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Antibiotic resistance

Using antibiotics incorrectly can cause some bacteria to change or permit resistant bacteria to grow. These changes make bacteria stronger, so most or all antibiotic medicines no longer work to kill them. This is called antibiotic resistance. Resistant bacteria continue to grow and multiply, making infections harder to treat.


Antibiotics work by killing bacteria or keeping them from growing. Resistant bacteria keep growing, even when antibiotics are used. This problem is seen most often in hospitals and nursing homes.

New antibiotics are created to work against some resistant bacteria. But there are now bacteria that no known antibiotic can kill. Infections with such bacteria are dangerous. Because of this, antibiotic resistance has become a major health concern.

Causes of Antibiotic Resistance

Antibiotic overuse is a main cause of antibiotic resistance. This occurs in both humans and animals. Certain practices increase the risk of resistant bacteria:

  • Using antibiotics when not needed. Most colds, sore throats, and ear and sinus infections are caused by viruses. Antibiotics don't work against viruses. Many people don't understand this and sometimes ask for antibiotics when not needed. This leads to an overuse of antibiotics. The Centers for Disease Control and Prevention (CDC) estimates that 1 in 3 antibiotic prescriptions are not needed.
  • Not taking antibiotics as prescribed. This includes not taking all of your antibiotics, missing doses, or using leftover antibiotics. Doing so helps the bacteria learn how to grow in spite of the antibiotic. As a result, the infection may not fully respond to treatment the next time the antibiotic is used.
  • Misuse of antibiotics. You should never buy antibiotics online without a prescription or take someone else's antibiotics.
  • Exposure from food sources. Antibiotics are widely used in agriculture. This can lead to resistant bacteria in the food supply.

Why Antibiotic Resistance Is a Concern

Antibiotic resistance causes a number of problems:

  • The need for stronger antibiotics with possibly severe side effects
  • Fewer choices of antibiotics to treat antibiotic resistant bacteria
  • More expensive treatment
  • Harder-to-treat illness can spread from person to person
  • More hospitalizations and longer stays
  • Serious health problems, and even death

How Antibiotic Resistant Bacteria Spread

Antibiotic resistance can spread from person to person or from animals to humans.

In people, it may spread from:

  • One patient to other patients or staff in a nursing home, urgent care center, or hospital
  • Health care staff to other staff or to patients
  • Patients to other people who come in contact with the patient

Antibiotic resistant bacteria may spread from animals to humans through:

  • Food sprayed with water that contains antibiotic resistant bacteria from animal feces

Help Prevent Antibiotic Resistance

To prevent antibiotic resistance from spreading:

Alternative Names

Antimicrobials - resistance; Antimicrobial agents - resistance; Drug-resistant bacteria



Centers for Disease Control and Prevention website. Antimicrobial resistance. Updated December 17, 2021. Accessed September 6, 2022.

Centers for Disease Control and Prevention website. Antibiotic resistance questions and answers. Updated August 23, 2022. Accessed September 6, 2022.

Opal SM, Pop-Vicas A. Molecular mechanisms of antibiotic resistance in bacteria. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 18.

Review Date 4/9/2022

Updated by: Jatin M. Vyas, MD, PhD, Associate Professor in Medicine, Harvard Medical School; Associate in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.