Isolation of Vibrio cholerae O139 synonym Bengal from the aquatic environment in Bangladesh: implications for disease transmission

Assay for Evaluating the Abundance of Vibrio cholerae and Its O1 Serogroup Subpopulation from Water without DNA Extraction

Cholera is a severe diarrheal disease caused by Vibrio cholerae, a natural inhabitant of brackish water. Effective control of cholera outbreaks depends on prompt detection of the pathogen from clinical specimens and tracking its source in the environment. Although the epidemiology of cholera is well studied, rapid detection of V. cholerae remains a challenge, and data on its abundance in environmental sources are limited. Here, we describe a sensitive molecular quantification assay by qPCR, which can be used on-site in low-resource settings on water without the need for DNA extraction. This newly optimized method exhibited 100% specificity for total V. cholerae as well as V. cholerae O1 and allowed detection of as few as three target CFU per reaction. The limit of detection is as low as 5 × 10³ CFU/L of water after concentrating biomass from the sample. The ability to perform qPCR on water samples without DNA extraction, portable features of the equipment, stability of the reagents at 4 °C and user-friendly online software facilitate fast quantitative analysis of V. cholerae. These characteristics make this assay extremely useful for field research in resource-poor settings and could support continuous monitoring in cholera-endemic areas.

Simultaneous Quantification of Vibrio metoecus and Vibrio cholerae with Its O1 Serogroup and Toxigenic Subpopulations in Environmental Reservoirs

Vibrio metoecus is a recently described aquatic bacterium and opportunistic pathogen, closely related to and often coexisting with Vibrio cholerae. To study the relative abundance and population dynamics of both species in aquatic environments of cholera-endemic and cholera-free regions, we developed a multiplex qPCR assay allowing simultaneous quantification of total V. metoecus and V. cholerae (including toxigenic and O1 serogroup) cells. The presence of V. metoecus was restricted to samples from regions that are not endemic for cholera, where it was found at 20% of the abundance of V. cholerae. In this environment, non-toxigenic O1 serogroup V. cholerae represents almost one-fifth of the total V. cholerae population. In contrast, toxigenic O1 serogroup V. cholerae was also present in low abundance on the coast of cholera-endemic regions, but sustained in relatively high proportions throughout the year in inland waters. The majority of cells from both Vibrio species were recovered from particles rather than free-living, indicating a potential preference for attached versus planktonic lifestyles. This research further elucidates the population dynamics underpinning V. cholerae and its closest relative in cholera-endemic and non-endemic regions through culture-independent quantification from environmental samples.

Wild waterfowl as potential vectors of Vibrio cholerae and Aeromonas species

OBJECTIVE

To study the hypothesis that migratory waterfowl are possible disseminators of Vibrio cholerae and Aeromonas.

METHODS

We monitored the presence of V. cholerae and Aeromonas in three wild waterfowl species.

RESULTS

V. cholerae and Aeromonas species were isolated and identified from intestine samples of little egrets and black-crowned night herons. Only Aeromonas species were isolated from black-headed gulls. The majority of Aeromonas isolates were A. veronii. Twenty-three V. cholerae serogroups were identified. V. cholerae serogroup O1 was found in the intestine DNA extractions from four little egrets and black-crowned night herons; six birds carried cholera toxin subunit A gene.

CONCLUSION

Wild waterfowl species may carry pathogenic V. cholerae O1 and non-O1 serogroups and Aeromonas species in their intestine. The migration of waterfowl is a potential mechanism for global distribution of V. cholerae and Aeromonas.

Prevalence of Vibrio cholerae in Coastal Alternative Supplies of Drinking Water and Association with Bacillus-Like Spore Formers

