R plasmids conferring multiple drug resistance from shigella isolated in Korea

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Abstract
SUMMARY: The majority (85%) of shigella isolated in 1980 and 1981 in Korea wereShigella flexneri, the others wereSh. sonnei(14%) with only a small number ofSh. dysenteriae. Only 14 of the 459 strains of shigella isolated were susceptible to all 12 drugs tested, and 445 were resistant to three or more drugs. Strains multiply resistant to the six drugs, chloramphenicol (Cm), tetracycline (Tc), streptomycin (Sm), sulfisomidine (Su), ampicillin (Ap) and trimethoprim (Tp) were most frequently encountered, followed by those resistant to Cm, Tc, Sm, Su and Tp. The complete patterns of resistance to drugs except nalidixic acid and rifampin in approximately 73% of drug-resistant strains were co-transferred toEscherichia coliby conjugation, indicating that the resistance was R plasmid-mediated. Randomly selected R plasmids conferring various patterns of resistance markers were tested for the incompatibility groups, and almost all of them were classified intoIncFII. Two of three R plasmids conferring resistance to Cm, Tc, Sm and Su were classified intoIncB and one toIncFII. Two R types with resistance markers of Cm, Tc, Sm and Ap were not classified with our standard plasmids used.