Characteristics of Salmonella Recovered From Stools of Children Enrolled in the Global Enteric Multicenter Study

BACKGROUND

The Global Enteric Multicenter Study (GEMS) determined the etiologic agents of moderate-to-severe diarrhea (MSD) in children under 5 years old in Africa and Asia. Here, we describe the prevalence and antimicrobial susceptibility of nontyphoidal Salmonella (NTS) serovars in GEMS and examine the phylogenetics of Salmonella Typhimurium ST313 isolates.

METHODS

Salmonella isolated from children with MSD or diarrhea-free controls were identified by classical clinical microbiology and serotyped using antisera and/or whole-genome sequence data. We evaluated antimicrobial susceptibility using the Kirby-Bauer disk-diffusion method. Salmonella Typhimurium sequence types were determined using multi-locus sequence typing, and whole-genome sequencing was performed to assess the phylogeny of ST313.

RESULTS

Of 370 Salmonella-positive individuals, 190 (51.4%) were MSD cases and 180 (48.6%) were diarrhea-free controls. The most frequent Salmonella serovars identified were Salmonella Typhimurium, serogroup O:8 (C2-C3), serogroup O:6,7 (C1), Salmonella Paratyphi B Java, and serogroup O:4 (B). The prevalence of NTS was low but similar across sites, regardless of age, and was similar among both cases and controls except in Kenya, where Salmonella Typhimurium was more commonly associated with cases than controls. Phylogenetic analysis showed that these Salmonella Typhimurium isolates, all ST313, were highly genetically related to isolates from controls. Generally, Salmonella isolates from Asia were resistant to ciprofloxacin and ceftriaxone, but African isolates were susceptible to these antibiotics.

CONCLUSIONS

Our data confirm that NTS is prevalent, albeit at low levels, in Africa and South Asia. Our findings provide further evidence that multidrug-resistant Salmonella Typhimurium ST313 can be carried asymptomatically by humans in sub-Saharan Africa.

Haitian Variant Vibrio cholerae O1 Strains Manifest Higher Virulence in Animal Models

Vibrio cholerae causes fatal diarrheal disease cholera in humans due to consumption of contaminated water and food. To instigate the disease, the bacterium must evade the host intestinal innate immune system; penetrate the mucus layer of the small intestine, adhere and multiply on the surface of microvilli and produce toxin(s) through the action of virulence associated genes. V. cholerae O1 that has caused a major cholera outbreak in Haiti contained several unique genetic signatures. These novel traits are used to differentiate them from the canonical El Tor strains. Several studies reported the spread of these Haitian variant strains in different parts of the world including Asia and Africa, but there is a paucity of information on the clinical consequence of these genetic changes. To understand the impact of these changes, we undertook a study involving mice and rabbit models to evaluate the pathogenesis. The colonization ability of Haitian variant strain in comparison to canonical El Tor strain was found to be significantly more in both suckling mice and rabbit model. Adult mice also displayed the same results. Besides that, infection patterns of Haitian variant strains showed a completely different picture. Increased mucosal damaging, colonization, and inflammatory changes were observed through hematoxylin-eosin staining and transmission electron microscopy. Fluid accumulation ability was also significantly higher in rabbit model. Our study indicated that these virulence features of the Haitian variant strain may have some association with the severe clinical outcome of the cholera patients in different parts of the world.

Changing facades of Vibrio cholerae: An enigma in the epidemiology of cholera

Cholera, caused by the Gram-negative bacterium Vibrio cholerae, has ravaged humanity from time immemorial. Although the disease can be treated using antibiotics along with administration of oral rehydration salts and controlled by good sanitation, cholera is known to have produced mayhems in ancient times when little was known about the pathogen. By the 21st century, ample information about the pathogen, its epidemiology, genetics, treatment and control strategies was revealed. However, there is still fear of cholera outbreaks in developing countries, especially in the wake of natural calamities. Studies have proved that the bacterium is mutating and evolving, out-competing all our efforts to treat the disease with previously used antibiotics and control with existing vaccines. In this review, the major scientific insights of cholera research are discussed. Considering the important role of biofilm formation in the V. cholerae life cycle, the vast availability of next-generation sequencing data of the pathogen and multi-omic approach, the review thrusts on the identification of suitable biofilm-inhibiting targets and the discovery of anti-biofilm drugs from nature to control the disease.

Intracellular and membrane-damaging activities of methyl gallate isolated from Terminalia chebula against multidrug-resistant Shigella spp

Shigella spp. (Shigella dysenteriae, Shigella flexneri, Shigella boydii and Shigella sonnei) cause bacillary dysentery (shigellosis), which is characterized by bloody mucous diarrhoea. Although a variety of antibiotics have been effective for treatment of shigellosis, options are becoming limited due to globally emerging drug resistance. In the present study, in vitro antibacterial activity of methyl gallate (MG) isolated from Terminalia chebula was determined by performing MIC, minimal bactericidal concentration (MBC) and time-kill kinetic studies. Bacterial membrane-damaging activity of MG was determined by membrane perturbation and transmission electron microscopy (TEM). Cellular drug accumulation, cell infection and assessment of intracellular activities of MG and reference antibiotics were performed using HeLa cell cultures. The bactericidal activity of MG against multidrug-resistant (MDR) Shigella spp. in comparison with other commonly used drugs including fluoroquinolone was demonstrated here. TEM findings in the present study revealed that MG caused the total disintegration of inner and outer membranes, and leakage of the cytoplasmic contents of S. dysenteriae. The level of accumulation of MG and tetracycline in HeLa cells incubated for 24  h was relatively higher than that of ciprofloxacin and nalidixic acid (ratio of intracellular concentration/extracellular concentration of antibiotic for MG and tetracycline>ciprofloxacin and nalidixic acid). The viable number of intracellular S. dysenteriae was decreased in a time-dependent manner in the presence of MG (4 × MBC) and reduced to zero within 20  h. The significant intracellular activities of MG suggested that it could potentially be used as an effective antibacterial agent for the treatment of severe infections caused by MDR Shigella spp.

