Use of standard definitions for the extent of antibiotic resistance in bacteria: a systematic review and framework...

Various terms are used to categorize the extent of antibiotic resistance in bacteria. It is important to standardize the classification of drug-resistant bacteria to ensure clarity and generalizability of evidence across different disciplines and inform policy.

A literature search for articles published between 2011 and August 2025 indexed in MEDLINE and EMBASE, which used the terms: multidrug resistance, extensively drug resistance, pan-drug resistance, difficult-to-treat or usual drug resistance in either the methods or results sections, and which reported bacterial pathogens relevant to human health was performed. Data extracted were analysed quantitatively using multivariable logistic regressions and qualitatively to examine the study characteristics that adopted various definitions.

From 2465 eligible records, the most commonly used definition was by Magiorakos et al. accounting for 54% (1340/2465) of the articles: 8% (197/2465) used different definitions, and the remaining 38% (928/2465) did not define drug resistance. Overall, MDR was the most frequently used term (97%, 2400/2465), followed by XDR then PDR. Gram-negative bacteria were the most commonly studied bacteria (84%, 2078/2465). Definitions that deviated from those proposed by Magiorakos et al. used a different number of antibiotic classes to define extent of resistance, included non-susceptibility to newer antibiotic classes, studied typically community-acquired bacteria and used resistance genotype instead of antibiotic susceptibility phenotype.

The progressive development of antibiotic resistance necessitates updated definitions to include newer antibiotic agents and genotypes. These revised definitions can also prioritize antibiotic classes according to their efficacy profile, toxicity and availability, and should be validated against clinical datasets to correlate with patient outcomes.