azithromycin (P = 0.053). The mean (95% confidence interval [CI]) fever clearance time for patients treated with azithromycin (5.8 days [5.1 to 6.5 days]) was shorter than that for patients treated with ofloxacin-azithromycin (7.1 days [6.2 to 8.1 days]) and ofloxacin (8.2 days [7.2 to 9.2 days]) (P < 0.001). Positive fecal carriage immediately posttreatment was detected in 19.4% (12/62) of patients treated with ofloxacin, 6.5% (4/62) of those treated with the combination, and 1.6% (1/62) of those treated with azithromycin (P = 0.006). Both antibiotics were well tolerated. Uncomplicated typhoid fever due to isolates of MDR S. enterica serovar Typhi with reduced susceptibility to fluoroquinolones (Nar) can be successfully treated with a 7-day course of azithromycin.
PMCID: PMC1803150  PMID: 17145784
15.  Typhoid in Kenya Is Associated with a Dominant Multidrug-Resistant Salmonella enterica Serovar Typhi Haplotype That Is Also Widespread in Southeast Asia▿ †  
Journal of Clinical Microbiology  2010;48(6):2171-2176.
In sub-Saharan Africa, the burden of typhoid fever, caused by Salmonella enterica serovar Typhi, remains largely unknown, in part because of a lack of blood or bone marrow culture facilities. We characterized a total of 323 S. Typhi isolates from outbreaks in Kenya over the period 1988 to 2008 for antimicrobial susceptibilities and phylogenetic relationships using single-nucleotide polymorphism (SNP) analysis. There was a dramatic increase in the number and percentage of multidrug-resistant (MDR) S. Typhi isolates over the study period. Overall, only 54 (16.7%) S. Typhi isolates were fully sensitive, while the majority, 195 (60.4%), were multiply resistant to most commonly available drugs—ampicillin, chloramphenicol, tetracycline, and cotrimoxazole; 74 (22.9%) isolates were resistant to a single antimicrobial, usually ampicillin, cotrimoxazole, or tetracycline. Resistance to these antibiotics was encoded on self-transferrable IncHI1 plasmids of the ST6 sequence type. Of the 94 representative S. Typhi isolates selected for genome-wide haplotype analysis, sensitive isolates fell into several phylogenetically different groups, whereas MDR isolates all belonged to a single haplotype, H58, associated with MDR and decreased ciprofloxacin susceptibility, which is also dominant in many parts of Southeast Asia. Derivatives of the same S. Typhi lineage, H58, are responsible for multidrug resistance in Kenya and parts of Southeast Asia, suggesting intercontinental spread of a single MDR clone. Given the emergence of this aggressive MDR haplotype, careful selection and monitoring of antibiotic usage will be required in Kenya, and potentially other regions of sub-Saharan Africa.
PMCID: PMC2884483  PMID: 20392916
16.  Evaluation of the current trend of nalidixic acid susceptibility in typhoidal Salmonellae; a marker of therapeutic failure for the fluoroquinolones 
Background and Objectives
Typhoid is a major health problem faced by the developing countries like Pakistan. More than 20 million cases are reported annually worldwide. Currently fluoroquinolones are the drugs of choice to treat typhoid fever. In vivo resistance to fluoroquinolones leading to therapeutic failure is developing rapidly and is becoming a major concern for the clinicians. The objective of this study was to determine the sensitivity pattern of Nalidixic acid over the last four years
Material and Methods
A descriptive cross sectional study was carried out at the Microbiology Department of the Army Medical College, National University of Sciences and Technology, Rawalpindi from January 2006 to December 2009. All the isolates were dealt with standard microbiological procedures. The antimicrobial sensitivity of Nalidixic acid and Ciprofloxacin was determined using Kirby-Bauer disc diffusion method as per the guidelines of Clinical and Laboratory Standard Institute (CLSI).
Out of 240 isolates, 111 were Salmonella typhi and 129 were Salmonella paratyphi A. The resistance of the typhoidal Salmonella to Nalidixic acid has reached significant levels and it seems only a matter of time when hundred percent resistance will be encountered. All isolates were sensitive to Ciprofloxacin on disc diffusion method.