The scarcity of hygienic drinking water is a normal phenomenon in the coastal areas of Bangladesh due to the high salinity of ground water. The inhabitants of this locality, therefore, live on alternative supplies of water including rain-fed pond water, and rainwater with persistent complex microbial interactions therein, often contaminated with life-threatening pathogens. Hence, this study was aimed at analyzing the prevalence of Vibrio cholerae (Vc) in the alternative drinking waters of Mathbaria, a coastal subdistrict neighboring the Bay of Bengal, the efficacy of pond sand filter (PSF) and the co-association among Bacillus-like spore formers (Sf) and Vc. Vc presumably entrapped into the membrane filter was enriched in alkaline peptone water medium and was isolated on selective thiosulfate-citrate-bile salts-sucrose and taurocholate-tellurite-gelatin agar media. They were finally identified by immunochromatographic one step rapid test and serology test. A total of 26% Vc positive samples were obtained out of 100 [ponds—48, household (HH)—29, and PSFs—23] where 13% cases were pathogenic (Vc O1) and 13% were non-pathogenic (Vc non-O1/non-O139). The distribution of Vc as observed was 33, 26, and 13.8% in waters derived from pond surface, PSF, and HH reservoirs, respectively, and for pathogenic type, it was 62.5%, 50%, and nil, respectively. Although none of the samples was identified with pathogenic Vc O139, the statistics represents a significant and augmentative risk of cholera outbreak in the focused area. The antibiotic sensitivity pattern in this study resembled the trend observed during last few years for Vc. The PSF demonstrated its inability to remove Vc from any of the samples and in addition, the filter itself was evidenced to be the source of pathogens and spores in further contamination and transmission. The development of biofilm in the PSF could be hypothesized as the reservoir in contaminating pathogen-free water samples. From the test of homogeneity, the risk levels of alternative water sources were estimated equal regarding Vc. Simultaneously, it was determined statistically that the prevalence of Vc, by no means, is influenced by Bacillus-like Sf be it for pond surface, HH, or PSF derived water.

International collaborative research on infectious diseases by Japanese universities and institutes in Asia and Africa, with a special emphasis on J-GRID

In developed countries including Japan, malignant tumor (cancer), heart disease and cerebral apoplexy are major causes of death, but infectious diseases are still responsible for a high number of deaths in developing countries, especially among children aged less than 5 years. World Health Statistics published by WHO reports a high percentage of mortality from infectious diseases in children, and many of these diseases may be subject to transmission across borders and could possibly invade Japan. 　Given this situation, the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan initiated Phase I of the Program of Founding Research Centers for Emerging and Reemerging Infectious Disease, which ran from FY 2005 to 2009, and involved 8 Japanese universities and 2 research centers. The program was established for the following purposes: 1) creation of a domestic research structure to promote the accumulation of fundamental knowledge about infectious diseases, 2) establishment of 13 overseas research collaboration centers in 8 countries at high risk of emerging and reemerging infections and at which Japanese researchers are stationed and conduct research in partnership with overseas instructors, 3) development of a network among domestic and overseas research centers, and 4) development of human resources. 　The program was controlled under MEXT and managed by the RIKEN Center of Research Network for Infectious Diseases (Riken CRNID). Phase II of the program was set up as the Japan Initiative for Global Research Network on Infectious Diseases (J-GRID), and has been running in FY 2010-2014. 　Phase III will start in April 2015, and will be organized by the newly established Japanese governmental organization "Japan Agency for Medical Research and Development (AMED)", the so-called Japanese style NIH. 　The Collaborative Research Center of Okayama University for Infectious Diseases in India (CRCOUI) was started up in 2007 at the National Institute of Cholera and Enteric Disease, Kolkata, India. Major projects of CRCOUI are concerned with diarrheal diseases such as, 1) active surveillance of diarrheal patients, 2) development of dysentery vaccines, 3) viable but nonculturable (VBNC) Vibrio cholerae, and 4) pathogenic mechanisms of various diarrhogenic microorganisms. 　This review article outlines project of J-GRID and CRCOUI which the authors carried out collaboratively with NICED staff members.

Detection of Vibrio cholerae O1 and O139 in environmental waters of rural Bangladesh: a flow-cytometry-based field trial

Presence of Vibrio cholerae serogroups O1 and O139 in the waters of the rural area of Matlab, Bangladesh, was investigated with quantitative measurements performed with a portable flow cytometer. The relevance of this work relates to the testing of a field-adapted measurement protocol that might prove useful for cholera epidemic surveillance and for validation of mathematical models. Water samples were collected from different water bodies that constitute the hydrological system of the region, a well-known endemic area for cholera. Water was retrieved from ponds, river waters, and irrigation canals during an inter-epidemic time period. Each sample was filtered and analysed with a flow cytometer for a fast determination of V. cholerae cells contained in those environments. More specifically, samples were treated with O1- and O139-specific antibodies, which allowed precise flow-cytometry-based concentration measurements. Both serogroups were present in the environmental waters with a consistent dominance of V. cholerae O1. These results extend earlier studies where V. cholerae O1 and O139 were mostly detected during times of cholera epidemics using standard culturing techniques. Furthermore, our results confirm that an important fraction of the ponds' host populations of V. cholerae are able to self-sustain even when cholera cases are scarce. Those contaminated ponds may constitute a natural reservoir for cholera endemicity in the Matlab region. Correlations of V. cholerae concentrations with environmental factors and the spatial distribution of V. cholerae populations are also discussed.

