Evaluation of the impact of Shigella virulence genes on the basis of clinical features observed in patients with shigellosis

INTRODUCTION

Shigella continues to cause significant morbidity and mortality each year, mostly in under-five children living in developing countries. We investigated the association between Shigella virulence genes and shigellosis.

METHODOLOGY

We randomly selected 61 S. flexneri strains isolated from patients in Bangladesh between 2009 and 2013, and evaluated the presence of 140 MDa large-virulence-plasmid (p140), and 22 virulence genes including ipaH, ial, toxin, and T3SS-related genes.

RESULTS

We found p140 in 79% (n = 48) and ipaBCD in 90% (n = 55) strains, while seven strains were missing the p140. The prevalence of ial was 89%, ipgC and ipgE was 85%, and the prevalence for the remaining genes was < 85%. During the multivariate analysis, we found that instead of sen, the Shigella enterotoxin gene set along with several other virulence genes such as ipgA, icsB, ipgB1, spa15, and mxiC, were significantly influencing multiple clinical features relevant to shigellosis, including bloody stool, mucoid stool, and rectal straining.

CONCLUSIONS

We believe our model will help to determine the actual disease burden by directly looking for the genetic material in clinically suggestive patients, especially when detecting the causative organisms by traditional means is difficult.

Characterization of a serologically atypical Shigella flexneri Z isolated from diarrheal patients in Bangladesh and a proposed serological scheme for Shigella flexneri

Background

Atypical Shigella flexneri Z variant, that agglutinate with E1037 group factor specific monoclonal antisera against Shigella flexneri IV-I but not with other group or type specific antisera, has continuously being isolated in Bangladesh since 1997. Later this serotype has been reported in Indonesia, China and Argentina. Despite being a provisional serotype, continuous isolation of these strains in diverse geographical regions implicated a great necessity to study the overall characteristics of these strains. Therefore, we extensively characterized S. flexneri Z strains using various phenotypic and molecular tools.

Method

Of 3569 S. flexneri isolated between 1997 and 2015, 95 strains were identified as S. flexneri Z using a panel of polyvalent absorbed antisera and monoclonal antisera of S. flexneri (MASF). Of them, randomly selected 65 strains were molecular O-serotyped using multiplex PCR and characterized using different phenotypic and molecular techniques (i.e.biotyping, plasmid profile, virulence marker and PFGE) to determine relationship with other subserotypes of S. flexneri.

Results

All these atypical S. flexneri Z strains were agglutinated with MASF B and IV-I antisera. Concordantly, these strains were positive to opt-gene, responsible for MASF IV-I sero-positive phenotype. However, molecular O-serotyping of all 65 strains could not differentiate between Z and Yb giving similar amplification products (wzx1-5 and opt). Contrarily, MASF based serotypic scheme distinguished among Z and Yb as well as Ya. All these S. flexneri Z showed typical biochemical reaction of S. flexneri, harboured a 140 MDa virulence plasmid and virulence markers namely ipaH, ial, sen, sigA and sepA genes. Along with the virulence plasmid, small plasmids (2.6, 1.8 and 1.6 MDa) were present as core plasmid. Moreover, a middle ranged plasmid and a 4.0 MDa sized plasmid were observed in 65% and 20% strains, respectively. Analysis of PFGE on XbaI-digested chromosomal DNA of Bangladeshi strains showed that S. flexneri Z had a close relatedness with Ya and Yb but completely different than the strains of Xa, Xb, 2a and 2b. This observation was found to be unequivocal while the overall result of biotyping, plasmid profile, and virulence factors was compared. Therefore, we conclude that these atypical serotype Z isolated in Bangladesh had a clonal relationship with Ya and Yb of Bangladesh and the opt gene played an important role in serotypic switching among them. Current serotyping scheme of S. flexneri strains fails to place many such atypical strains (1c, 1c+6, 1d, type 4, and 4c) including S. flexneri Z isolated from different parts of the world. Therefore, an updated serotyping scheme for identification of subserotypes of S. flexneri has been proposed to avoid multiple naming of the same subserotype having similar agglutination pattern.

Clonality, virulence and antimicrobial resistance of enteroaggregative Escherichia coli from Mirzapur, Bangladesh

Purpose

This study investigates the virulence and antimicrobial resistance in association with common clonal complexes (CCs) of enteroaggregative Escherichia coli (EAEC) isolated from Bangladesh. The aim was to determine whether specific CCs were more likely to be associated with putative virulence genes and/or antimicrobial resistance.

Methodology

The presence of 15 virulence genes (by PCR) and susceptibility to 18 antibiotics were determined for 151 EAEC isolated from cases and controls during an intestinal infectious disease study carried out between 2007–2011 in the rural setting of Mirzapur, Bangladesh (Kotloff KL, Blackwelder WC, Nasrin D, Nataro JP, Farag TH et al.Clin Infect Dis 2012;55:S232–S245). These data were then analysed in the context of previously determined serotypes and clonal complexes defined by multi-locus sequence typing.

Results

Overall there was no association between the presence of virulence or antimicrobial resistance genes in isolates of EAEC from cases versus controls. However, when stratified by clonal complex (CC) one CC associated with cases harboured more virulence factors (CC40) and one CC harboured more resistance genes (CC38) than the average. There was no direct link between the virulence gene content and antibiotic resistance. Strains within a single CC had variable virulence and resistance gene content indicating independent and multiple gene acquisitions over time.

Conclusion

In Bangladesh, there are multiple clonal complexes of EAEC harbouring a variety of virulence and resistance genes. The emergence of two of the most successful clones appeared to be linked to either increased virulence (CC40) or antimicrobial resistance (CC38), but increased resistance and virulence were not found in the same clonal complexes.

