Molecular characterization of Vibrio cholerae O139 bengal isolated from water and the aquatic plant Eichhornia crassipes in the River Ganga, Varanasi, India

Genomic and functional insights into antibiotic resistance genes floR and strA linked with the SXT element of Vibrio cholerae non-O1/non-O139

The emergence and spread of antibiotic-resistant bacterial pathogens are a critical public health concern across the globe. Mobile genetic elements (MGEs) play an important role in the horizontal acquisition of antimicrobial resistance genes (ARGs) in bacteria. In this study, we have decoded the whole genome sequences of multidrug-resistant Vibrio cholerae clinical isolates carrying the ARG-linked SXT, an integrative and conjugative element, in their large chromosomes. As in others, the SXT element has been found integrated into the 5'-end of the prfC gene (which encodes peptide chain release factor 3 involved in translational regulation) on the large chromosome of V. cholerae non-O1/non-O139 strains. Further, we demonstrate the functionality of SXT-linked floR and strAB genes, which confer resistance to chloramphenicol and streptomycin, respectively. The floR gene-encoded protein FloR belongs to the major facilitator superfamily efflux transporter containing 12 transmembrane domains (TMDs). Deletion analysis confirmed that even a single TMD of FloR is critical for the export function of chloramphenicol. The floR gene has two putative promoters, P1 and P2. Sequential deletions reveal that P2 is responsible for the expression of the floR. Deletion analysis of the N- and/or C-terminal coding regions of strA established their importance for conferring resistance against streptomycin. Interestingly, qPCR analysis of the floR and strA genes indicated that both of the genes are constitutively expressed in V. cholerae cells. Further, whole genome-based global phylogeography confirmed the presence of the integrative and conjugative element SXT in non-O1/non-O139 strains despite being non-multidrug resistant by lacking antimicrobial resistance (AMR) gene cassettes, which needs monitoring.

Antibiotic-Resistant Vibrio cholerae O1 and Its SXT Elements Associated with Two Cholera Epidemics in Kenya in 2007 to 2010 and 2015 to 2016

Multidrug-resistant Vibrio cholerae O1 strains have long been observed in Africa, and strains exhibiting new resistance phenotypes have emerged during recent epidemics in Kenya. This study aimed to determine the epidemiological aspects, drug resistance patterns, and genetic elements of V. cholerae O1 strains isolated from two cholera epidemics in Kenya between 2007 and 2010 and between 2015 and 2016. A total of 228 V. cholerae O1 strains, including 226 clinical strains isolated from 13 counties in Kenya during the 2007-2010 and 2015-2016 cholera epidemics and two environmental isolates (from shallow well water and spring water isolates) isolated from Pokot and Kwale Counties, respectively, in 2010 were subjected to biotyping, serotyping, and antimicrobial susceptibility testing, including the detection of antibiotic resistance genes and mobile genetic elements. All V. cholerae isolates were identified as El Tor biotypes and susceptible to ceftriaxone, gentamicin, and ciprofloxacin. The majority of isolates were resistant to trimethoprim-sulfamethoxazole (94.6%), streptomycin (92.8%), and nalidixic acid (64.5%), while lower resistance was observed against ampicillin (3.6%), amoxicillin (4.2%), chloramphenicol (3.0%), and doxycycline (1.8%). Concurrently, the integrating conjugative (SXT) element was found in 95.5% of the V. cholerae isolates; conversely, class 1, 2, and 3 integrons were absent. Additionally, 64.5% of the isolates exhibited multidrug resistance patterns. Antibiotic-resistant gene clusters suggest that environmental bacteria may act as cassette reservoirs that favor resistant pathogens. On the other hand, the 2015-2016 epidemic strains were found susceptible to most antibiotics except nalidixic acid. This revealed the replacement of multidrug-resistant strains exhibiting new resistance phenotypes that emerged after Kenya's 2007-2010 epidemic. IMPORTANCE Kenya is a country where cholera is endemic; it has experienced three substantial epidemics over the past few decades, but there are limited data on the drug resistance patterns of V. cholerae at the national level. To the best of our knowledge, this is the first study to investigate the antimicrobial susceptibility profiles of V. cholerae O1 strains isolated from two consecutive epidemics and to examine their associated antimicrobial genetic determinants. Our study results revealed two distinct antibiotic resistance trends in two separate epidemics, particularly trends for multidrug-associated mobile genetic elements and chromosomal mutation-oriented resistant strains from the 2007-2010 epidemic. In contrast, only nalidixic acid-associated chromosomal mutated strains were isolated from the 2015-2016 epidemic. This study also found similar patterns of antibiotic resistance in environmental and clinical strains. Continuous monitoring is needed to control emerging multidrug-resistant isolates in the future.

Resistance of Vibrio cholera to antibiotics that inhibit cell wall synthesis: A systematic review and meta-analysis

Objective: Cholera is a challenging ancient disease caused by Vibrio cholera (V. cholera). Antibiotics that prevent cell wall synthesis are among the first known antibiotic groups. Due to its high consumption, V. cholera has developed resistance to the majority of antibiotics in this class. Resistance to recommended antibiotics for the treatment of V. cholera has also increased. In light of the decrease in consumption of certain antibiotics in this group that inhibit cell wall synthesis and the implementation of new antibiotics, it is necessary to determine the antibiotic resistance pattern of V. cholera and to employ the most effective treatment antibiotic. Method: An comprehensive systematic search for relevant articles was conducted in PubMed, Web of Science, Scopus, and EMBASE through October 2020. Stata version 17.1 utilized the Metaprop package to execute a Freeman-Tukey double arcsine transformation in order to estimate weighted pooled proportions. Results: A total of 131 articles were included in the meta-analysis. Ampicillin was the most investigated antibiotic. The prevalence of antibiotic resistance was in order aztreonam (0%), cefepime (0%), imipenem (0%), meropenem (3%), fosfomycin (4%), ceftazidime (5%), cephalothin (7%), augmentin (8%), cefalexin (8%), ceftriaxone (9%), cefuroxime (9%), cefotaxime (15%), cefixime (37%), amoxicillin (42%), penicillin (44%), ampicillin (48%), cefoxitin (50%), cefamandole (56%), polymyxin-B (77%), carbenicillin (95%) respectively. Discussion: Aztreonam, cefepime, and imipenem are the most efficient V. cholera cell wall synthesis inhibitors. There has been an increase in resistance to antibiotics such as cephalothin, ceftriaxone, amoxicillin, and meropenem. Over the years, resistance to penicillin, ceftazidime, and cefotaxime, has decreased.

Global status of antimicrobial resistance among environmental isolates of Vibrio cholerae O1/O139: a systematic review and meta-analysis

Background

Vibrio cholerae O1/O139 were the predominant circulating serogroups exhibiting multi-drug resistance (MDR) during the cholera outbreak which led to cholera treatment failures.

