Antibiotic Susceptibility Testing
- Also Known As:
- Sensitivity Testing
- Drug Resistance Testing
- Culture and Sensitivity
- C & S
- Antimicrobial Susceptibility
- Formal Name:
- Bacterial and Fungal Susceptibility Testing

This page was fact checked by our expert Medical Review Board for accuracy and objectivity. Read more about our editorial policy and review process.
At a Glance
Why Get Tested?
To determine the likelihood that a particular antibiotic or antifungal drug will be effective in stopping the growth of the bacteria or fungi causing your infection
When To Get Tested?
As follow up to a positive bacterial or fungal culture; when selecting the best treatment for a bacterial or fungal infection requires laboratory testing; when your infection is not responding to treatment
Sample Required?
A sample from an infected site is cultured on specialized media to recover the bacteria or fungus that is causing the infection. The method used to collect a sample from an individual depends on the type of culture performed (e.g., urine culture, blood culture, sputum culture, etc.).
Test Preparation Needed?
None
What is being tested?
Susceptibility is a term used when microbe such as bacteria and fungi are unable to grow in the presence of one or more antimicrobial drugs. Susceptibility testing is performed on bacteria or fungi causing an individual’s infection after they have been recovered in a culture of the specimen. Testing is used to determine the potential effectiveness of specific antibiotics on the bacteria and/or to determine if the bacteria have developed resistance to certain antibiotics. The results of this test can be used to help select the drug(s) that will likely be most effective in treating an infection.
Bacteria and fungi have the potential to develop resistance to antibiotics and antifungal drugs at any time. This means that antibiotics once used to kill or inhibit their growth may no longer be effective.
Although viruses are microbes, testing for their resistance to antiviral drugs is performed less frequently and by different test methods. This article is limited to the discussion of bacterial and fungal susceptibility testing.
During the culture process, pathogens are isolated (separated out from any other microbes present). Each pathogen, if present, is identified using biochemical, enzymatic, or molecular tests. Once the pathogens have been identified, it is possible to determine whether susceptibility testing is required. Susceptibility testing is not performed on every pathogen; there are some that respond to established standard treatments. For example, strep throat, an infection caused by Streptococcus pyogenes (also known as group A streptococcus), can be treated with ampicillin and does not require a test to predict susceptibility to this class of antibiotics.
Susceptibility testing is performed on each type of bacteria or fungi that may be relevant to the individual’s treatment and whose susceptibility to treatment may not be known. Each pathogen is tested individually to determine the ability of antimicrobials to inhibit its growth. This is can be measured directly by bringing the pathogen and the antibiotic together in a growing environment, such as nutrient media in a test tube or agar plate, to observe the effect of the antibiotic on the growth of the bacteria. Resistance can also be determined by detection of a gene that is known to cause resistance to specific antibiotics.
Common Questions
View Sources
Sources Used in Current Review
Street, T. (Updated 2014 March 13). Antimicrobial Susceptibility. Medscape. Available online at https://emedicine.medscape.com/article/2103786-overview?pa=rOBA1lN0uZhjg0bJO6bD2AgpF2o0ma5fK6AeuJMPuepOQ4%2B%2BoTWGQm%2Be5C5zB%2BCc43mU9jD%2B1DtnxY47OmyybA%3D%3D. Accessed April 2018.
Arena, F. et al. (2015). Antibiotic Susceptibility Testing: Present and Future. Medscape. Available online at https://www.medscape.com/viewarticle/851528_1. Accessed April 2018.
Grigorenko, E. and Stalons, D. R. (2016 October 5). Addressing Antibiotic Resistance with Molecular Diagnostics. Clinical Lab Products. Available online at http://www.clpmag.com/2016/10/addressing-antibiotic-resistance-molecular-diagnostics/. Accessed April 2018.
Syal, K. et al. (2017). Current and Emerging Techniques for Antibiotic Susceptibility Tests. Available online at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5479269/. Accessed April 2018.
Vorvick, L. J. (Reviewed 2017 January 26). Sensitivity Analysis. MedlinePlus. Available online at https://medlineplus.gov/ency/article/003741.htm. Accessed April 2018.
Maurer, F. P. et al. (2017 March 30). Advances in Rapid Identification and Susceptibility Testing of Bacteria in the Clincal Microbiology Laboratory: Implications for Patient Care and Antimicrobial Stewardship Program. Infectious Disease Reports. Available online at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5391540/. Accessed April 2018.
(Updated 2017 December 7). Antibiotic Resistance Questions and Answers. Centers for Disease Control and Prevention. Available online at https://www.cdc.gov/antibiotic-use/community/about/antibiotic-resistance-faqs.html. Accessed April 2018.
(© 1995-2018). Antimicrobial Susceptibility, Anaerobic Bacteria, MIC. Mayo Medical Laboratories. Available online at https://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/56031. Accessed April 2018.
