In vitro susceptibility of cephalothin-resistant Enterobacteriaceae and Pseudomonas aeruginosa to Amikacin and selected new beta-lactam agents

Amikacin was evaluated in vitro by agar dilution testing against 148 different clinical isolates of cephalothin-resistant Enterobacteriaceae and Pseudomonas aeruginosa in parallel with cephalothin, cefoxitin, moxalactam, N-formimidoyl thienamycin, ceftriaxone, and cefmenoxime. Cefsulodin was also evaluated against 39 isolates of P. aeruginosa. More than 80% of all isolates tested were also gentamicin resistant, as determined by disk testing. Moxalactam and amikacin had comparable high activities against Proteus species, Escherichia coli, Serratia species, and Providencia species, and both amikacin and N-formimidoyl thienamycin had comparably high activities against the Klebsiella-Enterobacter group. N-Formimidoyl thienamycin was the most active agent against P. aeruginosa, followed by cefsulodin and amikacin.