Determination of Interpretive Breakpoints for Ceftazidime Disc‐diffusion Susceptibility Testing Using Single‐Strain Regression Analysis

Abstract

Interpretive breakpoints for ceftazidime disc‐diffusion susceptibility testing were determined using single‐strain regression analysis (SRA). Regression lines were determined for a total of 58 strains representing 15 species, from inhibition zone diameters obtained for discs containing six different ceftazidime concentrations. Statistical analysis for excluding non‐linearity of test‐results was performed. A minimum of five tests on consecutive days was required for maximal precision of regression analysis according to the SRA‐method. Calculated regression lines showed similarities within individual and groups of bacterial species. A minimum of five strains could be used to represent these groups. Interpretive breakpoints according to recommended MIC‐limits were determined for each species taking into consideration confidence limits for zone correlates of MIC‐values. Single‐strain regression analysis for the determination of interpretive breakpoints for ceftazidime disc‐diffusion susceptibility testing in individual laboratories.

Setting interpretive breakpoints for antimicrobial susceptibility testing using disk diffusion

“…SRA can be done in individual laboratories where interlaboratory variation otherwise would have resulted in erroneous interpretations. The SRA method has been applied to several combinations of antimicrobials and species [15,[37][38][39][40][41][42][43][44]. A simple explanation of SRA with a review was published in 1991 [45].…”