Mixed Cultures, Unusual Phenotypes, and Confirmation

Distinguish a likely technical error from a plausible unusual resistance phenotype by checking identification–AST concordance and intrinsic resistance patterns.

Select confirmatory methods for flagged Gram-positive resistance phenotypes such as methicillin resistance in staphylococci and vancomycin resistance in enterococci.

Perform and interpret the D-test for inducible clindamycin resistance.

Select appropriate phenotypic or molecular follow-up for suspected ESBL or carbapenemase production in Gram-negative bacteria.

Explain why automated colistin results may be unreliable and when broth microdilution confirmation is required.