Outbreak of cholera caused by Vibrio cholerae O1 El Tor variant strain in Bihar, India

An outbreak of cholera struck Bihar, an Indian state, in August 2008 following a massive flood. Here we report the phenotypic and genotypic characteristics of Vibrio cholerae strains isolated from patients with diarrhea. Rectal swabs were obtained from patients with diarrhea who were admitted to medical camps or the hospital, and the strains were biochemically and serologically characterized. V. cholerae was isolated from 21 (65.6%) of 32 rectal swabs. Serological studies revealed that all the 21 isolates belonged to V. cholerae O1 Ogawa. Mismatch amplification mutation assay (MAMA)-PCR showed that the isolates belonged to El Tor variant group, and pulsed-field gel electrophoresis (PFGE) proved that these isolates were of a different lineage than the conventional El Tor variant strains. These isolates were resistant to several drugs, including ampicillin, streptomycin, tetracycline, nalidixic acid, and furazolidone. The uniqueness of the current report arises from the fact that records of cholera in Bihar are availiable for the early 1960s but not for the next 4 decades. Moreover, the present study is the first to report a cholera outbreak in Bihar that was caused by an El Tor variant strain.

Comparison between Single Dose Azithromycin and Six Doses, 3 Day Norfloxacin for Treatment of Cholera in Adult

AIM

To evaluate the efficacy of single dose Azithromycin (1 gram) in treatment of cholera in adults. A randomized, controlled clinical trial on 120 adults with acute watery diarrhoea and moderate to severe dehydration compared the efficacy of azithromycin (1 gram) single dose and Norfloxacin (400 mg) twice daily for three days in treating cholera. Data were analysed for 64 patients who were stool culture positive for Vibrio cholerae. In conjunction with rehydration therapy, 32 patients received Azithromycin and 32 patients received Norfloxacin. Patients in the two treatment groups had comparable clinical characteristics on admission.

CONCLUSIONS

Result shows Azithromycin and Norfloxacin has got almost similar efficacy in reducing stool output, duration of diarrhoea and fluid requirement in cholera positive cases.

Development of a PCR-restriction fragment length polymorphism assay for detection and subtyping of cholix toxin variant genes of Vibrio cholerae

Cholix toxin (ChxA) is an exotoxin reported in Vibrio cholerae non-O1/non-O139. Apart from its prototype (ChxA I) we have recently identified two novel variants of this toxin, ChxA II and ChxA III. Our previous investigations indicated that the first two variants may instigate extra-intestinal infections and ChxA II can be more lethal than ChxA I in mice. However, all three cholix toxins (ChxA I to III) failed to show any enterotoxicity in rabbit ileal loops. In this study we developed a PCR-restriction fragment length polymorphism (RFLP) assay to differentiate all three chxA variants to further understand the importance of each subtype. By using 53 V. cholerae non-O1/non-O139 strains harbouring chxA genes, which were previously categorized by sequencing, and various other strains as negative controls, the PCR-RFLP assay showed 100 % typability and specificity. Furthermore, when applied to differentiate additional V. cholerae strains, which were also screened for the chxA gene by colony hybridization, this assay identified chxA I and chxA II genes among 18.5 % and 4.5 % of non-O1/non-O139 strains (n = 178), respectively. One non-O1/non-O139 strain was untypable due to the insertion of an IS911-like element. Interestingly, the chxA I gene was detected in 10 out of 137 cholera toxin gene-negative V. cholerae O1 strains. These results suggest that the PCR-RFLP assay developed in this study can be a rapid and simple method to differentiate the chxA subtypes.

Genomic correlates of variability in immune response to an oral cholera vaccine

Cholera is endemic to many countries. Recent major outbreaks of cholera have prompted World Health Organization to recommend oral cholera vaccination as a public-health strategy. Variation in percentage of seroconversion upon cholera vaccination has been recorded across populations. Vaccine-induced responses are influenced by host genetic differences. We have investigated association between single-nucleotide polymorphic (SNP) loci in and around 296 immunologically relevant genes and total anti-lipopolysaccharide (LPS) antibody response to a killed whole-cell vaccine, comprising LPS from multiple strains of Vibrio cholerae. Titers derived from standard vibriocidal assays were also analyzed to gain further insights on validated SNP associations. Vaccination was administered to 1000 individuals drawn from India. Data on two independent random subsets, each comprising ∼500 vaccinees, were used for discovery of genomic associations and validation, respectively. Significant associations of four SNPs and haplotypes in three genes (MARCO, TNFAIP3 and CXCL12) with AR were discovered and validated, of which two in TNFAIP3 and CXCL12 were also significantly associated with immunity (fourfold increase in vibriocidal titers). CXCL12 is a neutrophil and lymphocyte chemoattractant that is upregulated in response to V. cholerae infection. LPS in the vaccine possibly provides signals that mimic those of the live bacterium. TNFAIP3 promotes intestinal epithelial barrier integrity and provides tight junction protein regulation; possible requirements for adequate response to the vaccine. LPS is a potent activator of innate immune responses and a ligand of MARCO. Variants in this gene have been found to be associated with LPS response, but not with high vibriocidal titer level.

Diagnostic microbiologic methods in the GEMS-1 case/control study

To understand the etiology of moderate-to-severe diarrhea among children in high mortality areas of sub-Saharan Africa and South Asia, we performed a comprehensive case/control study of children aged <5 years at 7 sites. Each site employed an identical case/control study design and each utilized a uniform comprehensive set of microbiological assays to identify the likely bacterial, viral and protozoal etiologies. The selected assays effected a balanced consideration of cost, robustness and performance, and all assays were performed at the study sites. Identification of bacterial pathogens employed streamlined conventional bacteriologic biochemical and serological algorithms. Diarrheagenic Escherichia coli were identified by application of a multiplex polymerase chain reaction assay for enterotoxigenic, enteroaggregative, and enteropathogenic E. coli. Rotavirus, adenovirus, Entamoeba histolytica, Giardia enterica, and Cryptosporidium species were detected by commercially available enzyme immunoassays on stool samples. Samples positive for adenovirus were further evaluated for adenovirus serotypes 40 and 41. We developed a novel multiplex assay to detect norovirus (types 1 and 2), astrovirus, and sapovirus. The portfolio of diagnostic assays used in the GEMS study can be broadly applied in developing countries seeking robust cost-effective methods for enteric pathogen detection.

Comparative analysis of the genomes of Shigella dysenteriae type 2 & type 7 isolates

BACKGROUND & OBJECTIVES

The four species of the genus Shigella, namely, S. dysenteriae , S. flexneri, S. boydii and S. sonnei cause a wide spectrum of illness from watery diarrhoea to severe dysentery. Genomes of these four species show great diversity. In this study, NotI, XbaI or I-CeuI restriction enzyme digested genomes of two Shigella dysenteriae isolates belonging to the serotypes 2 and 7 were extensively analyzed to find their relatedness, if any, with the whole genome sequenced strains of S. dysenteriae type 1 and S. flexneri type 2a.