Objective

This meta-analysis aimed to evaluate the weighted pooled resistance (WPR) rates in V. cholerae O1/O139 isolates obtained from environmental samples.

Methods

We systematically searched the articles in PubMed, Scopus, and Embase (until January 2020). Subgroup analyses were then employed by publication year, geographic areas, and the quality of studies. Statistical analyses were conducted using STATA software (ver. 14.0).

Results

A total of 20 studies investigating 648 environmental V. cholerae O1/O139 isolates were analysed. The majority of the studies were originated from Asia (n = 9). In addition, a large number of studies (n = 15 i.e. 71.4%) included in the meta-analysis revealed the resistance to cotrimoxazole and ciprofloxacin. The WPR rates were as follows: cotrimoxazole 59%, erythromycin 28%, tetracycline 14%, doxycycline 5%, and ciprofloxacin 0%. There was increased resistance to nalidixic acid, cotrimoxazole, furazolidone, and tetracycline while a decreased resistance to amoxicillin, ciprofloxacin, erythromycin, chloramphenicol, ampicillin, streptomycin, and ceftriaxone was observed during the years 2000–2020. A significant decrease in the doxycycline and ciprofloxacin-resistance rates in V. cholerae O1/O139 isolates was reported over the years 2011–2020 which represents a decrease in 2001–2010 (p < 0.05).

Conclusions

Fluoroquinolones, gentamicin, ceftriaxone, doxycycline, kanamycin, and cefotaxime showed the highest effectiveness and the lowest resistance rate. However, the main interest is the rise of antimicrobial resistance in V. cholerae strains especially in low-income countries or endemic areas, and therefore, continuous surveillance, careful appropriate AST, and limitation on improper antibiotic usage are crucial.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13756-022-01100-3.

MLST/MVLST Analysis and Antibiotic Resistance of Vibrio cholerae in Shandong Province of China

Background:

Vibrio cholerae is an important bacterium causing profuse watery diarrhea. Cholera had swept the whole Shandong province from 1975 to 2013.

Methods:

From epidemiological data and pulsed-field gel electrophoresis data, we selected 86 V. cholerae isolates appearing in Shandong Province in China from 1975 to 2013 and characterized them by multilocus sequence typing (MLST)/multi-virulence locus sequence typing (MVLST), antibiogram and analysis of genes related to antibiotic resistance.

Results:

Combined MLST/MVLST data revealed 33 sequence types and a major group. Within the group, 3 subgroups (ST1, ST24 and ST29) were revealed, prevalent in the strains isolated during the 1980s, 1990s and 21st century, respectively. All the O1 isolates after 1990 were found to be El Tor variants harboring the classical ctxB gene. The tcpA gene of O139 strains had a mutation at amino acid position 62 (N→D). Antibiotic resistance of V. cholerae increased over time. Most El Tor variants between 1998 and 1999 were resistant to trimethoprim/sulfamethoxazole. The O139 strain, since its appearance in 1997, had significantly broader spectrum of antibiotic resistance than O1 variants. The presence of the SXT element corresponds to the trend of growing drug resistance.

Conclusion:

The analysis of genotypic polymorphism and enhanced resistance of V. cholerae indicated continuous variation and evolution of this pathogenic agent in Shandong Province.

Quantifying the dynamics of sub-daily to seasonal hydrological interactions of Ganges river with groundwater in a densely populated city: Implications to vulnerability of drinking water sources

Groundwater resources in South Asian cities are facing immense stress due to over-extraction leading to environmental, social and economic instabilities. The perennial mega rivers of Himalayas form the lifeline for South Asia, underpinning food and water security for a large population both directly and indirectly through exchange with groundwater systems. The present study delineates the spatio-temporal variation in patterns and processes of sub-hourly to annual-scale hydrological exchanges between the Ganges and its adjoining highly exploited aquifer in a urban-peri urban reach. Multivariate statistical analyses established river water-groundwater interaction in this region with ~40% loading of first principal component, i.e river water during monsoon on the shallow aquifer. The part of the aquifer detached from the main confined aquifer show an influence of precipitation (the second principal component) with loading of ~90%. Again the part of the aquifer suffering infiltration of local surface water bodies show effect of precipitation with a second principal loading of ~80%. Fourier transformation is used in the hydrograph to remove influence of heavy urbanization on the hydrographs. This study proves that the phenomenon of infiltrating river water during monsoon plays a primary role in controlling aquifer storage although contaminating the aquifer simultaneously. However, during pre and post-monsoon the flow path reversal helps in maintaining river baseflow. Cross-correlation between the river and piezometric series show increased delay of pressure head propagation of the infiltrating river waterfront, with increasing distance. These observations are also substantiated by stable isotope signatures. The present study provides an understanding of potential groundwater vulnerability resulting from waste water and irrigational contamination through river water intrusion which would eventually lead the government to implement proper water and environmental management policies towards availability of long-term sustainable water resources for the residents.

Exploring the allochthonous pollution influence on bacterial community and co-occurrence dynamics of River Ganga water through 16S rRNA-tagged amplicon metagenome

River Ganga is one of the largest and most sacred rivers of India. This river is largely affected by anthropogenic activities causing significant increase in water pollution. The impact of drains discharging polluted water on the bacterial community dynamics in the river remains unexplored. To elucidate this, the targeted 16S rRNA V3-V4 variable region amplicon sequencing and bioinformatic analysis were performed using water from upstream, drain, and downstream of river Ganga. Analysis revealed significant difference in relative abundances of bacterial communities. The increase in bacterial abundance and alpha diversity was detected in the downstream compared to the upstream. Environmental factors were found significantly different between upstream and downstream water. At the phyla level, highly abundant taxa such as Proteobacteria, Actinobacteria, Planctomycetes, Bacteroidetes, and Verrucomicrobia were observed. Bacterial genera like Prevotella, Bacteroides, Blautia, and Faecalibacterium (fecal indicator) had higher abundance in the downstream site. Network co-occurrence revealed that bacterial communities have a modular profile with reduced interaction in drain and downstream water. The network of co-occurring bacterial communities consists of 283 nodes with edge connectivity of 6900, 7074, and 5294 in upstream, drain, and downstream samples, respectively. Upstream communities exhibited the highest positive interaction followed by the drain and the downstream sites. Additionally, highly abundant pathogenic species such as Acinetobacter baumannii and Prevotella copri were also detected in all samples. This study suggests the drain to be allochthonous pollution vector that significantly contributes to bacterial community enrichment. From the results of this study, it is apparent that the lotic water may be used as the ecological reference to understand and monitor the variations in the bacterial communities and their co-occurrence dynamics in the fresh water ecosystems.

