Superior activity of N-formimidoyl thienamycin against gentamicin-resistant Pseudomonas aeruginosa

N-Formimidoyl thienamycin (N-F-thienamycin), cefotaxime, moxalactam, and cefsulodin were tested by agar dilution against 125 isolates of Pseudomonas aeruginosa, Serratia marcescens, Klebsiella pneumoniae, and Providencia stuartii. Against gentamicin-susceptible P. aeruginosa, N-F-thienamycin and cefsulodin were most active. Only N-F-thienamycin inhibited gentamicin-resistant P. aeruginosa at less than or equal to 4 microgram/ml. N-F-thienamycin's activity equaled or surpassed that of the other antibiotics tested against both the gentamicin-susceptible and -resistant Enterobacteriaceae.