Resistance in microbiology refers to the ability of microorganisms to survive and proliferate despite exposure to agents or conditions that would normally inhibit or kill them.
Mechanisms and Evolution
Antimicrobial resistance arises through genetic mutations or acquisition of resistance determinants via horizontal gene transfer. Changes to target sites, production of enzymes that degrade or modify antibiotics, active efflux pumps, and reduced permeability of the cell envelope are common strategies. Bacteria can carry resistance genes on plasmids, transposons or integrons, facilitating rapid dissemination across species. Selective pressure from antibiotic misuse in medicine, agriculture and animal husbandry promotes the survival of resistant populations and encourages the accumulation of multiple resistance genes, leading to multidrug resistance. Some bacteria exhibit intrinsic resistance due to structural features, such as the impermeable outer membrane of Gram negative organisms or the lack of a peptidoglycan target in Mycoplasma species. Resistance can also develop against heavy metals, disinfectants and environmental stresses like heat, acidity and oxidative stress, highlighting the broad adaptive capacity of microorganisms.
Clinical Impact and Examples
Clinically, resistant pathogens pose significant challenges. Methicillin‑resistant Staphylococcus aureus (MRSA) produces altered penicillin‑binding proteins that render β‑lactam antibiotics ineffective. Vancomycin‑resistant enterococci modify the D‑Ala‑D‑Ala terminus of their cell wall precursors to reduce drug binding. Extended‑spectrum β‑lactamase–producing Gram‑negative bacteria hydrolyze third‑generation cephalosporins, while multidrug‑resistant Mycobacterium tuberculosis strains require complex treatment regimens. Resistance is not limited to antibiotics: some molds withstand high osmotic pressure in jams and syrups, and bacterial spores resist heat and desiccation. Understanding these mechanisms guides the development of new therapeutics and stewardship practices.
Resistance reflects the evolutionary capacity of microbes to overcome threats. Addressing this phenomenon requires prudent use of antimicrobials, surveillance of resistance genes and investment in novel treatments.
Related Terms: Antibiotic Resistance, Plasmid, Efflux Pump, Beta‑Lactamase, Mutation