Assessment and Antibiotic Resistance Profiling in Vibrio Species Isolated from Wild Birds Captured in Danube Delta Biosphere Reserve, Romania

Antimicrobial and multidrug-resistant bacteria are a major problem worldwide and, consequently, the surveillance of antibiotic-resistant bacteria and assessment of the dissemination routes are essential. We hypothesized that migratory birds, coming from various environments, would carry more numerous Vibrio strains than sedentary species, with increased risk to be passed to their contacts or environment in habitats they transit or nest in. Similarly, we presumed that strains from migratory birds will show multidrug resistance. A total of 170 oral and rectal swabs were collected from wild birds captured in different locations of the Danube Delta (Malic, Sfantu-Gheorghe, Letea Forest) and processed using standardized selective media. V. cholerae strains were confirmed by serology and molecular methods and, subsequently, their susceptibility was evaluated. The prevalence of Vibrio species by host species, habitat type, and location was interpreted. The isolated Vibrio species were identified as Vibrio cholerae 14.33%, V. fluvialis 13.33%, V. alginolyticus 12%, V. mimicus 17.33%, V. vulnificus 10.88%, with V. parahaemolyticus and V. metschnikovii (16%) also being prevalent. Of the 76 Vibrio spp. isolates, 18.42% were resistant towards at least three antimicrobials, and 81.57% demonstrated a multidrug resistance phenotype, including mainly penicillins, aminoglycosides, and macrolides. The results of the present study indicate higher numbers of Vibrio strains in migratory (74.66%) than in sedentary birds (25.33%), confirming our hypothesis. Furthermore, the increased pathogenicity of Vibrio spp. strains, isolated from wild migratory and sedentary birds, was confirmed by their increased multiple antibiotic resistance (MAR) index (0.09–0.81).

River Ganges water as reservoir of microbes with antibiotic and metal ion resistance genes: High throughput metagenomic approach

The large scale usage of antibiotics and trace elements leads to their progressive release in the environment, and ultimately the spread of antibiotic resistance genes (ARGs) and metal ion resistance genes (MRGs) in bacteria. A high-throughput metagenomic sequencing of the microbial community in water and sediments in the river Ganges harboring resistance genes was performed. The results revealed that the river harbors a broad spectrum of resistance genes with high abundance in sediments. The highly dominant ARGs type was beta-lactam, multidrug/efflux and elfamycin. The ARGs such as (tuf, parY, ileS, mfd) were highly abundant in water and sediments. The MRGs subtype acn was the most abundant metal resistance gene in water and sediments. Majority of ARGs types showed significant (p ≤ 0.05) positive correlation with the MRGs types in the river environment suggesting their distribution and transfer to be possibly linked. Taxonomic classification revealed that Proteobacteria and Actinobacteria were the two most abundant phyla in water and sediments. Arcobacter, Terrimicrobium, Acidibacter and Pseudomonas were the most abundant genera. This study suggests that antibiotics and metals are the driving force for the emergence of resistance genes, and their subsequent propagation and accumulation in the environmental bacteria. The present metagenomic investigation highlights significance of such study, and attracts attention for the mitigation of pollutants associated with the propagation of ARGs and MRGs in the river environment.

Deep urban groundwater vulnerability in India revealed through the use of emerging organic contaminants and residence time tracers

Demand for groundwater in urban centres across Asia continues to rise with ever deeper wells being drilled to avoid shallow contamination. The vulnerability of deep alluvial aquifers to contaminant migration is assessed in the ancient city of Varanasi, India, using a novel combination of emerging organic contaminants (EOCs) and groundwater residence time tracers (CFC and SF₆). Both shallow and intermediate depth private sources (<100 m) and deep (>100 m) municipal groundwater supplies were found to be contaminated with a range of EOCs including pharmaceuticals (e.g. sulfamethoxazole, 77% detection frequency, range <0.0001-0.034 μg L^-1), perfluoroalkyl substances (e.g. PFOS, range <0.0001-0.033 μg L^-1) as well as a number of pesticides (e.g. phenoxyacetic acid, range <0.02-0.21 μg L^-1). The profile of EOCs found in groundwater mirror those found in surface waters, albeit at lower concentrations, and reflect common waste water sources with attenuation in the subsurface. Mean groundwater residence times were found to be comparable between some deep groundwater and shallow groundwater sources with residence times ranging from >70 to 30 years. Local variations in aquifer geology influence the extent of modern recharge at depth. Both tracers provide compelling evidence of significant inputs of younger groundwater to depth >100 m within the aquifer system.

Antibiotic Susceptibility of Non-Cholera Vibrios Isolated from Farmed and Wild Marine Fish (Argyrosomus japonicus), Implications for Public Health

This study aimed to evaluate the antibiogram and antibiotic resistance genes (ARGs) of Vibrio isolates recovered from a marine fish (Argyrosomus japonicus) and water samples from two commercial dusky kob aquaculture farms and the Kariega estuary, South Africa, and to evaluate these findings for their public health implications. A total of 277 molecularly confirmed Vibrio isolates consisting of 126 Vibrio fluvialis, 45 Vibrio vulnificus, 30 Vibrio Parahaemolyticus, and 76 vibrios belonging to species of the genus other than Vibrio cholerae were subjected to susceptibility testing to 15 antibiotics by the disc diffusion method. Multiple antibiotic resistance index (MARI) was used to determine the antibiotic resistance-associated health risk, while polymerase chain reaction was used to evaluate the presence of 14 ARGs for nonsusceptible strains. Highest resistances were recorded to amoxicillin (76.2%), ampicillin (67.5%), erythromycin (38.3%), and doxycycline (35.0%), while susceptibilities were highest to gentamicin (100%), followed by norfloxacin (97.8%), florfenicol (90.3%), tetracycline (87.7%), and chloramphenicol (87.4%). We recorded a 58.5% multidrug resistance (resistance to ≥2 antimicrobial classes). MARI did not vary significantly between sites (p > 0.05); however, values of >0.2 were recorded in 40% (108/277) of all strains tested. ARG markers, ampC, blaOXA, tetA, tetM, dfr1, sul1, sul2, ermB, nptII, strA, and SXT integrase, were detected in one or more strains with ermB (82.5%), sul2 (53.8%), strA (44%), dfr1 (42.3%), and tetM (38.3%) being the most abundant. Healthy marine finfish (dusky kob) and their environment can serve as reservoirs for antibiotic resistant vibrios and ARGs, which could be disseminated to humans and other susceptible bacteria and this therefore becomes a public health concern.