METHODS

Pulsed-field gel electrophoresis (PFGE) technique was used to determine the diversity of Shigella genomes by rapid construction of physical maps. DNA end labelling, Southern hybridization and PCR techniques were also applied for mapping purposes.

RESULTS

The intron-coded enzyme I-CeuI cuts the bacterial genome specifically at its rrn operon. PFGE of I-CeuI digested S. dysenteriae genomes were found to carry seven rrn operons. However, I-CeuI profiles showed distinct restriction fragment polymorphism (RFLP) between the isolates as well as with the whole genome sequenced isolates. Further studies revealed that the genome sizes and I-CeuI linkage maps of the S. dysenteriae type 7 and type 2 isolates were similar to that of S. dysenteriae type 1 and S. flexneri type 2a genomes, respectively.

INTERPRETATION & CONCLUSIONS

Our findings indicate that the type 7 and type 1 isolates of S. dysenteriae were probably evolved from a same precursor, while the type 2 and S. flexneri type 2a were probably evolved and diversified from a common progenitor.

Molecular epidemiology of Vibrio cholerae causing outbreaks & sporadic cholera in northern India

BACKGROUND & OBJECTIVES

Several outbreaks of cholera have been reported in Chandigarh region during a span of seven years from 2002-2008. The genetic characteristics of Vibrio cholerae isolates obtained during these outbreaks have not been adequately studied. The aim of this study was to do molecular typing of V. cholerae isolated from the sporadic and outbreak cases by pulsed-field gel electrophoresis (PFGE), Rep-PCR and ribotyping.

METHODS

Fifty representative isolates of V. cholerae from outbreak as well as sporadic cases were subjected to molecular typing by PFGE, 173 isolates (163 clinical and 10 environmental) were typed by rep-PCR and ribotyping. Ribotyping was done by determination of rRNA restriction pattern of BglI restriction digestion and hybridization with 7.2 kb rRNA probe of pKK3535 plasmid using DIG DNA labelling and detection kit. Universal VC1 primer was used for rep-PCR.

RESULTS

PFGE generated 15 pulsotypes, of which four matched the published pulsotypes and there were 11 new pulsotypes. PFGE was the most discriminatory method that could differentiate between isolates belonging to single ribotype. Pulsotype P1 corresponding to known pulsotype H1 was the major pulsotype till 2003. Pulsotype P3 corresponding to known pulsotype L emerged in 2004. The 2007 outbreaks in Punjab and Haryana were caused by P5 though P1 and P3 were isolated from the sporadic cases from the same region. The 2008 outbreak was caused by pulsotypes P6 and P7. Ribotype IV was the most predominant followed by RIII. This ribotype was not isolated after 2003 and ribotype IV became the most predominant 2004 onwards. Of the two unknown ribotypes (UNI and UN2), UNI was more common (27 isolates). Rep-PCR was the least discriminatory and divided all clinical isolates into four major profiles. The dendrogram analysis of PFGE revealed similarity of some clinical isolates with environmental isolates indicating the genetic relatedness.

INTERPRETATION & CONCLUSION

Our findings showed that Rep-PCR was least discriminatory method. Ribotyping was a reliable and reproducible method. Ribotype IV was predominant ribotype followed by RIII. A total of 15 pulsotypes were generated and 11 of these were not reported earlier. Genetic relatedness was shown by clinical and environmental isolates which needs to be confirmed in future studies.

Multiple infection and microdiversity among Helicobacter pylori isolates in a single host in India

Helicobacter pylori is one of the most diverse bacterial species that chronically infects more than 70% of Indian population. Interestingly, data showing microdiversity of the H. pylori strains within a particular gastric niche remained scarce. To understand the extent of genetic diversity among H. pylori strains within a given host, 30 patients with gastro-duodenal problems were subjected to endoscopy and from each patient 10 single colonies were isolated. Characterization of each of these 10 single colonies by DNA fingerprinting as well as genotyping of several important genetic markers viz. cagA, vacA, iceA, vapD, cag PAI empty site, IS605, RFLP and two other genetic segments within cag PAI revealed that all of the 30 patients were infected with more than one strain and sometimes strains with 5 to 6 types of genetic variants. Analyses of certain genetic loci showed the microdiversity among the colonies from single patient, which may be due to the recombination events during long-term carriage of the pathogen. These results suggest that most of the patients have acquired H. pylori due to repeated exposure to this pathogen with different genetic make-up, which may increase the possibility of super infections. Genetic exchanges between these unrelated H. pylori strains may support certain H. pylori variant to grow better in a given host than the parental strain and thereby increasing the possibility for the severity of the infection.

Significant association of the dupA gene of Helicobacter pylori with duodenal ulcer development in a South-east Indian population

A novel virulence factor, duodenal ulcer-promoting gene A (dupA), in Helicobacter pylori has been found to be associated with disease in certain populations but not in others. This study analysed a South-east Indian population as part of the debate about the relevance of dupA for the prediction of clinical outcomes. A total of 140 H. pylori strains isolated from duodenal ulcer (DU) (n = 83) and non-ulcer dyspepsia (NUD) patients (n = 57) were screened by PCR and dot-blot hybridization to determine the presence of the ORFs jhp0917 and jhp0918. Part of jhp0917-jhp0918 was sequenced to search for the C/T insertion that characterizes dupA and the levels of dupA transcripts were also assessed. The PCR and dot-blot results indicated the presence of jhp0917 and jhp0918 in 37.3 % (31/83) and 12.2 % (7/57) of H. pylori strains isolated from DU and NUD patients, respectively. Sequencing analysis showed insertion of a C at nt 1386 in the 3' region of jhp0917, forming the dupA gene in 35 strains. RT-PCR analysis detected the dupA transcript in 28 of these 35 strains. The expression level of the dupA transcript varied from strain to strain, as shown by real-time PCR. The results demonstrated that analysis based on PCR only for dupA may produce an erroneous interpretation. The prevalence of dupA was significantly greater among strains isolated from patients with DU than from patients with NUD in this population (P = 0.001, odds ratio = 4.26, confidence interval = 1.60-11.74). Based on these findings, dupA can be considered a biomarker for DU patients in India. The reported discrepancies for this putative virulence marker in different populations may be due to the genome plasticity of H. pylori.

