beta-Lactamases of Pseudomonas aeruginosa and susceptibility against beta-lactam antibiotics.

A total of 4093 non-replicate Pseudomonas aeruginosa isolates supplied by 10 French hospitals from September 1981 to August 1983 was examined for susceptibility to ticarcillin (TIC) and to 11 other beta-lactam antibiotics. Overall incidence of TIC-resistance was low (20.9%) but variable between hospital, unit and culture site and primarily mediated by a constitutive beta-lactamase as observed by iodometric detection (66.3%). As suggested by analytical isoelectrofocusing on gel, PSE-1 (CARB-2) and OXA types were predominant but new types appeared. The comparative in vitro activities of 12 antipseudomonal beta-lactams appreciated by microtiter MICs with an inoculum of 10(5) CFU were established according to phenotype: TIC-susceptible, TIC-R with a constitutive beta-lactamase (PSE-1, OXA-1, OXA-2, OXA-3, PSE-2 and a new type, TEM-1 and TEM-2 and derepressed cephalosporinase) or without detectable activity. Different patterns of resistance were demonstrated, but imipenem, ceftazidime and aztreonam were the most active antibacterial agents.