The prevalence of Listeria monocytogenes in the environment of dairy farms.

The prevalence of Listeria monocytogenes in the environment of dairy farms was surveyed from December 1993 to June 1994 in one city of Hokkaido. L. monocytogenes was isolated from 3 out of 5 farms investigated. Serovar 4b organism was isolated from the brain stem of a cow from one farm which was clinically diagnosed as having listeriosis. The same serovar of L. monocytogenes was also isolated from the rectal contents of a healthy cow, straw on the floor, straw in the barn, and silage scattered around the silo from the same farm. At another farm, with no reported cases of bovine listeriosis, serovar 1/2 organism was isolated from the same types of samples as the above mentioned farm except from straw on the floor. The difference in the isolation rates of the organism from straw on the floor between the two farms (22%:5/23 vs 0%:0/24) is considered to be caused by the different feeding methods of silage between the two farms.