(© 2018). Anitmicrobial Susceptibility – mecA/mecC Genes by PCR. Arup Laboratories. Available online at http://ltd.aruplab.com/Tests/Pub/0060211. Accessed April 2018.
Rifai, N. et al. (© 2018). Tietz Textbook of Clinical Chemistry and Molecular Diagnostics, Sixth Edition. Antimicrobial Resistance and Testing Considerations for Key Bacterial Pathogens, pp . 173700014 – 173700024. Available online at https://expertconsult.inkling.com/read/rifai-tietz-textbook-clinical-chemistry-molecular-diagnost-6e/chapter-75/antimicrobial-resistance-and. Accessed April 2018.
(Updated 2018 April 2). About AR Laboratory Testing and Resources. Centers for Disease Control and Prevention. Available online at https://www.cdc.gov/drugresistance/laboratories.html. Accessed April 2018.
(2018 April 3). Containing Unusual Resistance. Centers for Disease Control and Prevention. Available online at https://www.cdc.gov/vitalsigns/containing-unusual-resistance/index.html. Accessed April 2018.
Antimicrobial Resistance. Association of Public Health Laboratories. Available online at https://www.aphl.org/programs/infectious_disease/Pages/Antimicrobial-Resistance.aspx. Accessed April 2018.
Sources Used in Previous Reviews
Thomas, Clayton L., Editor (1997). Taber’s Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby’s Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.
(2004 April). The Problem of Antibiotic Resistance. National Institute of Allergy and Infectious Diseases [On-line information]. Available online at http://www.niaid.nih.gov/factsheets/antimicro.htm.
(2003 April 4). Antibiotic Resistance, A Growing Threat. US Food and Drug Administration [On-line information]. Available online at http://www.fda.gov/oc/opacom/hottopics/anti_resist.html.
(2004 February 19). Using Antibiotics Sensibly. Mayoclinic.com, Infectious Disease Center [On-line information]. Available online at http://www.mayoclinic.com/invoke.cfm?id=FL00075.
(2003 November). Multidrug-Resistant Tuberculosis Fact Sheet. American Lung Association [On-line information]. Available online at http://www.lungusa.org/site/pp.asp?c=dvLUK9O0E&b=35815.
Bren, L. (2003 September, Revised). The Battle of the Bugs: Fighting Antibiotic Resistance. U.S. Food and Drug Administration, FDA Consumer magazine [On-line information]. Available online at http://www.fda.gov/fdac/features/2002/402_bugs.html.
Henry’s Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson RA and Pincus MR, eds. Philadelphia: 2007, Pp 1048-1057.
(March 14, 2009) MedlinePlus Medical Encyclopedia. Sensitivity Analysis. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003741.htm. Accessed May 2009.
Forbes, B. et. al. (© 2007). Bailey & Scott’s Diagnostic Microbiology, Twelfth Edition: Mosby Elsevier Press, St. Louis, Missouri. Pp 187-214.
(2007 August 6). Get Smart: Know When Antibiotics Work, Frequently Asked Questions. CDC [On-line information]. Available online at http://www.cdc.gov/getsmart/index.html. Accessed June 2009.
Sutphen, S (2007 August 30). Antibiotic Resistance in the Emergency Room: The First Line of Defense. Medscape CME [On-line information]. Available online at http://www.medscape.com/viewarticle/562056. Accessed 8-24-08.
Barclay, L. (2008 July 3). Medscape Medical Household Antibacterial Product Use May Promote Microbial Resistance. Medscape Medical News [On-line information]. Available online at http://www.medscape.com/viewarticle/577055. Accessed June 2009.
Nicasio, A. et. al. (2008 May 13). The Current State of Multidrug-Resistant Gram-Negative Bacilli in North America. Medscape from Pharmacotherapy [On-line information]. Available online at http://www.medscape.com/viewarticle/572674. Accessed June 2009.
(2009 August 27). Treatment Multi-drug Resistant and Extensively Drug-Resistant Tuberculosis: Current Status and Future Prospects. Medscape Reuters Health Information [On-line information]. Available online at http://www.medscape.com/viewarticle/706826. Accessed June 2009.
(© 1995-2013). Antimicrobial Susceptibility, Aerobic Bacteria, MIC. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/8073. Accessed August 2013.
Vorvick, L. (Updated 2013 January 22). Sensitivity analysis. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003741.htm. Accessed August 2013.
Hazen, K. (Revised 2013 February). Susceptibility Testing. Merck Manual for Healthcare Professionals [On-line information]. Available online through http://www.merckmanuals.com. Accessed August 2013.
Street, T. and Schmidt, S. (Updated 2012 October 18) Antimicrobial Susceptibility. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/2103786-overview. Accessed August 2013.
McPherson, R. and Pincus, M. (© 2011). Henry’s Clinical Diagnosis and Management by Laboratory Methods 22nd Edition: Elsevier Saunders, Philadelphia, PA. Pp 11117-1128.
Ask a Laboratory Scientist