Isolation and Characterization of Enteropathogenic Escherichia coli (EPEC) in Paediatric Diarrhoeal Patients by Detection of bfpA gene by PCR and HeLa cell Adherence Assay

This study has been undertaken to investigate the isolation and identification of EPEC strains from paediatric diarrhoeal patients. The study was carried out in the department of Microbiology, Sir Salimullah Medical College & Mitford Hospital, Bangladesh during January to December, 2011. Total 272 samples were studied. Samples from patients with diarrhoea were collected from two tertiary care hospital. At first Esch. coli were isolated from these specimens using standard microbiological techniques and then EPEC strains were identified on the basis of presence of bundle forming pilus (bfpA) gene. Virulence of EPEC strains were determined by detection of bfpA gene and observing localized adherence (LA) in HeLa cell adherence assay. Esch. coli was isolated and identified from all the 272 samples from patients using standard microbiological techniques. Among 272 samples 20(7.35%) isolates were identified as EPEC on the basis of presence of bfpA gene detected by polymerase chain reaction. EPEC strains were identified from those 240 samples, from which Esch. coli had been isolated only. Out of twenty EPEC strains, 17 strains (85%) showed a pattern of localized adherence in Hela cell adherence assay. EPEC strains can be identified by bfpA gene detection and by adherence assays. HeLa cell adherence assay is the most specific method for detection of EPEC strains which has bfpA gene, responsible for localized adherence (LA) in HeLa cell line. Rapid and reliable detection of EPEC is required for successful microbiological surveillance and for treatment of EPEC mediated diarrhoeal disease.

Species-wide whole genome sequencing reveals historical global spread and recent local persistence in Shigella flexneri

Shigella flexneri is the most common cause of bacterial dysentery in low-income countries. Despite this, S. flexneri remains largely unexplored from a genomic standpoint and is still described using a vocabulary based on serotyping reactions developed over half-a-century ago. Here we combine whole genome sequencing with geographical and temporal data to examine the natural history of the species. Our analysis subdivides S. flexneri into seven phylogenetic groups (PGs); each containing two-or-more serotypes and characterised by distinct virulence gene complement and geographic range. Within the S. flexneri PGs we identify geographically restricted sub-lineages that appear to have persistently colonised regions for many decades to over 100 years. Although we found abundant evidence of antimicrobial resistance (AMR) determinant acquisition, our dataset shows no evidence of subsequent intercontinental spread of antimicrobial resistant strains. The pattern of colonisation and AMR gene acquisition suggest that S. flexneri has a distinct life-cycle involving local persistence.

MICROBIAL CONTAMINATION OF STREET VENDED FOODS FROM A UNIVERSITY CAMPUS IN BANGLADESH

The microbiological quality of street vended food samples from Dhaka, Bangladesh was evaluated. The objective of the study was to identify the presence of common pathogens (Escherichia coli, Shigella spp, Salmonella and Vibrio spp) and to describe the molecular characterization of E coli, a commonly found pathogen in various street foods. Fifty food samples were collected from fixed and mobile vendors from two sampling locations (Mohakhali and Aftabnagar) in Dhaka city, Bangladesh. The tested samples included deep fried and fried snacks; quick lunch items; pickles; fruit chutney; baked items; spicy, sour and hot snacks etc: Juices, tamarind water and plain drinking water were also tested. Sterile polythene bags were used for collecting 200 g of each category of samples. They were tested for the presence of microorganisms following conventional microbiological processes. Biochemical tests followed by serology were done for the confirmation of Shigella and Salmonella. Serological reaction was carried out for confirmation of Vibrio spp. DNA was isolated for the molecular characterization to detect the pathogenic E. coli by polymerase chain reaction (PCR). Out of 50 food samples, six (12%) were confirmed to contain different species of E. coli and Shigella. Molecular characterization of E. coli revealed that three samples were contaminated with enteroaggregative E. coli (EAEC) and one was contaminated with enterotoxigenic E. coli (ETEC). Shigellaflexneri X variant was detected in one food item and Shigella flexneri 2a was found in drinking water. All these enteric pathogens could be the potential cause for foodborne illnesses.

Enteroaggregative Escherichia coli have evolved independently as distinct complexes within the E. coli population with varying ability to cause disease

Enteroaggregative E. coli (EAEC) is an established diarrhoeagenic pathotype. The association with virulence gene content and ability to cause disease has been studied but little is known about the population structure of EAEC and how this pathotype evolved. Analysis by Multi Locus Sequence Typing of 564 EAEC isolates from cases and controls in Bangladesh, Nigeria and the UK spanning the past 29 years, revealed multiple successful lineages of EAEC. The population structure of EAEC indicates some clusters are statistically associated with disease or carriage, further highlighting the heterogeneous nature of this group of organisms. Different clusters have evolved independently as a result of both mutational and recombination events; the EAEC phenotype is distributed throughout the population of E. coli.

