Plate count
The plate count (synonym colony count , surface-viable count , plate count , Miles-and-Misra method ) is a microbiological method for determining the number of colony forming units and thus the number of living cells of micro-organisms in a sample.
principle
The plate count creates a mostly logarithmic, serial dilution series from a sample . Most of the time, the dilution is done with phosphate-buffered saline or liquid nutrient medium as a diluent. An equal part of each dilution stage is plated out on three solid nutrient media (triplicates). This is followed by incubation of the nutrient media with the microorganisms at a suitable temperature, usually for one to three days at 30 to 37 ° C. The microorganisms isolated by the dilution grow into separate colonies , which can then be counted at a dilution stage suitable for counting.
The numerical values of the triplicates of a dilution level are arithmetically averaged in order to increase the statistical significance of the value, whereas offsetting different dilution levels leads to a reduction in accuracy. Finally, the value is multiplied by the dilution factor to determine the value for the undiluted sample.
Individual evidence
- ^ AA Miles, SS Misra, JO Irwin: The estimation of the bactericidal power of the blood. In: The Journal of hygiene. Volume 38, Number 6, November 1938, ISSN 0022-1724 , pp. 732-749, PMID 20475467 , PMC 2199673 (free full text).
- ^ AJ Hedges: Estimating the precision of serial dilutions and viable bacterial counts. In: International journal of food microbiology. Volume 76, Number 3, June 2002, ISSN 0168-1605 , pp. 207-214, PMID 12051477 .