Comparative in-vitro activities of newer cephalosporins cefclidin, cefepime, and cefpirome against ceftazidime- or imipenem-resistant Pseudomonas aeruginosa.

Three hundred and thirty-four recent clinical isolates of Pseudomonas aeruginosa were examined for susceptibility to cefclidin, cefepime, and cefpirome. Of these strains, 28.7% were resistant to ceftazidime, and 23.4% were resistant to imipenem. About half of those resistant to ceftazidime were also resistant to imipemem. Although 37.4% and 59.6% of the isolates were resistant to cefepime and cefpirome respectively, and most or all ceftazidime-resistant strains showed resistance to cefepime and cefpirome, only 3.9% were resistant to cefclidin. Ceftazidime-resistant, but cefclidin-susceptible, P. aeruginosa produced high levels of chromosomal cephalosporinases. Of the compounds tested, cefclidin showed the lowest affinity for these enzymes, suggesting that its high activity against P. aeruginosa resistant to several beta-lactams was mainly due to its high resistance to enzymatic hydrolysis. Thirteen strains resistant to cefclidin were also resistant to both cefepime and cefpirome, and eight and three of these strains were resistant to ceftazidime and imipenem, respectively. A penicillinase, which hydrolyzed cefclidin, was detected in the cefclidin-resistant P. aeruginosa, which was similar to the OXA-1 beta-lactamase.