Antimicrobial resistance and genetic diversity of the SXT element in Vibrio cholerae from clinical and environmental water samples in northeastern Thailand

Multidrug resistance in V. cholerae has been increasing around the world including northeastern Thailand. The aquatic environment is a reservoir of V. cholerae and might be an important source of resistant strains. The aims of this study were to investigate the phylogenetic relationships of int_SXT gene sequences from 31 clinical and 14 environmental V. cholerae O1 and non-O1/non-O139 isolates and 11 sequences amplified directly from environmental water samples. We also amplified class 1 integrons, the SXT elements (targeting the int_SXT gene) and antimicrobial resistance genes directly from water samples. Phylogenetic analysis displayed two major distinct clusters (clusters 1 and 2). Most V. cholerae O1 (19/20, 95%) and non-O1/non-O139 isolates (8/11, 72.7%) from clinical sources, and all sequences obtained directly from water samples, belonged to cluster 1. Cluster 2 mostly comprised environmental non-O1/non-O139 isolates (10/12, 83.3%). We successfully amplified the SXT elements directly from17.5% of water samples. Associated resistance genes were also amplified as follows: sul2 (41.3% of water samples), dfrA1 (60%), dfr18 (33.8%), strB (70%) and tetA (2.5%). Class 1 integrons were not found in water samples, indicating that the SXT element was the major contributor of multidrug resistance determinants in this region. The SXT element and antimicrobial resistance genes could be transferred from clinical V. cholerae O1 to environmental V. cholerae non-O1/non-O139 was demonstrated by conjugation experiment. These findings indicate that there may have been cross dissemination and horizontal gene transfer (HGT) of the SXT element harbored by V. cholerae O1 and non-O1/non-O139 strains isolated from clinical and environmental water sources. Environmental water might be an important source of antimicrobial resistance genes in V. cholerae in this region. Direct detection of antimicrobial resistance genes in water samples can be used for monitoring the spread of such genes in the ecosystem.

Sequences of a co-existing SXT element, a chromosomal integron (CI) and an IncA/C plasmid and their roles in multidrug resistance in a Vibrio cholerae O1 El Tor strain

The ongoing seventh cholera pandemic is attributed to Vibrio cholerae O1 El Tor biotype strains. Although antibiotic therapy ameliorates symptoms in patients and reduces pathogen transfer to the environment, multidrug resistance remains a major clinical threat. An O1 El Tor strain isolated from a patient in 1998 was intermediate or resistant to 13 antibiotics and could potentially produce extended-spectrum β-lactamase (ESBL), which is very rare in O1 strains. Using genome sequencing, three relevant genetic elements were identified in this strain: a hybrid SXT element (ICEVchCHN1307); a new IncA/C plasmid (pVC1307); and a chromosomal integron. Twenty antibiotic resistance genes were located on them, including blaTEM-1, blaCTX-M-14 and phenotypically silenced tetRA genes. These data elucidate the role of individual genetic components in antibiotic resistance and the accumulation of drug resistance genes in V. cholerae.

Virulence factors in environmental and clinical Vibrio cholerae from endemic areas in Kenya

BACKGROUND

Since 1971, Kenya has had repeated cholera outbreaks. However, the cause of seasonal epidemics of cholera is not fully understood and neither are the factors that drive epidemics, both in Kenya and globally.

OBJECTIVES

The objectives of the study were to determine the environmental reservoirs of V. cholerae during an interepidemic period in Kenya and to characterise their virulence factors.

METHODS

One hundred (50 clinical, 50 environmental) samples were tested for V. cholerae isolates using both simplex and multiplex polymerase chain reaction.

RESULTS

Both sediments and algae from fishing and landing bays yielded isolates of V. cholerae. Clinical strains were characterised along with the environmental strains for comparison. All clinical strains harboured ctxA, tcpA (El Tor), ompU, zot, ace, toxR, hylA (El Tor) and tcpI genes. Prevalence for virulence genes in environmental strains was hylA (El Tor) (10%), toxR (24%), zot (22%), ctxA (12%), tcpI (8%), hylA (26%) and tcpA (12%).

CONCLUSION

The study sites, including landing bays and beaches, contained environmental V. cholerae, suggesting that these may be reservoirs for frequent epidemics. Improved hygiene and fish-handling techniques will be important in reducing the persistence of reservoirs.

Cholera outbreaks in India

Cholera is a global health problem as several thousands of cases and deaths occur each year. The unique epidemiologic attribute of the disease is its propensity to occur as outbreaks that may flare-up into epidemics, if not controlled. The causative bacterial pathogen Vibrio cholerae prevails in the environment and infects humans whenever there is a breakdown in the public health component. The Indian subcontinent is vulnerable to this disease due its vast coastlines with areas of poor sanitation, unsafe drinking water, and overcrowding. Recently, it was shown that climatic conditions also play a major role in the persistence and spread of cholera. Constant change in the biotypes and serotypes of V. cholerae are also important aspects that changes virulence and survival of the pathogen. Such continuous changes increase the infection ability of the pathogen affecting the susceptible population including the children. The short-term carrier status of V. cholerae has been studied well at community level and this facet significantly contributes to the recurrence of cholera. Several molecular tools recognized altering clonality of V. cholerae in relation with the advent of a serogroup or serotype. Rapid identification systems were formulated for the timely detection of the pathogen so as to identify and control the outbreak and institute proper treatment of the patients. The antimicrobials used in the past are no longer useful in the treatment of cholera as V. cholerae has acquired several mechanisms for multiple antimicrobial resistance. This upsurge in antimicrobial resistance directly influences the management of the disease. This chapter provides an overview of cholera prevalence in India, possible sources of infection, and molecular epidemiology along with antimicrobial resistance of V. cholerae.

Cholera outbreaks in Nigeria are associated with multidrug resistant atypical El Tor and non-O1/non-O139 Vibrio cholerae

Background

The current millennium has seen a steep rise in the number, size and case-fatalities of cholera outbreaks in many African countries. Over 40,000 cases of cholera were reported from Nigeria in 2010. Variants of Vibrio cholerae O1 El Tor biotype have emerged but very little is known about strains causing cholera outbreaks in West Africa, which is crucial for the implementation of interventions to control epidemic cholera.

Methodology/Principal Findings

V. cholerae isolates from outbreaks of acute watery diarrhea in Nigeria from December, 2009 to October, 2010 were identified by standard culture methods. Fifteen O1 and five non-O1/non-O139 strains were analyzed; PCR and sequencing targeted regions associated with virulence, resistance and biotype were performed. We also studied genetic interrelatedness among the strains by multilocus sequence analysis and pulsed-field gel electrophoresis. The antibiotic susceptibility was tested by the disk diffusion method and E-test. We found that multidrug resistant atypical El Tor strains, with reduced susceptibility to ciprofloxacin and chloramphenicol, characterized by the presence of the SXT element, and gyrA^Ser83Ile/parC^Ser85Leu alleles as well CTX phage and TCP cluster characterized by rstR^ElTor, ctxB-7 and tcpA^CIRS alleles, respectively, were largely responsible for cholera outbreaks in 2009 and 2010. We also identified and characterized a V. cholerae non-O1/non-O139 lineage from cholera-like diarrhea cases in Nigeria.

