Association of heavy metal tolerance with multiple antibiotic resistance in bacterial isolated from wetlands of lake Victoria basin Kenya
Sikuku, Mutuku Christopher
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A study was carried out to determine the heavy metal concentrations in the wetlands of Lake Victoria basin and their effect on bacterial resistance to ten commonly used antibiotics. Water and sediment samples for heavy metal analysis and microbiological assays were randomly collected from sewage outfalls and points bordering heavy metal activity settlements. Heavy metal analysis was done using flame Atomic Absorption Spectrometer (F-AAS). The microbiological assays targeted heterotrophic bacteria, coliforms and enteric pathogens. The isolates were subjected to heavy metals;- mercury, nickel, chromium and copper in the laboratory to assess their levels of tolerance. Antibiotic susceptibility testing was carried out to check for antibiotic resistance. Sediment samples recorded a higher level of heavy metals with a mean range of 31.97109.9, lead; 3.48-183.66, zinc; 3.01-17.03, nickel; 1.93-214.61. copper; 17.01-65.91, cobalt; and 2.08-25.89 mg/g chromium compared to water samples whose mean range was as follows;- lead; 0.77-0.94, manganese; 0.10-3.10, zinc; 0.23-1.16, cadmium 0.020.04, and copper 0.51-0.57 mg/1. There was a significant relationship in the amounts of heavy metals in water samples and the bacterial counts, r = 0.637, p < 0.05. The study showed a significant difference in percentage tolerance to the four, heavy metals tested. (f = 4.25, P = 0.011, P < 0.05). Mercury recorded the highest toxicity followed by chromium and nickel. Copper was the least toxic to the microorganisms. 53.8% of the total isolates showed multidrug resistance. They were significantly resistant (p < 0.05) to cefuroxime (67.7%), cotrimoxazole (65%), tetracycline (62.4%) and ampicillin (53%). They were however highly sensitive to, gentamycin (98.9%), kanamycin (83.9%) and norfloxacin (79.6%). The study showed no significant difference in multidrug resistance in the three bacteria groups (F =1.75 P = 0.191 P > 0.05). however er, multidrug resistance in the enteric pathogenic bacteria (mean % multi drug resistance 65.15%) was higher than in heterotrophs (mean 46.52%) and coliform bacteria (mean 6.36%). There was a significant relationship between chromium tolerance with resistance to cefuroxime (p < 0.000), Nickel tolerance with resistance to cefuroxime (p < 0.05) and mercury tolerance with resistance to ampicillin (p < 0.05). Plasmid DNA finger printing of the metal tolerant and antibiotic resistant isolates showed a positive relationship in number of isolates carrying plasmids and the number having multiple drug resistance (r = 0.372, P = 0.261) suggesting that heavy metal pollution in wetlands induces multidrug resistance. The high degree of resistance to common antibiotics like ampicillin, cotrimoxazole and cefuroxime can therefore be attributed to the inflow of heavy metal rich effluent into the wetlands of the Lake basin resulting to co-selection of both metal tolerant and antibiotic resistant microbial species. This requires intervention measure s to curb the potential health hazard posed by heavy metal pollution in the aquatic ecosystems.