Comparative Activities of the Oxa-β-Lactam LY127935, Cefotaxime, Cefoperazone, Cefamandole, and Ticarcillin Against Multiply Resistant Gram-Negative Bacilli

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Abstract
A total of 91 multiply resistant bacterial strains, including Klebsiella pneumoniae (32 strains), Pseudomonas aeruginosa (16 strains), and Serratia marcescens (43 strains), were collected during hospital epidemics of nosocomial infection from 1975 to 1979. These strains were resistant to gentamicin, tobramycin, cephalothin, chloramphenicol, and ampicillin. Their susceptibility to three new broad-spectrum β-lactams, LY127935 (a 1-oxa-β-lactam), cefotaxime (HR 756), and cefoperazone (T 1551), was compared with the susceptibility of random strains of nine species of aerobic gram-negative bacilli collected in the same hospital in 1979. Susceptibility to cefamandole and ticarcillin was also determined. Strains of staphylococci and streptococci from that hospital and two nearby city-county hospitals were also compared for the three new cephalosporins and other effective antibiotics. The agar dilution method was used to measure the minimum inhibitory concentration for each antibiotic. The multiply resistant strains (minimum inhibitory concentration for gentamicin ≥ 8 μg/ml) usually were as susceptible to the three new broad-spectrum β-lactams as were non-multiply resistant strains. Both Klebsiella pneumoniae and Serratia marcescens , including multiply resistant and non-multiply resistant strains, were most susceptible to the 1-oxa-β-lactam LY127935 and cefotaxime. P. aeruginosa (both multiply resistant and non-multiply resistant strains) were most susceptible to cefoperazone. All three new β-lactams were active against non-multiply resistant strains of Escherichia coli, Enterobacter spp., Proteus spp., and Citrobacter spp. Providencia stuartii were most susceptible to cefotaxime and the 1-oxa-β-lactam LY127935. The three new β-lactams were all less active against staphylococci (especially methicillin-resistant Staphylococcus aureus ) than cephalothin. Streptococcus pyogenes and S. pneumoniae were very susceptible to cefotaxime and cefoperazone, though less susceptible to LY127935. None of the three new β-lactams was active against S. faecalis . All were very active against both penicillinase-positive and -negative strains of Neisseria gonorrhoeae .