Resistance to Nalidixic acid predicting therapeutic failure with fluoroquinolones is on a steady rise.
PMCID: PMC3279808  PMID: 22347587
Nalidixic acid resistance; Therapeutic failure; typhoid; typhoidal Salmonella
17.  Identification by PCR of Non-typhoidal Salmonella enterica Serovars Associated with Invasive Infections among Febrile Patients in Mali 
In sub-Saharan Africa, non-typhoidal Salmonella (NTS) are emerging as a prominent cause of invasive disease (bacteremia and focal infections such as meningitis) in infants and young children. Importantly, including data from Mali, three serovars, Salmonella enterica serovar Typhimurium, Salmonella Enteritidis and Salmonella Dublin, account for the majority of non-typhoidal Salmonella isolated from these patients.
We have extended a previously developed series of polymerase chain reactions (PCRs) based on O serogrouping and H typing to identify Salmonella Typhimurium and variants (mostly I 4,[5],12:i:-), Salmonella Enteritidis and Salmonella Dublin. We also designed primers to detect Salmonella Stanleyville, a serovar found in West Africa. Another PCR was used to differentiate diphasic Salmonella Typhimurium and monophasic Salmonella Typhimurium from other O serogroup B, H:i serovars. We used these PCRs to blind-test 327 Salmonella serogroup B and D isolates that were obtained from the blood cultures of febrile patients in Bamako, Mali.
Principal Findings
We have shown that when used in conjunction with our previously described O-serogrouping PCR, our PCRs are 100% sensitive and specific in identifying Salmonella Typhimurium and variants, Salmonella Enteritidis, Salmonella Dublin and Salmonella Stanleyville. When we attempted to differentiate 171 Salmonella Typhimurium (I 4,[ 5],12:i:1,2) strains from 52 monophasic Salmonella Typhimurium (I 4,[5],12:i:-) strains, we were able to correctly identify 170 of the Salmonella Typhimurium and 51 of the Salmonella I 4,[5],12:i:- strains.
We have described a simple yet effective PCR method to support surveillance of the incidence of invasive disease caused by NTS in developing countries.
Author Summary
The genus Salmonella has more than 2500 serological variants (serovars), such as Salmonella enterica serovar Typhi and Salmonella Paratyphi A and B, that cause, respectively, typhoid and paratyphoid fevers (enteric fevers), and a large number of non-typhoidal Salmonella (NTS) serovars that cause gastroenteritis in healthy hosts. In young infants, the elderly and immunocompromised hosts, NTS can cause severe, fatal invasive disease. Multiple studies of pediatric patients in sub-Saharan Africa have documented the important role of NTS, in particular Salmonella Typhimurium and Salmonella Enteritidis (and to a lesser degree Salmonella Dublin), as invasive bacterial pathogens. Salmonella spp. are isolated from blood and identified by standard microbiological techniques and the serovar is ascertained by agglutination with commercial antisera. PCR-based typing techniques are becoming increasingly popular in developing countries, in part because high quality typing sera are difficult to obtain and expensive and H serotyping is technically difficult. We have developed a series of polymerase chain reactions (PCRs) to identify Salmonella Typhimurium and variants, Salmonella Enteritidis and Salmonella Dublin. We successfully identified 327 Salmonella isolates using our multiplex PCR. We also designed primers to detect Salmonella Stanleyville, a serovar found in West Africa. Another PCR generally differentiated diphasic Salmonella Typhimurium and monophasic Salmonella Typhimurium variant strains from other closely related strains. The PCRs described here will enable more laboratories in developing countries to serotype NTS that have been isolated from blood.
PMCID: PMC2834738  PMID: 20231882
18.  High-throughput bacterial SNP typing identifies distinct clusters of Salmonella Typhi causing typhoid in Nepalese children 
BMC Infectious Diseases  2010;10:144.
Salmonella Typhi (S. Typhi) causes typhoid fever, which remains an important public health issue in many developing countries. Kathmandu, the capital of Nepal, is an area of high incidence and the pediatric population appears to be at high risk of exposure and infection.
