Analysis of resistance, cross-resistance and antimicrobial combinations for Pseudomonas aeruginosa isolates from 1997 to 2009.

Pseudomonas aeruginosa is a nosocomial and community-acquired pathogen associated with considerable patient morbidity and mortality. Multidrug resistance in P. aeruginosa is a concern owing to the limited therapeutic options available to treat infections due to this organism. In this study, rates of antimicrobial resistance of P. aeruginosa isolates collected by The Surveillance Network Database-USA (Eurofins Medinet, Chantilly, VA) from 1997 to 2009 were examined. The patient population and specimens were stratified according to patient setting and age as well as specimen source. Multidrug resistance was defined as resistance to three or more of the following antimicrobial agents: aztreonam; cefepime; ciprofloxacin; imipenem; gentamicin; and piperacillin/tazobactam (TZP). A total of 924740 P. aeruginosa isolates were examined in this study. Changes in resistance rates to individual antimicrobial agents were <5% for all agents except ciprofloxacin. There was a statistically significant decreasing rate of multidrug-resistant P. aeruginosa to four, five and six antimicrobial agents. For isolates resistant to imipenem, aztreonam and gentamicin, ciprofloxacin had the highest cross-resistance rates. The greatest coverage against P. aeruginosa was by the combination of TZP plus amikacin (94%) followed by aztreonam plus amikacin (90%). Pseudomonas aeruginosa resistance rates remained steady or minimally declined to all antimicrobials from 1997 to 2009. Amongst the β-lactams, TZP has the greatest activity against P. aeruginosa.