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About AR Laboratory Testing and Resources

Laboratory tests can help guide patient treatment, detect emerging threats, and prevent the spread of antibiotic resistance. CDC’s Antibiotic Resistance Laboratory Network (AR Lab Network) supports nationwide lab capacity to

  • rapidly detect antibiotic resistance in healthcare, food, and the community, and
  • inform local responses to prevent spread and protect people.

The AR Lab Network includes labs in 50 states, five cities, and Puerto Rico, including seven regional labs and the National Tuberculosis Molecular Surveillance Center (National TB Center).

Types of Resistance Tests

See Also
Clinical lab resources for lab testing and protocols.

Identification of Pathogens

Laboratories work to identify and confirm the genus and species pathogens (germs that can cause disease) with resistance. These are often the first tests performed by the AR Lab Network. This is done through one of two methods:

  • Biochemical tests: Classifying a particular species by the way it uses different biological chemicals, like proteins or sugars.
  • Mass spectrometry: A specialized technique that looks for a pathogen’s protein “fingerprint.”

Colonization Screening

Colonization screening is a process set up to detect and reduce the risk of germs spreading in a healthcare facility (in this case, germs with unusual resistance). Some people can carry germs without becoming sick or showing symptoms, known as colonization. People who are colonized can spread the germs to others without knowing it. When unusual resistance is identified in a patient, healthcare workers screen other patients to see if they are colonized with the same resistant germ. This can prompt additional infection control actions reducing the risk of spread and protect patients.

Molecular Testing

Molecular testing is a collection of techniques used to detect specific genes within a germ, including those that have and can share resistance. These tests can be used to diagnose infections and guide treatment for patients.

Examples of pathogens tested through CDC’s AR Lab Network:

  • Acinetobacter
  • Candida, including Candida auris(C. auris)
  • Carbapenem-resistant Enterobacteriaceae (CRE)
  • Clostridium difficile (C. difficile)
  • Neisseria gonorrhoeae(N. gonorrhoeae)
  • Salmonella
  • Streptococcus pneumoniae(S. pneumoniae)
  • Mycobacterium tuberculosis(M. tuberculosis)

Phenotypic Carbapenemase Test

A phenotypic carbapenemase test uses culture (a medium to grow bacteria) instead of the molecular test method to determine if the pathogen produces an enzyme called carbapenemase. If carbapenemase is produced, then a carbapenem antibiotic is ineffective and will not kill the pathogen.

Susceptibility Testing

Susceptibility testing is a type of lab test that cultures (grows) the pathogen in order to show how sensitive a germ is to different antibiotics. These tests can be used to help select the best drug choice for a drug-resistant infection, and also provide data to monitor how a pathogen’s resistance profile might change over time.

Whole Genome Sequencing (WGS)

WGS is a laboratory procedure that provides a very precise DNA fingerprint that can help link cases to one another, allowing an outbreak to be detected and solved sooner.

How the AR Lab Network Works

The AR Lab Network increases and sustains lab capacity nationwide. This effort results in a more rapid response for finding AR and preventing its spread.

Enhancing collaboration results in more rapid response for detecting resistance.  (chart graphic)

Enhancing collaboration results in more rapid response for detecting resistance.

Healthcare Facility Labs and Public Health Department Labs

When healthcare facility labs suspect CRE or carbapenem-resistant Pseudomonas aeruginosa (CRPA), they send the isolates (bacteria isolated from a specimen, like blood) to the public health department labs, also known as jurisdictional labs. The public health labs confirm the species identity of the bacteria, and do additional susceptibility and molecular testing to characterize (describe) the CRE and CRPA isolates. In addition to CRE and CRPA, every state health department can test for enteric (gut) bacteria like Salmonella. When public health labs identify unusual resistance, they notify CDC and can send the isolates to their regional labs for additional testing if needed.

Regional Labs and National TB Center

The regional labs help track changes in resistance and identify outbreaks. Since outbreak response varies by state, the support may also vary by state or threat discovered. In general, the regional labs provide support by

  • doing additional tests to further characterize the threat,
  • providing support to respond to the threat by performing colonization screening tests for CRE or CRPA, or an emerging fungal threat like auris, and
  • tracking and monitoring discoveries that are found.

The regional labs coordinate local efforts and are located in the following state health departments:

  • Maryland,
  • Minnesota,
  • New York,
  • Tennessee,
  • Texas,
  • Washington, and
  • Wisconsin.

The public health department labs will send some pathogen isolates, like CRE and CRPA, to the regional labs when support is needed, but the AR Lab Network receives other pathogens in different ways. For example, the AR Regional Labs are processing N. gonorrhoeae isolates through CDC activities, including two projects called the Gonococcal Isolate Surveillance Project (GISP) and the Strengthening the United States Response to Resistant Gonorrhea (SURRG). This work is a key part of monitoring antibiotic-resistant gonorrhea trends to help ensure that the recommended drug treatment for gonorrhea works.

The National TB Center is coordinated from the Michigan Department of Health and Human Services, and is equipped to perform WGS for isolates of M. tuberculosis in the U.S. The National TB Center receives all available isolates from the state health departments.


CDC coordinates the AR Regional Lab and provides technical expertise. The regional labs share the unusual resistance with CDC to confirm tests. When threats are reported, CDC works with across the different labs to support outbreak response and create tailored solutions. CDC also adds new isolates to the AR Isolate Bank for drug and diagnostic test development.

Read details on how the AR Lab Network works.

Printable Fact Sheets about Testing