Comparative population structure analysis of Campylobacter jejuni from human and poultry origin in Bangladesh

Campylobacter jejuni is the most important cause of antecedent infections leading to Guillain-Barré syndrome (GBS) and Miller Fisher syndrome (MFS). The objective of the present study was to define the genetic diversity, population structure, and potential role of poultry in the transmission of Campylobacter to humans in Bangladesh. We determined the population structure of C. jejuni isolated from poultry (n = 66) and patients with enteritis (n = 39) or GBS (n = 10). Lipooligosaccharide (LOS) typing showed that 50/66 (76 %) C. jejuni strains isolated from poultry could be assigned to one of five LOS locus classes (A-E). The distribution of neuropathy-associated LOS locus classes A, B, and C were 30/50 (60 %) among the typable strains isolated from poultry. The LOS locus classes A, B, and C were significantly associated with GBS and enteritis-related C. jejuni strains more than for the poultry strains [(31/38 (82 %) vs. 30/50 (60 %), p < 0.05]. Multilocus sequence typing (MLST) defined 15 sequence types (STs) and six clonal complexes (CCs) among poultry isolates, including one ST-3740 not previously documented. The most commonly identified type, ST-5 (13/66), in chicken was seen only once among human isolates (1/49) (p < 0.001). Amplified fragment length polymorphism (AFLP) revealed three major clusters (A, B, and C) among C. jejuni isolated from humans and poultry. There seems to be a lack of overlap between the major human and chicken clones, which suggests that there may be additional sources for campylobacteriosis other than poultry in Bangladesh.

Genomic analysis of the emergence of 20th century epidemic dysentery

Background

Shigella dysenteriae type 1 (Sd1) causes recurrent epidemics of dysentery associated with high mortality in many regions of the world. Sd1 infects humans at very low infectious doses (10 CFU), and treatment is complicated by the rapid emergence of antibiotic resistant Sd1 strains. Sd1 is only detected in the context of human infections, and the circumstances under which epidemics emerge and regress remain unknown.

Results

Phylogenomic analyses of 56 isolates collected worldwide over the past 60 years indicate that the Sd1 clone responsible for the recent pandemics emerged at the turn of the 20^th century, and that the two world wars likely played a pivotal role for its dissemination. Several lineages remain ubiquitous and their phylogeny indicates several recent intercontinental transfers. Our comparative genomics analysis reveals that isolates responsible for separate outbreaks, though closely related to one another, have independently accumulated antibiotic resistance genes, suggesting that there is little or no selection to retain these genes in-between outbreaks. The genomes appear to be subjected to genetic drift that affects a number of functions currently used by diagnostic tools to identify Sd1, which could lead to the potential failure of such tools.

Conclusions

Taken together, the Sd1 population structure and pattern of evolution suggest a recent emergence and a possible human carrier state that could play an important role in the epidemic pattern of infections of this human-specific pathogen. This analysis highlights the important role of whole-genome sequencing in studying pathogens for which epidemiological or laboratory investigations are particularly challenging.

Electronic supplementary material

The online version of this article (doi: 10.1186/1471-2164-15-355) contains supplementary material, which is available to authorized users.

Plasmid-mediated sulfamethoxazole resistance encoded by the sul2 gene in the multidrug-resistant Shigella flexneri 2a isolated from patients with acute diarrhea in Dhaka, Bangladesh

In this study, mechanisms of plasmid-mediated sulfamethoxazole resistances in the clinical strains of multi-drug resistant (MDR) Shigella flexneri 2a were elucidated for the first time in Bangladesh. From 2006 to 2011, a total of 200 S. flexneri 2a strains were randomly selected from the stock of the Enteric and Food Microbiology Laboratory of icddr,b. Antimicrobial susceptibility of the strains showed 73%, 98%, 93%, 58%, 98%, 64% and 4% resistance to trimethoprim-sulfamethoxazole, nalidixic acid, ampicillin, erythromycin, tetracycline, ciprofloxacin and ceftriaxone respectively. Plasmid profiling revealed heterogeneous patterns and interestingly, all the trimethoprim-sulfamethoxazole resistant (SXT(R)) strains yielded a distinct 4.3 MDa plasmid compared to that of the trimethoprim-sulfamethoxazole susceptible (SXT(S)) strains. Curing of this 4.3 MDa plasmid resulted in the susceptibility to sulfamethoxazole alone suggesting the involvement of this plasmid in the resistance of sulfamethoxazole. Moreover, PCR analysis showed the presence of sul2 gene in SXT(R) strains which is absent in SXT(S) strains as well as in the 4.3 MDa plasmid-cured derivatives, confirming the involvement of sul2 in the resistance of sulfamethoxazole. Furthermore, pulsed-field gel electrophoresis (PFGE) analysis revealed that both the SXT(R) and SXT(S) strains were clonal. This study will significantly contributes to the knowledge on acquired drug resistance of the mostly prevalent S. flexneri 2a and further warrants continuous monitoring of the prevalence and correlation of this resistance determinants amongst the clinical isolates of Shigella and other enteric pathogens around the world to provide effective clinical management of the disease.

Etiological diversity of diarrhoeal disease in Bangladesh

BACKGROUND

This study compared the diversity of common diarrhoeal pathogens and antimicrobial susceptibility in four hospitals in Bangladesh.

METHODOLOGY

A total of 13,959 diarrhoea patients, comprising rural Mirzapur (2,820), rural Matlab (2,865), urban Dhaka (5,287) and urban Mirpur (2,987) were included under the diarrhoeal disease surveillance system of icddr,b during 2010-2011; stool specimens were tested for Shigella spp., Vibrio cholerae, enterotoxigenic Escherichia coli and rotavirus.

