Life and death in bacterial cultures


By now, you should understand dilutions and the general process of counting bacteria.  We will use these methods to determine the concentration of viable E. coli in a culture over a 96 hour period.

Before you leave the applet, print your data graph.
You will need it for your report

  
 

Your culture was started at time t = 0. When your specify a time, the absorbance of the culture will be displayed.  Determine the CFU/ml as function of time.   A culture with A = 1 contains ~107 bacteria/ml, a culture with A = 2 contains ~109 bacteria/ml.

If none of the plates are within the "countable" range, go back and plate out different volumes -- your dilutions have been stored at 4°C and there is essentially no growth or loss of viability under these conditions.

NOTE: We record the number of CFU/ml in scientific notation i.e. e6 means 106.  Record your data and generate a graph of CFU/ml over time.

WRITE-UP

 

Based on your observations, answer the following questions.

  • How long does it take to reach the maximum CFU/ml?
  • What is the CFU/ml at the end of the experiment?  how does that compare to the maximum CFU/ml. 
  • Why does the CFU/ml drop?   Propose an experiment to resolve whether death is random or whether bacteria with specific variations survive preferentially? 
Use Wikipedia | revised 19 March 2005