PULSED-FIELD FINGERPRINTING OF LISTERIAE - IDENTIFICATION OF GENOMIC DIVISIONS FOR LISTERIA-MONOCYTOGENES AND THEIR CORRELATION WITH SEROVAR

Clamped homogeneous electric field (CHEF) electrophoresis was optimize d for genomic analyses of Listeria monocytogenes. Various human, anima l, food, and environmental isolates, as well as strains representing o ther Listeria species, were separately digested with rarely cutting en donucleases. Of 176 L. monocytogenes strains analyzed, the enzymes Asc I and ApaI established 63 and 72 unique restriction endonuclease diges tion profiles (REDP), respectively. The 22 non-L. monocytogenes strain s exhibited 18 AscI and 19 ApaI unique REDP. Statistical analyses of R EDP information using the Dice coincidence index and principal compone nt analysis revealed two distinct genomic divisons of L. monocytogenes that also correlated with the flagellar (H) antigen type: division I contained serovar 1/2a, 1/2c, 3a, and 3c strains, and division II cont ained serovar 1/2b, 3b, 4b, 4d, and 4e strains. Division I isolates di gested with ApaI were further grouped into cluster IA (serovar 1/2c an d 3c) and cluster IB (serovar 1/2a and 3a) strains. Likewise, division Il isolates digested with ApaI were further grouped into cluster IIA (serovar 1/2b and 3b) and cluster IIB (serovar 4b, 4d, and 4e) strains . These data indicate that genotypic data generated by CHEF can be dir ectly related to phenotypic data generated by serotyping for establish ing the overall relatedness of isolates. Moreover, these data further substantiate that CHEF analysis is a reproducible and highly discrimin ating method for characterizing L. monocytogenes strains at the molecu lar level.