Chapter 5.8 Microscopic Counts

Question 1

Microbial cells are enumerated by what?

Are they reliable?

(Definition of enumerated - to ascertain the number of : count)

Answer 1

Microscopic Observations

No

Question 2

What are the limitations of microscopic counts?

Hint: There are a lot

Answer 2

• Cannot distinguish between live and dead cells without special stains
• Small cells can be overlooked
• Precision is difficult to achieve
• Phase-contrast microscope required if a stain is not used
• Cell suspensions of low density (<106 cells/ml) hard to count
• Motile cells need to immobilized
• Debris in sample can be mistaken for cells

Question 3

What is a second method for enumerating (counting) cells in a liquid sample?

Answer 3

Using a flow cytometer

A Flow Cytometer uses lasers, fluorescent dyes, and electronics