CENTA is a newly synthesized, beta-lactamase-labile, chromogenic cephalosporin reagent which changes color from light yellow (K maximum ca. 340 nm) to chrome yellow (A maximum ca. 405 nm) concomitant with hydrolysis of the betalactam ring. This compound offers promise as a diagnostic reagent comparable to other chromogens (PADAC and nitrocefin) for the early detection of betalactamase-producing clinical isolates, while retaining some antimicrobial effect against Escherichia coli, Klebsiella spp., Proteus mirabilis, Staphylococcus aureus, and non-enterococcal Streptococcus spp. CENTA is relatively unaffected by commonly used microbiological media and human serum.

Cefodizime (HR221) is a new a-methoxyimino cephalosporin developed by Hoechst-Roussel with a reported serum half-life of over 2 h. In vitro susceptibility studies showed that the cefodizime spectrum includes all those Enterobacteriaceae, staphylococci, Streptococcus spp., Haemophilus spp., and Neisseria spp. normally susceptible to cefotaxime (HR756) or ceftizoxime (FK749) or both. Cefodizime was less active (two-to eightfold) than cefotaxime or ceftizoxime against some enteric species, but was the most potent drug against some strains of Morganella spp. and Proteus vulgaris. Enterococci, methicillin-resistant Staphylococcus aureus, and most Pseudomonas spp. were resistant to cefodizime (median minimum inhibitory concentrations, 264 Ag/ml). Acinetobacter spp. and Pseudomonas aeruginosa strains required cefodizime concentrations of 32 ,tg/ml to inhibit 50% of tested strains. Cefodizime was very stable to hydrolysis by Richmond-Sykes type I, II, III, and IV beta-lactamases, as well as the enzyme derived from Bacillus cereus. The reference PADAC and nitrocefin substrate hydrolysis by a type I beta-lactamase was markedly inhibited (>80%) by cefodizime at concentrations 0.4 to 4% of substrate concentration. Cefodizime was active against 43% of bacteria which were resistant to cephalothin and cefamandole and against 58% of those resistant to aminoglycosides.

azo-p-dimethylanaline cephalosporin (PADAC), a chromogenic reagent which is purple and changes to yellow upon cleavage of its beta-lactam ring, was evaluated in comparison with other chromogenic cephalosporins. PADAC exhibited little antimicrobial activity against gram-negative bacteria, but did have good activity (minimum inhibitory concentration, 0.12 to 0.5 ,ug/ml) against Staphylococcus aureus, a quality comparable to nitrocefin. Nitrocefin, however, demonstrated an unexpected and uniquely potent activity against Streptococculs faecalis (minimum inhibitory concentration,-0.06 to 0.12 p.g/ml). The relative hydrolysis rate of PADAC when subjected to six different beta-lactamases was substantially greater than that of cephacetrile, but less than that of nitrocefin. The relative hydrolysis rates of PADAC and nitrocefin were comparable with type Illa beta-lactamase and that derived from Bacillus cereus. The inhibition of betalactamase hydrolysis of the chromogenic cephalosporin substrates by six enzymestable inhibitors was generally greater with PADAC than with nitrocefin. Unlike nitrocefin, PADAC mixed with 50% human serum or various broth culture media showed no evidence of color change or degradation over several hours. The subsequent enzyme hydrolysis rates of such mixtures were the same as in phosphate buffer. Beta-lactamase-containing bacterial suspensions and clinical specimens containing such bacteria produced positive visual and spectrophotometric color changes when mixed with PADAC or nitrocefin. Although color changes occurred more slowly with PADAC than with nitrocefin, PADAC was not adversely influenced (non-enzyme-related color change) by the protein content of specimens. PADAC appears to be a promising alternative for betalactamase diagnostic testing in the clinical and research microbiology laboratory.

Three concentrations of the penicillanic acid sulfone, sulbactam were tested in combination with cefoperazone against 632 recent clinical bacterial isolates. Cefoperazone was effective alone (less than or equal to 16 micrograms/mL) against 95% of Enterobacteriaceae and combined with 4 micrograms/mL sulbactam inhibited 99.5% of strains. This coverage of enteric bacilli was superior to timentin (99.1%), ceftazidime (98.2%), and tobramycin (90.9%). The minimum inhibitory concentrations (MICs) of cefoperazone-susceptible strains also were markedly decreased by sulbactam (overall MIC90s, 8.0 micrograms/mL for cefoperazone and 1.0 microgram/mL for cefoperazone and 4.0 micrograms/mL for sulbactam). Sulbactam also expanded the spectrum of cefoperazone against Acinetobacter species, some rare Pseudomonas species, and Bacteroides fragilis group species. Sulbactam had direct antimicrobial activity against the acinetobacters and Pseudomonas acidovorans, but the increased activity of cefoperazone-sulbactam against some other Pseudomonas species and anaerobes was attributed to beta-lactamase inhibition. The cefoperazone MICs against beta-lactamase producing Staphylococcus species also were lowered to the level of enzyme-deficient strains. Cefoperazone bactericidal activity was improved by 4.0 micrograms/mL sulbactam, and no antagonism was observed. beta-lactamase hydrolysis studies confirmed a slow hydrolysis of cefoperazone only by TEM beta-lactamases and a high-grade resistance to enzyme breakdown by sulbactam. Differential beta-lactamase affinity studies for cefoperazone and sulbactam showed potential efficacy and applications to plasmid-mediated TEM and OXA enzymes and only marginal effective sulbactam inhibition of Pseudomonas and Klebsiella species enzymes. Disk diffusion studies on 556 strains confirmed the applicability of the cefoperazone 75-micrograms disk to testing routine isolates other than enterococci and methicillin-resistant Staphylococcus aureus. The addition of 4.0 micrograms sulbactam/mL in a fixed concentration to dilution test systems and 15 micrograms sulbactam to the 75 micrograms cefoperazone disk were recommended for in vitro tests. Susceptibility and resistant interpretive criteria for the disk and dilution tests can be applied with confidence. Only 0.4% false-susceptibility errors and a 97.5% absolute interpretive agreement were achieved using the 75 micrograms cefoperazone/15 micrograms sulbactam disk.

No abstract