Multidrug-resistant (MDR) bacteria are strains that resist the action of multiple classes of antimicrobial agents. They survive exposures that would normally inhibit or kill susceptible organisms, making infections harder to treat.
Explanation
MDR bacteria have acquired mechanisms that allow them to evade the inhibitory effects of unrelated antimicrobial compounds. One working definition states that multidrug resistance occurs when a strain is non susceptible to at least one agent in three or more antimicrobial categories. Resistance can arise by accumulation of multiple resistance genes on plasmids, transposons or chromosomes, often acquired through horizontal gene transfer. A single gene encoding an efflux pump or porin alteration may also confer cross resistance across several drug classes by reducing cellular uptake or actively exporting many compounds. Uncontrolled antibiotic use in health care, agriculture and community settings selects for these traits, and prolonged therapy allows resistant subpopulations to proliferate. Once established, MDR strains spread easily within hospitals and across borders, posing a serious public health threat. The limited activity of available antibiotics against MDR organisms means infections may require combination therapy, use of drugs with greater toxicity, or procedures to remove infected tissues. Surveillance and antibiotic stewardship programmes are essential to slow the emergence and dissemination of multidrug resistance.
Clinical Examples and Significance
- MDR Mycobacterium tuberculosis is defined as tuberculosis resistant to isoniazid and rifampicin, the two most potent first‑line agents. Treatment requires lengthy regimens of second‑line drugs.
- MDR Gram‑negative bacteria such as Escherichia coli, Klebsiella pneumoniae and Acinetobacter baumannii often carry extended‑spectrum beta‑lactamases and carbapenemases, limiting options to polymyxins or novel combinations.
- MDR Staphylococcus aureus and Enterococcus faecium resistant to beta‑lactams and aminoglycosides can cause hospital‑acquired bloodstream and wound infections.
- Prevention strategies include prudent antibiotic use, infection control measures in healthcare facilities, and development of new antimicrobial agents or alternative therapies.
Widespread multidrug resistance compromises the effectiveness of available antibiotics and threatens to reverse gains in infectious disease control. Understanding the genetic basis of MDR and implementing global stewardship are critical to preserve antimicrobial efficacy. Research into novel targets and combination therapies offers hope for combating these resilient pathogens.
Related Terms: Resistome, Efflux Pump, ESBL, Carbapenemase, Antibiotic Stewardship