Identification of Listeria monocytogenes based on the detection of a 68-kilodalton cell-surface antigen

Conventional procedures for the detection of Listeria monocytogenes require selective enrichment and isolation, followed by several potentially lengthy identification steps. To facilitate the identification of the bacterium, polyclonal antibodies against a 68-kDa cell-surface antigen of L. monocytogenes were used to develop a sandwich enzyme-linked immunosorbent assay (ELISA). Of 51 strains of L. monocytogenes tested, 50 (98%) produced positive results using the ELISA method, whereas 17 non-Listeria strains yielded negative reactions. However, the polyclonal antibodies were found to cross-react with L. innocua and some strains of L. welshimeri. Further purification of the antibodies by affinity chromatography was impractical, since the increase in sensitivity was accompanied with decreased specificity. It is proposed that a combination of the ELISA with a single biochemical test, such as phosphoinositol-specific phospholipase C (PI-PLC), arylamidase, or hemolytic activity could differentiate L. monocytogenes (PI-PLC [+], hemolysin [+], arylamidase [-]) from L. innocua and L. welshimeri (PI-PLC [-], hemolysin [-], arylamidase [+]), thus considerably reducing the number of steps required and the length of time necessary for the identification of L. monocytogenes.