*Fadare, O. S., Olalekan, P., and *Salam, L. B.
Department of Biological Sciences (Microbiology Unit), Faculty of Basic and Applied Sciences, Elizade University, Wuraola Ade Ojo Avenue, P. M. B. 002, Ilara-Mokin, Ondo State, Nigeria
*Correspondence to: olalekan.fadare@elizadeuniversity.edu.ng; +2348169001041; ORCiD: 0000-0002-1749-2238 *Correspondence to: lateef.salam@elizadeuniversity.edu.ng; +234 810 245 0606; ORCID: 0000-0001-8353-534X
Abstract:
Background: Aquaculture environments are increasingly recognized as reservoirs for antimicrobial-resistant bacteria due to the routine use of antibiotics such as tetracyclines. Members of the family Enterobacteriaceae readily acquire and disseminate resistance determinants, posing risks to food safety and public health. In Nigeria, molecular data on tetracycline resistance in aquaculture systems remain limited. This study investigated the occurrence and molecular basis of tetracycline resistance among Enterobacteriaceae isolated from earthen catfish ponds in Akure, Nigeria.
Methodology: Composite samples were collected from five different locations within each of two randomly selected commercial-scale earthen catfish ponds and pooled for analysis. The resulting samples were cultured on selective media. Antibiotic susceptibility of four representative isolates was performed by the Kirby–Bauer disc diffusion method against ampicillin, cefuroxime, ciprofloxacin and tetracycline. The isolate exhibiting phenotypic tetracycline resistance was further characterized by 16S rRNA gene sequencing and phylogenetic analysis. Polymerase chain reaction (PCR) assay was used to detect tetracycline resistance genes (tetA and tetM) in the isolate.
Results: All four representative isolates were fully resistant to ampicillin and cefuroxime but susceptible to ciprofloxacin. One isolate (EP9) displayed complete resistance to tetracycline. Molecular identification revealed EP9 as Escherichia albertii, confirmed by phylogenetic clustering within a distinct E. albertii clade. PCR analysis detected the presence of the tetA gene (210 bp) in EP9, while tetM was not detected.
Conclusion: This study provides molecular evidence that earthen catfish ponds in Akure harbour tetracyclineresistant Escherichia albertii. The detection of the plasmid-mediated tetA gene underscores the role of aquaculture systems as reservoirs and dissemination hubs for clinically relevant antimicrobial resistance genes, highlighting the need for strengthened antibiotic stewardship and routine AMR surveillance in aquaculture.
Keywords: Escherichia albertii, Enterobacteriaceae, Aquaculture tetracycline resistance, Nigeria
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