abstract
A total of 336 Listeria isolates from ready-to-eat (RTE) meat products and meat-processing environments,
consisting of 206 Listeria monocytogenes, and 130 Listeria innocua isolates, were characterized by disc
diffusion assay and minimum inhibitory concentration (MIC) values for antimicrobial susceptibility
against twenty antimicrobials. Resistance to one or two antimicrobials was observed in 71 L. monocytogenes
isolates (34.5%), and 56 L. innocua isolates (43.1%). Multidrug resistance was identified in 24
Listeria isolates, 18 belonging to L. innocua (13.9%) and 6 to L. monocytogenes (2.9%). Oxacillin resistance
was the most common resistance phenotype and was identified in 100% Listeria isolates. A medium
prevalence of resistance to clindamycin (39.3% isolates) and low incidence of resistance to tetracycline
(3.9% isolates) were also detected. Listeria isolates from RTE meat products displayed higher overall
antimicrobial resistance (31.3%) than those from the environment (13.4%). All the strains assayed were
sensitive to the preferred antibiotics used to treat listeriosis. Results showed that although antimicrobial
resistance in L. monocytogenes still occurs at a low prevalence, L. innocua can form a reservoir of resistance
genes which may transfer between bacterial species, including transference to organisms capable
of causing disease in humans.