Bacterial inhibition test
A bacterial inhibition assay ( English bacterial inhibition assay , also of bacterial inhibition assay ) is a microbiological method for the semiquantitative determination of the concentration of a nutrient by cell culture of bacteria on a solid nutrient medium . Conversely, the bacterial inhibition test can also be used to determine auxotrophies in the metabolism of microorganisms.
principle
The addition of a sample with a nutrient missing in the nutrient medium leads to an accelerated growth of microorganisms for which this nutrient is essential with increasing concentration . The accelerated growth of the microorganisms used leads to enlarged diameters of the colonies on the solid nutrient medium after an incubation typical for the microorganism, usually for one to three days at temperatures between 30 and 37 ° C. Then the diameter of the colonies is compared with the diameter of a dilution series of positive controls and the concentration of the missing substance is estimated.
Guthrie test
The Guthrie test is a variant of the bacterial inhibition test to determine phenylalanine , e.g. B. to determine phenylketonuria in newborns. A drop of blood was dropped on a filter paper, dried and placed on a solid nutrient medium with a bacterial culture of Bacillus subtilis (ATCC 1651) without phenylalanine. The nutrient medium also contains B-2-thienylalanine, which prevents the growth of Bacillus subtilis in the absence of phenylalanine. Depending on how much phenylalanine diffuses from the dried blood drop into the nutrient medium , the larger the colonies are after incubation. In comparison to nutrient media with known phenylalanine concentrations, the amount of phenylalanine contained in the blood drop can be determined. The Guthrie test can determine 180 - 240 μmol / L (3 - 4 mg / dL) phenylalanine. Occur in a healthy person 120 μmol / L (2 mg / dL). The Guthrie test is in good agreement with other methods for determining phenylalanine.
Individual evidence
- ↑ Guthrie, R. & Susi, AA (1963): A Simple Phenylalanine Method for Detecting Phenylketonuria in Large Populations of Newborn Infants. In: Pediatrics Vol. 32, pp. 318-343. PMID 14063511 .
- ↑ S. Vallian, H. Moeini: A quantitative bacterial micro-assay for rapid detection of serum phenylalanine in dry blood-spots: application in phenylketonuria screening. In: Journal of applied genetics. Volume 47, number 1, 2006, ISSN 1234-1983 , pp. 79-83, doi : 10.1007 / BF03194603 , PMID 16424613 .
- ↑ R. Fingerhut, M. Stehn, A. Kohlschütter: Comparison of four different phenylalanine determination methods. In: Clinica Chimica Acta . Volume 264, Number 1, August 1997, ISSN 0009-8981 , pp. 65-73, PMID 9267704 .