Transferable tetracycline resistance in Listeria monocytogenes from food in Italy

Mechanisms of tetracycline resistance were investigated in two recent Listeria monocytogenes isolates from food, with L. innocua 52P tetr as a control. Tetracycline resistance was transferred conjugatively from all three strains to L. ivanovii and from one isolate and the control to Enterococcus faecalis. Molecular analysis demonstrated a chromosomal location for the tet determinant, which was identified as tetM in all cases. These studies are the first to show that L. monocytogenes from food could be a source of tetracycline resistance genes able to spread to other micro-organisms.