Conclusions/Significance

The recent Nigeria outbreaks have been determined by multidrug resistant atypical El Tor and non-O1/non-O139 V. cholerae strains, and it seems that the typical El Tor, from the beginning of seventh cholera pandemic, is no longer epidemic/endemic in this country. This scenario is similar to the East Africa, Asia and Caribbean countries. The detection of a highly virulent, antimicrobial resistant lineage in Nigeria is worrisome and points to a need for vaccine-based control of the disease. This study has also revealed the putative importance of non-O1/non-O139 V. cholerae in diarrheal disease in Nigeria.

Cholera is acute watery diarrhoea, severely dehydrating, caused by Vibrio cholerae, a bacterium ubiquitous in aquatic environments. Cholera is a global threat, particularly, in areas where sanitary conditions, such as drinking water and sewage, are not available. Seven cholera pandemics, all originating in Asia, occurred. The ongoing pandemic, the 7th, has been caused by V. cholerae El Tor biotype. Recently, El Tor has undergone genetic changes and the strains being referred to as “atypical” El Tor are rapidly replacing the original El Tor in many areas. The atypical El Tor is characterized by multi-antibiotic resistance and changes in the major virulence determinants. Cholera caused by atypical strains may be more clinically severe. In Africa, cholera outbreaks are occurring with increasing frequency and severity, as demonstrated by the recent major outbreaks in Nigeria, Angola, Mozambique and Zimbabwe. Here, we performed a comprehensive characterization of V. cholerae isolated from different recent outbreaks in Nigeria. Our results show that cholera outbreaks in Nigeria are driven by atypical El Tor strains, as worldwide.

Antibiotic resistance of Vibrio cholerae O1 El Tor strains from the seventh pandemic in China, 1961-2010

Antibiotic resistance is observed with increasing frequency among epidemic Vibrio cholerae strains in some countries. In this study, the antibiotic resistance profiles of V. cholerae O1 El Tor strains isolated in China from 1961 to 2010 were analysed. The frequency of antibiotic resistance among the seventh pandemic El Tor isolates from China remained low, except for resistance to nalidixic acid (45.9%), tetracycline (11%) and trimethoprim/sulfamethoxazole (38.5%). All test strains in the first multiyear epidemic in the 1960s were sensitive to all test antibiotics, whereas strains from the 1990s and later showed a rapid increase in the prevalence of resistance. The class I integron was present primarily among strains isolated between 1993 and 1998, and the prevalence of the SXT element was much greater among strains isolated after 1993. This study determined the regional resistance characteristics of epidemic clones in China and serves as a warning of the rapid dissemination of resistance in the past 20 years.

Drug resistance in Vibrio cholerae strains isolated from clinical specimens

Cholera is a serious epidemic and endemic disease caused by the Gram-negative bacterium Vibrio cholerae. SXT is an integrative conjugation element (ICE) that was isolated from a V. cholerae; it encodes resistance to the antibiotics chloramphenicol, streptomycin and sulfamethoxazole/trimethoprim. One hundred seven V. cholerae O1 strains were collected from cholera patients in Iran from 2005 to 2007 in order to study the presence of SXT constin and antibiotic resistance.The study examined 107 Vibrio cholerae strains isolated from cholera prevalent in some Iranian provinces. Bacterial isolation and identification were carried out according to standard bacteriological methods. Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) to four antibiotics (chloramphenicol, streptomycin, sulfamethoxazole, and trimethoprim) were determined by broth microdilution method. PCR was employed to evaluate the presence of established antibiotic resistance genes and SXT constin using specific primer sets.The resistance of the clinical isolates to sulfamethoxazole, trimethoprime, chloramphenicol, and streptomycin was 97%, 99%, 99%, and 90%, respectively. The data obtained by PCR assay showed that the genes sulII, dfrA1, floR, strB, and sxt element were present in 95.3%, 95.3%, 81.3%, 95.3%, and 95.3% of the V. cholerae isolates.The Vibrio strains showed the typical multidrug-resistance phenotype of an SXT constin. They were resistant to sulfamethoxazole, trimethoprime, chloramphenicol, and streptomycin. The detected antibiotic resistance genes included dfrA for trimethoprim and floR, strB, sulII and int, respectively, for chloramphenicol, streptomycin, sulfamethoxazole, as well as the SXT element.

SXT constin among Vibrio cholerae isolates from a tertiary care hospital

BACKGROUND & OBJECTIVES

The SXT element, also known as 'constin' (conjugable, self transmissible, integrating element) is an integrating conjugative element (ICE) in Vibrio cholerae discovered in the chromosome of epidemic V. cholerae O139 strain MO10 (SXT MO10 ) which arose in late 1992 in Chennai, India. SXT related ICEs have become widespread and currently, most if not all Asian V. cholerae clinical isolates contain SXT related ICEs. The present study attempts to determine the presence of SXT Int gene in V. cholerae recovered between 2005 to 2007 in a tertiary care hospital, demonstrate its conjugal nature and also detect co-presence and co-transfer of plasmids in representative isolates.

METHODS

This prospective study was done on 116 V. cholerae isolates [114- O1 (107 ogawa and 7 inaba) and 2 - Non O1 Non O139 V. cholerae] from watery stools between 2005 to 2007 recovered from equal number of patients. PCR was carried out using SXT Int specific primers that produced a 592 bp internal fragment of SXT element, and rifampicin resistant strain of E.coli K-12 was used as recipient in conjugation experiments to study transfer of SXT, as also co-transfer of resistance to tetracycline, erythromycin, and nalidixic acid. Antibiotic susceptibility was performed against various antibiotics.

RESULTS

Of the 116 isolates, 110 (94.8%) were positive for SXT element by PCR. It was demonstrated in 94.7 per cent of the O1, and 100 per cent of non O1 non O139 V. cholerae. All 2005 isolates, 25 per cent of 2006 isolates and 96.6 per cent of 2007 isolates were positive for SXT. Thirty two drug resistance patterns were observed and the 2007 isolates showed resistance to as many as eight antibiotics. The resistance of SXT positive isolates was higher than those of SXT negative and the typical drug resistance pattern corresponding to SXT ET and SXT MO10 was shown by only one V. cholerae O1 isolate. Successful conjugal transfer of SXT was seen in 31 (88.6%) of the 35 isolates studied without any co-transfer while, presence of plasmids was observed in two of the 31 donor V. cholerae studied.

INTERPRETATION & CONCLUSIONS

The demonstration of SXT element and its successful horizontal transfer in V. cholerae isolates studied emphasizes the need for its detection to monitor antibiotic resistance and dissemination in V. cholerae.