Isolation of viable but nonculturable Vibrio cholerae O1 from environmental water samples in Kolkata, India, in a culturable state

Previously, we reported that viable but nonculturable (VBNC) Vibrio cholerae was converted into a culturable state by coculture with several eukaryotic cell lines including HT-29 cells. In this study, we found that a factor converting VBNC V. cholerae into a culturable state (FCVC) existed in cell extracts of eukaryotic cells. FCVC was nondialyzable, proteinase K-sensitive, and stable to heating at <60°C for 5 min. We prepared thiosulfate citrate bile salts sucrose (TCBS) plates with FCVC (F-TCBS plates). After confirming that VBNC V. cholerae O1 and O139 formed typical yellow colonies on F-TCBS plates, we tried to isolate cholera toxin gene-positive VBNC V. cholerae from environmental water samples collected in urban slum areas of Kolkata, India and succeeded in isolating V. cholerae O1 El Tor variant strains harboring a gene for the cholera toxin. The possible importance of VBNC V. cholerae O1 as a source of cholera outbreaks is discussed.

Environmental reservoirs and mechanisms of persistence of Vibrio cholerae

It is now well accepted that Vibrio cholerae, the causative agent of the water-borne disease cholera, is acquired from environmental sources where it persists between outbreaks of the disease. Recent advances in molecular technology have demonstrated that this bacterium can be detected in areas where it has not previously been isolated, indicating a much broader, global distribution of this bacterium outside of endemic regions. The environmental persistence of V. cholerae in the aquatic environment can be attributed to multiple intra- and interspecific strategies such as responsive gene regulation and biofilm formation on biotic and abiotic surfaces, as well as interactions with a multitude of other organisms. This review will discuss some of the mechanisms that enable the persistence of this bacterium in the environment. In particular, we will discuss how V. cholerae can survive stressors such as starvation, temperature, and salinity fluctuations as well as how the organism persists under constant predation by heterotrophic protists.

Multi-drug resistant toxigenic Vibrio cholerae O1 is persistent in water sources in New Bell-Douala, Cameroon

BACKGROUND

Cholera has been endemic in Douala, since 1971 when it was first recorded in Cameroon. Outbreaks have often started in slum areas of the city including New Bell. Despite the devastating nature of outbreaks, always resulting in high mortality and morbidity, a paucity of information exists on the reservoirs of the causative agent, V. cholerae, and factors maintaining its persistence. This has complicated disease prevention, resulting in frequent outbreaks of cholera. We investigated water sources in New Bell for contamination with V. cholerae O1 with pathogenic potential, to highlight their role in disease transmission. Antibiotic susceptibility pattern of isolates and the environmental factors maintaining its persistence were investigated.

METHOD

Water samples from various sources (taps, dug wells, streams) were analyzed for contamination with V. cholerae O1 using standard methods. Antibiotic susceptibility was determined by disc diffusion method. Pathogenic potential of isolates was determined by analyzing for genes for cholera toxin (ctx), toxin co-regulated pilus (tcpA), and zonula occludens toxin (zot) by PCR. Physico-chemical characteristics of water (pH, temperature and salinity) were investigated using standard methods. The Spearman's Rank correlation was used to analyze the relationship between physico-chemical factors and the occurrence of V. cholerae O1. Differences were considered significant at P≤0.05.

RESULTS

Twenty-five V. cholerae O1 strains were isolated from stream and well samples in both dry and rainy seasons. Twenty-three (92%) isolates were multidrug resistant. All isolates had genes for at least one virulence factor. Cholera toxin gene was detected in 7 isolates. Of the 15 isolates positive for tcpA gene, two had Classical type tcpA while 13 had tcpA El Tor. All tcpA Classical positive isolates were positive for ctx gene. Isolates were grouped into nine genotypes based on the genes analyzed. pH and salinity significantly correlated with isolation of V. cholerae O1.

