Characteristics of R plasmids expressed by dysenteric bacteria

: One hundred and eighty-six clinical strains of Enterobacteriaceae isolated in the Krasnodar region and Krasnodar in 1982 from patients with acute intestinal diseases were studied. 137 strains of Shigella were investigated in detail. It was shown that S. flexneri, S. sonnei, S. boydii and S. dysenteriae accounted for 77, 15, 5 and 2 per cent, respectively. 78.1 per cent of the wild Shigella strains were resistant to antibiotics and in 43.9 per cent of the strains this property was controlled by conjugative R plasmids. 11 variants of the antibiotic resistance spectra were revealed. However, strains of SmTcApCm, SmTc and SmTcAp phenotypes were the most frequent. Among the resistant strains 80.3 per cent were resistant to tetracycline, 75.7 per cent to streptomycin, 50.4 per cent to ampicillin, 31.7 per cent to chloramphenicol, 1.8 per cent to trimethoprim, and 0.9 per cent to kanamycin. The investigation showed that the strains isolated in one region usually had similar phenotypes of antibiotic resistance. The frequency of the plasmid transfer varied from 10(-1) to 10(-7). However, the majority of the plasmids were transferred at a frequency of 10(-4)-10(-5). Only one of the investigated plasmids had a capacity for transmitting fd phage sensitivity to the host cells. 33 plasmids belong to the fi+ type and the others belong to the fi- type. The majority of the plasmids have molecular weights of 46 to 50 mD.