[Spread and transfer of plasmid resistance in Escherichia coli].

Drug resistance of 186 E. coli strains isolated in 1977-1978 from patients and carriers, as well as from the environment was studied with respect to 8 widely used antimicrobial drugs, i.e. tetracycline, streptomycin, chloramphenicol, ampicillin, neomycin, kanamycin, nalidixic acid and sulfanilamides. All of the strains were resistant to sulfanilamides, 39% of the strains were resistant to at least one antibiotic and 5.2% of the strains were resistant to nalidixic acid. Multiple resistance was observed in 60% of the isolates. II variants of various combinations of r-determinants were found. Strains resistant to 2 or 3 antibiotics and combinations of tetracycline + streptomycin and tetracycline + kanamycin + neomycin were most frequent. The number of the antibiotic resistant strains isolated from the humans and environment was 40.5 and 36.8% respectively. The multiple resistance spectra of the strains isolated from the humans were more variable. No transmissive r-determinants were found in the strains resistant to one antibiotic. However 85% of polyresistant E. coli carried conjugative R plasmids. Transmission of the determinants of resistance to ampicillin (90%), streptomycin (80%), chloramphenicol (71.4%), neomycin and kanamycin (55.5%) was most frequent, while the determinants of resistance to tetracycline (37%) were least frequent. The frequency of transmissive R plasmids in the strains isolated from the humans was higher than that in the strains isolated from the environment. It was shown that most of the conjugative plasmids were of fi- character.