Identification and enumeration of beta-hemolytic Listeria monocytogenes in naturally contaminated dairy products.
A DNA probe was used to identify hemolytic Listeria monocytogenes in naturally contaminated dairy products: unpasteurized milk, ricotta cheese, and imported semisoft cheeses. Of 34 milk samples, 12 were suspected to contain hemolytic L. monocytogenes; 1 contained greater than 6000 viable organisms/g. The ricotta cheese, although temperature-abused, had a titer of 3.6 x 10(6) beta-hemolytic L. monocytogenes cells/g, whereas the semisoft cheeses reached a maximum of 5.6 x 10(6) cells/g. Pure cultures of L. monocytogenes isolated from both types of cheese were found positive by the CAMP test and the DNA probe.
D000818:Animals; D002611:Cheese; D004269:DNA, Bacterial / Q000302:isolation & purification*; D003611:Dairy Products; D006461:Hemolysis; D008089:Listeria monocytogenes / Q000032:analysis*; D008892:Milk
D004269:DNA, Bacterial