Transfer of Gentamicin Resistance from Pseudomonas aeruginosa Strains Highly Resistant to Gentamicin and Carbenicillin

Abstract

Bi-resistance to high concentrations of gentamicin and carbenicillin began to appear in strains of Pseudomonas aeruginosa from the urine of patients in several clinics and stations of our area. Nine out of 142 ‘urine strains’ of Ps. aeruginosa isolated from July to November 1971 are highly resistant to the above-mentioned antibiotics and also to others. Four additional strains appeared to be highly resistant to carbenicillin only, retaining their relative susceptibility to gentamicin. Transfer of both G^R and Ca^R determinants to E. coli K₁₂ recipient strains, however, did not take place. Thus, rifampicin-resistant high-level mutants of four G^SCa^S wild type strains of Ps. aeruginosa were obtained and used as recipients for both G^R and Ca^R determinants. Three bi-resistant G^RCa^R strains (No. 138, 140 and 110) transferred G^R determinants to individual Ri^R recipients, but none transferred Ca^R. The transfer was inter-strain specific and no general recipient mutant was so far obtained.