Re-evaluations of disk diffusion quality control ranges for 11 drugs: report from the QC working group of the national committee for clinical laboratory standards.

A multi-laboratory re-evaluation protocol was initiated in 2001 to address broad-based concerns about the appropriateness of contemporary disk diffusion quality control (QC) guidelines of several antimicrobials in the tables of the M2-A7 standard of the National Committee for Clinical Laboratory Standards (NCCLS). This study that conformed to the NCCLS M23-A2 guideline demonstrates the dynamic processes that result in modification or development of these 11 QC zone diameter ranges. These changes included long-term QC problems for cefazolin (new range, 21-27 mm) and trimethoprim/sulphamethoxazole (new range, 23-29 mm) when tested against Escherichia coli ATCC 25922, and ticarcillin (new range, 21-27 mm) versus Pseudomonas aeruginosa ATCC 27853. All proposed ranges have been approved by the NCCLS for publication in M100-S12 tables in 2002.