A Comparative Analysis of CLSI and EUCAST Interpretations of Intermediate Antimicrobial Susceptibility: Navigating the Gray Zone

Abstract

Antimicrobial susceptibility testing (AST) is fundamental to the effective management of infectious diseases. Accurate interpretation of AST results guides clinicians in selecting appropriate antimicrobial agents and optimizing dosing regimens. Central to this process are the interpretive categories assigned to antimicrobial-organism combinations, which translate in vitro data into clinically relevant predictions of therapeutic success. However, the interpretation of intermediate susceptibility, particularly concerning the concepts of "Susceptible, Dose-Dependent" (SDD) employed by the Clinical and Laboratory Standards Institute (CLSI) and "Susceptible, Increased Exposure" favored by the European Committee on Antimicrobial Susceptibility Testing (EUCAST), has been a source of ongoing debate and refinement within clinical microbiology. This essay presents a comparative analysis of these two interpretive approaches, exploring their historical context, underlying principles, clinical implications, and the ongoing evolution of AST interpretation.