Detection of drug susceptibility and resistant genes in selected food borne Listeria monocytogens in China

Objective To understand the drug susceptibility and relationship between antibiotic resistant genes and resistant phenotype in selected food borne Listeria monocytogenes strains in China. Methods The drug susceptibility of 203 food borne Listeria monocytogenes strains was detected by broth micro dilution test as recommended by Clinical and Laboratory Standards Institute. A total of 20 antibiotics, including gentamicin, ampicillin, penicillin, tetracycline, doxycycline, imipenem, erythromycin, ciprofloxacin, levofloxacin, cephalothin, rifampin, vancomycin, chloramphenicol, trimethoprim-sufamethoxazole, ampicillin-sulbactam, norfloxacin, polymyxin B sulfate, nitrofurantoin, clindamycin and cefuroxime, were used in the drug susceptibility test. Polymerase chain reaction(PCR) was conducted to detect 9 resistance genes and transposon Tn916. Results The resistant rates of the food borne Listeria monocytogenes strains to polymyxin B sulfate, nitrofurantoin, cefuroxime, clindamycin, tetracycline, doxycycline, ciprofloxacin, norfloxacin, chloramphenicol were 98.52%,55.66%,50.25%,12.81%,2.46%,1.97%,0.99%,0.99% and 0.49%, respectively. In the 203 food borne Listeria monocytogenes strains, tetM gene was only found in 5 tetracycline-resistant strains,3 of which were positive for Tn916. Conclusion Different levels of antibiotic resistance were detected in the tested food borne Listeria monocytogens, in which 83 strains were multi-drug resistant, demonstrating the risk of causing food borne Listeria monocytogenes infection Therefore, we should enhance the management of antibiotic use, insure food safety and improve public health.