Transferable drug resistance in Pseudomonas aeruginosa

Three strains of Pseudomonas aeruginosa were demonstrated to transfer double-drug resistance by conjugation to a P. aeruginosa recipient at frequencies of 10(-4) to 10(-2) per recipient cell. Two of the three strains also transferred to Escherichia coli at frequencies which were 10(3)- to 10(5)-fold lower, but the third strain could not be demonstrated to do so. The latter strain, however, conferred maleness on the Pseudomonas recipient. The transfer of streptomycin resistance was associated with the acquisition of streptomycin phosphorylase by both P. aeruginosa and E. coli recipients. Maximal broth mating frequencies were obtained with nonagitated cultures less than 1 mm in depth. A pyocine selection system based on donor sensitivity and recipient resistance is described and appears to have future value as a generalized selective device for use after matings.