Distinct repeat motifs at the C-terminal region of CagA of Helicobacter pylori strains isolated from diseased patients and asymptomatic individuals in West Bengal, India

BACKGROUND

Infection with Helicobacter pylori strains that express CagA is associated with gastritis, peptic ulcer disease, and gastric adenocarcinoma. The biological function of CagA depends on tyrosine phosphorylation by a cellular kinase. The phosphate acceptor tyrosine moiety is present within the EPIYA motif at the C-terminal region of the protein. This region is highly polymorphic due to variations in the number of EPIYA motifs and the polymorphism found in spacer regions among EPIYA motifs. The aim of this study was to analyze the polymorphism at the C-terminal end of CagA and to evaluate its association with the clinical status of the host in West Bengal, India.

RESULTS

Seventy-seven H. pylori strains isolated from patients with various clinical statuses were used to characterize the C-ternimal polymorphic region of CagA. Our analysis showed that there is no correlation between the previously described CagA types and various disease outcomes in Indian context. Further analyses of different CagA structures revealed that the repeat units in the spacer sequences within the EPIYA motifs are actually more discrete than the previously proposed models of CagA variants.

CONCLUSION

Our analyses suggest that EPIYA motifs as well as the spacer sequence units are present as distinct insertions and deletions, which possibly have arisen from extensive recombination events. Moreover, we have identified several new CagA types, which could not be typed by the existing systems and therefore, we have proposed a new typing system. We hypothesize that a cagA gene encoding higher number EPIYA motifs may perhaps have arisen from cagA genes that encode lesser EPIYA motifs by acquisition of DNA segments through recombination events.

Evaluation of a rapid dipstick test for identifying cholera cases during the outbreak

BACKGROUND & OBJECTIVES

Intermittent cholera outbreaks are major problem in many of the states of India. It is essential to identify cholera at the earliest for timely mobilization of public health responses and to abort the outbreaks. The present study was a part of a diarrhoeal outbreak investigation in Secunderabad, India, during May 2009 where the usefulness of Crystal VC rapid dipstick kit was assessed for detecting the aetiologic agent of the outbreak.

METHODS

Stool specimens were collected from 15 hospitalized patients with acute watery diarrhoea and analyzed for detection of cholera vibrios using Crystal VC rapid dipstick kit and the usefulness of the kit was determined by comparative analysis of the same set of specimens using both microbiological and real-time PCR (RT-PCR) based assays.

RESULTS

Detection of Vibrio cholerae O1 from 10 of 15 specimens was recorded using dipstick assay. Microbiological methods detected V. cholerae O1 positivity among 11 specimens. However, RT-PCR based assay showed all 15 specimens positive for the presence of V. cholerae O1. In addition, the same assay showed that the pathogen load in the dipstick as well as RT-PCR positive specimens ranged from 10 6 colony forming units (cfu)/ml or more.

INTERPRETATION & CONCLUSIONS

Crystal VC kit had the potential to identify cholera cases in 10 min in field conditions without having good laboratory support. Therefore, dipstick kit may be considered as cholera detecting tool in diarrhoeal outbreak investigations. Specimens from clinically typical cholera cases, if negative by dipstick, should be reanalyzed by culture based methods.

Storing drinking-water in copper pots kills contaminating diarrhoeagenic bacteria

Microbially-unsafe water is still a major concern in most developing countries. Although many water-purification methods exist, these are expensive and beyond the reach of many people, especially in rural areas. Ayurveda recommends the use of copper for storing drinking-water. Therefore, the objective of this study was to evaluate the effect of copper pot on microbially-contaminated drinking-water. The antibacterial effect of copper pot against important diarrhoeagenic bacteria, including Vibrio cholerae O1, Shigella flexneri 2a, enterotoxigenic Escherichia coli, enteropathogenic E. coli, Salmonella enterica Typhi, and Salmonella Paratyphi is reported. When drinking-water (pH 7.83 +/- 0.4; source: ground) was contaminated with 500 CFU/mL of the above bacteria and stored in copper pots for 16 hours at room temperature, no bacteria could be recovered on the culture medium. Recovery failed even after resuscitation in enrichment broth, followed by plating on selective media, indicating loss of culturability. This is the first report on the effect of copper on S. flexneri 2a, enteropathogenic E. coli, and Salmonella Paratyphi. After 16 hours, there was a slight increase in the pH of water from 7.83 to 7.93 in the copper pots while the other physicochemical parameters remained unchanged. Copper content (177 +/- 16 ppb) in water stored in copper pots was well within the permissible limits of the World Health Organization. Copper holds promise as a point-of-use solution for microbial purification of drinking-water, especially in developing countries.

Culture-independent real-time PCR reveals extensive polymicrobial infections in hospitalized diarrhoea cases in Kolkata, India

Culture-independent identification of diarrhoeal aetiological agents was performed using DNA harvested from diarrhoeal stool specimens with SYBR-Green-based real-time PCR targeting Vibrio cholerae, Vibrio parahaemolyticus, Campylobacter spp., Shigella spp. and three different pathotypes of diarrhoeagenic Escherichia coli. Conventional culture-dependent methods detected bacterial enteropathogens in 68 of 122 diarrhoeal stool specimens. Of 68 specimens, 59 (86.8%) had a single pathogen and the remaining nine (13.2%) had polymicrobial infections with multiple pathogens. Re-analysis of the 68 specimens by culture-independent real-time PCR methods showed that 25 (36.8%) specimens contained single pathogen and 43 (63.2%) specimens contained mixed infections with multiple pathogens. The prevalence of such high levels of polymicrobial infections would not have been detected without using real-time PCR. Culture-dependent analysis assigned 54 of the 122 selected archived specimens as 'no known aetiology'. However, re-analysis of these samples by real-time PCR showed the presence of single or multiple pathogens among 34 (63%) of these specimens. Estimation of relative pathogen load by real-time PCR in the stool specimens indicated that the inability of conventional culture-dependent methods to detect the pathogens was related to lower colony-forming units of the pathogen, as reflected by lower C(t) values. Detection of high levels of polymicrobial infection by real-time PCR indicates that in the settings like Kolkata and its surroundings, where cholera and other enteric diseases are endemic, the concept of one pathogen one disease might need to be re-evaluated.

