Assessment of antibiotic resistance patterns in two potential probiotic bacteria, Lactococcus lactis subsp. cremoris NABRII64 and Lactococcus lactis subsp. cremoris NABRII66 isolated from rainbow trout (Oncorhynchus mykiss) intestine

This study aimed to investigate the phenotypic and genotypic patterns of antibiotic resistance in two potential probiotic lactic acid bacteria, Lactococcus lactis subsp. cremoris (NABRII64 and NABRII66) isolated from the rainbow trout intestine. The phenotypic susceptibility pattern of the strains was studied based on the Minimum Inhibitory Concentration (MIC) of eight most commonly used antibiotics in medicine and veterinary including ampicillin, kanamycin, gentamicin, streptomycin, erythromycin, clindamycin, tetracycline, and chloramphenicol. After comparing the MICs with standard values recommended by European Food Safety Authority (EFSA), the nature of phenotypic resistance observed in bacterial strains was investigated by polymerase chain reaction (PCR) through plasmid DNA extraction. The results of the phenotypic evaluation indicated the tetracycline resistance in both bacterial strains (MIC<4mg/L). Genotyping of antibiotic resistance genes including tet (S), tet (L), tet (M), tet (O), tet (W) and tet (K) indicated the presence of tet (S) and tet (M) resistance genes in plasmid DNA of both bacterial strains. These results exhibited the acquired resistance and the presence of two tetracycline resistance genes in the plasmid DNA of two bacterial strains, NABRII64 and NABRII66. However, further studies are required to understand the nature of the acquired resistance mechanism in the future.