Characterization and Mobilization of Nonconjugative Plasmids Encoding Resistance to Streptomycin and Sulfanilamide

Abstract

Most of nonconjugative streptomycin (Sm)- and sulfanilamide (Su)-resistance of clinical isolates belonging to various species of Enterobacteriaceae and Pseudomonas were encoded by an Inc Q plasmid, molecular size of which was 5.5Md. The SmSu plasmids were efficiently mobilized by Inc P plasmids between E. coli strains. Inc I group and Inc F group plasmids could mobilize the Inc Q plasmids at lower efficiencies. The Inc Q plasmid was also mobilized to various species of Enterobacteriaceae at high frequencies without accompanying the conjugative Inc P plasmid; as a result, most of the SmSu-resistant transconjugants were nontransferable. The above results may explain the wide distribution of nonconjugative SmSu strains among clinical isolates.