Abstract
In Salmonella typhimurium phage type 204c isolated in Britain, gentamicin resistance is specified by plasmids of the I1 compatibility group which also confer resistance to apramycin. These plasmids have been subdivided into three types within the I1 group on the basis of their antibiotic resistance specificity, their ability to produce colicin Ib and their restriction enzyme digest fragmentation patterns. All three have been identified in strains from cattle, but as yet only two types have been found in strains from humans. It is suggested that the use of apramycin in animal husbandry is responsible for the appearance of gentamicin resistance in multiresistant strains of phage type 204c, a phage type already epidemic in bovine animals and with an increasing incidence in humans.