Pathogenic Bacteria, Endocrine-disrupting Chemicals in Water and Associated Pathology in Oreochromis Niloticus in Lake Victoria, Kenya

Abstract

The objective of the study was to investigate: (a) Establish types and loads of bacteria in the water and Oreochromis niloticus of Lake Victoria, and to assess their antimicrobial susceptibility profiles, (b) the presence and quantification of estrogenic endocrine disrupting chemicals (EDCs) in the water; and (c) document pathological changes in the Lake fish organs. Water and fish samples were collected from fourteen sites in Kisumu and Homa Bay. A total of 86 water samples for bacteriology and 74 water samples were collected for estrogenic endocrine disrupting chemicals analysis. Additionally, 144 live Oreochromis niloticus fish from Dunga and Tilapia landing sites in Kisumu and Homa Bay pier were examined. Seven organs namely; liver, kidney, spleen, intestines, skin, gonads and gills were taken from each fish and cultured for bacteria, identified and established their loads; and histopathological lesions were determined from the seven organs. 62 bacteria were tested against 9 antimicrobial agents using the modified controlled diffusion technique. In the EDCs analysis, estrone (E1), 17-β estradiol (E2), and ethynyl estradiol (EE2) were extracted from the water samples usingSolid-phase extraction columns. The estrogens were then characterized and quantified using respective oestrogen competitive enzyme-linked immune-absorbency assay (ELISA) kits. The fish organs underwent routine histopathological processing, and were stained with hematoxylin and eosin. Lesions were scored according to their severity and effect on the fish's health. To assess the differences in organ indices between the sampling sites/season, the Kruskal-Wallis statistic was used. The study found that the mean (log10 cfu/ml) water bacterial loads varied according to the source of water. The river water had higher bacterial loads ranging from 6.08 ± 0.21 to 6.91 ± 0.22, while Kisumu and Homa Bay lake water had lower bacterial loads ranging from 3.86 ± 0.19 to 5.34 ± 0.1. The highest mean bacterial load was recorded in Kisat River waters in xxvi Kisumu. Staphylococcus aureus was the most prevalent bacteria found in both the river and landing sites at 23.5% and 17.6%, respectively. Potential pathogenic bacteria isolated in water and fish samples, included Escherichia coli, Vibrio, Salmonella, Aeromonas, Proteus, Enterobacter, Staphylococcus, and Streptococcus species. External organs of the fish had the highest bacterial load, with the skin having a bacterial load of 6.42 ± 0.12 log cfu/inch2, while the kidney had the lowest with 2.91 ± 0.04 log cfu/ml. The Kisumu water had more bacteria isolated per sample than Homa Bay water, based on the relative concentration of bacteria in the water and fish organ samples. The bacterial isolates from water deostrated a high level of resistance (>50%) to the 9 antimicrobials tested. All water samples from sites in Kisumu and Homa Bay contained EDCs at varying concentrations. Specifically, the concentrations of estrone, 17-β estradiol, and ethynyl estradiol ranged from 2.72 to 175.9 pg/ml, 1.16 to 28.42 pg/ml, and pg/ml, respectively. The concentrations of estrogens were higher in the river water than in the landing sites water. Furthermore, the study found a positive correlation between oestrogen concentrations in the river and the landing sites, except for 17-β estradiol and ethynyl estradiol in the river water (p<0.05). The detection of estrogenic endocrine disrupting chemicals in all sites indicate a high level of pollution in Lake Victoria's water, highest in Kisumu compared to Homa Bay in the Winam Gulf. To assess the health of resident Oreochromis niloticus, histopathological analysis was performed on four organs including liver, kidney, spleen and gonads. Lesions were observed in all organs, with the highest number found in the gills followed by the liver. The most prevalent lesions on the liver were melanomacrophages and fatty liver degeneration, while neutrophil infiltration and epithelial necrosis was prominent in the gills. The statistical analysis did not show any significant differences in the organs tested (liver, kidney, spleen, and gonads) (p>0.05) on Kruskal-Wallis statistical analysis...............................................