title: Evaluation of two standardized disk methods for testing antimicrobial susceptibility of Pseudomonas aeruginosa and of the Enterobacteriaceae.
abstract: Two standardized disk diffusion susceptibility testing methods were compared using Pseudomonas aeruginosa and members of the Enterobacteriaceae. The standard Bauer-Kirby method and the agar overlay method of Barry et al. were compared using carbenicillin (50- and 100-mug disks), gentamicin, polymyxin B, and colistin sulfate. Both methods gave nearly comparable zone sizes with the enteric bacilli. However, with P. aeruginosa the agar overlay method gave zones 1 to 2 mm smaller than the Bauer-Kirby method with all drugs except gentamicin. In spite of these small differences, further examination of minimal inhibitory concentration-zone size correlations indicated that the same interpretive zone standards can be applied to either diffusion technique. For testing carbenicillin against Pseudomonas sp., 50-mug disks were unsatisfactory, especially with the agar overlay method; 100-mug disks were far superior with both methods.
mesh_terms: D002228:Carbenicillin / Q000494:pharmacology*; D004058:Diffusion; D004755:Enterobacteriaceae / Q000187:drug effects*; D005069:Evaluation Studies as Topic; D005839:Gentamicins / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D011113:Polymyxins / Q000494:pharmacology*; D011550:Pseudomonas aeruginosa / Q000187:drug effects*
chemical_list: D005839:Gentamicins; D011113:Polymyxins; D002228:Carbenicillin