[Plasmids of antibiotic-resistant strains of Shigella isolated in Leningrad and Leningrad region].

Sensitivity of 232 strains of Shigella spp. isolated in Leningrad and the Leningrad Region in 1984-1989 (193 strains of S. sonnei and 39 strains of S. flexneri) was tested by the method of serial dilutions with respect to 14 antibacterial drugs. 94 per cent of the isolates were resistant to 2 and more antibiotics, strains resistant to streptomycin and tetracycline being the most frequent, i.e. 94 and 91.8 per cent respectively. Among the 6 antibiotic resistance spectra detected, 2 predominated, i.e. TcSm and ApCbCmTcSm resistance spectra (47.2 and 39.9 per cent of the resistant strains respectively). The drug resistance in 49.5 per cent of the resistant strains was determined by conjugative R plasmids. Five types of conjugative R plasmids were revealed. They mainly contained genes determining resistance to streptomycin (100 per cent), ampicillin (97 per cent), carbenicillin (97 per cent), tetracycline (96 per cent) and chloramphenicol (90.1 per cent). The conjugative plasmid type with the molecular weight of 64 mD carrying the genes of resistance to ampicillin, carbenicillin, chloramphenicol, tetracycline and streptomycin was the most frequent in the Shigella isolates.