Epidemiological application of differentiating multiresistant Salmonella typhimurium DT104 by plasmid profile.

Human isolates of multiresistant Salmonella typhimurium definitive phage type (DT) 104 in England and Wales are currently second in number only to those of S. enteritidis phage type 4. Differentiation of strains is essential in epidemiological investigations and the value of one method, plasmid profile typing, has been assessed in a study of 600 isolates of S. typhimurium DT 104 with multiresistant antibiograms (R-types) ACSSuT, ACSSuTCp and ACSSuTTm from humans, food animals, human food, pets, and animal feed made in England and Wales from January 1990 to April 1996. Twenty plasmid profile (PP) types have been identified in isolates of R-type ACSSuT and ACSSuTCp. One profile type, with a single plasmid of 60 megadaltons-PP type A-has predominated, but identification of PP type has proved useful in some epidemiological investigations. A further four PP types have been identified in isolates of DT 104 R-type ACSSuTTm, in which resistance to trimethoprim is encoded by a plasmid of 4.6 megadaltons and the two commonest PP types are related to those also common in DT 104 R-type ACSSuT. Methods of differentiating within the commonest profile type are now needed.