Measuring Microbial Growth

Basic Principles of Microbial Growth Measurement

Microbial growth refers to the increase in the number of microorganisms in a culture.
Growth usually occurs in two stages: the lag phase where microorganisms are adapting to the environment, and the exponential (log) phase where the population multiplies rapidly.
Measuring microbial growth helps to determine the rate at which populations are increasing, and aids in predicting their growth patterns.

Direct Methods

The plate count method involves spreading a known volume of the culture on an agar surface and counting the colonies after incubation.
The most probable number method is used when microorganisms cannot be cultured easily. It is a statistical method based on the concept of dilution series.
The microscopic count includes counting the number of microbial cells directly through a specially designed counting chamber.

Indirect Methods

In the turbidimetric method, the degree of cloudiness (turbidity) in the broth culture indicates microbial growth.
The dry weight measure is used for filamentous bacteria and fungi. The organism is filtered, dried and weighed to determine growth.
The dilution method is often used when the number of microorganisms is too large to count. Successive dilutions are made, then the plate count method is used to count cells.

Certain environmental factors, such as temperature, pH levels, available nutrients, and light exposure, can significantly influence microbial growth.
Each microorganism has its preferred growth conditions. Mikroorganismus, such as thermophiles, thrive in high temperatures, while acidophiles prefer acidic environments.
It’s crucial to control these factors in the laboratory to ensure successful cultivation and accurate growth measurements.