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Definitions
A directory of terms related to antibiotic treatment, useful for discussing the development of antibiotic resistance. (Sources: Alliance for the Prudent Use of Antibiotics, Union of Concerned Scientists, US Centers for Disease Control and Prevention.)
A
Antibacterial
An agent that interferes with the growth and reproduction of bacteria.
Antibiotic resistance
Antibiotic resistance occurs when an antibiotic has lost its ability to effectively control or kill bacterial growth; in other words, the bacteria are 'resistant' and continue to multiply in the presence of therapeutic levels of an antibiotic.
Antibiotic susceptibility
The opposite of resistance. This applies to bacteria that killed or inhibited by an antibiotic. Susceptibility to one antibiotic does not mean susceptibility to all.
Antibiotics
A chemical compound that can kill or inhibit the growth of a bacteria without causing the host (such as a human or animal) significant damage.
Antimicrobials
A broad term used to describe any agent that interferes with the normal function of microscopic organisms, including bacteria, fungi, yeast, viruses and protozoa. Antibiotics, which affect only bacteria, are one type of antimicrobial.
B
Bacteria
Single-celled microscopic organisms that often live together in colonies.
Biodiversity
The number of living organisms, and the variability among them and their environments.
Broad-spectrum antibiotics
An antibiotic is termed 'narrow-spectrum' or 'broad-spectrum' depending on the range of bacterial types that it affects (see Narrow-spectrum antibiotics). Broad-spectrum antibiotics are active against a wider number of bacterial types and thus may be used to treat a variety of infectious diseases; they are particularly useful when the infecting bacteria is unknown. Examples of broad-spectrum antibiotics are the aminoglycosides, the second and third generation cephalosporins, the quinolones and some synthetic penicillins. Narrow-spectrum antibiotics are active against a select group of bacterial types. Examples of narrow-spectrum antibiotics are the older penicillins (penG), the macrolides and vancomycin.
C
Colonisation
Colonisation occurs when a new species of bacteria develops a colony (a group of the same type of bacteria) in a new location, such as the human intestinal tract. Bacteria can colonise a host without causing infection or disease.
Commensal
Usually refers to a microorganism that lives in close contact with a host organism (human, animal or plant) without causing disease in the host. Commensal organisms can be beneficial to the host. Some microorganisms can be a commensal for one host species but cause disease in another.
E
Ecosystem
A place with living (e.g. animals, plants, microorganisms) and nonliving (e.g. soil, water, rocks) elements that form a complex web of interdependency.
Enteric bacteria
Bacteria that live in the intestines of humans or animals.
F
Flora
Populations of commensal bacteria normally present in the intestine, body openings, and on the skin.
Food-borne pathogens
Infectious organisms associated with livestock that can cause diseases in humans. They include Salmonella, Campylobacter, E. coli O157:H7, and Listeria.
G
Generic vs. trade name (non-generic) antibiotics
Commercially available antibiotics may be referred to by two different names. The generic name is the common family identification provided by chemists — for example, Amoxicillin. The trade name is given to it by the manufacturer and is often used by doctors and pharmacists when prescribing and dispensing the drugs. One trade name for Amoxicillin is Augmentin.
Gram-positive and gram-negative bacteria
Bacteria are distinguished into types depending on how they stain in a dye test. When gram-positive bacteria are stained, the cell wall holds the dye inside and the bacteria are stained dark purple. The cell walls of gram-negative bacteria are more permeable — they do not retain much of the dye —so their cell walls do not show much stain.
Growth promoters
A class of substances, usually antibiotics, used at low doses to promote the growth of food animals, such as cows.
M
Methicillin-resistant Staphylococcus aureus (MRSA)
A bacterial strain named because it is resistant to methicillin. In practice, MRSAs are generally resistant to many antibiotics, and some are resistant to all but vancomycin.
Multidrug resistance
The ability of an organism to resist several different drugs.
N
Narrow-spectrum antibiotics
An antibiotic may be classified as 'narrow-spectrum' or 'broad-spectrum' depending on the range of bacterial types that it affects. Narrow-spectrum antibiotics are active against a select group of bacterial types. Examples of narrow-spectrum antibiotics are the older penicillins (penG), the macrolides and vancomycin.
Natural selection
The process by which organisms that are better adapted to their environment thrive and multiply. Organisms that are less well adapted to their environment fail to thrive and do not reproduce successfully.
Nosocomial infections
Infections that are acquired in a hospital while undergoing treatment for a different condition.
O
Opportunistic infection
An infection caused by an organism that is usually benign, such as a commensal bacterium.
S
Selective pressure
The influence exerted by some factor (such as an antibiotic) on natural selection to promote one group of organisms over another. In the case of antibiotic resistance, antibiotics cause a selective pressure by killing susceptible bacteria, allowing antibiotic-resistant bacteria to survive and multiply.
Subtherapeutics
Drugs used at levels that are too low to be effective in controlling disease; antibiotics are commonly used in subtherapeutic doses for promoting the growth of food animals, such as cows.
Superbug
Some bacterial strains have become resistant to so many antibiotics that they are sometimes referred to as 'superbugs' or 'supergerms.' Examples of superbugs are Staphylococcus aureus that are resistant to methicillin and vancomycin, Pseudomonas aeruginosa (a cause of many lung and burn infections), vancomycin-resistant Enterococcus faecalis (VRE, which can cause an infection in the digestive system), and multidrug-resistant Mycobacterium tuberculosis (the bacteria that causes tuberculosis). Some of these strains resist all known antibiotics — more than 100 different drugs.
Surveillance systems
The ongoing systematic collection and analysis of data. The data may lead to actions to prevent and control an infectious disease.
Susceptibility
A measure of how well antimicrobials affect bacteria. Susceptible bacteria can be killed or inhibited by an antimicrobial.
V
Virus
An extremely small infective agent, visible only with an electron microscope. Viruses can cause disease in humans, animals and plants. Viruses consist of a protein coat and either a DNA or RNA strand of genetic material. Viruses can reproduce only inside a host cell by using the cell's machinery to reproduce. Thus, viruses are considered either the simplest type of organism or a complex, non-living, molecule. Viruses are not killed by antibiotics.
