Heavy metal and associated antibiotic resistance of fecal coliforms, fecal streptococci and pathogens isolated from wastewaters of abattoirs in Nairobi, Kenya

Abstract

Objective: The pollution of the environment with toxic heavy metals is increasing globally with industrial progress. Microorganisms can be good bio-accumulators of particulate and soluble forms of heavy metals and subsequently resist antibiotics. The present study aimed at assessing the resistance pattern to multiple heavy metals by wastewater bacteria and associated antibiotic resistance. Methodology and results: Standard microbiological methods were used to isolate fecal streptococci, fecal coliforms, Vibrio and Salmonella species from raw animal wastewaters and sludge samples obtained from three abattoirs around Nairobi city. A total of 30 samples were collected. Agar diffusion and tube dilution methods were used to assess the heavy metal resistance while sensitivity to antibiotics was determined by the agar diffusion method. From the 40 isolates obtained, 27 showed multiple resistance to heavy metals. Resistance pattern was as follows; Hg 9 (33.3%), Co 11 (40.7%), Cu 18 (66.7%), Zn 19 (70.4%), Pb 21 (77.8%), and Ni 24 (88.9%). Out of the 27 resistant strains, 5 (18.5%) showed resistance to 5 different metal ions and only 1 (3.7%) showed resistance to two different metal ions. With each of the six metals tested, there was a tendency towards a high frequency of resistance among the isolates to lincomycin (77.8%), tetracycline (70.4%) and ampicillin (66.7%). Conclusion and application of findings: In the present study, heavy metal resistance associated with multiple drug resistance was detected in the bacterial isolates from the wastewater and sludge of the cattle, sheep and goat abattoirs. The high degree of resistance to common antibiotics could be attributed to the contamination of the wastewaters and sludge with heavy metals possibly from animal feeds or drinking waters, leading to co-selection of both metal tolerant and antibiotic resistant microbial species. This requires intervention measures to curb the potential health hazard that heavy metal pollution pose in the environment. The identified heavy metal resistant bacteria could be useful for bioremediation of heavy metals contaminated sewage and wastewaters, but the coupled antibiotic resistance is a worrying phenomenon.

Keywords: Heavy metal resistant bacteria, antibiotic resistance, wastewaters, sludge, animals