Comparison of Procedures for Isolating Listeria monocytogenes in Soft, Surface-Ripened Cheese.

Ninety samples of soft, surface-ripened cheese from a lot previously identified to contain Listeria were assayed for Listeria monocytogenes by three procedures. These included: (a) cold enrichment, (b) the Food and Drug Administration enrichment procedure, and (c) the selective enrichment procedure of Doyle and Schoeni (Appl. Environ. Microbiol. 15:1127, 1986). L. monocytogenes was isolated from 41 of the 90 cheese samples. The organism was isolated from only 9 of the 41 L. monocytogenes -positive samples by more than one procedure. Most isolations (21) were made by the cold enrichment procedure, with 16 and 13 isolations made by the FDA and Doyle-Schoeni procedures, respectively. In most instances, the organism was isolated from a cheese sample by only one procedure.