Detection of potential risk of wastewater effluents for transmission of antibiotic resistance from Vibrio species as a reservoir in a peri-urban community in South Africa

We assessed the antibiogram characteristics of some Vibrio species isolated from wastewater final effluents in a typical peri-urban community of South Africa. Marked resistances were noted against erythromycin (100%), chloramphenicol (100%), nitrofurantoin, cefuroxime and cephalothin (90-95%) in V. parahaemolyticus, V. fluvialis and V. vulnificus, respectively. Fourteen antibiotypes were identified, with multiresistance to 8-10 antibiotics being common. The antibiotypes AMP, PEN, STR, SUL, TMP, COT, CHL, ERY, CIP and PB demonstrated by V. fluvialis were the most prevalent (17.24%). Eight putative antibiotic resistance genes were identified with floR being the mostly (100%) detected in all the three species while tet(A) was the least with 65% prevalence in V. vulnificus, 7.14% in V. parahaemolyticus and none in V. fluvialis. These results demonstrate that the treated effluent system are reservoirs for various antibiotic resistance genes which could be disseminated to inhabitants downstream the plant and pose health risk to the communities who are dependent upon the watershed for domestic and recreational purposes.

Water microbiology. Bacterial pathogens and water

Water is essential to life, but many people do not have access to clean and safe drinking water and many die of waterborne bacterial infections. In this review a general characterization of the most important bacterial diseases transmitted through water—cholera, typhoid fever and bacillary dysentery—is presented, focusing on the biology and ecology of the causal agents and on the diseases’ characteristics and their life cycles in the environment. The importance of pathogenic Escherichia coli strains and emerging pathogens in drinking water-transmitted diseases is also briefly discussed. Microbiological water analysis is mainly based on the concept of fecal indicator bacteria. The main bacteria present in human and animal feces (focusing on their behavior in their hosts and in the environment) and the most important fecal indicator bacteria are presented and discussed (focusing on the advantages and limitations of their use as markers). Important sources of bacterial fecal pollution of environmental waters are also briefly indicated. In the last topic it is discussed which indicators of fecal pollution should be used in current drinking water microbiological analysis. It was concluded that safe drinking water for all is one of the major challenges of the 21st century and that microbiological control of drinking water should be the norm everywhere. Routine basic microbiological analysis of drinking water should be carried out by assaying the presence of Escherichia coli by culture methods. Whenever financial resources are available, fecal coliform determinations should be complemented with the quantification of enterococci. More studies are needed in order to check if ammonia is reliable for a preliminary screening for emergency fecal pollution outbreaks. Financial resources should be devoted to a better understanding of the ecology and behavior of human and animal fecal bacteria in environmental waters.

Does water hyacinth on East African lakes promote cholera outbreaks?

Cholera outbreaks continue to occur regularly in Africa. Cholera has been associated with proximity to lakes in East Africa, and Vibrio cholerae has been found experimentally to concentrate on the floating aquatic plant, water hyacinth, which is periodically widespread in East African lakes since the late 1980s. From 1994 to 2008, Nyanza Province, which is the Kenyan province bordering Lake Victoria, accounted for a larger proportion of cholera cases than expected by its population size (38.7% of cholera cases versus 15.3% of national population). Yearly water-hyacinth coverage on the Kenyan section of Lake Victoria was positively associated with the number of cholera cases reported in Nyanza Province (r = 0.83; P = 0.0010). Water hyacinth on freshwater lakes might play a role in initiating cholera outbreaks and causing sporadic disease in East Africa.

Environmental reservoirs for enterotoxigenic Escherichia coli in south Asian Gangetic riverine system

Forecasting diarrheagenic E. coli contamination of aquatic resources to prevent outbreaks largely depends on rapid and accurate diagnostic testing in a few hours. Real-time PCR is widely used for quick culture-free quantitative enumeration of pathogenic bacteria in environmental samples. In this study, real-time PCR in molecular beacon format was used for detection and culture-free quantitative enumeration of enterotoxigenic Escherichia coli (ETEC) harboring LT1 gene in a sewage-impacted south Asian Gangetic riverine system. The quantitative budget for ETEC in surface water was observed to vary significantly (DMRT, p < 0.05) among the sites. Aquatic flora (Eichhornia crassipes, Potamogeton crispus, Potamogeton pectinatus, Ranunculus sceleratus, Polygonum glabrum, Pontederia cordata, Najas indica and strands of Spirogyra spp.) collected between sites 1 and 9 exhibited significant high levels of ETEC in comparison to their representatives collected from pristine area. The level of ETEC harboring LT1 gene observed in leafy vegetables cultivated along the banks was in the following order: mint leaves > coriander > spinach > methi leaves. The study suggests that the aquatic flora and cultivated leafy vegetables in the south Asian Gangetic riverine system are environmental reservoirs for enterotoxigenic Escherichia coli.

Antibiotic susceptibility profiles of some Vibrio strains isolated from wastewater final effluents in a rural community of the Eastern Cape Province of South Africa

BACKGROUND

To evaluate the antibiogram and antibiotic resistance genes of some Vibrio strains isolated from wastewater final effluents in a rural community of South Africa. V. vulnificus (18), V. metschnikovii (3), V. fluvialis (19) and V. parahaemolyticus (12) strains were isolated from final effluents of a wastewater treatment plant (WWTP) located in a rural community of South Africa. The disk diffusion method was used for the characterization of the antibiogram of the isolates. Polymerase chain reaction (PCR) was employed to evaluate the presence of established antibiotic resistance genes using specific primer sets.

RESULTS

The Vibrio strains showed the typical multidrug-resistance phenotype of an SXT element. They were resistant to sulfamethoxazole (Sul), trimethoprim (Tmp), cotrimoxazole (Cot), chloramphenicol (Chl), streptomycin (Str), ampicillin (Amp), tetracycline (Tet) nalidixic acid (Nal), and gentamicin (Gen). The antibiotic resistance genes detected includes dfr18 and dfrA1 for trimethoprim; floR, tetA, strB, sul2 for chloramphenicol, tetracycline, streptomycin and sulfamethoxazole respectively. Some of these genes were only recently described from clinical isolates, demonstrating genetic exchange between clinical and environmental Vibrio species.

CONCLUSIONS

These results demonstrate that final effluents from wastewater treatment plants are potential reservoirs of various antibiotics resistance genes. Moreover, detection of resistance genes in Vibrio strains obtained from the wastewater final effluents suggests that these resistance determinants might be further disseminated in habitats downstream of the sewage plant, thus constituting a serious health risk to the communities reliant on the receiving waterbodies.

