antimicrobial sensitivity test

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antimicrobial sensitivity test

A laboratory method of determining the susceptibility of bacteria to antibiotics. The specimen obtained is cultured in various liquid dilutions or on solid media containing various concentrations of antimicrobial drugs in disks placed on the surface of the media. The disk-type test is not completely reliable. Synonym: culture and sensitivity test


1. killing microorganisms, or suppressing their multiplication or growth.
2. an agent that kills microorganisms or suppresses their multiplication or growth.
Antimicrobial agents are classified functionally according to the manner in which they adversely affect a microorganism. Some interfere with the synthesis of the bacterial cell wall. This results in cell lysis because the contents of the bacterial cell are hypertonic and therefore under high osmotic pressure. A weakening of the cell wall causes the cell to rupture, spill its contents, and be destroyed. The penicillins, cephalosporins and bacitracin are examples of this group of antimicrobials.
A second group of antimicrobial agents interfere with the synthesis of nucleic acids. Without DNA and RNA synthesis a microorganism cannot replicate or translate genetic information. Examples of antimicrobials that exert this kind of action are griseofulvin, fluoroquinolones and rifampicin.
A third group of antimicrobial agents change the permeability of the cell membrane, causing a leakage of metabolic substrates essential to the life of the microorganism. Their action can be either bacteriostatic or bactericidal. Examples include amphotericin B and polymyxin B.
A fourth group of antimicrobial agents interfere with metabolic processes within the microorganism. They are structurally similar to natural metabolic substrates, but since they do not function normally, they interrupt metabolic processes. Most of these agents are bacteriostatic. Examples include the sulfonamides, aminosalicylic acid (PAS) and isoniazid (INH).
A fifth group interfere with translation of proteins by the ribosome. This action may be bacteriocidal, if errors in translation are induced (aminoglycosides) or bacteriostatic, if translation is inhibited (macrolides, tetracyclines, chloramphenicol).

antimicrobial resistance
ability of a microorganism to resist the effects of an antimicrobial agent. May be an intrinsic characteristic or acquired by selection for mutation or by acquisition of a resistance gene from other microorganisms.
antimicrobial sensitivity test
an in vitro test of the effectiveness of selected antibacterial agents against bacteria recovered from a patient. Paper disks impregnated with various agents are placed on an inoculated agar plate (disk diffusion) or the agent is added to broth cultures. Inhibition of growth is interpreted as an indication of bacterial sensitivity to the antibacterial.
subtherapeutic antimicrobial therapy
used mainly in mass medication programs as preventive measures against unspecified infectious diseases. Carries the risks of creating resistant strains of organisms, and of resulting in unacceptable residues in human food.
antimicrobial therapy
antimicrobial agents may be administered topically, orally, or injected. There are special needs for special circumstances. Aquarial fish, for example, may be treated by incorporating the agent in the feed or by injection. Immersing the fish in a tank containing a solution of the agent is satisfactory only for superficial infections because the drug is not absorbed directly through the skin and the intake is very slow.
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