Phenotypic antimicrobial resistance patterns in Pseudomonas aeruginosa and Acinetobacter: results of a Multicenter Intensive Care Unit Surveillance Study, 1995-2000.

Susceptibility data from the Intensive Care Unit (ICU) Surveillance Study for 10,361 isolates of Pseudomonas aeruginosa and 2,573 isolates of Acinetobacter tested at centers in the United States during 1995 to 2000 were analyzed. In all years, amikacin was the most active antimicrobial agent against P. aeruginosa, and imipenem was the most active agent against Acinetobacter. Resistance of both organisms to common therapeutic agents tested throughout the analysis period increased from 1995 to 2000, although the increase was not consistent for all drugs from year to year. The increases were higher among Acinetobacter, and for both organisms, the increase in resistance was greatest for ciprofloxacin. Among all P. aeruginosa tested in 1999 and 2000, resistance to ciprofloxacin was 9-11% higher for isolates from patients on general hospital wards than those from ICUs. Of the 3424 ICU isolates of P. aeruginosa tested in 1999 and 2000, 77 (2.2%) were multidrug-resistant (i.e., resistant to piperacillin, ceftazidime, imipenem, and gentamicin). Twenty (3.9%) isolates of Acinetobacter in 1999 and seven (1.9%) in 2000 were resistant to imipenem, ceftazidime, piperacillin-tazobactam, ciprofloxacin, and amikacin. Although resistance in both P. aeruginosa and Acinetobacter increased, multidrug-resistant (to > or =4 agents) strains were uncommon.