2.8 Enumeration of Bacterial Growth

Petroff - Hausser Counting chamber

a grid used to count the number of cells

Petroff - Hausser Counting chamber pro and cons

Pros:
fast and simple
cell morphology can be observed
contamination can be detected
Cons:
Can’t distinguish from live and dead
Small cells can’t be distinguish
Moving organisms are hard to count

Optical density and cell density

Using the turbidity of a cell culture to indirectly calculate the cell density

OD reading pro and cons

Pros:
rapid and no samples are destroyed
Cons
can’t distinguish from live and dead cells
can’t distinguish between different species
Indirect calculation of cell density from optical density

OD₆₀₀ of E. Coli

0.1 = 1×10¹⁸ cells/mL

Viable cell count

use serial dilution to count the number of colonies on a plate

Pour plate method

bacterial sample is mixed with agar
Pros: no spreading tools needed
Cons": Needs good timing and embeds cells into agar

Spread Plate Method

Spread bacterial containing agar to a plate
Pros:
Colones are well spread and easy to count
Cons:
Need spreading tools
Prepare agar plates

Most Probable Number Method

a probabilistic method to estimate the number of colifor bacteria in a sample. Serial dilution is done and tubes have a indicators that cange colors

Flow cyotmetry

A small tube that allows on cell at a time to flow through and gives each cell a fluorescent tag to distinguish between dead and live cells