Antimicrobial Resistance

Antimicrobial resistance (AMR) is the ability of microorganisms - bacteria, viruses, fungi, and parasites - to survive exposure to medicines that once killed them or stopped their growth. Driven by the use and misuse of antimicrobials across human health, agriculture, and the environment, and spreading freely across borders, AMR is a cross-cutting global health challenge that threatens to undermine the treatment of common infections.

Definition

Antimicrobial resistance is the capacity of microorganisms to withstand the effects of antimicrobial medicines to which they were previously susceptible, reducing or eliminating the effectiveness of those drugs and making infections harder to treat.

Scope

This entry treats antimicrobial resistance as a global public-health and One Health problem: how resistance arises and spreads at the population level, its measured global burden, the drivers across sectors, and stewardship as a response. It does not provide antimicrobial selection, dosing, or individual treatment guidance. Mechanisms of resistance at the molecular level are covered by the microbiology entry cross-linked below.

Core questions

• How does antimicrobial resistance emerge and spread within and between populations?
• What is the global burden of drug-resistant infections?
• Which sectors - human medicine, agriculture, the environment - drive the selection of resistance?
• What is antimicrobial stewardship and why is coordinated global action required?

Key concepts

• Selection pressure from antimicrobial use and misuse
• Multidrug-resistant and priority pathogens
• One Health (human, animal, environmental sectors)
• Antimicrobial stewardship
• Empty drug-development pipeline
• Transboundary spread of resistant organisms

Mechanisms

At the population level, exposure to antimicrobials exerts selection pressure that favours the survival and spread of resistant organisms; broad and often inappropriate use across human medicine, animal husbandry, and agriculture amplifies this pressure, which is why AMR is framed as a One Health problem spanning human, animal, and environmental domains. Resistant organisms and resistance genes move between people, animals, food, and the environment and across borders, while a sparse pipeline of new antimicrobials limits the ability to replace drugs that lose effectiveness. The molecular mechanisms by which microbes acquire and express resistance are described in the microbiology entry on antimicrobial resistance.

Clinical relevance

Awareness of AMR as a population-level threat underpins prudent antimicrobial use and infection prevention, and helps professionals and students appreciate why preserving drug effectiveness is a collective responsibility. The entry describes population-level patterns and drivers and is not a basis for individual antimicrobial selection or treatment decisions.

Epidemiology

Systematic global estimates attribute a large and rising number of deaths to bacterial antimicrobial resistance, with the burden falling disproportionately on lower-income regions and on a defined set of priority pathogens; these analyses establish AMR as a leading global cause of death linked to infection.

Evidence & guidelines

The global response is organised around antimicrobial stewardship, surveillance, infection prevention, and investment in new diagnostics and drugs, coordinated through One Health frameworks. This entry summarises that policy framing and does not provide prescribing or stewardship protocols for individual patients.

History

Concern that resistance was outpacing antimicrobial development grew through the 2000s, captured in the Infectious Diseases Society of America's 'Bad Bugs, No Drugs' framing of priority pathogens and an empty pipeline. By the 2010s, calls for global solutions (Laxminarayan and colleagues, 2013) and comprehensive burden estimates established AMR as a top-tier global health priority.

Debates

How to balance access to antimicrobials with the need to limit overuse.

Restricting antimicrobial use to slow resistance can conflict with ensuring access for people who need treatment, especially in low-income settings where lack of access still causes more deaths than resistance; reconciling access and conservation is a central policy tension.

Key figures

• Christopher Murray
• Ramanan Laxminarayan
• Helen Boucher

Seminal works

• murray-2022
• laxminarayan-2013
• boucher-2009

Frequently asked questions

What is the difference between antimicrobial and antibiotic resistance?

Antibiotic resistance refers specifically to bacteria withstanding antibiotics, while antimicrobial resistance is the broader term covering bacteria, viruses, fungi, and parasites resisting the medicines used against them.

Why is antimicrobial resistance called a One Health problem?

Because its drivers and spread cut across human medicine, animal agriculture, and the environment, so it can only be addressed by coordinated action across all three sectors.