Antibiotic Resistance Definition

Antibiotic Resistance is the adaptation of bacterial strains to certain of the antibiotic medications doctors prescribe to treat infections the bacteria cause, rendering the antibiotic ineffective.

Such adaptation is an evolutionary mechanism that allows the strain of bacteria to survive. Though in most situations the strain of bacteria remains sensitive to other antibiotics even as it develops resistance to a particular antibiotic, antibiotic resistance is a very serious concern in modern health care because the more common strains of bacteria are developing broad bases of resistance to multiple antibiotics. A few strains have mutated to resist all available antibiotics, presenting a worrisome challenge for fighting the infections they cause.

Bacteria, Infection, and Antibiotics

Bacteria are single-cell microorganisms that exist in broad families with numerous strains, or variations, within the same family. Under supportive circumstances each individual strain can cause unique and specific infections. Most bacteria that cause infection in people are normally present in the body and the environment. Ordinarily these bacteria are harmless or even beneficial to body functions, such as the bacteria in the gastrointestinal tract that aid in digestion. Normal flora bacteria become pathogenic when there is a breach, such as a wound, in the body’s protective mechanisms, or when something goes awry with the body’s balance of microorganisms and the immune system cannot keep bacterial growth in check.

Antibiotics kill bacteria, either by direct toxicity to the bacteria or by preventing the bacteria from reproducing. Antibiotics are effective for treating only bacterial infections; they cannot treat viral infections. Chronic conditions such as bronchitis and otitis media (middle EAR infection) are often viral, yet are among the top ailments for which doctors prescribe antibiotics. It is not possible to determine the cause of an infection by evaluating the symptoms, though certain characteristics make it more likely that an infection is bacterial. Only a laboratory culture of cells from the infection, in which cells of a bacterial strain may or may not grow in the lab, can identify the cause of an infection as bacterial.

How Bacteria Acquire Resistance

Bacteria reproduce rapidly, which gives them the opportunity to change rapidly. Over multiple generations the bacteria’s DNA—its genetic code— mutates to establish adaptations beneficial to the bacterial strain’s survival. These adaptations include increased resistance to the antibiotics that people take to fight the infections the strain causes. Bacteria generally mutate through one of three processes:

  • Spontaneous mutation is when changes occur within the DNA alter the bacteria’s adaptive ability across the bacterial strain. Resistance due to spontaneous mutation, also called evolutionary mutation, develops over multiple generations of the bacterial strain.
  • Transformation is when the DNA from resistant bacteria enter another bacteria that are not yet resistant. Also called DNA uptake, transformation expedites the mutation process to allow bacterial strains to become more rapidly resistant than they would through spontaneous mutation.
  • Plasmid transfer is when plasmids (molecules that contain incomplete fragments of genetic material) move among different kinds of bacteria. Plasmids impart limited genetic encoding related primarily to the survivability of a bacterial strain and can result in rapid adaptation to produce antibiotic resistance. Because antibiotic resistance has become a key purpose of plasmid transfer, researchers designate such plasmids as R plasmids.

Resistance resulting from spontaneous, or evolutionary, mutation is the most common adaptation process and accounts for most of the resistant strains of GONORRHEA and Staphylococcus aureus infections. Transformation, or DNA uptake, is a more sophisticated, biologically intentional process than spontaneous mutation.

Among the three mutation processes plasmid transfer is the most efficient and creates the greatest concern in regard to antibiotic resistance. Plasmids can transfer among different strains of bacteria within a bacterial family, sharing adaptive mutations for multiple resistance.

Plasmid transfer accounts for resistance to entire classifications of drugs such as the quinolones, a family of antibiotics that attack enzymes that facilitate DNA cleavage (the division of DNA in preparation for cell reproduction) in bacteria.

antibiotic resistance

Factors That Contribute to Antibiotic Resistance

Antibiotic use itself is the precipitating factor for the adaptive changes that occur in bacteria to result in antibiotic resistance, as these changes represent natural survival efforts. Key circumstances that further encourage survival adaptations include the following:

  • Inappropriate prescribing of antibiotics for infections that are viral or of uncertain cause. The US Centers for Disease Control and Prevention (CDC) believes about half of the 100 million antibiotic prescriptions US doctors write each year are unnecessary because the conditions they are treating are not bacterial.
  • Failing to complete the full course of antibiotic therapy, which allows some bacteria to escape eradication. It is important to take a therapeutic antibiotic long enough to kill all the bacter ia, extending through their complete life cycle, that are causing infection. Bacteria that are exposed to the antibiotic but do not die have the opportunity to undergo adaptive mutation, which results in antibiotic resistance.
  • Prophylactic antibiotics given to food animals such as cattle, pigs, and chickens to prevent them from getting infections that slow their growth. The constant exposure to the same antibiotics fosters adaptive mutation in bacteria that may then become infective agents in people. Humans become vulnerable to infection from resistant bacteria through eating meat from treated animals that is not thoroughly cooked, which allows the bacteria to enter the body. Exposure to the bacteria in environmental settings also is a source of infection.

Limiting Antibiotic Resistance

The most effective measure for reducing antibiotic resistance is to decrease the use of antibiotics. To this end, health experts offer these recommendations for individuals:

  • Take antibiotics only for infections that laboratory tests prove are bacterial.
  • Take all doses of the antibiotic for the full course of prescribed treatment.
  • Wash hands frequently with soap and warm water to prevent the spread of infection-causing bacteria and other pathogens.
  • Limit exposure to other people who are ill.
  • Choose meat and poultry products that are labeled antibiotic free.

Health experts also are reexamining the practice of antibiotic prophylaxis (administering antibiotics to prevent infection in people who are immunocompromised or exposed to risk for nosocomial infections). The US Food and Drug Administration (FDA), which oversees drug approval and prescribing practices in the United States, issued new regulations in 2003 that establish stringent criteria for doctors to follow in prescribing antibiotics and is spearheading public education efforts to improve public awareness of antibiotic resistance.


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