Incidence of plasmids in multiply-resistant salmonella isolates from diarrhoeal patients in Hong Kong from 1973–82

Abstract

SUMMARYPlasmids present in multiply-resistant salmonella strains includingSalmonella typhimurium, S. johannesburg, S. wandsworth, S. derby, S. newport, S. londonandS. choleraesuiscausing diarrhoea in patients in Queen Mary Hospital in Hong Kong from 1973–82 were studied. In multiply-resistantS. typhimurium, plasmids belonging to groupsF1me, H1, or H2and plasmids encoding trimethoprim-resistance which were compatible with standard plasmids of testable incompatibility groups were detected. InS. johannesburg, both the ASTCKSu- and ASCKSu- resistant strains which were predominant in two consecutive periods of an outbreak were found to harbour the same plasmid which belonged to the incompatibility group F1me. S. wandsworthstrains isolated from a hospital outbreak in 1980 harboured an identical R-plasmid belonging to group N. A few strains of the other salmonellae showing resistance to multiple antibiotics were found to harbour R-plasmids belonging to groups H1, H2and F1me. The only salmonella of the enteric fever group resistant to ampicillin, chloramphenicol and trimethoprim was anS. paratyphi Bstrain. The resistances were encoded on a plasmid of an unknown incompatibility group. The occurrence and distribution of plasmids in these salmonellae isolated within the 10-year period are discussed.