Sequence analysis of the actA gene of Listeria monocytogenes isolated from human

The region encoding proline-rich units of actA genes was amplified from 24 strains of Listeria monocytogenes using polymerase chain reaction (PCR). PCR products of 13 strains showed the expected size of 623 bp, whereas those of 11 strains showed a short size of 518 bp. The shortening of these PCR products resulted from the deletion of one proline-rich unit. These results indicate that ActA proteins are divided into at least two different types which are unrelated to bacterial serotypes.