Ceftazidime: in-vitro antibacterial activity and susceptibility to -lactamases compared with that of cefotaxime, moxalactam and other -lactam antibiotics

Abstract

The in-vitro antibacterial activity of ceftazidime was assessed against recent clinical isolates of common bacteria and also against reference strains that produced known beta-lactamases. The compound was active, though less so than cephaloridine against staphylococci and streptococci with MICs mostly 0.12-2 mg/l for streptococci and 8 mg/l for staphylococci, but enterococci (MICs > or =64 mg/l) and methicillin-resistant staphylococci (MICs 16-32 mg/l) were resistant. Penicillin-resistant pneumococci (MICs 2-4 mg/l) were much less sensitive than other pneumococci (MICs 0.12-0.25 mg/l). Ceftazidime was also active, but slightly less so than cefotaxime or moxalactam, against enterobacteria (MICs mostly 0.12-0.25 mg/l). Its activity was also inferior to that of cefotaxime against Neisseria gonorrhoeae (MICs mostly 0.03-0.06 mg/l) and Haemophilus influenzae (MICs mostly 0.06-0.25 mg/l). However it was about eightfold more active than cefotaxime or moxalactam against Pseudomonas aeruginosa (MICs mostly 1-4 mg/l), and it was also more active than these compounds against other pseudomonads. Ceftazidime was less active than cefoxitin against Bacteroides spp. (MICs mostly 16-64 mg/l for Bact. fragilis and 2-8 mg/l for other bacteroides) and less active than ampicillin or cefoxitin against other anaerobes. The compound was highly resistant to hydrolysis by most beta-lactamases including OXA-1 and the enzymes from Klebsiella 1082E and Proteus vulgaris PC37 which hydrolyse cefuroxime and cefotaxime. However, it was hydrolysed slowly by the enzyme from a highly ampicillin-resistant isolate of Bact. fragilis.