Diversity of determinants encoding carbenicillin, gentamicin, and tobramycin resistance in nosocomial Pseudomonas aeruginosa.

Plasmid pFMH1010, an 89-megadalton R plasmid, is endemic among members of the family Enterobacteriaceae at Hines Veterans Administration Hospital, Hines, Ill. It encodes resistance to nine antibiotics, including resistance to carbenicillin (Cb), gentamicin (Gm), and tobramycin (Tm). Pseudomonas aeruginosa strains resistant to carbenicillin, gentamicin, and tobramycin were isolated from five patients at Hines Veterans Administration Hospital from whom Serratia marcescens strains harboring pFMH1010 were also obtained. The P. aeruginosa strains were investigated to determine whether their Cb, Gm, and Tm characteristics derived from pFMH1010. One of the isolates, Ps559, was shown by Southern hybridization to contain approximately 76% of pFMH1010. Several lines of evidence suggested that the pFMH1010 sequences in Ps559 are integrated in the chromosome. Southern hybridization also demonstrated that the beta-lactam resistance of pFMH1010 is most probably due to the presence of sequences homologous with Tn3 and that these sequences are retained in Ps559. In two other Pseudomonas isolates, resistance to carbenicillin, gentamicin, tobramycin, and kanamycin was encoded by R plasmids unrelated to pFMH1010. In the last two isolates, resistance to gentamicin and tobramycin and several other antibiotics appeared to be chromosomally encoded, and it was rescuable from one of these strains by RP4-mediated mobilization.