Antibiogram

The antibiogram is a laboratory test to determine the sensitivity or resistance of pathogens to antibiotics. An antibiogram is recommended before each antibiotic therapy.

Agar diffusion test

When the agar diffusion test to be investigated microorganism is distributed in small amounts on the surface of a special planar Gelnährbodens and Gelnährboden then covered with circular plates made ​​of an absorbent material containing different antibiotics in a defined amount. Antibiotics dissolve in Gelnährboden and diffuse radially outward. The antibiotic diffuses from the further plate, the lower its concentration. At a certain distance from the plate, the concentration of the antibiotic is low so that the microorganism can grow, despite the presence of the antibiotic. After a period of incubation that is sufficient for a multiplication of the microorganisms to the visible growth of the Agargeloberfläche (for pathogenic bacteria usually 16 to 20 hours ), the radii of the zones of inhibition are measured and evaluated with respect to sensitivity or resistance of the microorganism.

The minimum inhibitory concentration (MIC) is the lowest concentration of an inhibitor at which the multiplication of the microorganism is not inhibited. The minimum bactericidal concentration (MBC ) is in contrast to the minimal inhibitory concentration (MIC ) is the concentration that is sufficient to kill 99.9 % of the individuals of the tested microorganism. These variables can not be determined by the agar diffusion test.

Microdilution

Of the micro-organism to be examined, a slurry is prepared in a liquid nutrient medium. Adding a defined quantity of an antibiotic to the latter. This is dürchgeführt with various concentrations of the antibiotic, for example, with a dilution series (1, 2, 4, 8, 16, 32 mg / L), one can carry out a MIC determination, which is more accurate than the determination of antibiotic sensitivity with the agar diffusion test. Multiplication of the microorganism can be seen at a turbidity of the culture medium: If it remains clear, the examined microorganism to the antibiotic at this concentration is sensitive.

Automated Determination of resistance

There are different devices that carry antibiotic resistance determination. These devices operate on the Mikrodilutationsmethode. The corresponding to the devices software evaluates the results and checks them for plausibility. Examples are:

  • VITEK of bioMerieux
  • Phoenix from Becton Dickinson

Evaluation

Is evaluated based on selected standards, such as

  • DIN
  • EUCAST
  • CLSI
Chloramphenicol
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