Enzootic occurrence of chloramphenicol-resistant Salmonella typhimurium var copenhagen in calf population.

Chloramphenicol (CP)-resistant Salmonella typhimurium var copenhagen was frequently isolated (44.1 to 76.7%) from dead, diseased, and healthy calves on 3 farms in 1973 in northern Japan. On 2 of the farms, CP-resistant salmonella appeared suddenly during an epizootic of salmonella infection, and persisted. Of 87 CP-resistant to tetracycline (TC), streptomycin (SM), and sulfonamides (SA), and the remaining 13 isolates from dead calves on a farm were resistant to TC, SM, SA, and kanamycin (KM). Resistance patterns of all CP-resistant isolates were transferred completely.