Assessment of vibrio cholerae in selected aquatic environments along the coastal areas of Tanzania: The case study of Tanga, Pwani and Dar es Salaam regions

Cholera is a human infectious disease caused by strains of the gram-negative bacterium Vibrio cholerae belonging to serogroup 01 or 0139. The natural habitat of the bacterium is the aquatic environments. In this study, the occurrence, diversity and comparison of the V cholerae from different aquatic environments of Tanzania and clinical isolates, were assessed. Field sampling was conducted for a period of one year (July 2009 - June 2010) in which water, sediment and plankton samples were collected once in a month. In addition, clinical isolates were obtained from Dar es Salaam and Tanga. V cholerae was detected by extracting total DNA from both environmental and clinical samples and amplifying V cholerae specific gene fragments by the Polymerase Chain Reaction (PCR) using species-specific primers, for the outer membrane protein (ompW) and the enterotoxigenic gene ctxA. The presence of V cholerae 01 and 0139 strains was confirmed using 01 -rfb and 0139-rfb specific primers, respectively, in the PCR analysis. Results show that V cholerae did occur in all studied habitats throughout the year. Among the 59 V cholerae obtained, 14 were 01, while only one was 0139 and 44 were non 01/0139. Out of 44 V cholerae non 01/0139, 40 were toxigenic V. cholerae. This shows that there is existence of varieties of V cholerae with toxigenic genes, raising the question whether these strains pose a health risk in the region. Using the molecular typing methods , extensive genetic diversity among V cholerae strains was observed. To conclude, the findings of the study provide the in situ evidence of the presence of the pathogenic V cholerae 01 and 0139 and pathogenic V cholerae non 01/0139 along the coastal waters of Tanzania posing a danger of being virulent