In-vitro susceptibility of clinical isolates of Serratia species to antimicrobial agents.

The in-vitro activities of 12 antimicrobial agents against a total of 80 clinical isolates of Serratia marcescens and Serratia liquefaciens were determined by a broth microdilution method. Ampicillin and cefazolin were totally inactive against these organisms. The other beta-lactam antibiotics such as piperacillin, cefotaxime, ceftazidime, and the aminoglycosides such as gentamicin, tobramycin and netilmicin showed poor or moderate activity against Serratia isolates. Aztreonam and amikacin inhibited most of the strains tested. Imipenem and ciprofloxacin were very active in inhibiting all strains. Within the genus, S. liquefaciens was more resistant to aztreonam, ceftazidime and amikacin than S. marcescens.