Antimicrobial activity of lactic acid bacteria isolated from the gut of African catfish (Clarias gariepinus) against multi-drug-resistant resident pathogens.

backgroundThe escalating threat of antimicrobial resistance (AMR) in aquaculture presents a significant challenge to the sustainability of fish farming and global health. Excessive and improper use of antibiotics in aquaculture is a primary driver of AMR, particularly in regions like Nigeria, where fish farming is a key sector of aquaculture. This study investigated the antimicrobial capability of Lactic Acid Bacteria (LAB) isolated from the intestines of African Catfish (Clarias gariepinus) in Nigeria as natural alternatives to antibiotics in animal feed. The aim was to assess LAB's effectiveness against enteric pathogens from African Catfish that demonstrated resistance to multiple antibiotics commonly used in aquaculture. METHODOLOGY: LAB and enteric pathogens were isolated from the intestines of African Catfish using selective growth media. Phenotypic identification methods, including morphological and biochemical tests, were initially employed, followed by confirmation of the most active strains through 16 S rRNA gene sequencing. Additionally, the antibiotic resistance profiles of both LAB and enteric pathogens were established using standard disc diffusion methods. The most resistant pathogens were selected for challenge tests to evaluate the antimicrobial efficacy of the LAB isolates.

resultsA total of 38 LAB isolates and 30 enteric pathogens were assessed, with 61% of the LAB isolates showing resistance to at least four of the eight antibiotics tested. In contrast, 50% of the enteric pathogens were susceptible to at least six of the antibiotics tested. When the LAB isolates were tested against the most resistant pathogens, which were molecularly identified as Enterobacter cancerogenus FP4C and Enterobacter cloacae FP5A, 48% of the LAB isolates demonstrated significant antimicrobial activity, with inhibition zones measuring ≥ 20 mm. DNA sequencing of the most active LAB isolates revealed a diverse range of species, including Weissella confusa (40%), Pediococcus pentosaceus (27%), Lactobacillus reuteri (20%), Lactobacillus murinus (7%), and Lactobacillus vaginalis (7%).

conclusionOur findings demonstrate the diverse LAB species present in the intestines of Nigerian catfish and their invitro antimicrobial effectiveness against resident AMR enteric pathogens. Although these LAB isolates show promise as potential antimicrobial agents, further testing, including in vivo studies and safety assessments, is required to confirm their suitability as probiotics in aquaculture applications.