We recently defined the population structure of S. Typhi, using new sequencing technologies to identify nearly 2,000 single nucleotide polymorphisms (SNPs) that can be used as unequivocal phylogenetic markers. Here we have used the GoldenGate (Illumina) platform to simultaneously type 1,500 of these SNPs in 62 S. Typhi isolates causing severe typhoid in children admitted to Patan Hospital in Kathmandu.
Eight distinct S. Typhi haplotypes were identified during the 20-month study period, with 68% of isolates belonging to a subclone of the previously defined H58 S. Typhi. This subclone was closely associated with resistance to nalidixic acid, with all isolates from this group demonstrating a resistant phenotype and harbouring the same resistance-associated SNP in GyrA (Phe83). A secondary clone, comprising 19% of isolates, was observed only during the second half of the study.
Our data demonstrate the utility of SNP typing for monitoring bacterial populations over a defined period in a single endemic setting. We provide evidence for genotype introduction and define a nalidixic acid resistant subclone of S. Typhi, which appears to be the dominant cause of severe pediatric typhoid in Kathmandu during the study period.
PMCID: PMC2897797  PMID: 20509974
19.  Molecular Typing of Multiple-Antibiotic-Resistant Salmonella enterica Serovar Typhi from Vietnam: Application to Acute and Relapse Cases of Typhoid Fever 
Journal of Clinical Microbiology  1999;37(8):2466-2472.
The rate of multiple-antibiotic resistance is increasing among Salmonella enterica serovar Typhi strains in Southeast Asia. Pulsed-field gel electrophoresis (PFGE) and other typing methods were used to analyze drug-resistant and -susceptible organisms isolated from patients with typhoid fever in several districts in southern Vietnam. Multiple PFGE and phage typing patterns were detected, although individual patients were infected with strains of a single type. The PFGE patterns were stable when the S. enterica serovar Typhi strains were passaged many times in vitro on laboratory medium. Paired S. enterica serovar Typhi isolates recovered from the blood and bone marrow of individual patients exhibited similar PFGE patterns. Typing of S. enterica serovar Typhi isolates from patients with relapses of typhoid indicated that the majority of relapses were caused by the same S. enterica serovar Typhi strain that was isolated during the initial infection. However, some individuals were infected with distinct and presumably newly acquired S. enterica serovar Typhi isolates.
PMCID: PMC85257  PMID: 10405386
20.  Characterization of Multidrug-Resistant Typhoid Outbreaks in Kenya 
Journal of Clinical Microbiology  2004;42(4):1477-1482.
We characterized by antibiotic susceptibility, plasmid analysis, incompatibility grouping, and pulsed-field gel electrophoresis (PFGE) of XbaI- and SpeI-digested DNA 102 Salmonella enterica serovar Typhi (serovar Typhi) isolated from recent outbreaks of typhoid in three different parts of Kenya. Only 13.7% were fully susceptible, whereas another 82.4% were resistant to each of the five commonly available drugs: ampicillin, chloramphenicol, and tetracycline (MICs of >256 μg/ml); streptomycin (MIC, >1,024 μg/ml); and cotrimoxazole (MIC of >32 μg/ml). Resistance to these antibiotics was encoded on a 110-kb self-transferable plasmid of IncHI1 incompatibility group. The MICs of nalidixic acid (MIC, 8 to 16 μg/ml) and ciprofloxacin (MIC of 0.25 to 0.38 μg/ml) for 41.7% of the 102 serovar Typhi isolates were 5- and 10-fold higher, respectively, than for sensitive strains. Amplification by PCR and sequencing of the genes coding for gyrase (gyrA and gyrB) and topoisomerase IV (parE and parC) within the quinolone resistance-determining region revealed that the increase in the MICs of the quinolones had not resulted from any significant mutation. Analysis of genomic DNA from both antimicrobial agent-sensitive and multidrug-resistant serovar Typhi by PFGE identified two distinct subtypes that were in circulation in the three different parts of Kenya. As the prevalence of multidrug-resistant serovar Typhi increases, newer, more expensive, and less readily available antimicrobial agents will be required for the treatment of typhoid in Kenya.
