Bacterial pollution indicators and their Physico-chemical environment in the inshore Waters of Lake Victoria, Kisumu city in Relation to enteric diseases

Abstract

Studies on Lake Victoria especially on the Nyanza Gulf has focused on fish kills, fish pathogens, algal blooms, limnological studies and eutrophication. This may be due to the fact that surveying water for faecal indicators is quite laborious, but an important water body such as Lake Victoria, at certain key points needs monitoring on a very regular basis. Population increase, agricultural, industrial and urban development in Lake Victoria's catchment area, soil erosion, introduction of exotic fish species, infestation of the water hyacinth and the subsequent alterations in the communities, contribute to changes in the water quality and the functioning of the ecosystem of the lake. This study is the first correlational study on the existence of faecal indicators in the shoreline waters of Lake Victoria. The study sought to establish the existence and magnitude, spatial and temporal variation of the various species of enteric bacterial pathogens in the inshore lake water by analysing the microbial quality of the water and establishing the link between the levels of pathogens and their relationship to the physical and chemical parameters of the lake. The existence, magnitude, spatial and temporal variation of the various species of enteric bacterial pathogens such as Salmonella, Vibrio, Escherichia coli, Total and faecal coliforms was studied for thirteen months between January 2002 and January 2003 from 5 different possible polluting sources along the inshore waters of Lake Victoria, Kisumu Town. Membrane Filter Technique was used for its accuracy. Samples were incubated using different culture media, selective and differential, specific for different species of bacteria. The results obtained show the presence of E. coli in the water sampled in various sites indicating faecal pollution. The incidence of both total and faecal coliforms were quite high for example mean total coliforms for Kisat River was 7.1 x 105 CFU I 100mI and 5.6 x 105 CFU I 100mI for 100m away from the inlet to the lake. This river had the highest densities of faecal coliforrns compared to all other sites that were studied. The XIV mean total coliform for log transformed data at the different sites and distances were analysed statistically. There were significant differences up to P:S 0.05 in the total coliform counts at different sites. For faecal coliform there was no significant difference between the distances of sampling. However, between sites there was a significant difference in the levels of faecal coliform up to P:S 0.01. There was no significant difference in Salmonella densities at P:S0.05. This was also true for Vibrio densities. The colonies were counted according to standard methods for examination of water and waste water using American Public Health Association (APHA) recommended protocol and biochemical tests were done for confirmatory results. Analytical Profile Index (API) 20E was used for species identification. The most important enteric pathogens identified in this study were Salmonella spp, Vibrio spp, E. coli, Enterobacter, Serratia, Klebsiella and Citrobacter. These pathogens also cause diseases other than the gastrointestinal tract, such r as the lungs and the urinary tract. This study recommends the establishment of a national or regional water quality monitoring agency for Lake Victoria with a municipal office doing very regular bacterial pollution indicator level analysis. This study also gives for the first time the varied enteric pathogenic species up to the species level. The species identification using API 20E and the confirmation of the existence of E. coli in the subcultured water samples is a sure indication of sewage pollution.