The standard, titled Quality Control for Commercially Prepared Microbiological Culture Media , provides specific guidelines for the quality assurance of ready-to-use culture media in clinical laboratories. It is primarily used to determine which media require routine retesting by the end-user and which are "exempt" due to proven reliability. Core Content & Scope
CLSI M22-A3 is the third edition of a Clinical and Laboratory Standards Institute (CLSI) guideline titled "Methods for Antimicrobial Disk Susceptibility Tests" (note: CLSI document codes sometimes vary; M22 series specifically covers antimicrobial susceptibility testing methods and interpretive criteria). This edition updates procedures, quality-control recommendations, and interpretive criteria for disk diffusion testing of bacteria to ensure reliable, reproducible susceptibility results across clinical microbiology laboratories. clsi m22a3 pdf
Here is the most important section for anyone who typed into a search engine hoping for a free download. Even for exempt media
: Detailed requirements for controlling contamination, physical imperfections (e.g., agar thickness, bubbles), and the use of working control cultures. The standard explicitly applies to
The standard explicitly applies to , ready-to-use microbiological culture media. It does not cover media prepared entirely in-house from raw ingredients (though those labs may still use it as a reference). Intended users include clinical labs, public health labs, veterinary diagnostics, and industrial microbiology facilities.
Even for exempt media, labs must check for physical defects such as: Cracked Petri dishes or tubes. Excessive bubbles or rough surfaces. Obvious contamination or hemolysis. Incorrect agar depth (less than 3 mm) or unequal filling.