[Sensitivity of Pseudomonas aeruginosa to beta-lactam antibiotics. Apropos of 338 strains isolated at the Regional Hospital Center at Nantes in 1984].

The MIC of 338 Pseudomonas aeruginosa strains isolated in 1984, in a French hospital, was determined by an agar dilution method, using seven beta-lactam antibiotics: ticarcillin, azlocillin, piperacillin, cefoperazone, ceftriaxone, cefsulodin and ceftazidime. The MIC50-MIC90 were respectively: 32-64, 8-32, 8-16, 8-16, 16-64, 4-16, 2-4 mg/l. Ticarcillin was the most frequently effective compound (95% of the strains were susceptible), 90% of the strains were susceptible to ceftazidime or piperacillin, 87% to azlocillin and 84% to cefsulodin. Cefoperazone and ceftriaxone were much less effective (43% and 19% of the strains, respectively). The study of the resistance patterns showed a higher percentage (80%) of strains susceptible to all the penicillins than the percentage of strains susceptible to cephalosporins, most of them however were susceptible to both cefsulodin and ceftazidime. It also showed the relatively low frequency of resistant strains by inducible cephalosporinase or decreased permeability. Serovar 0.12 was characterized by its multi-resistance to beta-lactam antibiotics.