Vol. 16, No. 3

ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Sept. 1979, p. 287-292 0066-4804/79/09-0287/06$02.00/0

In Vitro Activity of LY127935 MICHAEL BARZA,* FRANCIS P. TALLY, NILDA V. JACOBUS, AND SHERWOOD L. GORBACH

Infectious Disease Service, New England Medical Center Hospital, and Tufts University School of Medicine, Boston, Massachusetts 02111 Received for publication 4 June 1979

The activity of LY127935, a beta-lactam antibiotic of novel structure, was studied in vitro against facultative gram-negative bacilli, Staphylococcus aureus, and Bacteroides fragilis. The strains were recent clinical isolates, many of which were relatively resistant to other antibiotics. LY127935 exhibited striking activity against Escherichia coli, Klebsiella pneumoniae, Enterobacter sp., Proteus sp., Serratia marcescens, and B. fragilis with median miniimum inhibitory concentrations of -1.0 ,ug/ml. It was somewhat less active against Pseudomonas aeruginosa and S. aureus. Cefotaxime (HR 756) showed very similar activity except that it was substantially weaker against B. fragilis. LY127935 was more active than cefamandole, cefoxitin, or piperacillin; it was also as potent as tobramycin or amikacin against all species except for P. aeruginosa.

LY127935 is a new semisynthetic beta-lactam antibiotic. Its most striking chemical feature is the substitution of an oxygen molecule for the usual sulfur moiety in the cephem nucleus, a modification unique among beta-lactam antibiotics. Figure 1 shows the structural relationships of this newly synthesized compound, thienamycin, clavulanic acid, and cefoxitin. LY127935 appears to be freely soluble in water and is stable for 48 h at refrigerator temperatures at pH 6.

Preliminary studies (unpublished data) at the Lilly Research Laboratories, Indianapolis, Ind., as well as at Shionogi Research Laboratories, Osaka, Japan, indicated that LY127935 has potent activity against a wide range of gram-negative bacilli including Pseudomonas aeruginosa and some aminoglycoside-resistant pathogens (T. Yoshida, M. Narisada, S. Matsuura, W. Nagata, and S. Kuwahara, Progam Abstr. Intersci. Conf. Antimicrob. Agents Chemother. 18th, At-

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FIG. 1. Structures of LY127935, thienamycin, cefoxitin, and clavulanic acid. 287

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BARZA ET AL.

ANTIMICROB. AGENTS CHEMOTHER.

lanta, Ga., abstr. no. 151, 1978). The current report compares the in vitro activities of LY127935 and other new beta-lactam antibiotics against a variety of aerobic and facultative gramnegative bacilli, Staphylococcus aureus, and Bacteroides fragilis. MATERIALS AND METHODS Antibiotics. LY127935, cefamandole, tobramycin, and cephalothin were furnished by Eli Lilly and Co., Indianapolis, Ind.; cefotaxime (HR 756) was a gift from Hoechst-Roussel Pharmaceuticals Inc., Somerville, N.J.; cefoxitin was obtained from Merck, Sharp and Dohme Research Laboratories, Rahway, N.J.; carbenicillin came from J. B. Roerig, Div. of Pfizer Pharmaceuticals, New York, N.Y.; amikacin was obtained from Bristol Laboratories, Syracuse, N.Y.; nafcillin was obtained from Wyeth Laboratories, Philadelphia, Pa.; clindamycin was obtained from the Upjohn Co., Kalamazoo, Mich.; metronidazole came from G. D. Searle and Co., Chicago, Ill.; and piperacillin was obtained from Lederle Laboratories, Pearl River, N. Y. All drugs were supplied as dry powders except for tobramycin, which was provided in solution (1,000 ,g/ ml). Solutions of the test compounds were prepared ixnmediately before each evaluation. Organisms. Bacterial strains were recent clinical isolates obtained from the research laboratories of the Infectious Disease Division, Tufts-New England Medical Center Hospital. Most had been cultured from patients with active infections, some of whom had been treated with one or more courses of antibiotics. The isolates of B. fragilis had been collected over 2 years and had been maintained frozen in skim milk or on brain heart infusion agar slants supplemented with 0.5% yeast, 0.00005% vitamin K, and 0.0005% hemin. Procedures. Antibiotic susceptibility of aerobes and facultative organisms was determined by a microtiter technique using twofold dilutions of the antibiotic in Mueller-Hinton broth. The inoculum was prepared from a 6-h culture in Mueller-Hinton broth to contain approximately 105 colony-forming units (CFU) per ml; 5 x 103 CFU (0.05 ml) was introduced into each well. The final volume in each well was 0.1 ml. The minimal inhibitory concentration (MIC), determined after overnight incubation at 37°C, was the lowest concentration affording no visible growth. The minimal bactericidal concentration was the lowest concentration from which subculture on Mueller-Hinton broth agar was sterile. B. fragilis was studied by a modified agar-dilution method using a Steers replicator to inoculate approximately 104 CFU per spot onto brain heart infusion agar supplemented with 5% laked sheep blood and vitamin K, 10 ,ig/ml (14). The inoculum was prepared in brain heart infusion broth supplemented with 0.5% yeast, 0.00005% vitamin K, and 0.0005% hemin. Strict anaerobic chamber techniques were used throughout. For determination of inoculum effect, similar studies were carried out using suspensions containing 108, 106, and 104 CFU/ml, of which 0.05 ml was delivered into each well for aerobes and facultative organisms and 0.001 ml per spot for B. fragilis. The inoculum size was verified in each instance by direct colony

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Vol. 16, No. 3 ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Sept. 1979, p. 287-292 0066-4804/79/09-0287/06$02.00/0 In Vitro Activity of LY127935 MICHAEL B...
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