Final answer:
Microbial growth can be counted by direct methods using a microscope and counting chambers, or indirectly through spectrophotometry by measuring turbidity that estimates cell density.
Step-by-step explanation:
The two ways to count microbial growth are direct and indirect methods. Direct methods involve counting individual cells or colonies, typically using a microscope and specialized counting chambers, such as a Petroff-Hausser chamber or a hemocytometer. Indirect methods do not count the cells directly but instead estimate cell density by measuring the impact of the cellular population on a physical property, such as turbidity or light absorbance.
Spectrophotometry is an indirect method where a spectrophotometer measures the turbidity of a liquid culture by determining how much light passes through the suspension. Greater bacterial cell density results in higher turbidity, reducing light transmission and increasing absorbance.