In vitro activity of imipenem and six other beta-lactam antibiotics against aminoglycoside resistant gram-negative bacilli.

The in vitro activity of imipenem and six other beta-lactams (ampicillin, cefamandole, cefoxitin, ceftriaxone, ceftazidime, cefotaxime) against twenty Gram-negative bacilli resistant to clinically important aminoglycosides was studied. The bacterial strains showed high resistance (R) to gentamicin, tobramycin (R 100%), netilmicin (R 75%) and to the beta-lactams ampicillin (R 100%), cephamandole (R 90%) and cefoxitin (R 75%). The strains were susceptible to isepamicin (R 10%) and imipenem (R 10%) as well as susceptible to at least third generation cephalosporin. Three Pseudomonas aeruginosa strains were resistant to the majority of antibiotics, except for imipenem.