Antibiotic resistance in Listeria species isolated from catfish fillets and processing environment

Aims: To investigate the susceptibility of 221 Listeria spp. (86 Listeria monocytogenes, 41 Listeria innocua and 94 Listeria seeligeri-Listeria welshimeri-Listeria ivanovii) isolated from catfish fillets and processing environment to 15 antibiotics. Methods and Results: Listeria isolates were analysed by disc-diffusion assay for their resistance to 15 drugs. All isolates were resistant to cefotaxime and clindamycin but were sensitive to ampicillin, cephalothin, chloramphenicol, erythromycin, gentamycin, kanamycin, rifampin, streptomycin, sulfamethoxazole/trimethoprim and vancomycin. Unlike L. monocytogenes and L. seeligeri-L. welshimeri-L. ivanovii isolates, 22% of L. innocua isolates displayed tetracycline/oxytetracycline resistance. Screening of tet genes by PCR identified tet(M) gene in the chromosome of all tetracycline/oxytetracycline-resistant L. innocua. However, this gene was not associated with the integrase gene of Tn1545. Repetitive extragenic palindromic- and enterobacterial repetitive intergenic consensus-PCR typing methods showed no genotype-specific tetracycline resistance in the tet(M)-positive strains. Conclusions: Catfish fillets and processing environment were currently free of L. monocytogenes resistant to antibiotics commonly used in human listeriosis treatment. However, the presence of tet(M) gene in L. innocua raises the possibility of future acquisition of resistance by L. monocytogenes. Significance and Impact of the Study: These data will be helpful in improving background data on antibiotics resistance strains isolated from food and processing environment.