Evaluation of a restriction fragment length polymorphism typing method for Listeria monocytogenes

The results of an evaluation of restriction fragment length polymorphism (RFLP) typing for Listeria monocytogenes are presented. The method depends on the use of cloned DNA fragments from an L. monocytogenes (serovar 4b) strain to probe Southern blotted NciI restriction fragments derived from L. monocytogenes strains. Analyses of 862 isolates of serogroups 1/2, 3 and 4 were performed and a total of 32 RFLP patterns were observed. Interstrain RFLPs were common within serogroup 1/2 and the numerical index of discriminatory power for this group was 0.883. Serogroup 4 strains were divided into two major and three minor RFLP types, suggesting a high level of genotypic homogeneity, and the numerical index of discriminatory power was correspondingly low. The technique was found to be highly reproducible, and the stability of patterns was demonstrated by analyses of passaged strains and multiple isolates of the same strain from related specimens. RFLP typing is of value in epidemiological investigations involving strains of serogroup 1/2.