[Comparative in vitro activity of 6 recent beta-lactams against hospital strains of Acinetobacter calcoaceticus: role of the monobactam SQ 26,776].

Acinetobacter calcoaceticus is recognized as one of the most resistant nosocomial pathogens. Clinical isolates of Acinetobacter are usually resistant to most beta-lactam antibiotics and even to carbenicillin; 50% of the strains isolated in 1981-82 at the Bichat hospital were inhibited only at a concentration of 180 micrograms/ml. Recently several new molecules belonging to the beta-lactam group were discovered. Among them, monobactam SQ 26 776, a new broad spectrum highly potent monocyclic beta-lactam antibiotic, is resistant to beta-lactamase degradation and is able to inhibit especially Pseudomonas aeruginosa and Providencia. Its activity against 110 clinical strains of Acinetobacter was compared to that of 5 recent beta-lactam antibiotics which are resistant to beta-lactamase degradation (N-formimidoyl-thienamycin, cefotaxime, moxalactam, ceftriaxone, cefoperazone). 50% of the strains were inhibited at a concentration of 25 micrograms/ml and 90% at a concentration of 58 micrograms/ml of monobactam. The geometric mean was 27 micrograms/ml. For the other beta-lactam antibiotics, the MIC values (except for thienamycin), were superior to the critical values of bacterial susceptibility. N-formimidoyl-thienamycin is the most active compound against clinical isolates of Acinetobacter, with MIC 50 and MIC 90% being respectively of 0,4 and 0,8 micrograms/ml.