Low-frequency transduction of imipenem resistance and high-frequency transduction of ceftazidime and aztreonam resistance by the bacteriophage AP-151 isolated from a Pseudomonas aeruginosa strain

Bacteriophage AP-151, isolated from a multidrug resistant Pseudomonas aeruginosa strain, was found to transduce antibiotic resistance determinants to recipient strains of P. aeruginosa. Resistance to cefotaxime, ceftazidime, aztreonam, imipenem and meropenem was transduced as a block, at different frequencies, to two P, aeruginosa strains. Resistance was two logarithms higher (in the range 10(-5)) for cefotaxime, ceftazidime or aztreonam than for imipenem in recipient strain PAO-1670. The frequency of transduced imipenem resistance was also lower in recipient strain ML-1008, This phenomenon reflects the difference in the lytic activity of AP-151 in both strains, as the titer of the AP-151 phage in the PAO strain was found to be restricted to 10(-4)-10(-5) in contrast to the titer of the same phage in the ML strain which was 10(-10). The limited lytic activity in the PAO recipient strain was correlated with higher transducing activity. It can be concluded that some wild-type bacteriophages of P, aeruginosa might have highly individual relations between lytic and transducing activity in various potential recipient nosocomial strains of P, aeruginosa, The nature of resistance to ceftazidime and imipenem was studied using clavulanate and EDTA as inhibitors of individual class of beta-lactamases, indicating the presence of extended-spectrum beta-lactamase and a metallo-beta-lactamase in this isolate.