Demonstration of R factors from Pseudomonas aeruginosa.

Sixty strains of Pseudomonas aeruginosa were selected from our clinical stock cultures and used as donors of drug resistance to examine the presence of R factors. They were highly resistant to one or more of six drugs including tetracycline (TC), chloramphenicol (CM), streptomycin (SM), sulfanilamide (SA), carbenicillin (CPC), and kanamycin (KM). Three FP(-), auxotrophic mutants of P. aeruginosa were used as recipients, which had been made resistant to either rifampin (RMP) or KM by in vitro mutation. Each donor was mated with each of the three recipients, and 45 strains were found to transfer their resistance to one or more recipients. A second series of conjugation experiments using 45 exconjugants as donors showed that 23 could transfer their resistance. We conclude that these strains carry R factors that are transmissible to one or more recipients. Eleven carried resistance to (TC.CM.SM.SA.CPC), nine to (TC.CM.SM.SA), one to (TC.CM.SA.CPC), one to (TC.CM.SA), and one to (SM). All of these R factors could not be transmitted to other species belonging to the family Enterobacteriaceae.