Typing of Listeria monocytogenes for epidemiological studies using DNA probes

We have investigated the possibility of using restriction fragment length polymorphisms (RFLPs) to distinguish different strains of Listeria monocytogenes. Cloned DNA fragments (probes) were selected from a bacteriophage lambda gene library of L. monocytogenes (L1428). DNAs from two lambda clones consisting of a total of approximately 20kb of probe DNA were labelled with biotinylated dUTP for use in these experiments. The criteria for probe selection were the ability both to hybridise with all strains of L. monocytogenes and to reveal RFLPs. Southern blots of restriction endonuclease (Nci I) digested DNAs from test strains of L. monocytogenes were hybridized to the probe. Following washing, biotinylated probe remaining bound to the filters was detected using the Blugene reagents (Gibco/BRL). Under these experimental conditions strain-specific restriction fragments were revealed. We have examined 64 strains of L. monocytogenes belonging to serogroup 1/2 which were not apparently epidemiologically associated and 19 patterns were observed. Epidemiologically related strains gave identical patterns of restriction fragments.