Antimicrobial Resistance


What is antimicrobial resistance?

Microbes are tiny organisms such as bacteria, viruses, fungi, and parasites. Many microbes are harmless or even beneficial to humans. However, others cause disease in people, animals, and plants. For example, bacteria cause strep throat and food poisoning. Viruses cause the common cold and seasonal influenza. Fungi cause athlete’s foot and yeast infections. A parasite causes malaria. Antimicrobials are medications used to treat infections caused by microbes. Some examples are penicillin (an antibiotic), valacyclovir (an antiviral agent), or fluconazole (an antifungal agent).

Antimicrobial resistance refers to the ability of microbes to evolve in a way that allows them to continue to live and grow even in the presence of drugs designed to kill them. As a result, some anti-infective drugs are now less effective than when they were first introduced. Some types of infections have become harder to treat.

What contributes to the rate of antimicrobial resistance?

The following factors have a role in increasing the rate of antimicrobial resistance:

  • The fact that antimicrobial drugs are used at all causes microbes to resist them.
  • Prescribing antimicrobials when not needed, or at the wrong dose or length of time, prompts more microbes to become drug-resistant. Some healthcare providers give in to pressure from patients to “try something,” even when the exact cause of symptoms is not known. For example, viral infections such as the common cold should not be treated with antibiotics, because antibiotics kill only bacteria.
  • Treating an infection with a broad spectrum antimicrobial that works against a large variety of microbes instead of one that targets a specific microbe can increase the risk of resistance.
  • Antimicrobials are often used in hospitals where patients are seriously ill. The close contact among hospital workers and sick patients creates a situation that makes it easy for microbes to spread. Seriously ill hospital patients are prone to infections and often take antimicrobial drugs. However, the extensive use of such drugs along with close contact among sick patients creates a situation that makes it easy for drug-resistant microbes to spread from one person to another.
  • The use of antibiotics in agriculture to promote growth in food animals is viewed by some scientists as a major problem. Meat-producing animals given antibiotics can develop drug-resistant bacteria. These resistant bacteria may contaminate meat or other food products from animals. The resistant bacteria are then passed along to people who eat these foods.

How common is antimicrobial resistance?

According to the CDC, at least two million people a year in the U.S. become infected with bacteria that are resistant to antibiotics. At least 23,000 people die as a result. Each year, conditions caused by antimicrobial resistance causes:

  • An estimated $20 billion in additional healthcare costs
  • $35 billion in other costs to society as a whole
  • More than 8 million additional days of hospital care

Symptoms and Causes

What causes antimicrobial resistance?

Humans discovered antibiotics in the 1930s and have used them in medical practice since the 1940s. In contrast, microbes have lived on earth for 3.5 billion years in every type of environment possible, making them the most numerous and adaptable form of life on the planet. The ability of microbes to resist and outwit substances that can kill them has been built into their genetic makeup and perfected over billions of years.

The paths to resistance at the level of a microbe are as follows:

  1. When an antimicrobial agent is given to a patient, the agent kills most microbes. However, a few resistant microbes may survive.
  2. These microbes became resistant through a gene mutation (change) or by getting a resistance gene from other microbes around them.
  3. Resistant microbes are able to grow and rapidly spread to cause new infections that do not respond to the original antimicrobial agent.
  4. Through gene mutations, microbes adapt readily to new environmental conditions. They are also able to get genes from other microbes around them, including genes for drug resistance.

What are the symptoms of antimicrobial resistance?

If an infection will not go away even after the patient is given an antimicrobial drug, this may be a hint that antimicrobial resistance is present. In 2013, the Centers for Disease Control (CDC) published a report ranking 18 drug-resistant threats in the U.S. These threats include various forms of the following diseases:

  • Gonorrhea
  • Urinary tract infections
  • Infections caused by methicillin-resistant Staphylococcus aureus (MRSA)
  • Tuberculosis
  • Pneumonia
  • Malaria
  • Influenza
  • Candida (yeast) infections

If no progress is made in slowing the increase of antimicrobial resistance, common infections and minor injuries that have been effectively treated for decades may once again become fatal.

Diagnosis and Tests

How is antimicrobial resistance diagnosed?

Diagnostic laboratory tests can find which microbe is causing an infection and whether the microbes present are resistant to certain antimicrobials. However, these tests can take days or even weeks to produce results. This is because microbes must grow in a laboratory before they can be identified.

Management and Treatment

How is antimicrobial resistance treated?

Anyone with a drug-resistant infection should seek a doctor’s help. It may be possible to use a different drug, a higher dose, a longer period of treatment, multiple drugs in combination, or different non-drug treatments to cure the infection.

What complications can result from antimicrobial resistance?

Antimicrobial resistance can cause:

  • The development of more serious infections
  • Longer recovery times
  • Increased medical expenses
  • The use of more-expensive drugs or riskier procedures
  • Possible death


How can antimicrobial resistance be prevented?

It is not possible to completely eliminate antimicrobial resistance, as microbes will always be able to modify themselves and adapt to their environment. However, slowing the spread of antimicrobial resistance and developing new treatments are realistic goals. Reaching these goals will require action on a number of fronts.

Living With

How can people in general help?

  • Work closely with a physician to discuss symptoms and decide on the correct medicine to treat any illness.
  • Follow exactly the directions for any prescription medicine.
  • Never take another person’s prescription medicine or share yours with them.
  • Never save old prescription drugs for use at a later time.
  • Get vaccinations as recommended.
  • Follow good general health practices such as a proper diet, exercise, getting enough sleep, and good hygiene (especially frequent hand-washing) in order to prevent illness and the need for antimicrobial drugs.

How can healthcare workers and pharmacists help?

  • Follow programs for infection prevention and control in healthcare facilities.
  • Prescribe and dispense antimicrobial drugs only when needed.
  • Prescribe and dispense antimicrobial drugs meant only for the specific illness or microbe(s) being treated.

How can policymakers and government officials help?

  • Regulate and promote the correct use of antimicrobials and limit their use in food products.
  • Encourage the research and development of new treatments by pharmaceutical companies. This includes not only new antimicrobials but new vaccines and other drugs and therapies that can strengthen the immune system.
  • Provide information to the public on how to control antimicrobial resistance.

Reviewed by a Cleveland Clinic medical professional.

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy