Antimicrobial Susceptibility, Microbial Loads and Isolation of Plesiomonas shigelloides from African Sharptooth Catfish (Clarias gariepinus) Juveniles and Experimental Pond Water

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The aim of this study was to investigate the antimicrobial susceptibility, microbial loads and isolation of Plesiomonas shigelloides isolated from African catfish, Clarias gariepinus juveniles and experimental pond water. Microbial loads of pond water and fish tissues (gill, liver, and intestine) were evaluated using standard methods. Isolation and antibiotic susceptibility of the bacterial species were carried out using standard microbiological techniques. Antibiotic susceptibility of the isolates was assessed using a panel of 12 antibiotics by disc diffusion method and standard guidelines. The microbial loads in water from the experimental ponds ranged from 5.60 to 7.00 log 10 CFU/mL, while those in gill, liver, and intestine samples ranged from 6.40 to 7.00 log 10 CFU/g. The microbial loads were higher than the permissible limits for wastewater and fish tissues. The microscopic cell morphology analysis of presumptive P. shigelloides revealed 40 isolates of round-ended, straight rod shape, which were motile, positive to oxidase, catalase, mannitol, and citrate biochemical test, negative to urease, methyl red, and glucose biochemical test. Antibiotic susceptibility results showed that the presumptive P. shigelloides were 100% resistant to cefuroxime and cefotaxime, 87.5% to meropenem, and 77.5% to ceftazidime. However, the isolates were 0% resistant to gentamicin and amikacin of aminoglycoside derivatives, suggesting that these might be only two out of the 12 panels of antibiotics used that presumptive P. shigelloides might have responded to. The findings highlight the need for routine microbial monitoring, improved pond hygiene, and responsible antimicrobial use in catfish aquaculture. The observed in vitro susceptibility to gentamicin and amikacin may provide useful baseline information for future risk assessment and antimicrobial stewardship.

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