CONCLUSION

Multidrug resistant Vibrio cholerae O1 with pathogenic potential is present in some wells and streams in study area. pH and salinity are among the factors maintaining the persistence of the organism. Findings indicate an urgent need for potable water supply in study area and in addition, regular disinfection of water from contaminated sources to prevent outbreak of cholera.

VasH is a transcriptional regulator of the type VI secretion system functional in endemic and pandemic Vibrio cholerae

The gram-negative bacterium Vibrio cholerae is the etiological agent of cholera, a disease characterized by the release of high volumes of watery diarrhea. Many medically important proteobacteria, including V. cholerae, carry one or multiple copies of the gene cluster that encodes the bacterial type VI secretion system (T6SS) to confer virulence or interspecies competitiveness. Structural similarity and sequence homology between components of the T6SS and the cell-puncturing device of T4 bacteriophage suggest that the T6SS functions as a molecular syringe to inject effector molecules into prokaryotic and eukaryotic target cells. Although our understanding of how the structural T6SS apparatus assembles is developing, little is known about how this system is regulated. Here, we report on the contribution of the activator of the alternative sigma factor 54, VasH, as a global regulator of the V. cholerae T6SS. Using bioinformatics and mutational analyses, we identified domains of the VasH polypeptide that are essential for its ability to initiate transcription of T6SS genes and established a universal role for VasH in endemic and pandemic V. cholerae strains.

Seasonality of cholera from 1974 to 2005: a review of global patterns

Background

The seasonality of cholera is described in various study areas throughout the world. However, no study examines how temporal cycles of the disease vary around the world or reviews its hypothesized causes. This paper reviews the literature on the seasonality of cholera and describes its temporal cycles by compiling and analyzing 32 years of global cholera data. This paper also provides a detailed literature review on regional patterns and environmental and climatic drivers of cholera patterns.

Data, Methods, and Results

Cholera data are compiled from 1974 to 2005 from the World Health Organization Weekly Epidemiological Reports, a database that includes all reported cholera cases in 140 countries. The data are analyzed to measure whether season, latitude, and their interaction are significantly associated with the country-level number of outbreaks in each of the 12 preceding months using separate negative binomial regression models for northern, southern, and combined hemispheres. Likelihood ratios tests are used to determine the model of best fit. The results suggest that cholera outbreaks demonstrate seasonal patterns in higher absolute latitudes, but closer to the equator, cholera outbreaks do not follow a clear seasonal pattern.

Conclusion

The findings suggest that environmental and climatic factors partially control the temporal variability of cholera. These results also indirectly contribute to the growing debate about the effects of climate change and global warming. As climate change threatens to increase global temperature, resulting rises in sea levels and temperatures may influence the temporal fluctuations of cholera, potentially increasing the frequency and duration of cholera outbreaks.

Semi-nested polymerase chain reaction for detection of toxigenic Vibrio cholerae from environmental water samples

A rapid and sensitive direct cell semi-nested PCR assay was developed for the detection of viable toxigenic V. cholerae in environmental water samples. The semi-nested PCR assay amplified cholera toxin (ctxA2B) gene present in the toxigenic V. cholerae. The detection sensitivity of direct cell semi-nested PCR was 2 × 10(3) CFU of V. cholerae whereas direct cell single-step PCR could detect 2 × 10(4) CFU of V. cholerae. The performance of the assay was evaluated using environmental water samples after spiking with known number of Vibrio cholerae O1. The spiked water samples were filtered through a 0.22 micrometer membrane and the bacteria retained on filters were enriched in alkaline peptone water and then used directly in the PCR assay. The semi-nested PCR procedure coupled with enrichment could detect less than 1 CFU/ml in ground water and sea water whereas 2 CFU/ml and 20 CFU/ml could be detected in pond water and tap water, respectively. The proposed method is simple, faster than the conventional detection assays and can be used for screening of drinking water or environmental water samples for the presence of toxigenic V. cholerae.

