Occurrence and Molecular Characterization of Multidrug-Resistant Vegetable-Borne Listeria monocytogenes Isolates

Fresh vegetables play a significant role in the human diet. However, ready-to-eat (RTE) vegetables have been associated with increasing foodborne outbreaks including L. monocytogenes, which is a common human pathogen associated with foodborne infections resulting in listeriosis. This study aims to assess the resistance of vegetable-borne L. monocytogenes to antibiotics. L. monocytogenes was isolated and molecularly characterized using polymerase chain reaction (PCR) from 17 RTE vegetable samples. The confirmed L. monocytogenes was further assessed for phenotypic and genotypic antibiotic resistance using the disc diffusion test and PCR primers targeting six antibiotic classes and thirty-one related antibiotic resistance genes (ARGs), respectively. The results revealed that Listeria counts ranged from 1.60 to 3.44 log₁₀ CFU/g in the samples. The isolates exhibited high resistance against penicillin G, erythromycin, vancomycin, tetracycline, trimethoprim-sulfamethoxazole, and nitrofurantoin among the 108 isolates tested. A total of 71 multiple antibiotic resistance (MAR) phenotypes were observed in the isolates, which ranged from resistance to 3 to 13 antibiotics. The MAR index was ˃0.2 in 97% of the isolates. Some of the highly detected ARG subtypes included SulI (100%), TEM (76.9%), tetA (59%), and tetM (54.7%). The findings show a high occurrence of multidrug-resistant L. monocytogenes and clinical ARGs in fresh vegetables, which constitutes an immediate danger for the health security of the public.