RESULTS

Rotavirus was highest in Mirzapur (28%) followed by Dhaka (24%), Matlab (19%) and Mirpur (18%). Overall, Shigella was significantly more prevalent in rural sites (Mirzapur 13% and Matlab 7%), than in urban sites (Dhaka 3% and Mirpur 3%). Vibrio cholerae was more common in the urban sites of Dhaka (14%) and Mirpur (12%). 72% of Shigella isolates were susceptible to ciprofloxacin in Mirzapur, and 88% to mecillinam. In Dhaka, the figures for Shigella were 65% and 50%, in Matlab 65% and 85%, and in Mirpur 59% and 92% respectively. Susceptibility of Shigella to azithromycin and ceftriaxone in Dhaka was 74% and 95%, and in Mirpur 88% and 92% respectively.  Vibrio cholerae showed the highest resistance to trimethoprim-sulfamethoxazole (100% in Mirpur) and lowest resistance to ciprofloxacin (0% in Dhaka, Matlab and Mirpur) and azithromycin (30% in Dhaka to 7% in Mirzapur). Multidrug resistance (≥3 antibiotics) for Shigella were: Mirzapur (50%); Dhaka (36%); Matlab (23%) and Mirpur (37%); and for V. cholerae it was 26%, 37%, 49% and 23% respectively.

CONCLUSION

The isolation rates and antimicrobial susceptibility of Shigella spp. and V. cholerae along with rotavirus differed significantly in certain geographical sites.

Poultry as a possible source of non-typhoidal Salmonella enterica serovars in humans in Bangladesh

We investigated Salmonella enterica isolates from human clinical cases of gastroenteritis to determine the distribution of non-typhoidal Salmonella serovars in the human population, and compared them to isolates originating from poultry by serotyping, phage typing, plasmid profiling, pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST) to evaluate the potential role of poultry in human non-typhoidal salmonellosis in Bangladesh. Nine different serovars were identified among the human isolates of which Salmonella Paratyphi B var Java (S. Java), S. Kentucky, S. Enteritidis, S. Virchow and S. Weltevreden also were commonly isolated from poultry. The poultry isolates belonging to S. Java, S. Kentucky and S. Enteritidis were indistinguishable from human isolates or genetically closely related, based on PFGE profiles and MLST. S. Kentucky clone ST198 and S. Java clone ST43 both well-known cause of human infections were also isolated from poultry.

Changing emergence of Shigella sero-groups in Bangladesh: observation from four different diarrheal disease hospitals

BACKGROUND

Shigellosis continues to be a public health challenge for developing countries, including Bangladesh. The aim of the study is to demonstrate recent changes in Shigella sero-groups and their geographical diversity.

METHODS

Data were extracted from data archive of four diarrheal disease surveillance systems. A 2% sub sample from urban Dhaka Hospital (2008-2011; n = 10,650), and 10% from urban Mirpur Treatment Centre (2009-2011; n = 3,585), were enrolled systematically; whereas, all patients coming from the Health and Demographic Surveillance System area in rural Matlab (2008-2011; n = 6,399) and rural Mirzapur (2010-2011; n = 2,812) were included irrespective of age, sex, and disease severity. A fresh stool specimen was collected for identification of Shigella spp. Of them, 315 (3%) were positive for Shigella in Dhaka, 490 (8%) from Matlab, 109 (3%) from Mirpur and 369 (13%) from Mirzapur and considered as analyzable sample size.

RESULTS

Among all Shigella isolates regardless of age, significant decreases in percentage of S. flexneri over time was observed in Mirpur (55→29%; p value of χ(2)-for trend = 0.019) and Mirzapur (59→47%; p = 0.025). A non-significant decrease was also seen in Dhaka (58→48%), while in Matlab there was a non-significant increase (73→81%). Similar patterns were observed among under-5 children at all sites. Emergence of S. sonnei was found in Dhaka (8→25%; p<0.001) and Mirpur (10→33%; p = 0.015), whereas it decreased in Mirzapur (32→23%; p = 0.056). The emergence of S. boydii was seen in all ages in Mirzapur [(3→28%; p<0.001); (3→27%; p<0.001)]. On the other hand, we saw non-significant percent reductions in S. boydii in Dhaka [overall (25→16%); under-5 (16→9%)]. Decreasing rates of Shigella dysenteriae were observed in Matlab, Mirpur and Mirzapur; whereas, in Dhaka it remained unchanged.

CONCLUSION AND SIGNIFICANCE

Emergence of S. sonnei and S. boydii as important infectious diarrhea etiologies and variations in geographical diversity underscore the need for monitoring, with possible implications for vaccine development.

Occurrence and characterization of multidrug-resistant New Delhi metallo-β-lactamase-1-producing bacteria isolated between 2003 and 2010 in Bangladesh

The purpose of this study was to screen for reduced susceptibility against imipenem and the presence of the New Delhi metallo-β-lactamase-1 (NDM-1) gene in a collection of Enterobacteriaceae (Escherichia coli, Shigella spp. and Klebsiella pneumoniae) from different surveillance studies between 2003 and 2010 at the International Centre for Diarrhoeal Disease Research, Bangladesh. None of the E. coli (n = 1789) and Shigella spp. (n = 90) isolated between 2009 and 2010 from stool samples was resistant or had intermediate susceptibility to imipenem. Among 127 extended-spectrum β-lactamase-producing strains isolated during 2003-2009, three Klebsiella pneumoniae isolates (2.4 %) were resistant to imipenem and were positive for bla(NDM-1). All these NDM-1-producing strains were isolated in 2008 and were resistant to all antibiotics tested except for tigecycline and colistin. All three isolates were positive for bla(OXA-1) group, bla(CTX-M-1) group (bla(CTX-M-15)) and bla(SHV) genes, whilst two isolates were positive for 16S rRNA methylase (armA) and qnr (qnrB) genes. One isolate was positive for the bla(CMY) gene and one for the rmtB gene. The bla(NDM-1) gene was located on a conjugative plasmid of ~23-24 MDa. The PFGE patterns of the isolates were different from each other. This study highlights the occurrence of NDM-1-producing organisms in Bangladesh in 2008. The clonal diversity of the isolates and the transferability of bla(NDM-1) plasmids suggest a wider distribution of NDM-1-producing bacteria in Bangladesh.

