Differentiation of Salmonella typhimurium DT204c by plasmid profile and biotyping.

Seventy per cent of the United Kingdom isolates of Salmonella typhimurium from calves are phage type 204c and the study of the epidemiology of this organism requires additional methods of strain characterisation. This paper describes the applications of biotyping and plasmid-profile analysis for this purpose. One hundred and eleven isolates from 73 outbreaks of disease were examined. All belonged to the same primary biotype, although strains from 39 of the outbreaks differed in secondary tests in failing to ferment m-inositol at 25 degrees C. Four different antibiotic resistance patterns were detected among the isolates, which possessed seven distinct plasmid profiles. The spread of a distinct type through the calf marketing chain was investigated by using these techniques.