In-vitro studies with ceftazidime against aerobic gram-negative bacilli and Bacteroides fragilis group

The in-vitro susceptibility of recent clinical isolates of Gram-negative bacilli has been assessed for ceftazidime and compared to amikacin, gentamicin, carbenicillin, piperacillin, cefoperazone, moxalactam, ceftriaxone and ceftizoxime. Using the ICS-WHO agar dilution method, we found that ceftazidime was the most active beta-lactam agent tested against 147 isolates of Pseudomonas aeruginosa, with a mode MIC=2 mg/l and all but 2% of isolates inhibited at 32 mg/l. 100% of indole-positive and negative Proteus spp., 90% of Citrobacter spp., 100% of Acinetobacter spp. and 98% of Enterobacter spp. were inhibited. A total of 142 isolates from the latter 5 groups of organisms were tested. Cefoperazone and moxalactam were slightly more active by weight than ceftazidime versus Enterobacter spp., but against other Gram-negative bacilli ceftazidime was similar or more potent. Additionally, 72 clinical isolates of Bacteroides fragilis group were tested against ceftazidime, cefoperazone, ceftizoxime, ceftriaxone, and cefoxitin. Against these organisms cefoxitin and ceftizoxime were most active. Ceftazidime demonstrates potent in-vitro activity against Ps. aeruginosa and Enterobacteriaceae, but it is relatively less active against Bacteroides fragilis group than cefoxitin and ceftizoxime.