Cell number or concentration is an important data in microbiological research and laboratory analysis, reports Rice University. Procedures for counting cells rely on optical or electronic microscopes. However, some methods require other devices, such as plate readers. Today, the most used methods of cell counting include direct counting, culturing and reporter assays, according to Rapidmicrobiology.com.
Direct Counting
Direct counting is the oldest method in microbiology, in which the individual cells are magnified in a microscope to become visible to the naked eye, reports Rapidmicrobiology.com. Recently, the use of most sophisticated fluorescent microscopes, which can reflect light only from "labeled" cells--marked with chemical substances before observation--has made the task easier.
Culturing
Culturing is a method used for unicellular microorganisms, and it relies on the visible levels of growth, which are achieved under specific time, temperature, oxygen content, media nutrients and pressure, reports Rapidmicrobiology.com. After the incubation period, the plates or petri dishes with the grown culture of cells are rapidly counted using an electronic device called an automated plate reader.
Reporter Assays
Reporter assays are used with unicellular microorganisms that are not necessarily growing but show other kinds of metabolic activity. These methods include colorimetry, impedance and ATP (adenosine triphosphate), reports Rapidmicrobiology.com. Colorimetry uses color changes when dyes are added to a solution with different cells. The impedance method uses the changes in the medium's electric conductivity, caused by the cell metabolism. ATP uses a bio-luminescent reaction that happens inside the cell and is dependent on the levels of adenosine triphosphate molecules, present in the medium.
Tags: reports Rapidmicrobiology, adenosine triphosphate, unicellular microorganisms