Development of an ELISA specific for Listeria monocytogenes using a polyclonal antibody raised against a cell extract containing internalin B

We have developed a new enzyme-linked immunosorbent assay ( ELISA) that is specific to the foodborne pathogenic micro-organism Listeria monocytogenes. It is based on an antibody raised against an L. monocytogenes cell preparation optimized for extraction of internalin B. Only in a sandwich ELISA format was the protein A-purified antibody specific to L. monocytogenes. In a competitive ELISA format, the antibody recognizes other Listeria species. The sandwich ELISA shows no recognition of L. innocua, L. ivanovii, L. welshimeri, L. seeligeri, or L. grayii. It has a minimum detectable level for L. monocytogenes of log(10) 6.37 cfu ml(-1) in pure culture, is reproducible, and is unaffected by the presence of high numbers ( approximately log(10) 8.0 cfu ml(-1)) of the other Listeria species. Possible reasons for the format-dependent specificity are discussed. When the ELISA was applied to milk samples inoculated with L. monocytogenes reference material ( 5 cfu ml(-1)), there was a strong response to the enrichment cultures. The new assay may prove useful in detection of L. monocytogenes in enrichment cultures of food samples.