Use of a real time PCR assay for detection of the ctxA gene of Vibrio cholerae in an environmental survey of Mobile Bay

Toxigenic Vibrio cholerae, the etiological agent of cholera, is a natural inhabitant of the marine environment and causes severe diarrheal disease affecting thousands of people each year in developing countries. It is the subject of extensive testing of shrimp produced and exported from these countries. We report the development of a real time PCR (qPCR) assay to detect the gene encoding cholera toxin, ctxA, found in toxigenic V. cholerae strains. This assay was tested against DNA isolated from soil samples collected from diverse locations in the US, a panel of eukaryotic DNA from various sources, and prokaryotic DNA from closely related and unrelated bacterial sources. Only Vibrio strains known to contain ctxA generated a fluorescent signal with the 5' nuclease probe targeting the ctxA gene, thus confirming the specificity of the assay. In addition, the assay was quantitative in pure culture across a six-log dynamic range down to <10 CFU per reaction. To test the robustness of this assay, oysters, aquatic sediments, and seawaters from Mobile Bay, AL, were analyzed by qPCR and traditional culture methods. The assay was applied to overnight alkaline peptone water enrichments of these matrices after boiling the enrichments for 10 min. Toxigenic V. cholerae strains were not detected by either qPCR or conventional methods in the 16 environmental samples examined. A novel exogenous internal amplification control developed by us to prevent false negatives identified the samples that were inhibitory to the PCR. This assay, with the incorporated internal control, provides a highly specific, sensitive, and rapid detection method for the detection of toxigenic strains of V. cholerae.

Surveillance methodology for Vibrio cholerae in environmental samples

The purpose of this study was to examine the prevalence of Vibrio cholerae in environmental water samples by using a series of biochemical tests. A total of 223 V. cholerae-like bacteria were isolated from TCBS agar after spreading the alkaline peptone water enriched sewer (n = 21) and water (n = 16) samples. All oxidase positive isolates were subjected to confirmation for V. cholerae by seven other biochemical tests and polymerase chain reaction. Only 74.2% isolates were found to be V. cholerae by PCR using primers against an outer membrane protein (ompW) gene, out of which only 2 isolates were positive for cholera toxin (ctxAB) gene. Among the various biochemical tests studied, arginine hydrolysis, arabinose fermentation and string test showed 92 - 100% sensitivity and 42 - 67% specificity. Eight isolates including the toxigenic ones, showed agglutination with V. cholerae O1 antiserum. The present study showed that no biochemical test is 100% specific for V. cholerae. However, a few tests, if performed in a sequence after growing the alkaline peptone water enriched samples onto TCBS media can be used for screening of V. cholerae from the environmental samples. This study also showed that most of the environmental isolates are non-O1/non-O139 and the chances of presence of toxigenic V. cholerae are very rare in the environment.

Seasonal cholera caused by Vibrio cholerae serogroups O1 and O139 in the coastal aquatic environment of Bangladesh

Since Vibrio cholerae O139 first appeared in 1992, both O1 El Tor and O139 have been recognized as the epidemic serogroups, although their geographic distribution, endemicity, and reservoir are not fully understood. To address this lack of information, a study of the epidemiology and ecology of V. cholerae O1 and O139 was carried out in two coastal areas, Bakerganj and Mathbaria, Bangladesh, where cholera occurs seasonally. The results of a biweekly clinical study (January 2004 to May 2005), employing culture methods, and of an ecological study (monthly in Bakerganj and biweekly in Mathbaria from March 2004 to May 2005), employing direct and enrichment culture, colony blot hybridization, and direct fluorescent-antibody methods, showed that cholera is endemic in both Bakerganj and Mathbaria and that V. cholerae O1, O139, and non-O1/non-O139 are autochthonous to the aquatic environment. Although V. cholerae O1 and O139 were isolated from both areas, most noteworthy was the isolation of V. cholerae O139 in March, July, and September 2004 in Mathbaria, where seasonal cholera was clinically linked only to V. cholerae O1. In Mathbaria, V. cholerae O139 emerged as the sole cause of a significant outbreak of cholera in March 2005. V. cholerae O1 reemerged clinically in April 2005 and established dominance over V. cholerae O139, continuing to cause cholera in Mathbaria. In conclusion, the epidemic potential and coastal aquatic reservoir for V. cholerae O139 have been demonstrated. Based on the results of this study, the coastal ecosystem of the Bay of Bengal is concluded to be a significant reservoir for the epidemic serogroups of V. cholerae.

