Drug-Resistant Organisms

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Drug-Resistant Organisms

Normal results
Morbidity and mortality rates


Drug-resistant organisms include bacteria and other pathogens that are not affected by one or more pharmaceutical products. Stated differently, one or more drugs are no longer able to control or kill a particular bacterium or pathogen.


  • Testing of an organism for drug-resistance is done by a medical technologist or a clinical microbiologist.
  • Treatment of drug-resistant organism is typically ordered by a specialist in infectious diseases and administered by a nurse.


With the possible exception of being used as a biological weapon, there is no desired purpose for a drug-resistant organism.


In the 1940s, penicillin resistance to staphylococcus aureus was first reported. Other strains of pathogens have become drug resistant since that time. The rate of drug resistance is increasing more rapidly than the number of new drugs that are being discovered.


Drug-resistant organisms are pathogens that have become immune to the effects of one or more drugs that once controlled or eliminated them. One common mechanism for creating drug resistance is inadequate treatment. People discontinue use of a drug before all pathogens have been eliminated. Those that remain tend to be hardier and more difficult to kill. Over time, the remaining pathogens are likely to mutate and acquire immunity to a drug used to treat them.

Some pathogens have become resistant to more than one drug. Tuberculosis is an example of a pathogen that has become resistant to multiple drugs.

Examples of drug-resistant organisms include the following:

  • MRSA—methicillin-resistant Staphylococcus aureus
  • MRSE—methicillin-resistant Staphylococcus epidermitis
  • VRE—vancomycin-resistant enterococcus
  • PRSP—penicillin-resistant Streptococcus pneumonia
  • TB—mycobacterium tuberculosis


  • Is an organism drug-resistant?
  • Are alternative drugs available for treatment?
  • What is the cost of alternative drugs?
  • What are the side-effects of alternative drugs?


Drug-resistant organisms are identified by isolation and drug susceptibility testing. These procedures are conducted in a clinical laboratory by a medical technologist or a clinical microbiologist.


Appropriate treatment after being exposed to a drug-resistant organism is to administer a different drug to which an organism or pathogen is sensitive.

The Centers for Disease Control and Prevention recommend that the following steps be taken after possible contact or exposure to a drug-resistant organism:

  • Washing one’s hands with soap and hot water
  • Wearing disposable gloves if contact with body fluids contaminated with drug-resistant organisms is likely to occur; wash hands after removing the gloves
  • Towels and bedding used by persons with a drug-resistant organism should be regularly changed
  • Towels used by caregivers should be washed in hot water or discarded after use


Healthy persons have a low risk for contracting drug-resistant organisms. Centers for Disease Control and Prevention guidelines permit (but do not encourage) casual touching or brief hugging of persons with drug-resistant organisms. Washing hands with hot water and soap after casual contact with a person infected with drug-resistant organism is strongly encouraged.

The following risk factors increase the likelihood of becoming infected with a drug-resistant organism:

  • Having a serious or severe illness such as diabetes mellitus
  • Having chronic renal failure
  • Experiencing open skin lesions or a dermatitis


MDR— Multiple drug-resistance

XTB— Extreme drug-resistant tuberculosis

  • Having been recently catheterized or undergonerenal dialysis
  • Having been previously treated for a drug-resistant organism
  • Being over age 65
  • Taking a steroid or other drug that can suppress the immune system
  • Being hospitalized for more than 10 days

Normal results

An alternate drug, if available, must be found when an organism becomes drug-resistant.

Morbidity and mortality rates

Alternative drugs may have unwanted side-effects.

Accurate morbidity and mortality data are not generally available.


Alternatives may or may not be available. They may have unwanted side-effects or be more expensive than th drug to which a pathogen has become resistant.

An alternate drug, if available, must be found when an organism becomes drug-resistant.



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American Academy of Family Physicians. 11400 Tomahawk Creek Parkway, Leawood, KS 66211-2672. (913) 906-6000. E-mail: [email protected]. http://www.aafp.org.

American Academy of Pediatrics. 141 Northwest Point Boulevard, Elk Grove Village, IL 60007-1098. (847) 434-4000, Fax: (847) 434-8000. E-mail: [email protected]. http://www.aap.org/default.htm.

American College of Physicians. 190 N. Independence Mall West, Philadelphia, PA 19106-1572. (800) 523-1546, x2600, or (215) 351-2600. http://www.acponline.org.

American Medical Association. 515 N. State Street, Chicago, IL 60610. (312) 464-5000. http://www.ama-assn.org.


AIDS Treatment Data Network. “Information about drug resistance.” 2008 [cited February 25, 2008]. http://www.atdn.org/simple/resistance.html.

Centers for Disease Control and Prevention. “Information about drug resistance.” 2008 [cited February 22, 2008]. http://www.cdc.gov/drugresistance/.

National Institute of Allergy and Infectious Disease. “Information about drug resistance.” 2008 [cited February 24, 2008]. http://www3.niaid.nih.gov/topics/antimicrobialresistance/.

World Health Organization. “Information about drug resistance.” 2008 [cited February 24, 2008]. http://www.who.int/drugresistance/en/.

L. Fleming Fallon, Jr, MD, DrPH

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