Antibiogram, Metal Tolerance and Plasmid Profiles of Pathogens Isolated from Wastewaters and Sludge of Abattoirs in Nairobi, Kenya
Nyamboya, Rosemary Atieno
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Because of the prevalence of antibiotic resistant pathogenic bacteria, infectious diseases are becoming more difficult and expensive to treat. In Kenya, high levels of flouroquinone resistance of a bacterium, Neisseria gonorrhea have been widely reported. Antimicrobial resistance may be coded on plasmids, mutational events or on transposons. A growing body of evidence indicates that metal tolerance and antibiotic resistance are often found together in many clinical isolates and that metal and antibiotic resistance is closely associated. Besides having clinical consequences, resistant bacteria of animal origin may be the source of determinants of resistance for the possible transfer to human strains. Most of the previous studies have concentrated on clinical isolates from human and animal stools while studies targeting environmental isolates are limited. This study aimed at identifying fecal indicators and pathogens recovered from wastewaters used to clean animal carcass and sludge used as manure, from cattle slaughterhouse in Kayole and the separate sheep and goat slaughterhouses both in Kiamaiko, Nairobi and to determine susceptibility of isolated bacteria against 13 antibiotics and 6 heavy metals, in addition to studying plasmid profiles. Isolation of fecal indicators and pathogens was carried out using standard laboratory methods. Sensitivity to antibiotics was determined by the agar diffusion technique on Mueller-Hinton agar. Heavy metals tolerance was determined by well diffusion and tube dilution methods. Plasmid DNA was isolated using the alkaline lysis method. The fecal bacteria load was found to be 6.2 x 106, 5.3 x 105, 2.5 x 104, 2.9 x 104 and 5.0 x 106 CFU/100 mL for fecal streptococci and 3.4 x 105, 4.1 x 103, 3.0 x 104, 2.7 x 103 and 3.9 x 105 MPN/100 mL for fecal coliforms in cattle wastewater, cattle sludge, goat wastewater, sheep wastewater and a mixture of goat and sheep sludge, respectively. Pearson correlation analysis showed positive correlation between prevalence of fecal streptococci and fecal coliforms (r=0.931 at 0.01 level). Vibrio and Salmonella species were more frequently detected in samples which also showed high incidence of indicator organisms. There was high resistance to lincomycin (90 %), ampicillin (80 %) and methicillin (72.5 %) and low resistance to chloramphenicol (22.5 %). Another potential environmental threat noticed was heavy metal tolerance of the indicator organisms and pathogens to nickel, mercury, copper, zinc, lead and cobalt. Results of the test of toxicity in solid media agreed with those in liquid, however, inhibitory concentrations in solid media were much higher compared to those in liquid. Lead and nickel were the least toxic metals. Mercury was the most toxic component for all bacteria, followed by cobalt and then copper. Among the 40 bacterial isolates studied only 18 (45%) harbored between 1 - 2 kb plasmid DNA bands which ranged in size from 4kb to 10kb. The results showed the dynamics of resistance development in warm blooded animals usually used or consumed by humans. This study provided data on the level and risks of microbiological contamination as well as baseline data for the future assessment and monitoring of pollution levels of wastewaters. With regard to the high contamination level of the wastewaters and sludge with resistant bacteria as revealed in this study, treating of wastewaters and sludge is recommended, before using or discharging them into the environment and also proper use and disposal of antimicrobial agents. The metal-antibiotic double resistance detected in this study call for intervention measures to curb the potential health hazard that heavy metal pollution pose in the environment.