Antibiotic Resistance

Antibiotic resistance is the ability of microorganisms * , specifically bacteria, to adapt to and to withstand the effects of antibiotics. Such microorganisms are often called superbugs. As a result of antibiotic resistance, antibiotics for superbug infections may become far less effective or may not work at all, leaving doctors with few if any choices with which to treat them. Antibiotic resistance is a growing worldwide medical and health problem.

What Is Antibiotic Resistance?

Antibiotics are used to fight infections caused by bacteria. Usually this treatment kills the bacteria, and the person recovers, but at times a few unusually hardy bacteria do not die. These bacteria not only survive the antibiotic treatment, they also pass on their hardiness to their offspring so that the next generation is also resistant to antibiotics. Because antibiotics are a common treatment for infections, doctors have to try to find another drug that will work against the antibiotic-resistant infection. Unfortunately, options are limited, and in some cases, other treatments are not available.

Antibiotic Resistance

SOURCE: Antibiotic Resistance Threats in the United States, 2013. Centers for Disease Control and Prevention, April 2013. Illustration by Cenveo Publisher Services. © 2016 Cengage Learning®.
* , that makes them resistant to antibiotics.

Because of this ease of replication, the number of antibiotic-resistant bacteria can become very large. An example of this process was documented in China in 2015. Researchers in that country reported the existence of a gene in an increasing number of bacteria that confers resistance to the polymyxin family of drugs, which are used as the last line of defense to treat antibiotic-resistant gram-negative bacterial infections * . The gene, mcr-1, is found on small pieces of bacterial DNA known as plasmids. These plasmids have the capability to spread easily between bacteria and to confer resistance when spread. The gene has been found in meat samples in China as well as in hospitalized patients in that country. Of particular concern is the rapid spread of the gene in pork and chicken samples from the meat supply in China—an increase from 5 percent of samples tested in 2011 to about 25 percent of meat samples testing positive for the gene in 2014.

Antibiotic resistance can lead to bacterial infections that are extremely difficult to fight, and may cause serious illnesses in people and even death.

What Causes Antibiotic Resistance?

Antibiotics are effective for treating a wide range of illnesses. This pattern of effectiveness causes some doctors to prescribe antibiotics even when they are uncertain about a diagnosis and whether antibiotics will help. In addition, doctors often prescribe so-called broad-spectrum antibiotics that kill many different types of microbes, rather than selecting a more targeted antibiotic that works against the specific microbes that are causing the illness. Both the improper prescribing of antibiotics and the use of broad-spectrum antibiotics can promote antibiotic- resistant bacteria.

Dangerous antibiotic-resistant bacteria are prevalent in hospitals and becoming increasingly more common in non–health care community settings. An example is methicillin-resistant Staphylococcus aureus (MRSA), which is a type of bacterium that is resistant to antibiotics such as methicillin, penicillin, amoxicillin, and others. MRSA infections have also become increasingly common in other health centers and nursing homes and among people who already have weakened immune systems *

For example, infection from Clostridium difficile (commonly referred to as C. diff) presents a unique and alarming example of the effects of antibiotic resistance. Symptoms associated with C. diff infection include frequent episodes of watery diarrhea, fever, nausea, and abdominal pain. The C. diff organism itself is not significantly resistant to antibiotics that are prescribed to treat the infection. However, people who are treated for long periods of time with antibiotics for bacterial infections other than C. diff are very susceptible to developing C. diff infection as an adverse effect of antibiotic treatment. One of the first treatments attempted for those with C. diff infections is to discontinue all other antibiotics except for those proven effective in treating C. diff, if possible. Even with treatment, up to 20 percent of patients develop recurrent C. diff infections and may require stool transplants * to prevent future infections. Incidence of C. diff cases and deaths from this infection are rising in the United States, particularly among the elderly and medically vulnerable.

Most antibiotic-resistant infections occur in the community setting. For example, cases of drug-resistant tuberculosis (TB) are increasing worldwide. TB most commonly affects the lungs and can be spread through the air to other people. Infected individuals not complying with the full course of prescribed treatment, health care providers incorrectly prescribing medications, lack of access to the drug and taking drugs of poor quality are all factors linked to the increase in cases of drug-resistant TB. Some cases of TB have been classified as multi-drug resistant because the organism is resistant to the two most potent drugs used to treat TB, isoniazid and rifampin, which are prescribed to all people infected with TB. A rarer type of resistance, extensively drug-resistant TB, has also been identified. These individuals have TB that is resistant to isoniazid and rifampin in addition to drugs from the fluoroquinolone group and at least one other drug from secondary drugs used in the treatment of TB.

