Glossary · Dysbiosis and disease
Antimicrobial resistance
In one sentence
Antimicrobial resistance (AMR) is the ability of bacteria, viruses, fungi or parasites to stop responding to medicines that used to control them, making infections harder to treat.
Also known as: AMR · antibiotic resistance · antimicrobial resistances · drug-resistant infections · multidrug resistance
What is antimicrobial resistance?
Antimicrobial resistance (AMR) describes a microorganism that no longer responds to a drug that once inhibited or killed it. It covers antibiotics, antivirals, antifungals and antiparasitics, although the most pressing clinical problem is bacterial resistance to antibiotics.
The WHO lists AMR among the top global public health threats. The GRAM study published in The Lancet in 2022 (Murray et al.) estimated that, in 2019, bacterial AMR was directly responsible for about 1.27 million deaths and associated with around 4.95 million.
How it works
Microbes become resistant in two main ways:
- Mutations in their own genome that alter the drug’s target or its route into the cell.
- Horizontal gene transfer, often via plasmids, which lets a resistance gene move from one bacterium to another, sometimes across species.
Common mechanisms include enzymes that inactivate the drug (beta-lactamases and carbapenemases, for instance), target modification, reduced permeability and efflux pumps. Resistance to several antibiotic classes is called multidrug resistance (MDR); broader patterns are described as extensively drug-resistant (XDR).
How it is detected
Two approaches complement each other:
- Phenotypic: antimicrobial susceptibility testing measures how a cultured isolate behaves against each drug. It needs the organism to grow, so it depends on a positive blood culture or other culture.
- Genotypic: methods such as PCR or NGS detect genes or markers linked to resistance directly in the sample.
A detected gene does not always translate into clinical resistance, and a negative result does not rule it out, because some mechanisms are not in the reference databases. That is why both approaches are combined, and interpretation rests with the clinician who requested the test.
Example
An intensive care team is managing a patient with suspected sepsis who has already had antibiotics and whose blood cultures are negative. They request a metagenomic blood test. The report identifies an Enterobacterales species and a plasmid-borne carbapenemase gene. The finding does not replace susceptibility testing, but it prompts the team to review antibiotic cover and tighten infection-control measures while other results are pending.
Antimicrobial resistance at Xenogene
AMC CRITICAL is a clinical metagenomics test on venous blood for critical situations such as sepsis, transplantation or persistently negative blood cultures. According to its product page, alongside identifying microorganisms it looks for resistance plasmids and antibiotic resistance genes, flags multidrug-resistant (MDR) and extensively drug-resistant (XDR) patterns and includes alerts for multidrug-resistant pathogens. It is a support tool for healthcare professionals, who weigh these data against culture, susceptibility results and the patient’s course.
Frequently asked questions
What causes antimicrobial resistance?
Resistance is a natural process: microbes change genetically and those that survive a drug go on to multiply. According to the WHO, the misuse and overuse of antimicrobials in humans, animals and plants speeds up both its emergence and its spread.
Does finding a resistance gene mean the antibiotic will not work?
Not necessarily. A resistance gene points to a possible mechanism, but whether it is expressed and how much it matters depends on the organism and the setting. Genetic findings are read alongside phenotypic susceptibility testing, where available, and the clinical picture.
Is it my body that becomes resistant to antibiotics?
No. It is the microorganism that becomes resistant, not the person. Someone can carry resistant bacteria in their microbiota without symptoms and pass them on to others.
Related terms
- Sepsis
Sepsis is life-threatening organ dysfunction caused by a dysregulated host response to infection (Sepsis-3 definition, 2016). It is a medical emergency that needs immediate treatment.
- Bacteraemia
Bacteraemia is the presence of viable bacteria in the bloodstream, usually confirmed by blood cultures. It can be transient and harmless or part of a serious infection, and it is not the same as sepsis, which is defined by the body's response to infection.
- Blood culture
A blood culture incubates a blood sample in bottles of nutrient broth to find out whether live bacteria or fungi are circulating in the bloodstream. If anything grows, it is identified and tested against antibiotics to guide treatment.
- Clinical metagenomics
Clinical metagenomics (mNGS) is the untargeted sequencing of the genetic material in a patient sample to detect bacteria, viruses, fungi or parasites without choosing the pathogen in advance. It complements culture and susceptibility testing rather than replacing them.
- NGS (next-generation sequencing)
NGS (next-generation sequencing) is a family of technologies that read millions of DNA or RNA fragments in parallel in a single run, making it possible to study whole genomes, targeted genes or entire microbial communities at scale.
Educational content for healthcare professionals and the general public. It does not replace assessment by a healthcare professional: ordering and interpreting any test is the responsibility of the requesting clinician.
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