In vitro activity of LY127935, a new 1-oxa cephalosporin, against aerobic gram-negative bacilli

Abstract

A total of 434 clinical aerobic gram-negative bacillary isolates were tested against LY127935, a new 1-oxa cephalosporin, and compared with other cephalosporins, penicillins, and aminoglycosides by a broth microdilution technique. Cefotaxime (HR756), a new semisynthetic cephalosporin, and LY127935 were more active, and showed lower minimun inhibitory concentrations (rantes, -O.12 to 2.0 ,ug/ml), than cefamandole, cefoxitin, and cefazolin against Escherichia coli, Klebsiella spp., Enterobacter spp., Proteus mirabilis, indole-positive Proteus spp., Serratia marcescens, Providencia spp., and Citrobacter spp. Against P. aeruginosa, piperacillin, azlocillin, and mezlocillin were the most active betalactam agents; 64 ,ug/ml inhibited 99, 93, and 87%, of the isolates, respectively. LY127935 and cefotaxime at 16 ,ug/ml inhibited 71% of Pseudomonas isolates, whereas the aminoglycosides gentamicin, tobramycin, and amikacin at a concentration of 4 ,ug/ml inhibited 84, 88, and 93%, respectively. Minimum bactericidal concentrations were determined for all isolates and were generally the same as the minimum inhibitory concentrations.LY127935 is a new parenteral semisynthetic 1-oxa cephalosporin antibiotic which has been shown in preliminary in vitro testing to be highly active against gram-negative microorganisms including Pseudomonas aeruginosa and Enterobacteriaceae resistant to other cephalosporins and cephamycins (4). Determination of MICs. Minimum inhibitory concentrations (MICs) were determined by a microdilution technique as described by Barry (1). Antibiotic dilutions were prepared in Mueller-Hinton broth. With calibrated pipettes, 50 ,ul of each antibiotic dilution was transferred to each well of a U-shaped microtiter plate (Dynatech, Inc., Alexandria, Va.), with resulting final antibiotic concentrations ranging from 0.12 to 64 ug/ml.Organisms to be tested were picked from nutrient agar slants and suspended in 1 ml of Mueller-Hinton broth. After overnight incubation at 37°C, the cultures were adjusted to 10' colony-forming units per ml with a 0.5 McFarland standard and then diluted 1:1,000 with Mueller-Hinton broth. A 0.05-ml amount of the culture dilution was added to each well of the microtiter plate, resulting in a final inoculum of 5 x 104 colony-forming units per ml.The microtiter plates were incubated for 18 h 864 on May 9, 2018 by guest http://aac.asm.org/ Downloaded from

Comparative Activity of N‐Formimidoyl Thienamycin with Third Generation Cephalosporins and Ureido Penicillins against Multiple Resistant Serratia marcescens

“…Our study confirms earlier reports of good activity of moxalactam against multiple resistant and susceptible isolates of S. marcescens (4,5,9,13). Cefotaxime and moxalactam were simlarly effective with MIC's for 90% of the isolates being ::;;0.97 .ug/ml.…”

Comparative In Vitro Activities of N -Formimidoyl Thienamycin and Moxalactam Against Nonfermentative Aerobic Gram-Negative Rods

“…Moxalactam is a new beta-lactam antimicrobial agent with a broad spectrum of activity against aerobic and facultative gram-negative rods (2,4,5,8,16). Although there are fewer reports on N-formimidoyl thienamycin, this new more stable derivative of thienamycin also has an expanded spectrum of activity (7,14,17).…”

Activity of moxalactam and cefotaxime alone and in combination with ampicillin or penicillin against group B streptococci

“…The minimal inhibitory concentrations (MICs) of these agents for most strains of E. coli range from 0.06 to 0.125 ,ug/ml (7,17,18 …”

“…The minimal inhibitory concentrations (MICs) of these agents for most strains of E. coli range from 0.06 to 0.125 ,ug/ml (7,17,18 Synergy studies. In the checkerboard titration, the ampicillin-moxalactam combination was partially synergistic for 12 isolates (60%), additive for 3 (15%), and indifferent for 5 (25%).…”