Evidence for several waves of global transmission in the seventh cholera pandemic

Vibrio cholerae is a globally important pathogen that is endemic in many areas of the world and causes 3-5 million reported cases of cholera every year. Historically, there have been seven acknowledged cholera pandemics; recent outbreaks in Zimbabwe and Haiti are included in the seventh and ongoing pandemic. Only isolates in serogroup O1 (consisting of two biotypes known as 'classical' and 'El Tor') and the derivative O139 can cause epidemic cholera. It is believed that the first six cholera pandemics were caused by the classical biotype, but El Tor has subsequently spread globally and replaced the classical biotype in the current pandemic. Detailed molecular epidemiological mapping of cholera has been compromised by a reliance on sub-genomic regions such as mobile elements to infer relationships, making El Tor isolates associated with the seventh pandemic seem superficially diverse. To understand the underlying phylogeny of the lineage responsible for the current pandemic, we identified high-resolution markers (single nucleotide polymorphisms; SNPs) in 154 whole-genome sequences of globally and temporally representative V. cholerae isolates. Using this phylogeny, we show here that the seventh pandemic has spread from the Bay of Bengal in at least three independent but overlapping waves with a common ancestor in the 1950s, and identify several transcontinental transmission events. Additionally, we show how the acquisition of the SXT family of antibiotic resistance elements has shaped pandemic spread, and show that this family was first acquired at least ten years before its discovery in V. cholerae.

QRDR mutations, efflux system & antimicrobial resistance genes in enterotoxigenic Escherichia coli isolated from an outbreak of diarrhoea in Ahmedabad, India

BACKGROUND & OBJECTIVES

Diverse mechanisms have been identified in enteric bacteria for their adaptation and survival against multiple classes of antimicrobial agents. Resistance of bacteria to the most effective fluoroquinolones have increasingly been reported in many countries. We have identified that most of the enterotoxigenic Escherichia coli (ETEC) were resistant to several antimicrobials in a diarrhoea outbreak at Ahmedabad during 2000. The present study was done to identify several genes responsible for antimicrobial resistance and mobile genetic elements in the ETEC strains.

METHODS

Seventeen ETEC strains isolated from diarrhoeal patients were included in this study. The antimicrobial resistance was confirmed by conventional disc diffusion method. PCR and DNA sequencing were performed for the identification of mutation in the quinolone resistance-determining regions (QRDRs). Efflux pump was tested by inhibiting the proton-motive force. DNA hybridization assay was made for the detection of integrase genes and the resistance gene cassettes were identified by direct sequencing of the PCR amplicons.

RESULTS

Majority of the ETEC had GyrA mutations at codons 83 and 87 and in ParC at codon 80. Six strains had an additional mutation in ParC at codon 108 and two had at position 84. Plasmid-borne qnr gene alleles that encode quinolone resistance were not detected but the newly described aac(6')-Ib-cr gene encoding a fluoroquinolne-modifying enzyme was detected in 64.7 per cent of the ETEC. Class 1 (intI1) and class 2 (intI2) integrons were detected in six (35.3%) and three (17.6%) strains, respectively. Four strains (23.5%) had both the classes of integrons. Sequence analysis revealed presence of dfrA17, aadA1, aadA5 in class 1, and dfrA1, sat1, aadA1 in class 2 integrons. In addition, the other resistance genes such as tet gene alleles (94.1%), catAI (70.6%), strA (58.8%), bla TEM-1 (35.2%), and aphA1-Ia (29.4%) were detected in most of the strains.

INTERPRETATION & CONCLUSIONS

Innate gene mutations and acquisition of multidrug resistance genes through mobile genetic elements might have contributed to the emergence of multidrug resistance (MDR) in ETEC. This study reinforces the necessity of utilizing molecular techniques in the epidemiological studies to understand the nature of resistance responsible for antimicrobial resistance in different species of pathogenic bacteria.

Diarrheagenic pathogens in polymicrobial infections

During systematic active surveillance of the causes of diarrhea in patients admitted to the Infectious Diseases and Beliaghata General Hospital in Kolkata, India, we looked for 26 known gastrointestinal pathogens in fecal samples from 2,748 patients. Samples from about one-third (29%) of the patients contained multiple pathogens. Polymicrobial infections frequently contained Vibrio cholerae O1 and rotavirus. When these agents were present, some co-infecting agents were found significantly less often (p = 10 (-5) to 10 (-33), some were detected significantly more often (p = 10 (-5) to 10 (-26), and others were detected equally as often as when V. cholerae O1 or rotavirus was absent. When data were stratified by patient age and season, many nonrandom associations remained statistically significant. The causes and effects of these nonrandom associations remain unknown.

Diarrheagenic pathogens in polymicrobial infections

During systematic active surveillance of the causes of diarrhea in patients admitted to the Infectious Diseases and Beliaghata General Hospital in Kolkata, India, we looked for 26 known gastrointestinal pathogens in fecal samples from 2,748 patients. Samples from about one-third (29%) of the patients contained multiple pathogens. Polymicrobial infections frequently contained Vibrio cholerae O1 and rotavirus. When these agents were present, some co-infecting agents were found significantly less often (p = 10 (-5) to 10 (-33), some were detected significantly more often (p = 10 (-5) to 10 (-26), and others were detected equally as often as when V. cholerae O1 or rotavirus was absent. When data were stratified by patient age and season, many nonrandom associations remained statistically significant. The causes and effects of these nonrandom associations remain unknown.

Colonization of the gut with Gram-negative bacilli, its association with neonatal sepsis and its clinical relevance in a developing country

This study examined the pattern of colonization of the neonatal gut by aerobic Gram-negative bacilli (GNB) and evaluated the association between gut colonization and sepsis in the developing world. This deserves attention because of the high incidence of sepsis and the differences in hygienic environments in developing countries compared with the developed world. The study was carried out on neonates in a tertiary-care government hospital. Serial gut samples were analysed (gastric aspirates and stool samples) for GNB. Blood samples of cases showing clinical signs of sepsis were also analysed for septic screening and culture positivity. Antibiograms, serotyping and PFGE were carried out to evaluate the relatedness of the gut and blood isolates. A diverse array of GNB was isolated from the gut of the neonates, Klebsiella pneumoniae being most common, followed by Escherichia coli. The rate of isolation of GNB was consistently higher in stool samples compared with gastric aspirate samples. Colonization was influenced by a stay in the neonatal intensive care unit and by the prolonged use of a feeding tube. GNB were the cause of sepsis in the majority of cases, with K. pneumoniae being the most frequently isolated GNB from the blood. Acinetobacter baumannii, Escherichia coli, Enterobacter cloacae and Burkholderia cepacia were the other GNB recovered from the blood of the neonates. Neonates with GNB in the gut had a higher incidence of clinical sepsis than those without. In 50 % of cases, the genotypes of the organisms found in the blood were indistinguishable from their gut counterpart. These results show that the neonatal gut is colonized with a diverse array of GNB, and an association between gut colonization and neonatal sepsis was observed.

