title: Appraisal of disk sensitivity tests with mecillinam.
abstract: Disk susceptibility tests for mecillinam were carried out on 167 hospital isolates of Enterobacteriaceae from Vancouver. Inhibition zone sizes with eight experimental variations were compared by three-way analysis of variance. The Association of Clinical Pathologists' method gave significantly (p = 0.0002) larger zones than the Kirby Bauer method (24.9 +/- SD 7.5 and 23.4 +/- 7.3 mm, respectively). 10 microgram mecillinam disks from Mast Laboratories gave significantly (p = 0.0004) larger zones than the Baltimore Biological Laboratories (BBL) equivalent (24.9 +/- 7.6 and 23.4 +/- 7.2 mm, respectively). Differences between Oxoid Iso-sensitest agar and BBL Mueller Hinton agar were not quite significant (24.5 +/- 7.9 and 23.8 +/- 6.9 mm, respectively, p = 0.061). Each disk test method was significantly different from at least one other (Duncan multiple range test, alpha = 0.05). A semilogarithmic regression was established between the antibiotic disk inhibition zone and the MIC for each experimental variation. BBL Mueller Hinton and Oxoid Iso-sensitest media did not give significantly different results in MIC determinants by a surface inoculation method. An additional 146 organisms from hospitals in New York provided a wider range of organisms from a different location. Pooled data from both centres were used to identify breakpoints for mecillinam in the disk susceptibility test using the Kirby Bauer method with BBL disks and media. A 16-mm breakpoint with 10 microgram mecillinam disks provides a realistic and conservative prediction of probable response to attainable serum concentrations of this antibiotic.
mesh_terms: D000560:Amdinocillin / Q000494:pharmacology*; D004755:Enterobacteriaceae / Q000187:drug effects*; D008826:Microbial Sensitivity Tests; D010397:Penicillanic Acid / Q000494:pharmacology*
chemical_list: D010397:Penicillanic Acid; D000560:Amdinocillin