Molecular characterisation of Vibrio cholerae O1 strains carrying an SXT/R391-like element from cholera outbreaks in Kenya: 1994-2007

BACKGROUND

Over the last decade, cholera outbreaks in parts of Kenya have become common. Although a number of recent studies describe the epidemiology of cholera in Kenya, there is paucity of information concerning the diversity and occurrence of mobile genetic elements in Vibrio cholerae strains implicated in these outbreaks. A total of 65 Vibrio cholerae O1 El Tor serotype Inaba isolated between 1994 and 2007 from various outbreaks in Kenya were investigated for mobile genetic elements including integrons, transposons, the integrating conjugative elements (ICEs), conjugative plasmids and for their genotypic relatedness.

RESULTS

All the strains were haemolytic on 5% sheep blood and positive for the Vibrio cholerae El Tor-specific haemolysin toxin gene (hylA) by PCR. They all contained strB, sulII, floR and the dfrA1 genes encoding resistance to streptomycin, sulfamethoxazole, chloramphenicol and trimethoprim respectively. These genes, together with an ICE belonging to the SXT/R391 family were transferable to the rifampicin-resistant E. coli C600 en bloc. All the strains were negative for integron class 1, 2 and 3 and for transposase gene of transposon Tn7 but were positive for integron class 4 and the trpM gene of transposon Tn21. No plasmids were isolated from any of the 65 strains. All the strains were also positive for all V. cholera El Tor pathogenic genes except the NAG- specific heat-stable toxin (st) gene. None of the strains were positive for virulence genes associated with the V. cholerae classical biotype. All the strains were positive for El Tor-specific CTXphi bacteriophage rstrR repressor gene (CTXETPhi) but negative for the Classical, Calcutta, and the Environmental repressor types. Pulse Field Gel Electrophoresis (PFGE) showed that regardless of the year of isolation, all the strains bearing the SXT element were clonally related.

CONCLUSIONS

This study demonstrates that the V. cholerae O1 strains carrying an SXT/R391-like element implicated in recent cholera outbreaks in Kenya has not changed significantly between 1994 and 2007 and are clonally related.

Enterotoxigenic Escherichia coli in sewage-impacted waters and aquatic weeds: quantitative PCR for culture-independent enumeration

AIM

To develop quantitative PCR for culture-independent enumeration of enterotoxigenic Escherichia coli (ETEC) in sewage-impacted waters and aquatic weeds.

METHODS AND RESULTS

Two fluorescent probes (TaqMan and FRET) based on two different real-time PCR chemistries were designed in highly conserved region of LT1 gene encoding heat labile enterotoxin. Both the assays could detect 2 CFU ml(-1) from serially diluted (two-fold and ten-fold) culture of reference strain (E. coli MTCC 723). FRET performed better in terms of CT value and PCR efficiency than TaqMan. The presence of 10(6) CFU ml(-1) of nonpathogenic E. coli reduced the detection limit two-fold with both the probes. However, the performance for two chemistries in various environmental samples was significantly (student's t-test, P<0.05) different.

CONCLUSION

It could be inferred from this study that real-time PCR chemistries (TaqMan and FRET) could detect very few copies of target DNA in pure cultures, but may give varied response in the presence of nonspecific DNA and natural inhibitors present in environmental sample matrices.

SIGNIFICANCE AND IMPACT OF THE STUDY

The assays can be used for pre-emptive monitoring of aquatic weeds (a potential nonpoint source), surface and potable waters to prevent waterborne outbreaks caused by ETEC.

Detection of virulence-associated and regulatory protein genes in association with phage typing of human Vibrio cholerae from several geographical regions of the world

Vibrio cholerae O1, O139 and occasionally non-O1/non-O139 serogroups are most often responsible for epidemic and pandemic cholera. This study used genotypic patterns of PCR-based detection of virulence-associated and regulatory protein genes, along with phage typing, to characterize 86 V. cholerae strains. Thirty-eight of 53 O1 biotype El Tor strains harboured both tcpA classical and tcpA El Tor genes, and three El Tor strains lacked the V. cholerae O1-specific gene (Vc-O1); three O139 strains contained both Vc-O1 and Vc-O139 genes and seven out of ten non-O1/non-O139 strains possessed the Vc-O1 gene. The latter strains all harboured the virulence-associated genes ctxA, zot, ace, RS1, hlyA, ompU, rtxA and sxt. Two phage types, T27 and T25, were predominant in strains from different geographical regions of India, whereas more variation in phage susceptibility was observed for tetracycline-resistant strains from Kolkata. These results suggest that the pattern and distribution of virulence genes and phage types of V. cholerae are equally useful and discriminatory in tracing the origin of newly emerging strains.

Real time PCR for the rapid detection of vanA gene in surface waters and aquatic macrophyte by molecular beacon probe

Enterococci serve as an "indicator" of fecal contamination for recreational water quality. The vancomycin-resistant-enterococci (VRE) are emerging environmental contaminants in the surface waters. The aim ofthis study wasto develop a rapid and specific molecular beacon probe (MBP)-based real-time PCR assay for detection of vanA gene in surface waters and aquatic macrophyte. The limit of detection (LOD) of the MBP assay was 1 CFU/mL of VRE [r = 0.943; PCR efficiency = 99.7%] in 2-fold dilution format within 2.5 h and demonstrated high specificityfor environmental enterococci isolates exhibiting VanA phenotype (n=25). VRE were detected from downstream surface waters of the rivers impacted by point sources of pollution and recreational activities.The probe detected vanA gene in rootmat associated microbiota of E. crassipes (Mart) Solms. an aquatic nuisance weed, at eutrophic sites of the surface waters (ANOVA p < 0.001). In addition, the assay enabled detection of otherwise nondetectable vanA gene concentration in the upstream sites of two Indian rivers (Student's ttest p < 0.001). The MBP assay developed can be used for sensitive and rapid detection of VRE in surface waters and identification of nonpoint sources of pollution for implementation of preventive measures to protect human health.

Biogeographic patterns in genomic diversity among a large collection of Vibrio cholerae isolates

Vibrio cholerae strains are capable of inhabiting multiple niches in the aquatic environment and in some cases cause disease in humans. However, the ecology and biodiversity of these bacteria in environmental settings remains poorly understood. We used the genomic fingerprinting technique enterobacterial repetitive intergenic consensus sequence PCR (ERIC-PCR) to profile 835 environmental isolates from waters and sediments obtained at nine sites along the central California coast. We identified 115 ERIC-PCR genotypes from 998 fingerprints, with a reproducibility of 98.5% and a discriminatory power of 0.971. When the temporal dynamics at a subset of sampling sites were explored, several genotypes provided evidence for cosmopolitan or geographically restricted distributions, and other genotypes displayed nonrandom patterns of cooccurrence. Partial Mantel tests confirmed that genotypic similarity of isolates across all sampling events was correlated with environmental similarity (0.04 < or = r < or = 0.05), temporal proximity (r = 0.09), and geographic distance (r = 0.09). A neutral community model for all sampling events explained 61% of the variation in genotype abundance. Cooccurrence indices (C-score, C-board, and Combo) were significantly different than expected by chance, suggesting that the V. cholerae population may have a competitive structure, especially at the regional scale. Even though stochastic processes are undoubtedly important in generating biogeographic patterns in diversity, deterministic factors appear to play a significant, albeit small, role in shaping the V. cholerae population structure in this system.