Transferable plasmid-mediated quinolone resistance in association with extended-spectrum β-lactamases and fluoroquinolone-acetylating aminoglycoside-6'-N-acetyltransferase in clinical isolates of Vibrio fluvialis

Vibrio fluvialis, which causes cholera-like diarrhoea in humans, is one of the aetiological agents of acute diarrhoea in Kolkata, India, and is resistant to many antimicrobial agents. Two V. fluvialis isolates resistant to fluoroquinolones and β-lactam antimicrobials were found to have mutations in the quinolone resistance-determining regions (QRDRs) of GyrA at position 83 and of ParC at position 85 as well as carrying a 150 kb plasmid harbouring the quinolone resistance gene qnrA1, the ciprofloxacin-modifying enzyme-encoding gene aac(6')-Ib-cr and genes encoding for extended-spectrum β-lactamases such as bla(SHV) and bla(CTX-M-3). When this large plasmid was transferred to Escherichia coli by conjugation, the transconjugants showed a 10-75-fold increase in the minimum inhibitory concentrations of ciprofloxacin and norfloxacin. The qnrA1 gene was identified in a complex sul1-type integron in a plasmid of the transconjugants. Southern hybridisation and sequence analysis of qnrA1 and its flanking regions confirmed the presence of aac(6')-Ib-cr and bla(CTX-M-3) but these were not associated with the sul1-type integron. Pulsed-field gel electrophoresis (PFGE) revealed that the two V. fluvialis isolates belonged to different clones. Although the presence of many qnr alleles has been reported amongst enteric bacteria in Asian countries, this is the first report on the emergence of qnrA1 in India. qnrA1 along with aac(6')-Ib-cr and bla(CTX-M-3) genes on a mobile plasmid may spread to other bacterial species that are under the selective pressure of fluoroquinolones and β-lactam antimicrobials in this region.

Genetic characteristics and changing antimicrobial resistance among Shigella spp. isolated from hospitalized diarrhoeal patients in Kolkata, India

To study the prevalence pattern and trends in the phenotypic and genetic characteristics of shigellae, we tested 212 isolates isolated from diarrhoeal patients admitted to the Infectious Diseases Hospital, Kolkata, India, from November 2007 to October 2010. Prevalence of Shigella spp. was higher in the >5 years age group (69 %) than in children in the <5 years age group (31 %). Serotypes 2a, 3a and untypable isolates of Shigella flexneri were frequently detected. An increase in the isolation of Shigella sonnei (15 %) is a novel trend in this region. Fluoroquinolone resistance among S. flexneri serotypes 2a, 3a and other serogroups of shigellae is another evolving trend. The set gene was exclusively present in S. flexneri 2a, and the sen gene was detected in all serogroups. PFGE revealed the grouping of S. flexneri isolates according to their serotypes with approximately 80-100 % similarity, whilst Shigella dysenteriae type 2 and S. sonnei were clonal in nature. There was no demarcation in the prevalence of serotypes, antimicrobial resistance or clonality between the two age groups.

Influence of relative humidity in Vibrio cholerae infection: a time series model

BACKGROUND & OBJECTIVES

Spread of cholera in West Bengal is known to be related to its ecosystem which favours Vibrio cholerae. Incidence of cholera has not been correlated with temperature, relative humidity and rainfall, which may act as favourable factors. The aim of this study was to investigate the relational impact of climate changes on cholera.

METHODS

Monthly V. cholerae infection data for of the past 13 years (1996-2008), average relative humidity (RH), temperature and rainfall in Kolkata were considered for the time series analysis of Seasonal Auto-Regressive Integrated Moving Average (SARIMA) model to investigate relational impact of climatic association of V. cholerae infection and General Linear Model (GLM) for point estimation.

RESULTS

The SARIMA (1,0,0)(0,1,1) model revealed that monthly average RH was consistently linear related to V. cholerae infection during monsoon season as well as temperature and rainfall were non-stationary, AR(1), SMA(1) and SI(1) (P<0.001) were highly significant with seasonal difference. The GLM has identified that consistent (<10%) range of RH (86.78 ± 4.13, CV=5.0, P <0.001) with moderate to highest (>7 cm) rainfall (10.1 ± 5.1, CV=50.1, P <0.001) and wide (>5-10ºC) range of temperature (29.00 ± 1.64, CV=5.6, P <0.001) collectively acted as an ideal climatic condition for V. cholerae infection. Increase of RH to 21 per cent influenced an unusual V. cholerae infection in December 2008 compared to previous years.

INTERPRETATION & CONCLUSIONS

V. cholerae infection was associated higher RH (>80%) with 29°C temperature with intermittent average (10 cm) rainfall. This model also identified periodicity and seasonal patterns of cholera in Kolkata. Heavy rainfall indirectly influenced the V. cholerae infection, whereas no correlation was found with high temperature.

Antimicrobials & cholera: are we stranded?

Antimicrobial resistance poses a major threat in the treatment of infectious diseases. Though significant progress in the management of diarrhoeal diseases has been achieved by improved hygiene, development of new antimicrobials and vaccines, the burden remains the same, especially in children below 5 yr of age. In the case of cholera, though oral rehydration treatment is the mainstay, antimicrobial therapy is mandatory at times to reduce the volume of stool and shorten the duration of the disease. Though for many pathogens, antimicrobial resistance emerged soon after the introduction of antibiotics, Vibrio cholerae remained sensitive to most of the antibiotics for quite a long period. However, the scenario changed over the years and today, V. cholerae strains isolated world over are resistant to multiple antibiotics. A myriad number of mechanisms underlie this phenomenon. These include production of extended-spectrum beta-lactamases, enhanced multi-drug efflux pump activity, plasmid-mediated quinolone and fluoroquinolone resistance, and chromosomal mutations. Horizontal transfer of resistance determinants with mobile genetic elements like integrons and the integrating conjugative elements (ICEs), SXTs help in the dissemination of drug resistance. Though all strains isolated are not resistant to all antibiotics and we are not as yet "stranded", expanding spectrum of drug resistance is a definite cause for concern. Pipelines of discovery of new antibiotics are drying up as major pharmaceutical companies are losing interest in investing money in this endeavour, mainly due to the short shelf-life of the antibiotics and also due to the fast emergence of drug resistance. To address this issue, attempts are now being made to discover drugs which are pathogen specific and target their "virulence mechanisms". It is expected that development of resistance against such antibiotics would take much longer. This review briefly focuses on all these issues.