New strains of resistant bacteria are continually being identified that cause great concern in the health care community.

Patients may also contribute to the development of antibiotic resistance. Some individuals have developed great trust in the effectiveness of antibiotics and want prescriptions for them. A patient with a bad cold may request an antibiotic, however, a cold is caused by a virus, and antibiotics are not effective in treating viruses. To appease the patient, the doctor prescribes an antibiotic. Taking unneeded antibiotics kills some bacteria but leaves behind antibiotic-resistant bacteria that can then multiply.

Some scientists and health care professionals believe that antibiotic resistance may arise from the use of antibiotics to improve the health and the growth of cows and other agricultural livestock. According to the Union of Concerned Scientists, antibiotics are being overused on livestock. This overuse of antibiotics encourages the development of antibiotic-resistant strains of bacteria, which then arrive in the human diet through beef and other food products. Scientists still are not sure exactly how much effect livestock antibiotics have, but several organizations mounted campaigns to curtail the use of antibiotics to promote growth in livestock, so that people can purchase and eat antibiotic-free meats.

What Is the Effect of Antibiotic Resistance?

According to the World Health Organization (WHO), antibiotic resistance is creating unplanned-for issues in the treatment of HIV, tuberculosis, malaria, gonorrhea, and influenza. The Centers for Disease Control and Prevention (CDC) estimates that at least 2 million people become infected with bacteria that are resistant to antibiotics, and that at least 23,000 people die each year as a direct result of these infections.

Medical professionals are particularly alarmed because MRSA and similar infections have reached beyond the medical setting and are occurring in the general population, and among people who were perfectly healthy before the infection. Public outbreaks of infection with antibiotic-resistant bacteria have occurred among people who were evacuated from Hurricane Katrina in 2005; among members of some small religious groups; and even among players on the Tampa Bay Buccaneers football team in 2013. Outbreaks have occurred in schools, as when one high school student in Virginia died from an infection with an antibioticresistant strain of bacteria. MRSA infections have been reported among school wrestling, volleyball, and most frequently, football teams.

The concern over rising incidence of antibiotic resistance worldwide is so great that organizations such as WHO, the CDC, and similar organizations have categorized the bacterial pathogens that are becoming increasingly more resistant to available antibiotics into threat levels based on urgency. These threat levels include urgent threat level, serious threat level, and concerning threat level. The three pathogens currently classified at the urgent threat level are Clostridium difficile, carbapenem-resistant Enterobacteriaceae, and drug-resistant Neisseria gonorrhoeae.

Antibiotic resistance threats in the United States, by microorganism

Antibiotic resistance threats in the United States, by microorganism
SOURCE: Centers for Disease Control and Prevention, U.S. Department of Health and Human Services, 2013. © 2016 Cengage Learning ®.

How Are Antibiotic-Resistant Infections Treated?

When a patient has an infection that resists a certain antibiotic, medical professionals may try others until one is found that is effective. Doctors sometimes have limited choices because some of the drug options have dangerous side effects. In addition, doctors are increasingly finding that bacteria are resistant to more than one antibiotic, a particular problem in hospitals in which bacteria may be resistant to all of the available antibiotics. When this multidrug resistance develops, patients can become very ill or die. Doctors are alarmed about antibiotic resistance because they fear that surgery and other hospital procedures that once were considered safe may become much more dangerous because of the mounting risk of antibiotic-resistant infections.

Will New Treatments Become Available?

In response to the problem of antibiotic resistance, researchers are working to develop new drugs that attack the bacteria in a slightly different way than antibiotics typically do. For instance, researchers found a way to target an enzyme that helps bacteria exchange their DNA. By curbing the enzyme's function, they could stop the bacteria from passing on their resistance to other bacteria. Other scientists were using different methods to curtail resistant bacteria. This work presented a constant struggle because even the new drugs might be effective only for a short time if the bacteria are able to develop resistance to them, too.

