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How does antibiotic resistance develop and spread?

Resistance occurs when bacteria change so that the drugs used to treat the infections caused by them become ineffective

Systematic misuse and overuse of antibiotics in human medicine and food production has driven the development and spread of antibiotic resistance and consequently put every nation at risk.

Resistance occurs when bacteria change so that the drugs used to treat the infections caused by them become ineffective. The changes occur at molecular level resulting in the formation of superbugs, which cause infections that do not respond to treatment.

As standard treatments for infections become ineffective, infections will persist and spread to others.

World Health Organization poster - 'Antibiotic Resistance: How it spreads'. "Antibiotic resistance happens when bacteria change and become resistant to the antibiotics used to treat the infections they cause."

Image sourced from WHO Global Action Plan on Antimicrobial Resistance.

Natural selection

Antibiotics kill or impede the growth of bacteria that are susceptible to them. Bacteria that remain unaffected by them are left to flourish. This process is known as natural selection.

It is not just infection-causing bacteria that are affected by this selection process. Antibiotics affect the body’s entire microbiome (sometimes known as ‘good bacteria’), thus resulting in an imbalance that can seriously affect an individual’s overall health and wellbeing.

'How antibiotic resistance occurs'. This image shows the four steps of ABR: 1. Some bacteria cells in human body are resistant, 2. Antibiotics kill bacteria but resistant bacteria remain, 3. Antibiotic resistant bacteria multiply, 4. Antibiotic resistance spreads.

Image sourced from Public Health England Health Matters: Antimicrobial Resistance.

Rising resistance

Resistance that occurs when a patient takes antibiotics has been shown, in clinical studies, to persist in that patient’s microbiome for up to 12 months. Furthermore, the bacteria develop resistance not only to the causative drug, but to several others as well.

Exposing a patient to antibiotics when not necessary (for example ‘just in case’ or to meet patient demands) increases that patient’s risk that the antibiotics will fail when they are necessary.

Antibiotics have an impact both at individual and society levels. Why? Because the resistant bacteria that were selected (focus of infection or microbiota) due to the antibiotic treatment can be transmitted from the individual who has taken the antibiotic treatment to other human beings, animals or the environment.

Although resistance can occur naturally, the unnecessary use of antibiotics is rapidly accelerating the pace at which it develops and spreads. Misuse and overuse of antibiotics puts us all at risk.

Infographic showing how 'misusing and overusing antibiotics puts us all at risk' - shows the main influences in resistance. "You can help reduce antibiotic resistance: always follow the advice of a qualified healthcare professional when taking antibiotics".

Image sourced from the World Health Organization.

Reducing resistance

To assist efforts to reduce antibiotic resistance, WHO has introduced three classifications of antibiotics: the AWaRe classification (Access, Watch, Reserve).

  1. The Access group includes antibiotics which offer the best therapeutic value while minimising the potential for resistance.
  2. The Watch group includes antibiotics which are more prone to selecting for resistance. Antibiotics in the Watch group (such as erythromycin) should be the priority target for antibiotic stewardship programmes to optimise use.
  3. The Reserve group includes the ‘last resort’ antibiotics, such as meropenem, which are reserved for the treatment of infections due to multi-drug-resistant organisms.
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