Comparative activity of ceftizoxime against aminoglycoside-resistant aerobic gram-negative bacilli

The in vitro activity of ceftizoxime was compared with that of other beta-lactam antibiotics against 331 aminoglycoside (AG)-resistant clinical isolates. Two hundred and six AG-resistant, beta-lactamase producing, R-plasmid harbouring Enterobacteriaceae strains had MICs ranging from 0.0125 to 0.063 mg/l. AG-resistant Escherichia coli (36 strains) and Klebsiella pneumoniae (19) had MIC 90 values of 8 mg/l. Proteus rettgeri and P. vulgaris as well as Morganella morganii, resistant to several AGs, had MICs ranging from 0.5 to 4 mg/ml. Against all six isolates of AG-resistant Salmonella enteritidis the MIC90 was 0.5 mg/l. Twenty-seven strains of Serratia marcescens, most of which were resistant to beta-lactam and AG antibiotics, had MICs ranging from 0.5 to 8 mg/l. The AG-resistant strains of Enterobacteriaceae producing several AG-modifying enzymes (AAC(3); AAC(2'); AAC(6'); APH(3')) showed MICs ranging from 0.6 to 4 mg/l. Against 10 AG-resistant strains of Pseudomonas aeruginosa producing AAC(3), AAC(6') and APH(3') enzymes, the MICs ranged from 16 to 64 mg/l. In conclusion, ceftizoxime was equally or more active than cefotaxime, cefoperazone, ceftazidime and moxalactam against AG-resistant E. coli, Klebsiella, Morganella, Proteus, Serratia, Salmonella and R-plasmid harbouring Enterobacteriaceae. Ceftizoxime was less active than cefotaxime, moxalactam and ceftazidime against P. aeruginosa.