INSERTION-SEQUENCE IS200 CAN DIFFERENTIATE DRUG-RESISTANT AND DRUG-SENSITIVE SALMONELLA-TYPHI OF VI-PHAGE TYPE-E1 AND TYPE-M1

The type strains of Vi-phage types E1, M1 and A of Salmonella typhi, t ogether with drug-resistant and drug-sensitive strains of phage types E1 and M1 isolated in 1992 from patients associated with India or Paki stan, and a drug-resistant strain of phage type A isolated in South Af rica in 199 1, were characterised with respect to the presence of plas mids conferring resistance to antimicrobial drugs and their chromosoma l insertion sequence IS200 profiles. The three type strains, the drug- sensitive strains of Vi-phage types E1 and M1, and a strain of phage t ype M1 resistant to ampicillin and trimethoprim but not to chloramphen icol, did not contain plasmids. In contrast, for strains of phage type s E1 and M1 resistant to chloramphenicol, ampicillin and trimethoprim, and for the drug-resistant strain of phage type A, the complete spect rum of resistance was encoded by high molecular mass plasmids belongin g to the H-1 incompatibility group. Characterisation of IS200 profiles demonstrated that at least 13 IS200 copies were distributed on the ch romosome of all strains tested. Although the IS200 profiles of the typ e strains of Vi-phage types A, E1 and M1 were identical, it was possib le to distinguish between drug-sensitive and drug-resistant strains of Vi-phage types E1 and M1 isolated from patients infected in India and Pakistan by this method. It was concluded that although IS200 typing is not as discriminatory as phage typing for the primary subdivision o f S. typhi, it may be useful for certain epidemiological investigation s and, in particular, for investigating the origins of strains with mu ltiple drug resistance.