Typing of Listeria spp. by random amplified polymorphic DNA (RAPD) analysis.

Random amplified polymorphic DNA (RAPD) analysis, a variation of the polymerase chain reaction (PCR) in which a single primer is used, was evaluated for use as a simple and reliable method with which to type Listeria spp. Representatives of six species of Listeria were studied. Five isolates of L. innocua and four isolates of L. seeligeri were all distinguishable from one another, but the four isolates of L. ivanovii tested, although distinguishable from other Listeria spp., were not differentiated. Among L. monocytogenes serovars 1/2a (eight isolates), 1/2b (eight isolates) and 4b (10 isolates), at least six, three and six RAPD patterns were observed, respectively. Fourteen neonatal cross-infection sets of L. monocytogenes isolates, shown to be indistinguishable by serotyping and phage typing, were examined with three different primers. With one primer, three of the sets were shown to consist of closely related, but distinguishable, strains. In the other 11 cases, each set of strains was indistinguishable with all three primers. These preliminary data indicate that RAPD analysis has promise as a method for typing Listeria spp.