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MIC is the lowest concentration that prevents visible growth, while MBC is the lowest concentration that kills at least 99.9% of the original inoculum after subculture. Broth microdilution provides quantitative MIC results; agar dilution, disk diffusion, gradient strips, and automated panels offer other approaches to susceptibility testing. Specialized methods can detect resistance mechanisms or clarify ambiguous phenotypic results, including assays for resistance genes, beta-lactamases, altered penicillin-binding proteins, inducible MLS_B resistance, and ESBLs. Time-kill curves assess bactericidal activity and interactions over time. Results are interpreted using breakpoint standards from CLSI or EUCAST, which categorize isolates as susceptible, intermediate, or resistant.