PMCID: PMC387605  PMID: 15070992
21.  Antibiogram of Salmonella Isolates from Blood with an Emphasis on Nalidixic Acid and Chloramphenicol Susceptibility in a Tertiary Care Hospital in Coastal Karnataka: A Prospective Study 
Enteric fever is caused by the serotypes Salmonella Typhi, Salmonella Paratyphi A, Salmonella Paratyphi B and Salmonella Paratyphi C. After emergence of multidrug resistant Salmonellae Ciprofloxacin, a fluorquinolone antibiotic was the first-line therapy. Treatment failure was observed with Ciprofloxacin soon and such strains showed in-vitro resistance to Nalidixic acid. Recent reports suggest re-emergence of Chloramphenicol sensitive strains and increasing Nalidixic acid resistance. This study is aimed at detecting the current trend in the antibiogram of Salmonella isolates from blood culture in coastal Karnataka, with an emphasis on antibiotic susceptibility of Nalidixic acid and Chloramphenicol and evaluate, if there is a need to modify the strategies in the antibiotic therapy for enteric fever.
Materials and Methods:
Blood samples received for culture in the laboratory between June 2009 and August 2011 was cultured in Brain Heart infusion broth, bile broth or in a commercial BACTEC culture media. The growth from blood cultures were processed for identification and antibiotic susceptibility as per standard methods. Antibiotic susceptibility for Ampicillin, Trimethoprim-sulphamethoxazole, Chloramphenicol, Ciprofloxacin, Ceftriaxone and Nalidixic acid were noted.
Out of 9053 blood culture specimens received, Salmonella was isolated from 103 specimens. There were 85 Salmonella Typhi isolates, 16 Salmonella Paratyphi A and two Salmonella Paratyphi B. Salmonella Typhi and Salmonella Paratyphi A showed the highest resistance to Nalidixic acid. Salmonella Typhi showed highest susceptibility to Ceftriaxone and Salmonella Paratyphi A to trimethoprim-sulphamethoxazole and Chloramphenicol. Two isolates were multidrug resistant. One Salmonella Paratyphi A was resistant to Ceftriaxone.
Routine screening of Nalidixic acid susceptibility is practical to predict fluorquinolone resistance in Salmonella and preventing therapeutic failure while treating with it. It is worthwhile to consider replacing fluorquinolones with Chloramphenicol or Ceftriaxone as the first line of therapy for enteric fever. Periodic analysis of Salmonella antibiogram should be done to formulate the best possible treatment strategies.
PMCID: PMC3574501  PMID: 23440906
Ceftriaxone; Chloramphenicol; Nalidixic acid; resistance; Salmonella
22.  Epidemic Typhoid in Vietnam: Molecular Typing of Multiple-Antibiotic-Resistant Salmonella enterica Serotype Typhi from Four Outbreaks 
Journal of Clinical Microbiology  2000;38(2):895-897.
Multidrug-resistant Salmonella enterica serotype Typhi isolates from four outbreaks of typhoid fever in southern Vietnam between 1993 and 1997 were compared. Pulsed-field gel electrophoresis, bacteriophage and plasmid typing, and antibiotic susceptibilities showed that independent outbreaks of multidrug-resistant typhoid fever in southern Vietnam are caused by single bacterial strains. However, different outbreaks do not derive from the clonal expansion of a single multidrug-resistant serotype Typhi strain.
PMCID: PMC86238  PMID: 10655411
23.  Antimicrobial susceptibility of Salmonella enterica serovars in a tertiary care hospital in southern India 
Background & objectives:
Salmonella enterica serovars Typhi and Paratyphi are predominantly known to cause enteric fever. Multidrug resistance in S. Tphi and S. Paratyphi has emerged as a cause of concern. This study was done to evaluate status in antimicrobial susceptibility patterns of Salmonella enterica serovar Typhi (S. Typhi) and S. Paratyphi obtained from blood culture in a tertiary care hospital in south India.
Blood isolates of Salmonella species over a two year period between May 2009 and June 2011 were studied. A total of 322 isolates of Salmonella species were tested for antimicrobial susceptibility by Kirby-Bauer disc diffusion method. The MIC of ciprofloxacin was obtained by E-test, and azithromycin MIC was confirmed by agar dilution method for a limited number of isolates.