Toxigenic Vibrio cholerae in the aquatic environment of Mathbaria, Bangladesh

Toxigenic Vibrio cholerae, rarely isolated from the aquatic environment between cholera epidemics, can be detected in what is now understood to be a dormant stage, i.e., viable but nonculturable when standard bacteriological methods are used. In the research reported here, biofilms have proved to be a source of culturable V. cholerae, even in nonepidemic periods. Biweekly environmental surveillance for V. cholerae was carried out in Mathbaria, an area of cholera endemicity adjacent to the Bay of Bengal, with the focus on V. cholerae O1 and O139 Bengal. A total of 297 samples of water, phytoplankton, and zooplankton were collected between March and December 2004, yielding eight V. cholerae O1 and four O139 Bengal isolates. A combination of culture methods, multiplex-PCR, and direct fluorescent antibody (DFA) counting revealed the Mathbaria aquatic environment to be a reservoir for V. cholerae O1 and O139 Bengal. DFA results showed significant clumping of the bacteria during the interepidemic period for cholera, and the fluorescent micrographs revealed large numbers of V. cholerae O1 in thin films of exopolysaccharides (biofilm). A similar clumping of V. cholerae O1 was also observed in samples collected from Matlab, Bangladesh, where cholera also is endemic. Thus, the results of the study provided in situ evidence for V. cholerae O1 and O139 in the aquatic environment, predominantly as viable but nonculturable cells and culturable cells in biofilm consortia. The biofilm community is concluded to be an additional reservoir of cholera bacteria in the aquatic environment between seasonal epidemics of cholera in Bangladesh.

Multiplex real-time PCR detection of Vibrio cholerae

Cholera is an important enteric disease, which is endemic to different regions of the world and has historically been the cause of severe pandemics. Vibrio cholerae is a natural inhabitant of the aquatic environment and the toxigenic strains are causative agents of potentially life-threatening diarrhoea. A multiplex, real-time detection assay was developed targeting four genes characteristic of potentially toxigenic strains of V. cholerae, encoding: repeat in toxin (rtxA), extracellular secretory protein (epsM), mannose-sensitive pili (mshA) and the toxin coregulated pilus (tcpA). The assay was developed on the Cepheid Smart Cycler using SYBR Green I for detection and the products were differentiated based on melting temperature (Tm) analysis. Validation of the assay was achieved by testing against a range of Vibrio and non-Vibrio species. The detection limit of the assay was determined to be 10(3) CFU using cells from pure culture. This assay was also successful at detecting V. cholerae directly from spiked environmental water samples in the order of 10(4) CFU, except from sea water which inhibited the assay. The incorporation of a simple DNA purification step prior to the addition to the PCR increased the sensitivity 10 fold to 10(3) CFU. This multiplex real-time PCR assay allows for a more reliable, rapid detection and identification of V. cholerae which is considerably faster than current conventional detection assays.

Pathogen adaptation to seasonal forcing and climate change

Many diverse infectious diseases exhibit seasonal dynamics. Seasonality in disease incidence has been attributed to seasonal changes in pathogen transmission rates, resulting from fluctuations in extrinsic climate factors. Multi-strain infectious diseases with strain-specific seasonal signatures, such as cholera, indicate that a range of seasonal patterns in transmission rates is possible in identical environments. We therefore consider pathogens capable of evolving their 'seasonal phenotype', a trait that determines the sensitivity of their transmission rates to environmental variability. We introduce a theoretical framework, based on adaptive dynamics, for predicting the evolution of disease dynamics in seasonal environments. Changes in the seasonality of environmental factors are one important avenue for the effects of climate change on disease. This model also provides a framework for examining these effects on pathogen evolution and associated disease dynamics. An application of this approach gives an explanation for the recent cholera strain replacement in Bangladesh, based on changes in monsoon rainfall patterns.

Wastewater-grown duckweed may be safely used as fish feed

Duckweed has been used for the treatment of wastewater and as fish feed. A comparative study was carried out to determine (i) the efficacy of duckweed in treating hospital-based wastewater and (ii) the level of the microbial contamination of fish fed on wastewater-grown duckweed. There were two groups of ponds where fish farming was done. In one group of ponds (control ponds), duckweed that was grown using artificial fertilizer was used as fish feed; in another group (study ponds), wastewater-grown duckweed was used as fish feed. The faecal contamination of water, duckweed, and fish from study and control ponds were monitored by faecal coliform estimation. The presence of enteric pathogens among handlers, water, duckweed, and fish samples was also examined. It was observed that the faecal coliform counts of raw wastewater were 4.7 Log10CFU/mL, which was reduced to <1 Log10CFU/mL after treating with duckweed. There was no significant difference (P > 0.05) in faecal coliform counts in water collected from duckweed ponds and fish ponds of study and control areas. The wastewater-grown duckweed did not pose any health hazard to the handlers. These results demonstrated that the wastewater-treated duckweed may be safely used as fish feed.Key words: wastewater, duckweed, fish feed, contamination, safety.

