Fifty-three Listeria monocytogenes isolates obtained from Gorgonzola cheese and previously characterized with biochemical typing, serotyping and pulsed field gel electrophoresis (PFGE), were analyzed in this study. Seven virulence-associated genes were selected (actA, inlC, inlJ, plcA, prfA, hlyA and iap) and their presence was investigated using PCR. All virulence-associated genes were detected in 51 isolates. One isolate did not show amplification of the inlC gene and one other isolate, previously mis-identified as L. monocytogenes probably due to atypical phenotypes, resulted negative by PCR for all virulence genes and was identified as Listeria innocua by 16. S rRNA gene sequencing analysis. A multiplex PCR assay was used to evaluate the presence of markers specific for epidemic clones (ECs) of L. monocytogenes. The marker specific for the recently identified epidemic clone V (ECV) was detected in 38 of 43 (88%) of serotype 1/2a isolates. These findings suggest that Gorgonzola cheese can represent a significant source of L. monocytogenes and potential health risk for listeriosis as almost all isolates (94%) could be potentially virulent and that 38 (~. 72%) were presumptive positive ECV. PCR screening for both virulence-associated genes and EC markers may be useful for rapidly evaluating the epidemic potential and public health risk posed by L. monocytogenes in PDO Gorgonzola cheese and other dairy products.
All Science Journal Classification (ASJC) codes
- Food Science