Of the total of 322 isolates studied, 186 (57.8%) were S. Typhi, 134 (41.6%) were S. Paratyphi A, and two were S. Paratyphi B. Of these, 44(13.66%) were resistant to ciprofloxacin (MIC <0.50 μg/ml) and 296 (91.9%) were nalidixic acid resistant. Of these 296 nalidixic acid resistant isolates, 278 (94%) were susceptible to ciprofloxacin by MIC criteria (<0.5 μg/ml). Of the 262 isolates tested for azithromycin sensitivity, only 120 (46%) were susceptible, whereas 81 (31%) were resistant and 55 (21%) showed intermediate susceptibility. Of the isolates, 322 (90%) were susceptible to ampicillin and (95%) were susceptible to co-trimoxazole. However, all the isolates were susceptible to chloramphenicol and ceftriaxone.
Interpretation & conclusions:
Nalidixic acid resistance screening is not a reliable surrogate indicator of ciprofloxacin resistance. Ciprofloxacin MIC should to be routinely done. Azithromycin resistance appears to be emerging. However, isolates showed a high degree of susceptibility to ampicillin, co-trimoxazole and chloramphenicol. Thus, antibiotics like ampicillin and co-trimoxazole may once again be useful for the management of enteric fever in southern India.
PMCID: PMC3724263  PMID: 23703350
Antimicrobial susceptibility; azithromycin; ciprofloxacin; co-trimoxazole; Salmonella; typhoid
24.  Does chloramphenicol remain the drug of choice for typhoid? 
Epidemiology and Infection  1987;98(3):379-383.
Of 2356 strains of Salmonella typhi isolated in Britain in the 8-year period 1978-85, 2345 (99.53%) were sensitive to all antibiotics tested and 11 (0.47%) were chloramphenicol-resistant; chloramphenicol resistance was plasmid-mediated in 6 strains. It is concluded that chloramphenicol remains a satisfactory first-line choice of drug for typhoid fever in Britain.
PMCID: PMC2235375  PMID: 3595753
25.  Quantitation of Bacteria in Bone Marrow from Patients with Typhoid Fever: Relationship between Counts and Clinical Features 
Journal of Clinical Microbiology  2001;39(4):1571-1576.
Enteric fever is the only bacterial infection of humans for which bone marrow examination is routinely recommended. A prospective study of the concentrations of bacteria in the bone marrow and their relationship to clinical features was conducted with 120 Vietnamese patients with suspected enteric fever, of whom 89 had confirmed typhoid fever. Ninety-three percent of the Salmonella enterica serovar Typhi samples isolated were resistant to ampicillin, chloramphenicol, and co-trimoxazole. For 81 patients with uncomplicated typhoid and satisfactory bone marrow aspirates, the number of serovar Typhi CFU in bone marrow aspirates was a median value of 9 (interquartile range [IQR], 1 to 85; range, 0.1 to 1,580) compared to 0.3 (IQR, 0.1 to 10; range, 0.1 to 399) CFU/ml in simultaneously sampled blood. The ratio of individual blood counts to bone marrow counts was 10 (IQR, 2.3 to 97.5). The number of bacteria in blood but not bone marrow was correlated inversely with the duration of preceding fever. Thus, with increasing duration of illness the ratio of bone marrow-to-blood bacterial concentrations increased; the median ratio was 4.8 (IQR, 1 to 27.5) during the first week compared with 158 (IQR, 60 to 397) during the third week. After lysing the host cells, the median ratio of viable bone marrow to blood increased, reflecting the higher concentration of intracellular serovar Typhi in the bone marrow. Effective antibiotic pretreatment had a significantly greater effect in reducing blood counts compared to bone marrow counts (P < 0.001). Thus, bacteria in the bone marrow of typhoid patients are less affected by antibiotic treatment than bacteria in the blood. The numbers of bacteria in bone marrow correlated negatively with the white blood cell (R = −0.3, P = 0.006) and platelet counts (R = −0.32, P = 0.01) and positively with fever clearance time after treatment (R = 0.4, P < 0.001). The bacterial load in bone marrow therefore may reflect the clinical course of the infection, and high levels may suppress neutrophil proliferation.
PMCID: PMC87972  PMID: 11283089

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