RAPD- and actA gene-typing of Listeria monocytogenes isolates of human listeriosis, the intestinal contents of cows and beef.

Seventy-five L. monocytogenes isolates of human listeriosis, the intestinal contents of cows and beef were divided into 5 major clusters, 17 sub-clusters and 28 minor clusters by typing using random amplification of polymorphic DNA (RAPD). According to their major RAPD category, L. monocytogenes isolates serotyped as 1/2b and 4b were distinguished from L. monocytogenes isolates of serovars 1/2a and 1/2c. Moreover serovar 4b was distinguished from serovar 1/2b by a difference in the RAPD sub-cluster category. All L. monocytogenes were found to possess either actA gene Type I or II, and only one actA gene type was detected in each RAPD minor cluster. actA gene Type II was observed in 32.0%, 38.5% and 18.9% of isolates from humans, cows and beef, respectively, and was detected more frequently in serovar 4b (46.9%) than in serovars 1/2a (22.2%), 1/2b (7.7%) and 1/2c (0.0%). Twenty (80%) of 25 human isolates fell within three minor RAPD types (II-d (16%), V-p-1 (36%), V-p-2 (28%)). Two isolates from humans and beef were found to have the same RAPD type (Type IV-k-1), actA gene type (Type I) and serovar (1/2b). Our results suggest that only a few genotypes of L. monocytogenes are predominant in human listeriosis in Japan, although the human isolates were collected over a broad span of time and a wide geographical range. Our results also suggest that RAPD-, actA gene- and sero-typing can be useful for epidemiological analysis.