Disk diffusion susceptibility testing and broth microdilution quality control guidelines for BMY-28100, a new orally administered cephalosporin

Abstract

The BMY-28100 30-,ig-disk test was evaluated by using 615 clinical isolates. Regression analyses and error rates were determined, leading to the recommendation of 18-mm zone diameters (MIC correlate, .8.0 ,ug/ml) for susceptibility and c14-mm zone diameters (MIC correlate, .32 ,ug/ml) for resistance. Nearly ail false-susceptible disk test results were among the Providencia spp. and the beta-lactamase-positive Haemophilus influenzae strains. Susceptibility disk test results for these species should be interpreted with caution. The following broth microdilution MIC quality control guidelines were determined from results of a multilaboratory trial: Escherichia coli ATCC 25922, 1.0 to 4.0 Fig/ml; Enterococcusfaecalis ATCC 29212, 4.0 to 16 ,ug/ml; Staphylococcus aureus ATCC 29213, 0.25 to 1.0 ,ig/ml; and Pseudomonas aeruginosa ATCC 27853, >32 ,ug/ml.

Interpretive accuracy of the disk diffusion method for testing newer orally administered cephalosporins against Morganella morganii

“…Standardized susceptibility testing accuracy with the disk diffusion method for testing some newer orally administered cephalosporins against Morganella morganii has been questioned (5,6,8,15). The occurrence of serious interpretive errors (false-susceptible or very major errors) when the current criteria for these antimicrobial disks are employed could lead to inappropriate chemotherapy.…”

“…The occurrence of serious interpretive errors (false-susceptible or very major errors) when the current criteria for these antimicrobial disks are employed could lead to inappropriate chemotherapy. Studies have cited false-susceptible disk diffusion problems with cefetamet and cefixime when the interpretive criteria for these drugs were being established (5,8,9). To determine the extent of this problem, we tested 100 regionally acquired strains of M. morganii against eight cephems including cefdinir (9, 12), cefetamet (4,5), cefixime (3,4,10), cefpodoxime (4, 6), cefprozil (4,8,11), ceftibuten (1,4), cefuroxime (2,4), and loracarbef (4, 7).…”

“…The regression equ 0.84) is plotted as a dashed line. drugs in the NCCLS informatio table footnote (15), which lists ant not applicable for testing M. more the only organism to be implicated the other two members of the trit diffusion interpretive errors with some of the newer orally administered cephalosporins including cefetamet, cefprozil, and loracarbef (5,7,8). The extent of this problem remains to be studied with a larger group of recent clinical strains and is the subject of a study in progress.…”

Disk diffusion susceptibility testing for LY163892 (KT-3777), a new orally administered 1-carbacephem

“…Several investigational oral cephalosporins have wider spectra of antimicrobial activity, necessitating separate susceptibility testing (1, 3, 4). In addition, some of these newer agents have false-susceptibility disk testing rates that have required some modifications of test interpretive criteria (3,4,6). The studies reported here indicate that LY163892, cefaclor, and other available oral cephalosporins have virtually identical spectra of antimicrobial activity, except for H. influenza (9,10,13).…”

Inability of cephalothin testing to predict cefprozil susceptibility

“…Jones et al (6) reported 10% very major and 15% minor errors with cefprozil against H. influenza (all ,-lactamaseproducing strains). We did not observe as high a falsesusceptibility rate with cefprozil disks with H. influenza.…”