Antimicrobial Multidrug Resistance and Mechanisms of Action: An Overview

Antimicrobial multidrug resistance is the ability of microorganisms to withstand the effects of several antimicrobial agents, presenting a major challenge to modern healthcare systems worldwide. Although considerable research has been conducted, the molecular and evolutionary mechanisms underlying resistance are still not completely understood. This review brings together current knowledge to explain how resistance originates, spreads, and persists in different pathogens. Microorganisms may show primary resistance, which arises naturally without prior exposure to drugs, or acquired resistance, which develops after contact with antimicrobial agents. Intrinsic resistance is related to structural or functional traits that are naturally present in specific species. Strains that are extensively resistant demonstrate survival against a wide range of important drugs, while clinical resistance becomes evident when standard treatments fail to control infections effectively. Pathogens employ several mechanisms, including enzymatic inactivation of drugs, modification of target sites, reduced drug uptake, and active efflux systems. Parasitic and fungal pathogens often rely on impaired drug transport and altered molecular targets, whereas viruses adopt multiple strategies to escape the activity of antiviral drugs. The appearance of highly resistant organisms such as methicillin-resistant Staphylococcus aureus reflects the growing threat of so-called superbugs. The rapid spread of resistance, driven by genetic mutations and horizontal gene transfer, highlights its ability to disseminate quickly within microbial populations. A clear understanding of these molecular processes is essential to guide the development of new therapeutic strategies, improve clinical management, and strengthen global efforts to control antimicrobial resistance.