GENERAL MICROBIOLOGY - T.P. Pirog - 2004

6. MICROBIAL GROWTH

6.4. GROWTH PHYSIOLOGY

6.4.3 Growth of bacteria in a bacterial population

6.4.3.1. Determination of bacterial concentration

Not all Cells in a population are viable. Viable cells are considered to be those capable of forming colonies on/in an Agar medium or suspended in a liquid nutrient medium. These viable cells are detected using specialized Methods designed to quantify living cells. The Total Cell Count includes living, damaged, and dead cells. Therefore, a distinction is made between Methods for determining the total cell count and the viable cell count.

Total cell count. There are several methods for determining the total cell count:

the most common approach is microscopic counting of the total cell number in a thin layer using a counting chamber, or utilizing turbidity standards. This is one of the oldest methods, which involves comparing the turbidity of the test cell suspension with that of standard solutions of known cell concentration;

using an electronic counter, the operation of which is based on the decrease in conductivity of an electrolyte solution as a single bacterium passes through a narrow aperture;

if The Cell concentration is less than 10⁴ per 1 mL, the membrane filter method is employed (the sample is filtered through a membrane filter, after which the filter is dried, stained, clarified, and the cells are counted under a Microscope).

Viable cell count. This is determined by Koch's method (plating serial tenfold dilutions of the cell suspension onto Petri dishes with an agar medium). The Number of viable cells is determined by counting the colonies that have grown on the plates (sometimes referred to as colony-forming units, or CFU).