Emergence of multidrug-resistant NDM-1-producing Gram-negative bacteria in Bangladesh

The main objective of this study was to investigate the prevalence of bla (NDM-1) in Gram-negative bacteria in Bangladesh. In October 2010 at the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B) laboratories, 1,816 consecutive clinical samples were tested for imipenem-resistant Gram-negative organisms. Imipenem-resistant isolates were tested for the bla (NDM-1) gene. Among 403 isolates, 14 (3.5 %) were positive for bla (NDM-1), and the predominant species were Klebsiella pneumoniae, Acinetobacter baumannii, and Escherichia coli. All bla (NDM-1)-positive isolates were resistant to multiple antibiotics. Among β-lactamase genes, bla (CTX-M-1-group) was detected in ten isolates (eight bla (CTX-M-15)), bla (OXA-1-group) in six, bla (TEM) in nine, bla (SHV) in seven, and bla (VIM) and bla (CMY) in two isolates each. The 16S rRNA methylase gene, armA, was detected in five K. pneumoniae isolates and in one E. coli isolate. rmtB and rmtC were detected in a Citrobacter freundii and two K. pneumoniae isolates, respectively. qnr genes were detected in two K. pneumoniae isolates (one qnrB and one qnrS) and in an E. coli isolate (qnrA). Transferable plasmids (60-100 MDa) carrying bla (NDM-1) were detected in 7 of the 11 plasmid-containing isolates. Pulsed-field gel electrophoresis (PFGE) analysis grouped K. pneumoniae isolates into three clusters, while E. coli isolates differed significantly from each other. This study reports that approximately 3.5 % of Gram-negative clinical isolates in Bangladesh are NDM-1-producing.

Differential host immune responses to epidemic and endemic strains of Shigella dysenteriae type I

Shigella dysenteriae type 1 causes devastating epidemics in developing countries with high case-fatality rates in all age-groups. The aim of the study was to compare host immune responses to epidemic (T2218) and endemic strains of S. dysenteriae type 1. Shigellacidal activity of serum from rabbits immunized with epidemic or endemic strains, S. dysenteriae type 1-infected patients, and healthy adult controls from Shigella-endemic and non-endemic regions was measured. Immunogenic cross-reactivity of antibodies against Shigella antigens was evaluated by Western blot analysis. Oxidative burst and phagocytic responses of monocytes and neutrophils to selected S. dysenteriae type 1 strains were assessed by flow cytometry. Rabbit antisera against epidemic strain were less effective in killing heterologous bacteria compared to endemic antisera (p=0.0002). Patients showed an increased serum shigellacidal response after two weeks of onset of diarrhoea compared to the acute stage (3-4 days after onset) against their respective homologous strains; the response against T2218 and heterologous endemic S. dysenteriae type 1 strains was not significant. The serum shigellacidal response against all the S. dysenteriae type 1 strains was similar among healthy controls from endemic and non-endemic regions and was comparable with the acute stage response by patients. Compared to endemic strains of S. dysenteriae type 1, T2218 was significantly resistant to phagocytosis by both monocytes and neutrophils. No obvious differences were obtained in the induction of oxidative burst activity and cathelicidin-mediated killing. Cross-reactivity of antibody against antigens present in the epidemic and endemic strains showed some differences in protein/peptide complexity and intensity by Western blot analysis. In summary, epidemic T2218 strain was more resistant to antibody-mediated defenses, namely phagocytosis and shigellacidal activity, compared to endemic S. dysenteriae type 1 strains. Part of this variation may be attributed to the differential complexity of protein/peptide antigens.

Axonal variant of Guillain-Barre syndrome associated with Campylobacter infection in Bangladesh

BACKGROUND

Campylobacter jejuni enteritis is the predominant bacterial infection preceding Guillain-Barré syndrome (GBS), an acute postinfectious immune-mediated polyradiculoneuropathy. The purpose of this study was to define the clinical phenotype of GBS and the relation with preceding C jejuni infections in Bangladesh.

METHODS

We performed a prospective matched case-control hospital surveillance including 100 patients fulfilling the National Institute of Neurological Disorders and Stroke criteria for GBS from 2006 to 2007 in the Dhaka area of Bangladesh. Detailed clinical, electrophysiologic, serologic, and microbiologic data were obtained with a follow-up of 6 months.

RESULTS

GBS affected predominantly young adult males living in rural areas. Sixty-nine percent of the patients had clinical evidence of a preceding infection. The most frequent symptom was diarrhea (36%). The majority of patients had a pure motor variant of GBS (92%) with relatively infrequent cranial nerve involvement (30%). Twenty-five percent of patients required respiratory support. Electrophysiologic studies showed that 67% of patients had an axonal variant of GBS. Eleven patients (14%) died, and 23 (29%) remained severely disabled during the follow-up. Positive C jejuni serology was found in an unprecedented high frequency of 57% as compared with 8% in family controls and 3% in control patients with other neurologic diseases (p < 0.001). C jejuni infection was significantly associated with serum antibodies to the gangliosides GM1 and GD1a, axonal neuropathy, and greater disability.

CONCLUSIONS

We report an unusually high frequency of the axonal variant of Guillain-Barré syndrome in Bangladesh, associated with preceding Campylobacter jejuni infection, severe residual disability, and high mortality.

