AN APPARENT BENZOATE-RESISTANT STRAIN OF LISTERIA-MONOCYTOGENES RECOVERED FROM A MILK CLOTTING AGENT OF ANIMAL ORIGIN

A culture of Listeria monocytogenes was isolated from a milk clotting agent of animal origin by direct plating onto McBride Listeria Agar. This isolate was biochemically confirmed as L. monocytogenes and was highly virulent when tested with the mouse assay. The isolate was inactivated after 70 d, rather than 28 d as for other strains, in rennet extract containing 0.1% sodium benzoate. Sodium benzoate at 0.8 to 1.0% in rennet extract inactivated the pathogen after 28-56 d at 7-degrees-C. All test lots of rennet extract, before inoculation, were free of L. monocytogenes (direct plating and cold enrichment for up to 8 weeks).