Mold and Yeast Counts by Using Microscopy

Thoma Slide:

Thoma slide has a special slide. In Thoma slide the total volume is 0.1 ml which has 0,05 X 0,05mm side lenght and 0,1 mm depth small cubes placed in total 20 X 20. In order calculate the total number of microorganisms;


A: Total calculated yeast number in 0.1 mm

DF: dilution factor 10000: conversion factor

N: concentration of cells (CFU/ml)

In general 40X objectives are used when we used Thoma slide. The total magnification power of those lenses are not suffecient to see the bacterium. But not the yeast. Because of this reason we used Thoma slide in order to count YEAST cells. In counting method there is no need to stain the yeast. But 1 drop of methylene blue (50 ppm) can be applicable in order to differantiate the alive and the death cells.

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