Isolation and identification of cheese-smear bacteria inhibitory to Listeria spp.

A newly developed hydrophobic grid membrane method was used to rapidly screen 105 traditional French cheeses for surface smear microorganisms inhibitory to Listeria monocytogenes strain V7. Approximately 125,000 colonies comprising a wide variety of bacteria were examined of which less than 0.1% produced visible zones of inhibition. Isolates possessing antilisterial activity consisted of various strains of Enterococcus faecalis, Staphylococcus xylosus, Staphylococcus warneri and coryneform bacteria, including one orange coryneform resembling Brevibacterium linens. All strains of E. faecalis and the orange coryneform that inhibited L. monocytogenes V7 exhibited strong inhibition against a panel of 21 Listeria strains comprised of L. monocytogenes (14 strains), L. innocua (two strains), L. ivanovii (two strains), L. seeligeri (two strains) and L. welshimeri (one strain). The remaining cheese isolates showed moderate to weak inhibition towards the same set of Listeria strains. Inhibitory substances produced by all strains except the orange coryneform were sensitive to one or more of five proteolytic enzymes tested and were therefore classified as bacteriocin-like inhibitory agents.