Summary

The sensitivity of a number of beta-lactamase producing strains of Enterobacter aerogenes, Enterobacter cloacae, Enterobacter species, Escherichia coli, Haemophilus influenzae, Klebsiella pneumoniae, Proteus mirabilis, Proteus vulgaris, Pseudomonas aeruginosa and Serratia marcescens to cefamandole, cefoxitin, cefuroxime, cefotaxime and cefoperazone was determined in vitro. All bacterial cultures were examined for beta-lactamase production using the chromogenic cephalosporin compound 87/312. All strains were typed by means of antibiotic and chemotherapeutic sensitivities. Only non-identical strains were used. A tray method was used to determine the quantity of antimicrobial product necessary for a complete growth inhibition at various culture dilutions. The results showed that all strains of H. influenzae, especially in the dilution 2.10⁶, were sensitive to the five cephalosporins. The other species and genus of bacteria had a varying sensitivity to the five cephalosporins. Cefoperazone had potent activity against Ps. aeruginosa. Differences between the five cephalosporins with regard to the effect of culture dilution were only small.