DNA FRAGMENTS FROM REGIONS INVOLVED IN SURFACE-ANTIGEN EXPRESSION SPECIFICALLY IDENTIFY LISTERIA-MONOCYTOGENES SEROVAR-4 AND A SUBSET THEREOF - CLUSTER IIB (SEROTYPES 4B, 4D, AND 4E)

Listeria monocytogenes serotype 4b has frequently been implicated in s poradic as well as epidemic listeriosis, On the basis of pulsed-field fingerprinting, serotype 4b strains, along with strains of serotypes 4 d and 4e, constitute one genomic cluster (IIB), We have identified two genomic regions essential for the expression of surface antigens whic h previously were shown to be specific to cluster IIB strains, A DNA p robe of 1.1 kb derived from one of the regions (probe 1) hybridized on ly with strains of serotypes 4b, 4d, and 4e in Southern blots and dot blots, A different DNA probe of 0.3 kb (probe 2), derived from the oth er region, hybridized with all serovar 4 strains (serotypes 4b, 4a, 4c , 4d, and 4e). All other L. monocytogenes serotypes were negative with probe 1 or 2. Use of probe 1 in Southern blots of EcoRI-digested geno mic DNA revealed a restriction fragment length polymorphism in serotyp e 4b strains, with the hybridizing EcoRI fragments being 4.5 kb (strai ns of the epidemic clone) and either 4.5 or 5.0 kb (all other serotype 4b strains), Although the probes hybridized with a special group of l isteria innocua strains which also expressed the surface antigens, the latter could be readily distinguished by the size of the hybridizing EcoRI fragment with probe 1 (ca, 2.2 kb). These data suggest that the combined use of these probes with L. monocytogenes can readily and spe cifically identify cluster IIB strains as well as the entire serovar 4 complex.