Ways Of Counting Bacteria

Microscope & hemocytometer:

1. What is a hemocytometer? How does a hemocytometer work?
It is a device that counts microscopic particles. The hemocytometer works becuase it creates a volumetric grid in which is divided into many different sizes of cubes so that one can accurately count the amount of particles in that cube and apply to the concentration of the entire sample.
Optical Density method
2. How does a spectrophotometer work to count bacteria?
-It doesn't directly count the bacteria or bacterial colonies, instead it measures the contents of a "colonized" broth. Light is sent through a broth containing bacteria, and the amount of light that is able to shine through determines the concentration of the amount of bacteria in the broth. The more light that shines through, the less bacteria that are present, and vice versa.

Viable Count methods
3. What is the protocol for making a spread plate of a sample containing bacteria? How do you count the bacteria on the plate? First, dilute the bacterial broth, than streak it out on a plate. Once incubated, than one would count the colonies. Once one has the colony count, he or she can do some calculations to get the bacterial count of the original sample
4. How is the protocol for a pour plate different from that of a streak plate? In a pour plate one would add a ml of diluted bacterial broth which is poured out on a petri-dish. Then, 9 ml of agar medium is poured on top. The contents are mixed and incubated. Then one would count the colonies and do some calculations to find bacterial count.
5. Why would you use a pour plate rather than a streak plate? It seems easier to isolate specific colonies

Serial dilution of liquid samples
6. How can you count viable bacteria in a liquid sample when there is a high concentration of bacteria in your sample? You would dilute the solution and then count the bacteria. Use the CV=CV equation to do calculations based on the dilutions and bacterial count?

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