Intact cag pathogenicity island of Helicobacter pylori without disease association in Kolkata, India

Several genes including the cagA in the cag pathogenicity island (cag PAI) of Helicobacter pylori are thought to be associated with the gastroduodenal diseases and hence variation in the genetic structure of the cag PAI might be responsible for different clinical outcomes. Our study was undertaken to characterize the cag PAI of H. pylori strains from duodenal ulcer (DU) patients and asymptomatic or non-ulcer dyspepsia (NUD/AV) subjects from Kolkata, India. Strains isolated from 52 individuals (30DU and 22NUD/AV) were analyzed by PCR using 83 different primers for the entire cag PAI and also by dot-blot hybridization. Unlike H. pylori strains isolated from other parts of India, 82.6% of the strains used in this study had intact cag PAI, 9.6% had partially deleted cag PAI, and 7.7% of the strains lacked the entire cag PAI. Dot-blot hybridization yielded positive signals in 100% and 93.8% of PCR-negative strains for HP0522-523 and HP0532-HP0534 genes, respectively. An intact cagA promoter region was also detected in all cagA-positive strains. Furthermore, the expression of cagA mRNA was confirmed by RT-PCR for the representative strains from both DU and NUD/AV subjects indicating the active cagA promoter regions of these strains. A total of 66.7% of Kolkata strains produced a ∼390-bp shorter amplicon than the standard strain 26695 for the HP0527 gene, homologue of virB10. However, sequence analyses confirmed that the deletion did not alter the reading frame of the gene, and mRNA transcripts were detected by RT-PCR analysis. The strains isolated from DU and NUD/AV express CagA protein and possess a functional type IV secretion system, as revealed by Western blot analyses. Interestingly, no significant differences in cag PAI genetic structure were found between DU and NUD/AV individuals suggesting that other bacterial virulence factors, host susceptibility, and environmental determinants also influence the disease outcome at least in certain geographical locations.

Evaluation of a rapid immunochromatographic dipstick kit for diagnosis of cholera emphasizes its outbreak utility

We evaluated the Crystal VC, a commercially produced dipstick, for the rapid detection of Vibrio cholerae serotypes O1 and O139 directly from the stool samples of hospitalized diarrheal patients using the conventional bacteriological method as gold standard. The sensitivity and specificity of the dipsticks were about 92 and 73%, respectively. Introduction of the PCR-based method along with the classical bacteriological method as the gold standard for the evaluation of a kit may improve the sensitivity and specificity of the assay. The dipstick method requires minimal technical skill, and the test can be read in about 10 min. This dipstick test has the potential to act as an early warning system for cholera in many developing countries, especially during the start of an outbreak, which would ultimately lead to a decrease in the spread of the disease as well as the case fatality rate. Furthermore, the use of a rapid detection test will improve surveillance and thus reduce the burden of disease estimates, especially in remote settings.

Pathogenic potential of Aeromonas hydrophila isolated from surface waters in Kolkata, India

Members of the genus Aeromonas (family Aeromonadaceae) are medically important, Gram-negative, rod-shaped micro-organisms and are ubiquitous in aquatic environments. Aeromonas species are increasingly recognized as enteric pathogens; they possess several virulence factors associated with human disease, and represent a serious public health concern. In the present study, putative virulence traits of Aeromonas hydrophila isolates collected from different natural surface waters of Kolkata, India, were compared with a group of clinical isolates from the same geographical area using tissue culture and PCR assays. Enteropathogenic potential was investigated in the mouse model. Of the 21 environmental isolates tested, the majority showed cytotoxicity to HeLa cells (81 %), haemolysin production (71 %) and serum resistance properties (90 %), and they all exhibited multi-drug resistance. Some of the isolates induced fluid accumulation (FA ratio≥100), damage to the gut and an inflammatory reaction in the mouse intestine; these effects were comparable to those of clinical strains of A. hydrophila and toxigenic Vibrio cholerae. Interestingly, two of the isolates evoked a cell vacuolation effect in HeLa cells, and were also able to induce FA. These findings demonstrate the presence of potentially pathogenic and multi-drug-resistant A. hydrophila in the surface waters, thereby indicating a significant risk to public health. Continuous monitoring of surface waters is important to identify potential water-borne pathogens and to reduce the health risk caused by the genus Aeromonas.

An urban, water-borne outbreak of diarrhoea and shigellosis in a district town in eastern India

BACKGROUND

In September 2007, the Gayeshpur municipality reported a cluster of cases with diarrhoea. We aimed to identify the causative agent and the source of the disease.

METHODS

We defined a case as the occurrence of diarrhoea (> 3 loose stools/day) with fever or bloody stools in a resident of Gayeshpur in September-October 2007. We asked healthcare facilities to report cases, collected stool specimens from patients, constructed an epidemic curve, drew a map and calculated the incidence by age and sex. We also conducted a matched case-control study (58 in each group), calculated matched odds ratio (MOR) and population attributable fraction (PAF), as well as assessed the environment.

RESULTS

We identified 461 cases (attack rate: 46/1000 population) and isolated Shigella flexneri (serotype 2a and 3a) from 3 of 4 stool specimens. The attack rate was higher among females (52/1000) and those in the age group of 45-59 years (71/1000). The outbreak started on 22 September, peaked multiple times and subsided on 12 October 2007. Cases were clustered distal to a leaking pipeline that crossed an open drain to intermittently supply non-chlorinated water to taps. The 58 cases and 58 controls were matched for age and sex. Drinking tap water (MOR: 10; 95% CI: 3-32; PAF: 89%), washing utensils in tap water (MOR: 3.7; 95% CI: 1.2-11.3) and bathing in tap water (MOR: 3.5; 95% CI: 1.1-11) were associated with the illness.

CONCLUSION

This outbreak of diarrhoea and Shigella flexneri dysentery was caused by contamination of tap water and subsided following repair of the pipeline. We recommended regular chlorination of the water and maintenance of pipelines.

A large cholera outbreak due to a new cholera toxin variant of the Vibrio cholerae O1 El Tor biotype in Orissa, Eastern India

A total of 32 Vibrio cholerae isolates were collected during a recent large cholera outbreak in Eastern India. Biochemical and serological studies revealed that all of the isolates belonged to serogroup O1, biotype El Tor, serotype Ogawa. Two multiplex PCR assays confirmed the presence of various toxigenic and pathogenic genes - ace, ctxAB, hlyA, ompU, ompW, rfbO1, rtx, tcp, toxR and zot - in all of the isolates. Sequencing of the ctxB gene from the isolates revealed a novel mutation in the gene. Sequencing also confirmed the presence of altered cholera toxin B of the classical biotype in all of the El Tor isolates, suggesting infection of isolates by classical CTXPhi. The molecular diversity of V. cholerae isolates studied by enterobacterial repetitive intergenic consensus sequence PCR, BOX-PCR and randomly amplified polymorphic DNA analysis uniformly showed the clonal relationship among the outbreak V. cholerae O1 isolates. The results of this study suggest that cholera-causing V. cholerae strains are constantly evolving in epidemic areas, highlighting the potential of the emergence of more virulent strains.

