Spread of multiresistant strains of Salmonella typhimurium phage types 204 and 193 in Britain.

Spread of multiresistant strains of Salmonella typhimurium phage types 204 and 193 in Britain Since June 1977 two phage types of Salmonella typhimurium, both showing multiple drug resistance, have caused many infections in bovines and humans throughout Britain. The phage types are type 204, with resistance to chloramphenicol, streptomycin, sulphonamides, and tetracyclines (R-type CSSuT), and type 193, with resistance to ampicillin, chloramphenicol, neomycin-kanamycin, streptomycin, sulphonamides, and tetracyclines (R-type ACKSSuT). The CSSuT-resistant type 204 strain first appeared in calves in June 1977 and has subsequently caused infections in cattle in many areas of Britain.' Symptoms were of severe scouring and there was a high mortality rate among infected animals. There have been 56 human isolations of type 204 of R-type CSSuT, mostly from cases of mild enteritis. Some cases were in families in farming communities, but many had no obvious connection with farms. The strain has also been isolated from minced beef prepared for human consumption. In December 1977 strains of S typhimurium phage type 193 of R-type ACKSSuT affected calves on farms in Herefordshire and Worcestershire. Subsequently, infections occurred in bovines in many areas of England, Wales, and Scotland, and the transport of infected animals facilitated this spread. Human infections first occurred in December 1977, and by the end of June 1978 there had been 44 isolations of multiresistant type 193 strains. As with type 204, some infections occurred in farming families, but most had no direct connection with bovines. So far, there have been no isolations from milk or human foods. Characterisation of the resistance plasmids in the type 193 strains from both bovine and human sources showed that these strains had an identical plasmid content and represented a single clone. This had been derived from the epidemic phage type 204 strain of R-type CSSuT by the acquisition of an R factor of compatibility group I,, coding for resistance to ampicillin, kanamycin, and streptomycin (AKS). This plasmid inhibits the lysis of strains of S typhimuriwn by several typing phages. When the AKS-group I, plasmid is displaced from the multiresistant strains of phage type 193, the resultant lines belong to phage type 204 of S typhinmiriwm, and have the CSSuT R-type and plasmid content of the epidemic strain. Earlier studies showed that the CSSuT-resistant type 204 strain was derived from a strain of phage type 204 of R-type SuT, by the acquisition of an R factor of compatibility group H2, …