Activity of ceftazidime against Pseudomonas aeruginosa from bacteraemic and fibrocystic patients.

Minimum inhibitory and bactericidal levels of ceftazidime were determined for 337 isolates of Pseudomonas aeruginosa (135 mucoid, 202 non-mucoid) derived from fibrocystic patients, and 102 isolates of Ps. aeruginosa from blood or CSF. Fifty per cent of isolates of Pq. aeruginosa from all sources were inhibited by 2 mg/l of ceftazidime using inocula of 10(5)-10(6) colony forming units. Ninety per cent of the blood-culture and mucoid isolates were inhibited by 4 mg/l of ceftazidime, but more than 10 mg/l was required to inhibit 90% of the non-mucoid organisms. Bactericidal levels were close to the inhibitory levels. Of 30-isolates of Ps. cepacia, 50% were inhibited by 2 mg/l, and 90% by 4 mg/l of ceftazidime. Strains of pseudomonas derived from patients with fibrocystic disease were less susceptible than the strains from bacteraemic patients. Of the former, the mucoid strains were more susceptible than the non-mucoid strains. The patients with cystic fibrosis had been exposed to beta-lactam drugs for many years.