Characterization of antimicrobial resistance of foodborne Listeria monocytogenes

The objective of this study was to evaluate the susceptibility of 120 Listeria monocytogenes strains isolatedfrom food and food-processing environments to 19 antibiotics currently used in veterinary and humantherapy. Susceptibility tests were performed by using the automated VITEK2 system. Apart from penicillin,ampicillin and trimethoprim–sulfamethoxazole, for which clinical breakpoints for Listeria susceptibilitytesting are defined according to the Clinical and Laboratory Standard Institute (CLSI), in the present study theCLSI criteria for staphylococci were applied. Among the 120 tested strains, 14 (11.7%) displayed resistance toat least one antibiotic. In particular, resistance to one antibiotic was more common than multiple resistance,i.e., 10 (8.3%) isolates were resistant to one antibiotic, 3 (2.5%) to two antibiotics and one (0.8%) to fiveantibiotics. Resistance to clindamycin was the most common, followed by linezolid, ciprofloxacin, ampicillinand rifampicin, trimethoprim/sulphamethoxazole and, finally, vancomycin and tetracycline.This study shows that L. monocytogenes strains from food and food-processing environments are susceptible tothe antibiotics commonly used in veterinary and human listeriosis treatment. Considering that L. monocytogenesis slowly becoming antibiotic resistant, a continued surveillance of emerging antimicrobial resistance of thispathogen is important to ensure effective treatment of human listeriosis. These data are useful in improvingbackground data on antibiotic resistance of strains isolated from food and food environment.[...]