Micro Lab Bacterial Enumeration

An indirect method that measures the turbidity and absorbance of the sample

Spectrophotometry

A direct method that involves counting bacteria under a microscope

Petroff-Hausser

Performed through a series of serial dilutions

Viable plate count

Describes individual colonies on a plate's surface

Colony forming unit

Increase by a constant number with each generation

Arithmetic growth

Cloudiness of a fluid caused by large numbers of particles /organisims

Turbidity

The measure of the light intensity absorbed by a sample

Absorbance

Bacterial population size doubles with each generation

Binary fission

Determine the order for performing a dilution series.

1) Determine the dilutions of the dilution tubes

2) Determine the dilutions of the agar plates

3) Determine which plate is the countable plate

4) Calculate the concentration in the original tube

Determine the dilutions of the agar plates

Step 2

Calculate the concentration in the original tube

Step 4

Determine which plate is the countable plate

Step 3

Determine the dilutions of the dilution tubes

Step 1

Examples of exponential vs. arithmetic growth.

Generation: 1,2,3,4,5,6,7,8,9,10/ Arithmetic Growth: 1,2,3,4,5,6,7,8,9,10/ Exponential Growth: 1,2,4,8,16,32,64,128,256,512

Arithmetic Growth

stays the same number as the as the generation it is in. This is different from linear (arithmetic) growth in which a new cell is added with each generation so that one cell becomes two, followed by three,

Exponential growth

works through binary fission

Binary fission

Binary fission is a method of asexual reproduction during which a single cell (parent cell) will split into two cells (daughter cells). The process then continues as each of these cells divide into two more cells, thereby doubling the population size with each generation.

What is one of the reasons foodborne illnesses can occur so quickly?

If food is inadvertently inoculated with a pathogen and then improperly refrigerated, this small inoculum can rapidly expand to numbers that will result in illness.

What is an example of a foodborne illnesses?

Salmonella-Genus of bacteria (Zoonotic bacterial diseases)

Binary fission is a method of sexual reproduction where a single cell (parent cell) will split into four cells (daughter cells).

False- It is a method of asexual reproduction where a single cell will split into two daughter cells

A spectrophotometer measures absorbance as a function of _____.

individual cell number

oxygen availability

salt content

turbidity

water content

turbidity

One reason a spectrophotometer is useful for organism count estimations is because of its ability to differentiate between living and dead cells.

True

False

False- One limitation of a spectrophotometer is its inability to differentiate between living and dead cells

A Petroff-Hausser counting chamber holds a specific volume of sample and has a grid etched into its surface to enable counting of individual cells under a microscope.

True

False

True

If the 1:100 plate contained 50 colonies, the 1:1000 plate containined 200 colonies, and the 1:10000 dilution plate conatinined 1000 colonies, which plate would you use to determine the orginial culture concentrations?

1:100 plate with 50 colonies