A bi-modal transfer of antibiotic resistance by conjugation and transduction from an imipenem-resistant strain of Pseudomonas aeruginosa.

A strain of Pseudomonas aeruginosa No. 76/17224 resistant to carbenicillin (CAR), kanamycin (KAN), cefalotin (CLO), cefotaxime (CTX), ceftazidime (CAZ), aztreonam (AZA), imipenem (IMI) and ofloxacin (OFL) was isolated at the Frankfurt University Hospital. This strain transferred, by conjugation, antibiotic resistance determinants to CAR, CLO, CTX, CAZ and AZA. In addition, we isolated a wild-type phage from this strain. We used this phage to transduce the resistance determinants to four susceptible recipient strains of P. aeruginosa. The phage designated AP-76 transduced the resistance determinants to KAN, CAR, CTX and CAZ to all four recipient strains. Imipenem and aztreonam resistance determinants were directly transduced to two recipient strains only, i.e. to PAO-1670 and ML-1008. The IMI resistance determinant was not co-transduced with any other resistance determinant(s) selected directly. Our results indicated that IMI resistance determinant was not associated with other resistance determinants. IMI was actively hydrolysed by IMI-resistant transductants and this hydrolysis was inhibited by clavulanate but not by EDTA.