Distribution of R Factors among Shigella Strains Isolated in Japan (II)

Abstract

ABSTRACTShigella strains isolated in Japan from 1968 through 1970 were surveyed for drug resistance and distribution of R factors. Of the 2688 strains, 93.4% were resistant to either one or various combinations of four drugs, tetracycline (TC), chloramphenicol (CM), streptomycin (SM) and sulfanilamide (SA). Among these resistant strains, 74.2, 10.7, 1.48, and 13.6% were quadruply, triply, doubly, and singly resistant, respectively. Fifty‐eight per cent of these resistant strains were found to carry R factors when judged by transferability of the resistance. The isolation frequencies of R (TC. CM. SM. SA), R (CM. SM. SA), R (SM. SA), and R (TC. SM. SA) factors were 73.2, 13.0, 11.5, and 1.3%, respectively. The strains resistant to drugs other than the aforementioned four were very few; 4.3, 3.4, and 0.7% being resistant to ampicillin (APC), nalidixic acid (NA), and kanamycin (KM), respectively. Among 117 APC‐resistant strains, 97.4% could transfer their APC resistance together with other resistance markers. Seventeen out of 18 KM‐resistant strains could transfer KM resistance by mixed culture. But none of the NA‐resistant strains could transfer their NA resistance. The authors could demonstrate strains carrying two different R factors in a cell and one of them was consistently an R (SM. SA) factor. These results were very similar to those obtained in surveys of strains isolated from 1965 through 1967.