Virulence and Antimicrobial Resistance of Listeria monocytogenes Isolated from Ready-to-Eat Food Products in Romania

Abstract

<i>Listeria monocytogenes</i> (<i>L. monocytogenes</i>) poses a significant threat to food safety due to its ability to cause severe human illness and its resistance to various antibiotics and environmental conditions. This study investigated the prevalence, serotype distribution, virulence gene profiles, and antimicrobial resistance patterns of <i>L. monocytogenes</i> in ready-to-eat (RTE) food products from Romania. A total of 8151 samples were analyzed, including various processed dairy, bovine, poultry, pork, and fish products. Bacterial isolation was conducted using the classical standard method, followed by confirmation through biochemical and molecular testing. Among the isolated strains, serotypes 1/2a, 1/2b, and 1/2c were identified, with a prevalence of 75% for serotype 1/2a. Additionally, virulence genes specific to listeriolysin O (<i>hly</i>A) and regulatory factor A (<i>prf</i>A) were detected in all isolates. Antimicrobial susceptibility testing revealed varying resistance patterns among the <i>L. monocytogenes</i> strains. Trimethoprim-sulfamethoxazole and oxacillin showed the highest prevalence of resistance at 26.92% and 23.07%, respectively. However, all strains remained susceptible to ciprofloxacin, levofloxacin, and moxifloxacin. Notably, 23.07% of the isolates exhibited multidrug resistance, with the most common pattern being resistance to oxacillin, penicillin, and tetracycline. Analysis of antimicrobial resistance genes identified tetracycline resistance genes, particularly <i>tet</i>(C), <i>tet</i>(M), and <i>tet</i>(K), in a significant proportion of isolates. The presence of <i>amp</i>C and <i>dfr</i>D genes was also notable, indicating potential mechanisms of resistance. These results emphasize the necessity for ongoing surveillance of <i>L. monocytogenes</i> in RTE foods and emphasize the importance of thorough monitoring of antimicrobial resistance to guide public health strategies within the European Union.