Influence of antipseudomonal agents on Pseudomonas aeruginosa colonization and acquisition of resistance in critically ill medical patients

To assess the role of antipseudomonal agents on Pseudomonas aeruginosa colonization and acquisition of resistance.

Prospective cohort study.

Two medical intensive care units.

346 patients admitted for ≥ 48 h.

Analysis of data from an 8-month study comparing a mixing versus a cycling strategy of antibiotic use.

Surveillance cultures from nares, pharynx, rectum, and respiratory secretions were obtained thrice weekly. Acquisition of resistance was defined as the isolation, after 48 h of ICU stay, of an isolate resistant to a given antibiotic if culture of admission samples were either negative or positive for a susceptible isolate. Emergence of resistance refers to the conversion of a defined pulsotype from susceptible to non-susceptible. Forty-four (13%) patients acquired 52 strains of P. aeruginosa. Administration of piperacillin-tazobactam for ≥ 3 days (OR 2.6, 95% CI 1.09–6.27) and use of amikacin for ≥ 3 days (OR 2.6, 95% CI 1.04–6.7) were positively associated with acquisition of P. aeruginosa, whereas use of quinolones (OR 0.27, 95% CI 0.1–0.7) and antipseudomonal cephalosporins (OR 0.27, 95% CI 0.08–0.9) was protective. Exposure to quinolones and cephalosporins was not associated with the acquisition of resistance, whereas it was linked with usage of all other agents. Neither quinolones nor cephalosporins were a major determinant on the emergence of resistance to themselves, as resistance to these antibiotics developed at a similar frequency in non-exposed patients.