YTR 830, a new ,-lactamase inhibitor, combined with amoxicillin or carbenicillin, showed a synergistic effect similar to that observed with clavulanic acid, and generally better than that with sulbactam, against strains harboring chromosome-encoded penicillinases and broad-spectrum ,-lactamases or plasmiddetermined 13-lactamases. With ampicillin, YTR 830 showed the best synergistic activity of the inhibitors against Proteus morganii, Citrobacterfreundii, and Enterobacter cloacae and their mutants with a derepressed chromosome-encoded cephalosporinase.YTR 830 is a new derivative of penicillinate sulfone, which was previously shown to have a spectrum of activity similar to that of clavulanic acid when combined with amoxicillin against clinical isolates of Staphylococcus aureus, Haemophilus influenzae, and different Enterobacteriaceae (1). In this study we have compared YTR 830 with clavulanic acid and sulbactam, in combination with different 3-lactam antibiotics, against a range of bacteria harboring known Plactamases.YTR 830 was obtained from Taiho Pharmaceuticals; ampicillin was from Bristol Laboratories; amoxicillin, carbenicillin, and sodium clavulanate were from Beecham Laboratories; cefotaxime was from Roussel-Uclaf; cefoperazone and sulbactam were from Pfizer Inc. We studied strains harboring known chromosome-or plasmid-mediated ,Blactamases (2, 4). MICs (18 h) were determined by using the agar dilution method. Increasing concentrations of P-lactam antibiotics were added to Mueller-Hinton agar containing 8 ,ug of the inhibitor per ml, and about 104 CFU were deposited onto the surface of the agar plate with a Steers-type replicator device. The MICs of the different inhibitors were .32 ,ugIml. Synergy or antagonism was defined as a fourfold or greater decrease or increase, respectively, in the MIC of the

No abstract

The in vitro activities of the P-lactamase inhibitors YTR 830, clavulanate, and sulbactam combined with six P-lactams against 88 ,-lactamase-producing anaerobes were determined. When combined with the ,-lactams, the three ,-lactamase inhibitors showed no synergy against the 10 Bacteroides fragilis homology group II strains. When the B-lactams were combined with the inhibitors, their geometric mean MICs against the remaining 78 strains were reduced from 4.2 to 150.2 ,ug/ml to 0.2 to 12.9 ,ug/ml. The activity of the P-lactams combined with the P-lactamase inhibitors was significantly greater than that of the ,-lactams alone against all groups except B. fragilis homology group II, with 76 to 100% of the strains susceptible to ampicillin plus inhibitor and .90% susceptible to the other combinations.Although the antimicrobial susceptibility spectrum of anaerobes has remained relatively stable, P-lactamasemediated resistance to penicillin and other P-lactams has been described for species in the Bacteroides fragilis group and for other Bacteroides spp., Fusobacterium nucleatum, and Clostridium butyricum (3,7,15,18,19). Several studies have demonstrated that the ,-lactamase inhibitors clavulanate and sulbactam act synergistically in vitro with ,-lactams against P-lactamase-positive, but not P-lactamase-negative, anaerobic organisms (2,4,5,16,20,21). YTR 830 is a new ,-lactamase inhibitor (1) with activity comparable to that of clavulanate and superior to that of sulbactam against ,1-lactamase-producing members of the family Enterobacteriaceae (6, 10). The purpose of this study was to compare the in vitro activities of six P-lactams (ampicillin, ticarcillin, mezlocillin, piperacillin, apalcillin, and cefoperazone) The presence of 3-lactamase was detected by a chromogenic cephalosporin method on growth from enriched blood agar plates by using nitrocefin disks (BBL Microbiology Systems, Cockeysville, Md.), in accordance with standard practice (4, 10). Organisms were stored at -70°C in thioglycolateglycerol (85:15, vol/vol) and were subcultured on enriched blood agar plates before testing.Laboratory reference powders of the following agents were used: ticarcillin and clavulanate (Beecham Laboratories, Bristol, Tenn.); mezlocillin (Miles Laboratories, Inc., West Haven, Conn.); piperacillin (Lederle Laboratories, Pearl River, N.Y.); apalcillin (Wyeth Laboratories, Philadelphia, Pa.); cefoperazone and sulbactam (Pfizer Inc., New York, N.Y.); ampicillin (Bristol-Myers Laboratories, Wallingford, Conn.); cefoxitin (Merck Sharpe & Dohme, West Point, Pa.); and YTR 830 (Taiho Pharmaceuticals, Tokyo, Japan). The powders were dissolved and diluted in accordance with the instructions of the manufacturers, and the potency of the agents was checked by determination of the MICs for quality control strains.Susceptibility testing of the isolates was performed by agar dilution on Wilkins-Chalgren agar (Difco Laboratories, Detroit, Mich.) (14,17). Plates contained serial doubling dilutions of the 3-lactams (ampicillin, 0.125 to 256 ,ug/...

The in vitro synergistic activities of the P-lactamase inhibitors YTR 830, clavulanate, and sulbactam, combined with ampicillin, ticarcillin, mezlocillin, aziocillin, piperacillin, and apalcillin, were determined against 34 strains of members of the Enterobacteriaceae family, Pseudomonas aeruginosa, Aeromonas hydrophila, and Haemophilus influenzae with characterized plasmid or chromosomal j-lactamases or both.Strains were tested against fixed concentrations of ,-lactamase inhibitors (8 ,ig/ml) combined with doubling dilutions of (8-lactams. Synergy was defined as a fourfold or greater decrease in the MIC of the I8-lactam.Against Enterobacteriaceae producing Richmond and Sykes class III and V plasmid-mediated j-lactamases, synergy was obtained against most strains with YTR 830-and clavulanate-4-lactam combinations, with sulbactam being less effective. Against Enterobacteriaceae producing class I chromosomal I8-lactamases, combinations containing YTR 830 or sulbactam were more synergistic than combinations containing clavulanate. Against strains producing class V PSE enzymes, all three inhibitors were synergistic with piperacillin and apalcillin against strains producing PSE-1, -3, and -4 enzymes, while the PSE-2-producing strain was resistant to all inhibitors. YTR 830-0-lactam combinations were also synergistic against strains producing the novel P-lactamases OHIO-1, TLE-1, AER-1, and ROB-1. Overall, YTR 830 with piperacillin or apalcillin was the most effective combination.

Benzhydryl 2 beta-[(1,2,3-triazol-1-yl)methyl]-2 alpha-methylpenam- 3 alpha-carboxylate 1,1-dioxide was prepared by heating benzhydryl 2 beta-(azidomethyl)-2 alpha-methylpenam-3 alpha-carboxylate 1,1-dioxide with (trimethylsilyl)acetylene. The ester group was removed by hydrogenolysis to give sodium 2 beta-[(1,2,3-triazol-1-yl)methyl]-2 alpha-methylpenam-3 alpha-carboxylate 1,1-dioxide (3i, YTR-830), which was found to be a potent inhibitor of various bacterial beta-lactamases. A series of related compounds was prepared in a similar way, and all of these compounds show excellent beta-lactamase inhibitory properties.