Phenotypic Confirmation by Broth Microdilution and Reporting
- Phenotypic confirmation by broth microdilution is performed using either of the previously mentioned antimicrobial agents and testing in combination with clavulanic acid. A ≥ 3 twofold concentration decrease in an MIC between the agent tested alone, versus testing in combination with clavulanate is taken to be phenotypic confirmation of ESBL production.
- The same reporting should be followed as for the phenotypic confirmation by disc diffusion ONLY IF the new CLSI cephalosporin and aztreonam interpretive criteria have NOT been implemented.
- If using the current criteria, test interpretations do not need to be changed from susceptible to resistant.