Detection of genes coding for listeriolysin and Listeria monocytogenes antigen A (ImaA) in Listeria spp. by the polymerase chain reaction.

Two pairs of synthetic oligonucleotide primers were used in a polymerase chain reaction (PCR) protocol to detect targeted sequences in genes coding for listeriolysin O and Listeria monocytogenes antigen A (ImaA). Strains of Listeria spp. used in this study were isolated from clinical specimens, contaminated foods, and environmental sources. Primers were targeted to internal regions of the genes coding for listeriolysin (hlyA) and Listeria antigen (ImaA) and amplification fragments were detected after the PCR by agarose gel electrophoresis. PCR was performed using nucleic acids extracted from a collection of 74 strains of Listeria spp. including 18 reference strains, 41 L. monocytogenes, nine L. innocua, five L. seeligeri and one L. ivanovii, encompassing representative sources, serovars, and enzyme electrophoretic types. Although the listeriolysin gene was found exclusively in L. monocytogenes, some strains of serovar 4c were negative. Simultaneous presence of both genes was restricted to L. monocytogenes strains of serovars 1/2, 3, and 4. The ImaA gene was identified in five of 10 L. innocua strains and one L. ivanovii isolated from pork. Strains of L. seeligeri, L. welshimeri, and L. grayi were negative for both genes. The detection limits in the PCR were found to be 10 pg of nucleic acids for the hlyA gene and 1 pg for the ImaA gene.