In vivoR–plasmid transfer in a patient with a mixed infection of shigella dysentery

Abstract

SUMMARYTransfer of shigella R–plasmidsin vivohas seldom been demonstrated. Strains ofShigella dysenteriaetype 1 andShigella flexneritype 5b were isolated from a Bulgarian traveller who visited Vietnam and developed dysentery, which was treated with trimethoprim/sulfamethoxazole (TMP/SMZ) for a short time. Both species of shigellae are unusual in Bulgaria where strains ofS. sonneipredominate. Both shigella strains were multiresistant to the same antimicrobial agents. Each strain contained a 48–kilobase plasmid that conferred the entire resistance phenotype to a susceptibleEscherichia coli. Restriction endonuclease patterns of plasmid DNA from the respective strains were identical. Transmissible plasmids of the same resistance phenotypes and restriction patterns were isolated from the patient's colonicE. coli. Transconjugants hybridized to a dihydrofolate reductase type I–DNA probe. These studies support the hypothesis that R–plasmid transfer may occur between non-pathogenic, faecal strains and pathogenic shigellae, a process that may have been facilitated by inadequate treatment with TMP/SMZ at the onset of the illness.