Studies on R-plasmid-determined drug resistance in serotypes 792 (E. coli O 28a28c:K73) and 145-46 (E. coli O 164)

The drug resistance of 2368 strains belonging to serotypes 792 (E. coli O 28a28c:K73) and 145-46 (E. coli O 164) was studied. These serotypes were commonly found as causative agents of dysentery-like diseases in Bulgaria. It was established that the percentage of resistant strains of serotype 792 was by factor 2 higher than in serotype 145-46. This finding was connected to the epidemic spread of this serotype in children communities, where the antibiotic therapy is a routine practice. A great diversity was found in the drug resistance types. The tetracycline type ranged first, followed by the chloramphenicol, ampicillin, streptomycin, sulfonamide, tetracycline type. A large part of the resistant strains carried R-plasmids. Fin + R-plasmids, coding for a synthesis of F-specific pili and determining multiple drug resistance, were most frequently found. Some R-plasmids of serotype 792 strains inhibited the growth of several Shigella bacteriophages, whereas R-plasmids of serotype 145-46 did not show any inhibiting activity. It is suggested to use the type of drug resistance and the characteristics of R-plasmids as supplementary epidemiological markers.