Toxigenic Vibrio cholerae in the Aquatic Environment of Mathbaria, Bangladesh

Abstract

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.Toxigenic Vibrio cholerae O1 and O139 are causative agents of cholera (38), an acute dehydrating diarrhea, which occurs in epidemic (13, 31) and pandemic (23) forms. Since the first pandemic was recorded in 1817, as many as seven cholera pandemics have occurred (35). The most recent, the seventh pandemic, began in Indonesia (14), but cholera pandemics have usually begun in the Gangetic delta of the Indian subcontinent and then in other continents (10,40). Of the 206 O serogroups of V. cholerae, serovar O1 was the only recognized cause of cholera until late 1992. At that time an outbreak of acute watery diarrhea clinically resembling cholera erupted in India and southern Bangladesh (1, 10). The bacterium causing cholera-like diarrhea failed to agglutinate with any of the then existing 138 V. cholerae O antisera (1) and was thus designated O139 with the synonym "Bengal" to commemorate its emergence in the coast of the Bay of Bengal. Since then, O1 and O139 remain the two recognized serogroups causing epidemics of cholera.Epidemiological studies of V. cholerae O139, including its emergence, prevalence, and coexistence with O1 El Tor V. cholerae, have been conducted primarily in Bangladesh and India via systematic surveillance (19). In the Ganges delta region, cholera outbreaks occur seasonally (13,14), but variations in prevalence of the two epidemic serogroups O1 and O139 of V. cholerae are distinct ...

Biofilms in water, its role and impact in human disease transmission

“…V. cholerae serogroups O1 and O139 have been shown to survive year round, mostly in a nonculturable state, within clusters of biofilm in the ecosystem adjacent to the coast of the Bay of Bengal, accounting for the endemic cholera in that geographic region [7]. Biofilm-like, multicellular clumps of V. cholerae are found in human stools [8], and a recent epidemiological and ecological study offered firm evidence that bodies of water serving as drinking water sources harbored biofilm-bound, nonculturable V. cholerae O1 cells between epidemics occurring in the coastal villages of the Bay of Bengal seasonally [9].…”

Frequency of Vibrio cholerae in the Water and Plankton Samples of South- Western Coastal Aquatic Habitats of Bangladesh

“…In response to environmental stress in aquatic environments, such as low concentrations of nutrients and low temperatures, V. cholerae O1 and non-O1 adopt a viable state that enables them to carry out metabolic functions and form colonies without being culturable (Huq et al 1990, Colwell et al 1985, Brayton et al 1986, Colwell et al 1992. The above information suggest that the ecology of Vibrio cholerae is mostly correlated with water and plankton samples of aquatic environment and the non culturable cells play a significant role in the seasonal epidemics of cholera (Alam et al 2006).…”

“…In Bangladesh, cholera epidemics occur twice every year, the highest peak during post monsoon (September -January) and second smaller peak during pre monsoon (MarchMay). During inter-epidemic period V. cholerae cannot be cultured from the surface water, whereas in epidemic season it can be isolated from the patients' body as well as from surface water (Alam et al 2006). When V. cholerae is not causing havoc in the human intestine, it may be found in diverse aquatic environments such as estuaries, rivers, ponds etc.…”

International Collaborative Research on Infectious Diseases by Japanese Universities and Institutes in Asia and Africa, with a Special Emphasis on J-GRID

“…Studies from the same laboratory and others revealed that El Tor variant strains of V. cholerae have replaced seventh pandemic El Tor prototype strains in most of the cholera-endemic areas in Asia and Africa Safa et al, 2010 . Recent Haitian V. cholerae strains, pathogens of the cholera outbreak after the 2010 Great Earthquake, contained a unique mutation at the 58th nucleotide of the ctxB gene resulting in a change at the 20th position with an asparagine instead of histidine in the signal peptide region of cholera toxin B. CRCOUI showed that Haitian ctxB first appeared in Kolkata and also in Delhi Many investigators have suggested the existence of VBNC V. cholerae O1 and O139 in environmental water sources in cholera-endemic areas Roszak and Colwell, 1987;Alam et al, 2006 . Even between epidemic seasons, VBNC V. cholerae O1 is present as a biofilm Faruque et al, 2006;Alam et al, 2007 .…”