Biotyping of Vibrio cholerae O1: time to redefine the scheme

Considering the recent emergence of "hybrid biotype" and "El Tor variant", we propose to redefine the biotyping scheme for Vibrio cholerae O1 serogroup. The existing biotyping scheme has limitations and causes confusion as many of the hybrid biotype and El Tor variant strains have phenotypic and genetic changes. A revised biotyping scheme will play a significant role to understand the ecology, epidemiology and nature of infection of V. cholerae O1 strains in future.

Molecular characterization of shiga like toxin-producing Escherichia coli (STEC) isolates from pigs oedema

BACKGROUND & OBJECTIVE

An oedema outbreak occurred in a Guwahati pig farm. Escherichia coli isolates from different necropsy samples collected from the dead piglets with oedema were characterized to confirm the virulence.

METHODS

Haemolytic E. coli isolates recovered from liver, lung and intestine of pigs with oedema were examined for presence of genes encoding pathogroups such as enteropathogenic Escherichia coli (EPEC), (eae/bfpA), enteroaggregative Escherichia coli (EAggEC), (eagg), enterotoxigive Escherichia coil (ETEC), (elt/est) and shiga like toxin producing Escherichia coli (STEC), (stx1/ stx2) by PCR and molecular typing by randomly amplified polymorphic DNA-PCR (RAPD-PCR).

RESULTS

The three haemolytic E. coli recovered from diseased pigs were STEC because of presence of the stx2 and eae genes. Analysis by RAPD-PCR indicated that two of the three isolates were genetically related.

INTERPRETATION & CONCLUSION

The isolation of STEC isolates from pigs with oedema was shown. Although the three isolates were untypable, presence of eae and stx2 genes clearly indicated these as prime cause of pig oedema disease. Further, demonstration of STEC in pigs becomes a public health concern, as pigs are potential reservoir of such agents, which may cause human illness.

Emergence of tetracycline-resistant Vibrio cholerae O1 serotype Inaba, in Kolkata, India

Out of 2,235 diarrheal stool samples collected from patients admitted to the Infectious Diseases Hospital, Kolkata, 343 cases were positive for Vibrio cholerae (341, V. cholerae O1 and 2, O139). During the year 2004, infections caused by V. cholerae serotype Ogawa and Inaba were 93 and 7%, respectively, while in 2005, the Inaba isolation rate rose to 88% as compared to 12% for Ogawa. Susceptibility to antimicrobial agents revealed that the O1 strains were resistant to multiple antibiotics (ampicillin, co-trimoxazole, furazolidone, nalidixic acid and streptomycin) with reduced susceptibility to ciprofloxacin. Increased isolation of tetracycline-resistant strains (27.3% for Ogawa and 15% for Inaba) was noted in 2005. It appears that the population might be at risk of infection by the Inaba serotype and that tetracycline may not be useful for the treatment.

Molecular characterization of recent Vibrio cholerae O1, El Tor, Inaba strains isolated from hospitalized patients in Kolkata, India

OBJECTIVES

To study the phenotypic and genotypic characterization of newly emerged V. cholerae O1, Inaba strains isolated from patients with diarrhoea.

METHODS

Bacterial characterization was made using polymerase chain reaction, ribotyping, PFGE and RFLP.

RESULTS

After its first appearance in July 2004, O1 Inaba became the dominant serotype by March 2005 and totally replaced the former dominant serotype, Ogawa from May 2005. Most of the Inaba isolates belong to a new ribotype RIV. Ogawa and also some Inaba strains isolated during the same period were identified as RIII. Similarly, the majority of the Inaba isolates belong to 'H1' pulsotype and one isolate is type 'H', while the Ogawa isolates were mostly 'H' pulsotype. Presence of CTX prophage was detected in a single site of the chromosome with at least two RS elements.

CONCLUSIONS

There has been a switch of dominant serotype from Ogawa to Inaba in the Kolkata region. This is not necessarily due to emergence of a new clone but does serve as an epidemiological marker. Further analysis at the molecular level will be required to define this trend and to monitor future spread to other regions.

An inducible lambdoid prophage encoding cytolethal distending toxin (Cdt-I) and a type III effector protein in enteropathogenic Escherichia coli

Cytolethal distending toxins (CDTs) are inhibitory cyclomodulins, which block eukaryotic cell proliferation and are produced by a diverse group of Gram-negative bacteria, including Escherichia coli strains associated with intestinal and extraintestinal infections. However, the mode of transmission of the toxin gene clusters among diverse bacterial pathogens is unclear. We found that Cdt-I produced by enteropathogenic E. coli strains associated with diarrhea is encoded by a lambdoid prophage, which is inducible and infectious. The genome of Cdt-I converting phage (CDT-1Phi) comprises 47,021 nucleotides with 60 predicted ORFs organized into six genomic regions encoding the head and tail, virulence, integrase, unknown functions, regulation, and lysis. The genomic organization of CDT-1Phi is similar to those of SfV, a serotype-converting phage of Shigella flexneri, and UTI89, a prophage identified in uropathogenic E. coli. Besides the cdtI gene cluster, the virulence region of CDT-1Phi genome contains sequences homologous to a truncated cycle inhibiting factor and a type 3 effector protein. Mutation analysis of susceptible E. coli strain C600 suggested that the outer membrane protein OmpC is a putative receptor for CDT-1Phi. CDT-1Phi genome was also found to integrate into the host bacterial chromosome forming lysogens, which produced biologically active Cdt-I. Furthermore, phage induction appeared to cause enhanced toxigenicity of the E. coli strains carrying lysogenic CDT-1Phi. Our results suggest that CDT-1Phi is the latest member of a growing family of lambdoid phages encoding bacterial cyclomodulins and that the phage may have a role in horizontal transfer of these virulence genes.

PCR-based identification of common colonization factor antigens of enterotoxigenic Escherichia coli

Colonization factor antigens (CFAs) of enterotoxigenic Escherichia coli (ETEC) have been classified into several groups based on their distinct antigenicity. We describe here a PCR-based method to detect common CFAs of ETEC, which were characterized using conventional serology. This PCR assay is simple and sensitive for the detection of expressed CFA genes.