Involvement of the hap gene (mucinase) in the survival of Vibrio cholerae O1 in association with the blue-green alga, Anabaena sp

Mucinase is a soluble haemagglutinin protease, which may be important for the survival of Vibrio cholerae in association with mucilaginous blue-green algae (cyanobacteria). A comparative survival study was carried out with an Anabaena sp. and a wild-type V. cholerae O1 strain hap+ gene (haemagglutinin-protease), together with its isogenic mutant hap (hap-deleted gene). A simple spread plate technique was followed to count culturable V. cholerae O1 on taurocholate tellurite gelatin agar plate. The fluorescent antibody technique of Kogure et al. (1979) was used for the microscopical viable count of V. cholerae O1. Polymerase chain reaction (PCR) and Southern blot hybridization were carried out to detect a lower number of viable but nonculturable (VBNC) V. cholerae O1 from the laboratory-based experiments. The wild and mutant V. cholerae O1 strains survived in culturable form for 22 and 10 days. respectively, in association with the Anabaena sp., with the difference being statistically significant (P < 0.01). The fluorescent antibody technique, PCR, and hybridization results also showed that the wild strain survived better in the VBNC state than did the mutant VBNC strain in association with an Anabaena sp. These results indicate that the enzyme mucinase may play an important role in the association and long-term survival of V. cholerae O1 with a mucilaginous blue-green alga, Anabaena sp.

Molecular analysis of Vibrio cholerae O1, O139, non-O1, and non-O139 strains: clonal relationships between clinical and environmental isolates

A total of 26 strains of Vibrio cholerae, including members of the O1, O139, and non-O1, non-O139 serogroups from both clinical and environmental sources, were examined for the presence of genes encoding cholera toxin (ctxA), zonula occludens toxin (zot), accessory cholera enterotoxin (ace), hemolysin (hlyA), NAG-specific heat-stable toxin (st), toxin-coregulated pilus (tcpA), and outer membrane protein (ompU), for genomic organization, and for the presence of the regulatory protein genes tcpI and toxR in order to determine relationships between epidemic serotypes and sources of isolation. While 22 of the 26 strains were hemolytic on 5% sheep blood nutrient agar, all strains were PCR positive for hlyA, the hemolysin gene. When multiplex PCR was used, all serogroup O1 and O139 strains were positive for tcpA, ompU, and tcpI. All O1 and O139 strains except one O1 strain and one O139 strain were positive for the ctxA, zot, and ace genes. Also, O1 strain VO3 was negative for the zot gene. All of the non-O1, non-O139 strains were negative for the ctxA, zot, ace, tcpA, and tcpI genes, and all of the non-O1, non-O139 strains except strain VO26 were negative for ompU. All of the strains except non-O1, non-O139 strain VO22 were PCR positive for the gene encoding the central regulatory protein, toxR. All V. cholerae strains were negative for the NAG-specific st gene. Of the nine non-ctx-producing strains of V. cholerae, only one, non-O1, non-O139 strain VO24, caused fluid accumulation in the rabbit ileal loop assay. The other eight strains, including an O1 strain, an O139 strain, and six non-O1, non-O139 strains, regardless of the source of isolation, caused fluid accumulation after two to five serial passages through the rabbit gut. Culture filtrates of all non-cholera-toxigenic strains grown in AKI media also caused fluid accumulation, suggesting that a new toxin was produced in AKI medium by these strains. Studies of clonality performed by using enterobacterial repetitive intergenic consensus sequence PCR, Box element PCR, amplified fragment length polymorphism (AFLP), and pulsed-field gel electrophoresis (PFGE) collectively indicated that the V. cholerae O1 and O139 strains had a clonal origin, whereas the non-O1, non-O139 strains belonged to different clones. The clinical isolates closely resembled environmental isolates in their genomic patterns. Overall, there was an excellent correlation among the results of the PCR, AFLP, and PFGE analyses, and individual strains derived from clinical and environmental sources produced similar fingerprint patterns. From the results of this study, we concluded that the non-cholera-toxin-producing strains of V. cholerae, whether of clinical or environmental origin, possess the ability to produce a new secretogenic toxin that is entirely different from the toxin produced by toxigenic V. cholerae O1 and O139 strains. We also concluded that the aquatic environment is a reservoir for V. cholerae O1, O139, non-O1, and non-O139 serogroup strains.

