The homologous and heterologous regions within the iap gene allow genus- and species-specific identification of Listeria spp. by polymerase chain reaction.

The iap gene of Listeria species encodes protein p60. The comparison of iap-related genes from different Listeria species indicated common and variable regions within these genes which appeared to be specific for each Listeria species. On the basis of the iap gene sequences, pairs of polymerase chain reaction (PCR) primers which allowed the unambiguous identification of all members of the genus Listeria, of groups of related Listeria species, and of L. monocytogenes, exclusively, were selected. The PCR primers specific for L. monocytogenes yielded PCR products which represented essentially the repeat region of the iap gene. The size of these PCR products allowed an estimate of the number of the TN repeat units within the repeat region of the p60 protein of an L. monocytogenes strain. The data indicated that the number of repeat units differed among L. monocytogenes isolates.