Comparative susceptibilities of Campylobacter pylori to norfloxacin and other agents.

Twenty-one strains of Campylobacter pylori (Campylobacter pyloridis) were tested for susceptibility to norfloxacin and other agents by the serial agar dilution method. Ampicillin (MIC for 90% of isolates [MIC90], 0.016 micrograms/ml) and famotidine (MIC90, greater than 1,024 micrograms/ml) were, respectively, the most and the least active of the agents tested. Norfloxacin (MIC90, 1 microgram/ml) and imipenem (MIC90, 0.125 micrograms/ml) were substantially active against this organism.

Comparative in vitro activity of imipenem against Haemophilus influenzae and Haemophilus parainfluenzae.

A microdilution broth method was used to test 77 clinical isolates of Haemophilus influenzae and Haemophilus parainfluenzae, including beta-lactamase-positive and -negative strains, for susceptibility to ampicillin, chloramphenicol, and imipenem. Except for ampicillin against beta-lactamase-producing strains (MIC for 90% of strains [MIC90], greater than or equal to 128 micrograms/ml), all three antimicrobial agents had comparable in vitro activity (MIC90, less than or equal to 1 microgram/ml) against these bacterial strains.

Tentative interpretive criteria for in vitro antibacterial susceptibility testing with imipenem.

Imipenem is a member of a new class of highly potent beta-lactam antibiotics, carbapenems, with a very broad antibacterial spectrum. This study was undertaken to determine tentative interpretive criteria for in vitro susceptibility testing with 10-micrograms imipenem disks. A careful examination of the zone diameters and the corresponding MICs for 489 clinical isolates by regression-line analysis and the error rate-bounded classification scheme suggested the following guidelines: greater than or equal to 16 mm with an MIC correlate of less than or equal to 4 micrograms/ml for susceptible, 14 to 15 mm (8 micrograms/ml) for moderately susceptible, and less than or equal to 13 mm (greater than or equal to 16 micrograms/ml) for resistant. Lack of cross-resistance between imipenem and broad-spectrum cephalosporins such as cefotaxime and ceftazidime argues against their use as class disks to predict in vitro susceptibility of bacterial species to carbapenems.

Evaluation of three broth disk methods for testing the susceptibility of anaerobic bacteria to imipenem.

Imipenem is a member of a new class of highly potent beta-lactam antibiotics, carbapenems, with an antibacterial spectrum that includes nearly all currently known aerobic and anaerobic bacterial species of clinical significance. Although relatively stable in most standard laboratory media used for antimicrobial susceptibility testing, imipenem undergoes rapid inactivation in thioglycolate broth, a recommended medium for susceptibility testing of anaerobic bacteria by the broth disk method. In the current study, a panel of 36 anaerobic bacteria consisting of 28 clinical isolates and eight quality control strains was used to determine the suitability and accuracy of the broth disk methods with brain heart infusion, Schaedler, and anaerobic broths, in comparison to the reference agar dilution method, for the anaerobic susceptibility testing of imipenem. To achieve single test concentrations of approximately 8, 16, and 64 micrograms/ml for imipenem, cefoxitin, and piperacillin, respectively, which correspond to the MIC breakpoints of the test drugs, four 10-microgram imipenem disks, three 30-microgram cefoxitin disks, and three 100-microgram piperacillin disks were used in 5 ml of broth. The correlation between the reference agar dilution method and each of the three broth disk elution procedures evaluated was excellent, for imipenem (100% agreement) and somewhat less so for cefoxitin and piperacillin. Therefore, brain heart infusion, Schaedler, and anaerobic broths, but not thioglycolate broth, are suitable for anaerobic susceptibility testing of imipenem by the disk elution method.