Shiga toxin-producing Escherichia coli isolated from patients with diarrhoea in Bangladesh

The prevalence of Shiga toxin-producing Escherichia coli (STEC) and its characteristics were determined among hospitalized patients with diarrhoea and children with diarrhoea in an urban slum community of Dhaka city using sensitive culture and PCR methods. Stool samples were collected from 410 patients with diarrhoea enrolled in the 2% surveillance system (every 50th patient attending the hospital with diarrhoeal disease is included) at the ICDDR,B hospital and from 160 children of 2-5 years of age with diarrhoea living in an urban slum in Dhaka, between September 2004 and April 2005. Shiga toxin genes (stx) were detected by multiplex PCR in the enrichment broth of nine samples (2.2%) from hospitalized patients and 11 samples (6.9%) from the community patients. STEC was isolated from five stool samples with positive PCR results using a colony patch technique. All five isolates were positive in the Vero cell assay and PCR fragments of stx genes were confirmed by sequencing. Two isolates were positive for the E. coli attaching-and-effacing (eae) gene and four were positive for the enterohaemolysin (hlyEHEC) gene and enterohaemolysin production. The five isolates belonged to five different serotypes:O32:H25, O2:H45, O76:H19, ONT:H25 and ONT:H19. It can be concluded that STEC is not a common pathogen in Bangladesh among hospitalized patients with diarrhoea nor among mild cases of diarrhoea in the community.

Comparison of enterotoxigenicEscherichia coliisolated from surface water and diarrhoeal stool samples in Bangladesh

Enterotoxigenic Escherichia coli (ETEC) is a common cause of bacterial infection leading to acute watery diarrhea in infants and young children. Although the prevalence of ETEC is high in Bangladesh and infections can be spread through food and contaminated water, limited information is available about ETEC in the surface water. We carried out studies to isolate ETEC from surface water samples from ponds, rivers, and a lake from a site close to field areas known to have a high incidence of diarrhea in Dhaka, Bangladesh, and Matlab, Bangladesh. ETEC strains isolated from the water sources were compared with ETEC strains isolated from patients with diarrhea at two hospitals in these areas. ETEC were isolated from 30% (45 of 150) of the samples from the surface water sources and 19% (518 of 2700) of the clinical specimens. One hundred ETEC strains isolated from patients with similar phenotypes as the environmental strains were compared for phenotypic and genotypic properties. The most common O serogroups on ETEC were O6, O25, O78, O115, and O126 in both types of strains. Pulsed-field gel electrophoresis analyses of the ETEC strains showed that multiple clones of ETEC were present within each colonization factor type and that some clones detected in the environment were also isolated from the stools of patients. The strains showed multiple and similar antibiotic resistance patterns. This study shows that ETEC is prevalent in surface water sources in Bangladesh suggesting a possible reason for the endemicity of this pathogen in Bangladesh.Key words: enterotoxigenic Escherichia coli (ETEC), surface water samples, colonization factors, pulsed-field gel electrophoresis, toxin types.

The emerging strains of Shigella dysenteriae type 2 in Bangladesh are clonal

A total of 113 strains of Shigella dysenteriae type 2 isolated from patients attending the Dhaka diarrhoea treatment centre of ICDDR,B: Centre for Health and Population Research during the period 1999-2004 were studied. Serotype of the isolates was confirmed using commercially available antisera. Except for arabinose fermentation, all the strains had similar biochemical reactions. More than 60% of the strains were sensitive to commonly used antibiotics; only 6% (n=7) of the strains were resistant to nalidixic acid, and none of the strains were resistant to mecillinam and ciprofloxacin. All strains were invasive as demonstrated by the presence of a 140 MDa plasmid, ial, sen and ipaH genes, Congo Red absorption ability and by the Sereny test performed on representative strains. Plasmid patterns were heterogeneous but more than 50% of strains were confined to a single pattern. All strains possessed a 1.6 MDa plasmid and 87% of the strains contained a 4 MDa plasmid. Middle-range plasmids (90 MDa to 30 MDa) present in 36% of the strains were not associated with antibiotic resistance. All the strains were clustered within a single type with four subtypes by pulsed-field gel electrophoresis while ribotyping patterns of all the strains were identical.

Variation of toxigenic Vibrio cholerae O1 in the aquatic environment of Bangladesh and its correlation with the clinical strains

The diversity of toxigenic V. cholerae O1 in the aquatic environment of Bangladesh is not known. A total of 18 environmental and 18 clinical strains of toxigenic V. cholerae O1 were isolated simultaneously from four different geographical areas and tested for variation by the pulsed-field gel electrophoresis method. Environmental strains showed diversified profiles and one of the profiles was common to some environmental strains and most clinical strains. It appears that one clone has an advantage over others to cause disease. These findings suggest that the study of the molecular ecology of V. cholerae O1 in relation to its environmental reservoir is important in identifying virulent strains that cause disease.

Shigella serotypes among hospitalized patients in urban Bangladesh and their antimicrobial resistance

We studied the isolation of Shigella spp., and their antimicrobial resistance. S. flexneri (54 %) was most frequently isolated, followed by S. dysenteriae (20 %), S. boydii (16 %) and S. sonnei (10 %). Among S. flexneri (n = 122), 29 (24 %) were 2a, and 23 (19 %) were 2b. None of the Shigella strains were resistant to mecillinam or ciprofloxacin. Resistance to nalidixic acid was most frequent among S. dysenteriae type 1 (100%) followed by S. flexneri 2a (69%), and S. flexneri 2b (52 %). Systematic monitoring is needed to identify most prevalent serotypes, and to detect changes in the prevalence and antimicrobial resistance pattern.