Application of duplex-PCR in rapid and reliable detection of toxigenic Vibrio cholerae in water samples in Thailand

Toxigenic Vibrio cholerae, the cause of cholera, is a native flora of the aquatic environment which is transmitted through drinking water and still remains the leading cause of morbidity and mortality in many developing countries including Thailand. The culture method (CM), which is routinely used for assessing water quality, has not proven as efficient as molecular methods because the notorious pathogen survives in water mostly in a non-culturable state. We employed duplex-polymerase chain reaction (duplex-PCR) for detection of tcpA and ctxA genes in toxigenic V. cholerae, and compared PCR detection with CM in various waters of Khon Kaen Municipality, Thailand. We also evaluated the effect of different pre-PCR conditions on the results of ctxA and tcpA detection including: 1) water filtered and enriched in alkaline peptone water (APW) for 3 h before PCR, 2) water filtered without enrichment before PCR, and 3) use of only enrichment in APW for 6 h before PCR. Of the 96 water samples (taken from waste-water, potable and waste-water from patients' houses, and from rivers) tested, 48 (50%) were positive for ctxA and tcpA by duplex-PCR, whereas only 29 (30%) were positive for V. cholerae by CM. Of the 29 V. cholerae isolated by CM, 2 (7%) were toxigenic V. cholerae belonging to serovar O1, while the rests were non-O1/ non-O139. Results revealed, therefore, that ctxA and tcpA-targeted duplex PCR is more sensitive than CM for detection of toxigenic V. cholerae from water samples because CM detected much less toxigenic V. cholerae than the non-toxigenic V. cholerae. Template DNA as low as 100 fg or 23 cells of V. cholerae in the water sample was detected in duplex PCR. Pre-PCR filtration followed by enrichment for 3 h significantly increase in the efficiency of duplex-PCR detection of toxigenic V. cholerae.

Bibliography of environmental studies in natural characteristics and anthropogenic influences on the Ganga River

During the second half of the 20th century, the Ganga River ecosystem has been continuously altered by several ongoing anthropogenic processes, accommodating multi-dimensional pressure due to increase of nearly four-fold human population. For solution of any environmental issues of the river, the Earth System Science approach is required to have maximum socio-economic benefits to millions of people living in Indian and Bangladesh. A bibliography containing more than 250 references on environmental studies of the Ganga River was prepared to preserve its ecosystem by providing the baseline support in this regard.

Multiplex PCR for detection of antibiotic resistance genes and the SXT element: application in the characterization of Vibrio cholerae

This study describes a multiplex PCR assay for the detection of antibiotic resistance genes and the SXT element in Vibrio cholerae. Conditions were optimized to amplify fragments of sulII (encoding sulfamethoxazole resistance), dfrA1 (O1-specific trimethoprim resistance), dfr18 (O139-specific trimethoprim resistance), strB (streptomycin B resistance) and the SXT element simultaneously in one PCR. This multiplex PCR was evaluated on 142 V. cholerae isolates and the results correlated with the phenotypic antibiotic data obtained using a disc diffusion assay and a colony blot assay. Thus this one-step PCR can be used as a simple, rapid and accurate method for identification of antibiotic resistance profiles and could be used for the surveillance of the spread of antibiotic resistance determinants in epidemiological and environmental studies.

Characterization of the genetic background of Vibrio cholerae O1 biotype El Tor serotype Inaba strains isolated in Trivandrum, southern India

Isolates of Vibrio cholerae O1 biotype El Tor serotype Inaba associated with an outbreak of cholera in Trivandrum, southern India, were characterized. PCR testing revealed that all five isolates examined carried the TCP pathogenicity island, the CTX genetic element and the RTX toxin, and produced cholera toxin (CT). RFLP analysis revealed that these Inaba isolates possessed a single copy of the CTX element flanked by two tandemly arranged copies of the RS element upstream of the core region. The isolates were resistant to ampicillin, nalidixic acid, trimethoprim, sulfamethoxazole, streptomycin and the vibriostatic agent 2,4-diamino-6,7-diisopropylpteridine (O/129). Ribotyping of these Inaba isolates revealed a hybridization profile similar to a strain of serotype Ogawa prevalent in southern India.

Septaplex PCR assay for rapid identification ofVibrio choleraeincluding detection of virulence andintSXT genes

In this study, we describe a septaplex PCR assay for rapid identification of Vibrio cholerae including detection of the virulence and intsxt genes. Conditions were optimized to amplify fragments of ISRrRNA (encoding for 16S-23S rRNA gene, Intergenic spacer regions), O1rfb (O1 serogroup specific rfb), O139rfb (O139 serogroup specific rfb), ctxA (cholera toxin subunit A), tcpA (toxin coregulated pilus), and intsxt (sxt integron) simultaneously in a single PCR. The septaplex PCR was evaluated using 211 strains of V. cholerae and six water samples for in situ testing. PCR results were correlated with genotype data obtained by individual PCR and slot-blot assays. The one-step PCR described here can be used to identify V. cholerae accurately and rapidly. Also, the virulence and intsxt genes can be simultaneously detected, providing a useful method for monitoring pathogenic, intsxt-positive and nonpathogenic, intsxt-negative V. cholerae serogroups both in the environment and clinical settings.

Adhesion of Vibrio cholerae to granular starches

Cholera is a severe diarrheal disease caused by specific serogroups of Vibrio cholerae that are pathogenic to humans. Cholera can become epidemic and deadly without adequate medical care. Appropriate rehydration therapy can reduce the mortality rate from as much as 50% of the affected individuals to <1%. Thus, oral rehydration therapy (ORT) is an important measure in the treatment of this disease. To further reduce the symptoms associated with cholera, improvements in oral rehydration solution (ORS) by starch incorporation were suggested. Here, we report that V. cholerae adheres to starch granules incorporated in ORS. Adhesion of 98% of the cells was observed within 2 min when cornstarch granules were used. Other starches showed varied adhesion rates, indicating that starch source and composition play an important role in the interaction of V. cholerae and starch granules. Sugars metabolized by V. cholerae showed a repressive effect on the adhesion process. The possible mechanisms involved are discussed. Comparing V. cholerae adhesion with the adhesion of other pathogens suggests the involvement of starch degradation capabilities. This adhesion to granular starch can be used to improve ORT.