Bacterial growth curve

Lag phase

• bacteria hasn’t begun to reproduce yet (could last anywhere from 1-24 hours

Log phase

• bacteria growing and increasing in number rapidly

• exponential growth period

Stationary phase:

• number of cells dying = number of cells alive and still dividing

Death phase:

• number of cells dying is greater than number of cells dividing and growing

• decreasing at a logarithmic rate

What phase is it best to observe bacteria in?

The log or stationary phases because they are most active/most representative of the culture.

Plate counts:

• series of serial dilutions from an original inoculum

• 1:10 dilution factor each time

• transfer dilutions to petri plates using either the pour plate method or spread plate method and incubate them

• count colonies on plates containing 25-250 colonies and multiply that number by the dilution factor to get the number of colonies in the original inoculum