Altering trends in the dominance of Shigella flexneri serotypes and emergence of serologically atypical S. flexneri strains in Dhaka, Bangladesh

Of 469 recently isolated Shigella flexneri strains, 452 agglutinated with Shigella flexneri-specific monoclonal antibodies. Of these, 396 could be assigned to 10 of the currently recognized 15 serotypes, with S. flexneri 2b dominating (23.2%). Of the 56 untypeable strains which showed invasive properties, 17 were serologically atypical and the remaining 39 belonged to a new serotype.

Prevalence of enterotoxin genes in Aeromonas spp. isolated from children with diarrhea, healthy controls, and the environment

Aeromonads are causative agents of a number of human infections. Even though aeromonads have been isolated from patients suffering from diarrhea, their etiological role in gastroenteritis is unclear. In spite of a number of virulence factors produced by Aeromonas species, their association with diarrhea has not been clearly linked. Recently, we have characterized a heat-labile cytotonic enterotoxin (Alt), a heat-stable cytotonic enterotoxin (Ast), and a cytotoxic enterotoxin (Act) from a diarrheal isolate of Aeromonas hydrophila. Alt and Ast are novel enterotoxins which are not related to cholera toxin; Act is aerolysin related and has hemolytic, cytotoxic, and enterotoxic activities. We studied the distribution of the alt, ast, and act enterotoxin genes in 115 of 125 aeromonads isolated from 1, 735 children with diarrhea, in all 27 aeromonads isolated from 830 control children (P = 7 x 10(-4) for comparison of rates of isolation of aeromonads from cases versus those from controls), and in 120 randomly selected aeromonads from different components of surface water in Bangladesh. Aeromonas isolates which were positive only for the presence of the alt gene had similar distributions in the three sources; the number of isolates positive only for the presence of the ast gene was significantly higher for the environmental samples than for samples from diarrheal children; and isolates positive only for the presence of the act gene were not found in any of the three sources. Importantly, the number of isolates positive for both the alt and ast genes was significantly higher for diarrheal children than for control children and the environment. Thus, this is the first study to indicate that the products of both the alt and ast genes may synergistically act to induce severe diarrhea. In 26 patients, Aeromonas spp. were isolated as the sole enteropathogen. Analysis of clinical data from 11 of these patients suggested that isolates positive for both the alt and ast genes were associated with watery diarrhea but that isolates positive only for the alt gene were associated with loose stools. Most of the isolates from the three sources could be classified into seven phenospecies and eight hybridization groups. For the first time, Aeromonas eucrenophila was isolated from two children, one with diarrhea and another without diarrhea.

Evaluation of pulsed-field gel electrophoresis for typing of Shigella dysenteriae type 1

Pulsed-field gel electrophoresis (PFGE) has been used successfully to discriminate between strains of many different bacterial species. In this study, digestion of bacterial DNA with the restriction endonuclease NotI and PFGE were evaluated for the typing of isolates of Shigella dysenteriae type 1, an important cause of epidemic dysentery. There were 27 isolates from four outbreaks of dysentery, and 44 isolates from endemic dysentery cases and a laboratory culture collection. The epidemic isolates yielded two types each with two subtypes, whereas the endemic isolates and culture collection yielded eight types with numerous subtypes. These findings suggest that S. dysenteriae 1 can be typed by PFGE.

Phenotypic and genotypic changes in Vibrio cholerae O139 Bengal

To find reasons for the recent decline of Vibrio cholerae O139 Bengal cholera in Bangladesh, phenotypic and genotypic changes in O139 isolates obtained from patients with cholera from 1993 to 1996 were studied. The isolates were tested for the presence of ctx and tcpA genes, hemagglutinin/protease (HA/P), capsule, D-mannose-sensitive hemagglutinin (MSHA), L-fucose-sensitive hemagglutinin (FSHA), tube test (tube) and CAMP test (CAMP) hemolytic activities, resistance to 2,4-diamino-6,7-diisopropyl pteridine (O/129) and trimethoprim-sulfamethoxazole (TMP-SMX), and genotype by pulsed-field gel electrophoresis (PFGE). All isolates possessed ctx and tcpA genes, HA/P, and a capsule. Most isolates were negative for FSHA, but although the majority of the isolates were positive for MSHA, no discernible trend in the activity was found during the study period. All early isolates were CAMP hemolysin positive and resistant to the vibriostatic compound O/129 and TMP-SMX, the two properties that could be used for the presumptive diagnosis of O139 cholera. However, subsequently, isolates that were CAMP hemolysin negative and susceptible to TMP-SMX and O/129 were increasingly encountered, with all the 1996 isolates being so, which suggested that these properties can no longer be used for the presumptive diagnosis of O139 cholera. V. cholerae O139 isolates that were CAMP hemolysin positive and resistant to O/129 and TMP-SMX produced a disease of greater severity than that caused by the CAMP hemolysin-negative and susceptible isolates on the basis of the lengths of stay of the hospitalized patients. The study period witnessed the evolution of four different genotypes by PFGE. All of these data suggested that the V. cholerae O139 isolates have undergone changes in some properties. However, how these changes influenced their prevalence relative to that of V. cholerae O1 in human infection is not clear. Studies of the environmental factors will provide the key for an understanding of the relative abundance of these vibrios.

