Cefotaxime, cefoxitin, ceftazidime, and cefuroxime were tested in a multicenter study to establish susceptibility testing criteria and quality control guidelines for Neisseria gonorrhoeae. Interpretive criteria were established by using triplicate testing of at least 100 gonococcal strains having various susceptibility patterns to currently utilized drug regimens. Only a susceptible category was proposed for cefotaxime and ceftazidime (greater than or equal to 31 mm and less than or equal to 0.5 micrograms/ml) because of rare resistant isolates. The other interpretive crtieria were cefoxitin susceptible, greater than or equal to 28 mm (less than or equal to 2 micrograms/ml); intermediate, 24-27 mm (4 micrograms/ml), and resistant, less than or equal to 23 mm (greater than or equal to 8 micrograms/ml); cefuroxime-susceptible, greater than or equal to 31 mm (less than or equal to 1 micrograms/ml); moderately susceptible, 26-30 mm (2 micrograms/ml); and resistant, less than or equal to 25 mm (greater than or equal to 4 micrograms/ml). Quality control criteria were established by using multiple agar lots, three disk lots, and a number of replicates consistent with National Committee for Clinical Laboratory Standards M23-T guidelines.

Cefotaxime↗

PubMedDate not supplied

Aztreonam: antibacterial activity, beta-lactamase stability, and interpretive standards and quality control guidelines for disk-diffusion susceptibility tests.

In vitro activity of aztreonam was compared with that of ceftazidime, cefotaxime, cefoperazone, piperacillin, and ticarcillin against 656 representative bacterial pathogens. Aztreonam was not active against gram-positive cocci but was as active as the third-generation cephalosporins against the Enterobacteriaceae, Haemophilus influenzae, and Neisseria gonorrhoeae. Additional data for 5,262 gram-negative bacilli isolated in four separate medical centers documented the low incidence of resistance to aztreonam; 97.2% of 4,312 isolates of Enterobacteriaceae and 79% of 854 isolates of Pseudomonas aeruginosa were inhibited by less than or equal to 8.0 micrograms of aztreonam/ml. Additional studies confirmed the stability of aztreonam in the presence of seven different beta-lactamases. For disk-diffusion susceptibility tests, 30-micrograms disks are recommended, with interpretive breakpoints of less than or equal to 15 mm for resistance (MIC greater than or equal to 32 micrograms/ml), 16-21 mm for intermediate susceptibility (MIC, 16 micrograms/ml), and greater than or equal to 22 mm for susceptibility (MIC less than 8.0 micrograms/ml). For quality control of tests with 30-micrograms disks, zone-size limits for Escherichia coli (ATCC 25922) should be 28-36 mm and those for P. aeruginosa (ATCC 27853) should be 23-29 mm.

Aztreonam↗

PubMedDate not supplied

Ticarcillin: a collaborative in vitro comparison with carbenicillin against over 9,000 clinical bacterial isolates.

The minimal inhibitory concentrations of ticarcillin and carbenicillin were determined for 9,236 clinical bacterial isolates by the broth microdilution method at four participating laboratories. Ticarcillin showed significantly increased activity against Klebsiella pneumoniae (P less than .001), Pseudomonas aeruginosa (P less than .001) and Aeromonas hydrophilia (P less than .005) when compared to carbenicillin, but no signifcant differences were observed against other gram-negative organisms. Ticarcillin was consistently less active against the gram-positive cocci, and these differences were significant for Staphylococcus aureus (P less than .001), Streptococcus agalactiae (P less than .001), Staphylococcus epidermidis (P less than .001) and Streptococcus viridans (P less than .005). Significant regional and institutional differences in susceptibility to the two drugs were observed for several species, including common nosocomial pathogens such as S. aureus, P. aeruginosa, K. pneumoniae and Escherichia coli.

Bacillus↗