Scientists are also working to curb antibiotic resistance by optimizing the way antibiotics are currently being prescribed and used. For example, research is ongoing to determine if reducing the length of time certain common infections, such as ear infections in children, are treated with antibiotics has an impact on the development of resistance. In addition, some health care providers are prescribing older antibiotics or prescribing older antibiotics in combination with newer formulations in situations where newer antibiotics are known not to be as effective because of resistance.

In addition to developing new antibiotics, researchers have been working on new vaccines * that improve the body's ability to defend itself against the bacteria, and also working on bacteria-attacking viruses called bacteriophages. Despite these efforts, many medical professionals expressed concern that the new drugs were not coming quickly enough to restrain the growing problem of antibiotic resistance, and the number of deaths due to antibiotic-resistant infections might continue to rise. Because of concerns like these, antibiotic resistance is often described as a worldwide public health emergency.

Can an Antibiotic-Resistant Infection Be Avoided?

The CDC implemented the Campaign to Prevent Antimicrobial Resistance, which is designed to prevent antibiotic resistance in hospitals and other health care facilities. The campaign has the following four main strategies:

  1. Prevent infections in the first place, so that antibiotics are not necessary.
  2. Diagnose and treat infections effectively with the appropriate antimicrobial therapy.
  3. Use antimicrobials wisely.
  4. Prevent transmission, or the spread of the infection from one patient to another.

Beyond the steps that medical professionals can take, everyone can help reduce antibiotic resistance. Individuals can take several measures to reduce the chance of becoming infected:

In addition, medical professionals recommend that patients who have prescriptions for antibiotics follow their doctors' directions exactly. For instance, a patient should take the entire prescribed antibiotic as recommended by the doctor. Even if the patient starts to feel better, the person should take the remaining pills. Patients should not save antibiotics to use for a later illness and should never give them to someone else to take.

See also Bacterial Infections • Diarrhea • Infection • Staphylococcal Infections • Streptococcal Infections • Tuberculosis • Vaccines and Immunization


Books and Articles

Browne, Roy Robins. “Resistance to Antibiotics.” Issues 105 (2013): 26–28. Lew, Kristi. Antibiotics. New York: Marshall Cavendish Benchmark, 2014.


Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases, Division of Bacterial Diseases. “Get Smart: Know When Antibiotics Work.” April 17, 2015. (accessed March 16, 2016).

U.S. Food and Drug Administration. “Antibiotic Resistance.” December 3, 2014. (accessed March 16, 2016).


Alliance for the Prudent Use of Antibiotics. 136 Harrison Ave., M&V Suite 811, Boston, MA 02111. Telephone: 617-636-0966. Website: (accessed March 16, 2016).

Centers for Disease Control and Prevention. 1600 Clifton Rd., Atlanta, GA 30333. Toll-free: 800-232-4636. Website: (accessed March 16, 2016).

Union of Concerned Scientists. Two Brattle Sq., Cambridge, MA 02138-3780. Telephone: 617-547-5552. Website: (accessed March 16, 2016).

World Health Organization. Avenue Appia 20, 1211 Geneva 27, Switzerland. Telephone: 41 22 791 21 11. Website: (accessed March 16, 2016).

* microorganisms are tiny organisms that can only be seen using a microscope. Types of microorganisms include fungi, bacteria, and viruses.

* DNA or deoxyribonucleic acid (dee-OX-see-ry-bo-nyoo-klay-ik AH-sid) is the specialized chemical substance that contains the genetic code necessary to build and maintain the structures and functions of living organisms.

* gram-negative bacterial infections are serious infections caused by bacteria such as staphylococci (“staph”), streptococci (“strep”), pneumococci, and the bacteria responsible for causing diptheria and anthrax.

* immune system (im-YOON SIStem) is the system of the body composed of specialized cells and the substances they produce that helps protect the body against disease-causing germs.

* stool transplant, also referred to as fecal transplant, is a procedure that involves transplanting stool, or feces, from a healthy donor to the colon, or large intestine, of someone who has experienced recurrent C. diff infections.

* vaccines (vak-SEENS) are preparations of killed or weakened germs, or a part of a germ or product it produces, given to prevent or lessen the severity of the disease that can result if a person is exposed to the germ itself. Use of vaccines for this purpose is called immunization.

Disclaimer:   This information is not a tool for self-diagnosis or a substitute for professional care.

(MLA 8th Edition)