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Glossary of Terms Related to Antibiotic Resistance

CDC works with federal, state, and local partners to reduce antibiotic resistance and protect the public’s health. This work includes investigating outbreaks caused by resistant bacteria, identifying new antibiotic resistance threats, and recommending ways to help prevent illnesses and outbreaks caused by resistant bacteria.

The National Antimicrobial Resistance Monitoring System (NARMS) assists in outbreak investigations by testing bacteria from sick people, animals, and retail meats for antibiotic resistance. When paired with information collected during interviews with sick people about what they ate or were exposed to before becoming ill, resistance data can provide investigators with clues about the source of outbreaks.

This glossary defines some key terms related to antibiotic resistance that CDC uses to describe multistate outbreak investigations.

Antibiotic (also known as antimicrobial agent): A drug that kills or stops the growth of bacteria. Examples include penicillin and ciprofloxacin. 

Antibiotic resistance (also known as antimicrobial resistance): The ability of bacteria to resist the effects of an antibiotic. Antibiotic-resistant bacteria are not killed, and may continue to multiply, when a patient is treated with an antibiotic to which the bacteria are resistant.

Antibiotic resistance testing (also known as antimicrobial susceptibility testing): Laboratory testing performed on bacteria to find out if they are resistant to one or more antibiotics.

Drug class: Antibiotics are categorized into classes of drugs. Each class is defined by the way it kills or stops the growth of bacteria. NARMS uses the Clinical and Laboratory Standards Institute’s drug classes  to categorize antibiotics.

Isolates: Bacteria isolated from a specimen (e.g., stool, blood, food).

Multidrug-resistant (MDR) isolate: CDC typically uses this term to refer to an isolate that is resistant to at least one antibiotic in three or more drug classes. 

Non-susceptible isolate: An isolate that is either resistant or not completely susceptible to one or more antibiotics.

Panel: A set of antibiotics used to determine if an isolate is resistant to antibiotics and, if so, which ones. The set of antibiotics used differs by type of bacteria being tested.

Resistant isolate: An isolate that is resistant to one or more antibiotics.

Resistance pattern: A description of the antibiotic resistance testing results for an isolate. 

Resistance profile: A description of the resistance patterns for all isolates in an investigation. A resistance profile differs from a resistance pattern, which refers to the characteristics of a single isolate.

Specimen: A sample collected for laboratory testing. During outbreak investigations, samples may be collected from the blood, stool, or another location of a human or animal, and from food and the environment.

Susceptible isolate: An isolate that is not resistant to any of the antibiotics tested.