Plate diffusion test

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The plate diffusion test , an agar diffusion test , which is also known as a diffusion test or diffusion plate test , is a microbial test procedure.

In this process, solid nutrient media in the form of agar plates are used, which contain microorganisms as test organisms in finely suspended form. The presence of the test organisms is not visible at the start of the test; only after the agar plate has been incubated can the multiplication of the test organisms in the plate be seen as growth that can be seen with the naked eye, as cloudiness of the agar. Zones in which no reproduction took place remain clear. The observation and measurement of the growth zones can be used for the detection as well as for the qualitative and quantitative determination of growth-promoting substances ( vitamins , amino acids ) on the one hand and growth-inhibiting substances ( inhibitors such as antibiotics , toxins ) on the other.

There are various options for applying the test solutions to the prepared agar plate: They are either filled into holes punched out with a hollow drill (hole test), as a solution dried on filter paper discs (disc / plate test) or in small metal cylinders that are placed on the Surface of the plate were placed, pipetted (cylinder test).

After incubation, a circular zone of inhibition in cloudy growth in the rest of the agar plate, which is why the test as is evident in growth inhibitors inhibition zone is called. In the case of growth-promoting substances, a circular clouding zone appears around the application site with a clear remainder of the plate and this phenomenon is referred to as an auxanogram . By comparing the diameter of the inhibition or growth zone with those that are caused by solutions with known concentrations of active ingredient, the corresponding concentration of the test solution examined can be determined using a calibration curve.

The plate diffusion test is used for:

  • looking for new antibiotics
  • the determination of the spectrum and effectiveness of a new antibiotic
  • the creation of antibiograms to determine the sensitivity and resistance of microorganisms to antibiotics
  • the search for new production strains of vitamins and amino acids in biotechnology

For the exact standardization and reproducibility of the very versatile process, extensive controls and a very precise procedure are necessary.

literature

  • William S. Hewitt, Stephen Vincent: Theory and Application of Microbiological Assay . Academic Press, San Diego 1989, ISBN 0-12-346445-5