All the bacterial cultures that will be tested for the produ

All the bacterial cultures that will be tested for the production of acetoin are incubated for 72 hours. why? Give a detailed explanation.

Solution

For this, you need to know microbial growth kinetics. Bacterial growth kinetics is studied in four phases:

The first phase is known as lag phase. In this, when kept for incubation, the bacterial culture prepares itself for starting the growth and division process. Hardly any growth occurs in this phase.

The second phase is log phase, also known as exponential phase. In this rapid growth and division occurs in bacteria. For bacterial growth, cultures are incubated generally for 36-48 hours. Within this time range, the exponential phase is reached. Most primary metabolites are produced in this phase.

The third phase is stationary phase. In this phase, rapid cell division is ceased because of loss of culture. Most secondary metabolites are produced by reaction between primary metabolites in this phase. Acetoin is one of the secondary metabolites produced by bacteria. For achieving this phase, the cultures need to be incubated for more than 48 hours. After 48 hours i.e. two days, the media provided is totally exhausted, and now the bacterial growth and division has ceased further. In this phase, and the reaction vessel/culture plate has nothing except primary metabolites to react with each other and produce secondary metabolites.

Therefore, incubation of 72 hours is given in the above case.

A weak-positive or false negative reaction is also tested by incubation for a longer time (72 hours).