Association of Vibrio cholerae O1 with the cyanobacterium, Anabaena sp., elucidated by polymerase chain reaction and transmission electron microscopy

It has been hypothesized that Vibrio cholerae is an autochthonous flora of the estuarine and brackish water environment. Zooplankton and phytoplankton have been considered as possible reservoirs. The present study was carried out in microcosms to confirm the role of a cyanobacterium, Anabaena sp., as a reservoir of V. cholerae O1 using culture, polymerase chain reaction (PCR) and immunoelectron microscopy. Survival of culturable V. cholerae in microcosms was monitored by using tellurite taurocholate gelatin agar. Culturable V. cholerae were detected for up to 1 h in association with Anabaena sp. from a microcosm. However, viable but nonculturable (VBNC) V. cholerae O1 were detected for up to 25 months using PCR and immunoelectron microscopy. Results also showed that VBNC V. cholerae can multiply and maintain their progeny in the mucilaginous sheath of Anabaena sp. This is the first time that PCR and immunoelectron microscopy have been used to detect nonculturable V. cholerae in association with Anabaena sp. This study further clarifies the role of Anabaena sp. as a possible reservoir of cholera.

Tracking of clinical and environmental Vibrio cholerae O1 strains by combined analysis of the presence of toxin cassette, plasmid content and ERIC PCR

Clinical and environmental Vibrio cholerae O1 strains associated with the cholera epidemic in the Luanda province of Angola from 1991 to 1994 were tracked by toxin distribution, plasmid content and chromosomal polymorphism of the enterobacterial repetitive intergenic consensus (ERIC) sequences by PCR fingerprinting. To follow the distribution of ace, zot and ctxA toxin genes, 6 specific PCR tests were applied to 100 Vibrio strains, after preliminary hybridization experiments. Clinical isolates of Vibrio cholerae O1 were characterized by high stability of the toxigenic cassette and the presence of a large conjugative multi-resistant plasmid of incompatibility class C. Such characteristics were present in all isolates during the four years of the epidemic. Environmental strains, isolated from the river supplying water to the Luanda population showed three different genetic profiles: the presence of both cassette and plasmid, the presence of cassette only or absence of both. To assess the clonal relationship between the clinical isolates and the three groups of environmental strains, the strains were analyzed by PCR ERIC polymorphism. This analysis, supported by the toxin and plasmid content, suggested the stability of the epidemic strain in clinical cases during the epidemic and led to the finding that there was a strict genetic relationship of the epidemic strain with the environmental ones as characterized by the presence of the toxin cassette. The role of the water supply from Bengo River as a reservoir of the Vibrio epidemic strain is discussed.

Isolation of Vibrio cholerae O139 from the drinking water supply during an epidemic of cholera

In mid-1994, the public water supply was investigated in a medium-sized town in south India during an epidemic of cholera due to Vibrio cholerae O139. Vibrio cholerae O139 was isolated from the public water supply including one of the wells supplying the town, the central overhead tank, and domestic taps connected to the public supply. Following chlorination, the organism was no longer isolated from the water supply and the epidemic subsided. This demonstration of V. cholerae O139 in the drinking water supply of a town underlines the need for adequate treatment of the water supply.

Isolation of sucrose late-fermenting and nonfermenting variants of Vibrio cholerae O139 Bengal: implications for diagnosis of cholera

The sucrose-containing selective medium thiosulfate-citrate-bile salt-sucrose agar missed a sucrose nonfermenting and four sucrose late-fermenting variant strains of Vibrio cholerae O139 Bengal from diarrheal stools. These strains were, however, correctly identified as V. cholerae O139 on a sucrose-deficient selective medium, taurocholate-tellurite-gelatin agar.