Drug Resistance and Distribution of R Factors among Escherichia coli Strains

Abstract

Three hundred and thirty-eight strains of Escherichia coli from clinical sources were examined for their drug resistances and R factors in 1971. With reference to four drugs, i.e., tetracycline(TC), chloramphenicol (CM), streptomycin(SM) and sulfanilamide(SA), the SA-resistant strains were isolated most frequently followed by SM-, TC-and CM-resistant ones in decreasing order. Among those resistant to the aforementioned four drugs, 20.3, 19.0, 7.7 and 18.3% were single-, double-, triple-and quadruple-resistant, respectively. The R factors were demonstrated at a frequency of 29.2% among these resistant strains. From the strains possessing quadruple-resistance, the conjugationally transferable R factors were demonstrated most frequently (60.5%) followed by triple-(59.1%), double-(21.7%) and single-resistant strains (4.5%). The isolation frequencies of strains resistant to kanamycin (KM) and ampicillin (APC) were 1.5 and 4.7%, respectively; being fewer in numbers compared with those resistant to the four drugs. Strains resistant to cephaloridine, nalidixic acid, colistin, gentamicin C complex and furatridine were not isolated. Strains resistant to KM and APC were demonstrated mostly from those possessing multiple resistance with reference to the aforementioned four drugs. Among the strains carrying either APC-or KM-resistance, 76.9 and 100% respectively, were found to carry R factors, indicating that most of the APC-and KM-resistances were conferred by the R factors. Twenty percent of the R+ strains with reference to resistance to the four drugs carried two types of R factors in a cell, being in a hetero-R state, and 66.7% of the strains carrying R factors with APC-or KM-resistance were in a hetero-R state.Epidemiological surveys of drug-resistant strains isolated from clinical specimens indicated that Escherichia coli strains were isolated most frequently (45.5%), followed by Pseudomonas (26.4%), Proteus (13.2%), Klebsiella (10.9%) and others (4.0%) [5,9]. The occurrence of drug-resistant E. coli strains is serious in medical practice owing to their resistance to chemotherapy and as potential donors of their R factors to other enteric bacteria. This report deals with a survey of drug resistance of E. coli strains and their R factors. MATERIALS AND METHODSBacterial strains. Three hundred and thirty-eight strains of Escherichia coli were all isolated from clinical specimens, at the Hospital, School of Medicine, Chiba University and Niigata Prefectural Institute of Health in 1971, purified and stored in cooked meat medium. A substrain of E. coli K12 ML 1410 (met-nalr F-) (nalr : resistance to nalidixic acid) was used as the first recipient of the R factor. To confirm the transmissibility and resistance patterns of the R factors, E. coli K12 W3630 (mal-F-) was used as the second recipient of the R factor from ML1410 R+.

Gentic properties of an R factor carrying resistance to aminolgycoside antibiotics

“…The Rmsl51 factor is an fi+ R factor and belongs to the incompatibility group FII and this type of R factor is isolated frequently from bacterial strains which belong to the family Enterobacteriaceae. The R factors carrying TC.CM.SM.SA, CM.SM.SA, TC.SM.SA, and SM.SA resistance are isolated frequently and the genes governing SM resistance are commonly located on R factors (14,17). Rmsl51, however, does not possess SM resistance but confers resistance to other aminoglycoside antibiotics and APC resistance, although this factor is phylogenetically related to fi+ R100 (TC.CM.SM.SA) of the FII incompatibility group.…”

“…According to the type of segregation among the genes governing tra and drug resistance, we proposed a genetic map of Rmsl51. It is phylogenetically interesting to note that the order of genes on Rmsl51, i.e., -tet.tra-, -cml.tet.tra-, -tet.tra.amp-, is common to many R factors (4,6), and that the isolation frequency of R factors carrying single CM resistance or resistance to only aminoglycoside antibiotics is rather low (14,17).…”