ANTIMICROBIAL RESISTANCE AND VIRULENCE-ASSOCIATED GENES OF AEROMONADS ISOLATED FROM LAKE MANZALA WATER AND WILD NILE TILAPIA: IMPLICATIONS TO PUBLIC HEALTH AND THE LAKE MICROBIAL COMMUNITY

This study was conducted to investigate the prevalence, antimicrobial susceptibility, and molecular characterization of Aeromonas spp. from wild Nile tilapia from Lake Manzala and the lake water. Swabs from the surface, gills, and internal organs of apparently healthy Nile tilapia (n =100) and lake water (n = 25) were collected and examined bacteriologically for the presence of Aeromonas spp. The isolates obtained were tested for their susceptibility to 11 antimicrobial agents using the disk diffusion method. The presence of antibiotic resistance genes (bla(TEM), sul1, tetA(A), and aadA1) and virulence genes (enterotoxins) (aft, ast, and act) was determined using conventional polymerase chain reaction. Overall, Aeromonasspp. were recovered from 69% of Nile tilapia (Oreochromis niloticus) samples and 80% of water samples. Four types of aeromonads were detected in all the samples examined, namely, A. hydrophila, A. sobria, A. caviae, and A. schubertii, with A. hydrophila predominating in both the fish and the lake water samples. The antimicrobial resistance profiles of the isolates showed very high resistance to ampicillin, penicillin, sulfamethoxazole/trimethoprim, and oxytetracycline and considerable resistance to streptomycin. However, all isolates were sensitive to cefotaxime. Molecular characterization revealed the presence of the act (100%) and alt(37.5%) genes, but ast was not found in any of the isolates. Specific amplification bands of the antimicrobial resistance genes bla(TEM), sul1, and tetA(A) were detected in all the tested isolates, whereas aadA1 (12.5%) was found only in one isolate of A. hydrophila from Nile tilapia. The presence of these enterotoxigenic and resistant Aeromonas spp. in the fish and water samples from Lake Manzala could pose a potential public health threat to human consumers and fish handlers in the study area; moreover, these species carrya risk for the transfer of resistance genes to other microbial communities in the lake.