Construction of a physical map of the chromosome of Shigella flexneri 2a and the direct assignment of nine virulence-associated loci identified by Tn5 insertions

To establish the molecular basis of the chromosomal virulence genes of Shigella flexneri 2a (YSH6000), a Notl restriction map of the chromosome was constructed by exploiting Notl-linking clones, partial Notl digestion and DNA probes from various genes of Escherichia coli K-12. The map revealed at least three local differences in the placements of genes between YSH6000 and E. coli K-12. Using the additional Notl sites introduced by Tn5 insertion, nine virulence loci identified previously by random Tn5 insertions were physically mapped on the chromosome. To demonstrate the versatility of the Notl map in direct assignment of the virulence loci tagged by Tn5 to a known genetic region in E. coli K-12, the major class of avirulent mutants defective in the core structure of lipopolysaccharide (LPS) was examined for the sites of Tn5 insertions. The two Notl segments created by the Tn5 insertion in the Notl fragment were analysed by Southern blotting with two DNA probes for the 5' and 3' flanking regions of the rfa region, and shown to hybridize separately with each of them, confirming the sites of Tn5 in the rfa locus. This approach will facilitate direct comparison genetically mapped Tn5 insertion mutations of S. flexneri with genes physically determined in E. coli K-12.

Virulence-associated chromosomal loci of Shigella flexneri identified by random Tn5 insertion mutagenesis

Shigellae are the causative agents of bacillary dysentery and are capable of invading epithelial cells, multiplying therein and spreading into adjacent cells. To identify genes on the chromosome associated with the virulence phenotype, 9114 independent Tn5 insertion mutants were isolated in a virulent strain of Shigella flexneri. By using an in vitro assay for intercellular spread or an animal infection model, the Serény test, 50 chromosomal Tn5 mutants with reduced virulence were identified. The 50 mutants were characterized with respect to their virulence phenotypes, including three different mutations that affect invasion of epithelial cells, bacterial metabolism and structure of lipopolysaccharide. Mutants with reduced invasive ability were further characterized and it was found that two of them had decreased levels of IpaB, C and D antigens as well as the mRNA for the ipaBCD operon encoded by the large virulence plasmid, suggesting that positive regulatory elements for the ipaBCD operon are encoded by the chromosome. Assignment of the 50 Tn5 insertions of the mutants to the 19 NotI restriction fragments of the chromosomal DNA has permitted the identification of at least nine virulence-associated chromosomal loci.

Trimethoprim resistance gene in Shigella dysenteriae 1 isolates obtained from widely scattered locations of Asia

Trimethoprim-resistance genes of Shigella dysenteriae 1 strains, isolated from a different location of six different countries of Asia over a 5-year period were characterized by using three different dihydrofolate reductase (DHFR) gene probes. The trimethoprim-resistant (TMPR) strains hybridized only with the type I DHFR gene probe by colony hybridization. None of the strains hybridized with types II and III DHFR gene probes. Southern blot experiments using plasmid DNA extracted from these resistant strains indicated that the type I DHFR genes were either on a 20 MDa plasmid or might be located on the chromosome. None of the other plasmids present in S. dysenteriae 1 strains hybridized with the probe. This indicates that the TMP resistance in these S. dysenteriae 1 strains are mediated by type I DHFR enzyme, and there may be transposition of this type I DHFR gene occurs between the 20 MDa plasmid and the chromosome in this serotype of shigella.

Electropherotyping of plasmid DNA of different serotypes of Shigella flexneri isolated in Bangladesh

One hundred and twenty-five Shigella flexneri strains, isolated during January-December 1984, at the Dhaka treatment centre of the International Centre for Diarrhoeal Disease Research, Bangladesh, were serotyped using absorbed rabbit antisera specific for all type- and group-factor antigens, as well as a group of ten mouse and rat monoclonal antibodies. Electropherotypes of the plasmid deoxyribonucleic acid (DNA) were also determined. S. flexneri 2a was the predominant serotype followed by 3b, 1a, and 2b. The recently described E1037 antigen was also found in three strains of S. flexneri serotype 6. Electropherotyping of the plasmid DNA showed that three plasmids of approximately 140, 2.7, and 2 megadalton (MDa) were present, respectively, in 97, 97 and 94% of the 125 strains. Additional plasmids of various other sizes were also present in different serotypes except in serotype 2a. The additional plasmids again appeared to be specific for that particular serotype. For example, all 12 strains of S. flexneri 2b harboured an additional plasmid of approximately 1 MDa. Thus, electropherotyping of plasmid DNA of different serotypes of S. flexneri might be useful to differentiate S. flexneri from other species of Shigella and in identifying different serotypes of S. flexneri. Therefore, the common plasmids, plus the additional plasmids, could be used to identify epidemic, as well as sporadic, subclones of S. flexneri strains.

Plasmid analysis of Shigella dysenteriae type 1 isolates obtained from widely scattered geographical locations

Plasmid profiles and antimicrobial susceptibility patterns of 343 strains of Shigella dysenteriae type 1, obtained from 18 different geographical locations, were analyzed. Three plasmids, with molecular sizes of 140, 6, and 2 megadaltons (MDa), were present in 94, 98, and 96%, respectively, of the 343 strains isolated during either epidemic or nonepidemic periods from 1965 to 1987. In addition to these plasmids, 83% of the strains harbored a 4-MDa plasmid and 25% harbored a 20-MDa plasmid. Various plasmid profiles were observed in which the 140-, 6-, and 2-MDa plasmids occurred commonly, irrespective of the place of isolation and drug resistance pattern of the strains. Certain profiles showed significant association with drug resistance patterns. These findings suggest that three plasmids, of molecular sizes 140, 6, and 2 MDa, are unique to S. dysenteriae type 1 strains and may indicate the global spread of a pathogenic bacterial clone. Additionally, these core plasmids, plus plasmids of various other sizes, could be used to identify emerging subclones which are causing both epidemic and sporadic disease. Thus, plasmid profiles of S. dysenteriae type 1 strains can be used to monitor possible pandemic strains as well as individual epidemic strains.