Comparative activity of beta-lactam agents (carbapenem excepted) against Pseudomonas aeruginosa strains with CARB or OXA beta-lactamases

Abstract

Background: Ticarcillin resistance in Pseudomonas aeruginosa can be mediated by various beta-lactamases of the CARB and OXA groups.

Methods: We investigated the activity of seven beta-lactam agents and two beta-lactam-beta-lactamase inhibitor combinations against 216 P.aeruginosa strains with genotypically characterized beta-lactamases, including 137 CARB, 31 OXA-35, 25 OXA-10, 13 OXA-1 and 10 OXA-2. MICs were determined by the agar dilution method.

Results: The activities of ticarcillin and piperacillin were more affected by CARB than by OXA enzymes. beta-Lactamase inhibitors were poorly effective against OXA-1, OXA-35 and OXA-10. OXA-1 conferred resistance to cefepime and cefpirome but not to cefsulodin and aztreonam. Ceftazidime remained the most active agent against all groups of enzymes. Major differences in the susceptibility rates according to NCCLS and CASFM breakpoints were observed.

Conclusions: Significant differences were found in the resistance profile associated with the various types of CARB and OXA beta-lactamases in P. aeruginosa.