Phases of Growth

Bacteria multiply in a distinct pattern of growth, consisting of a cycle with four general phases:
  1. Lag:  The first phase of growth is called the "lag" phase, which is the longest period of the cycle, either several hours or days. They are very metabolically active, but are not getting any bigger.  Instead of growing new cells, it is a time when the cells are busy replicating various proteins and DNA in preparation for the next phase.
  2. Log/Exponential: The second phase derives its name from "logarithmic", meaning that there is massive or exponential growth as every chemical in the cell is being replicated as the process of cell division begins. This intense activity results in a dramatic increase to the bacterial colony in a short amount of time, however the cells become more vulnerable as well.
  3. Stationary:  The third phase indicates a slow down to the rapid growth.  As resources are used or toxic products accumulate, the rate of cell death begins to match the rate of cell division. Thus, the entire colony slows it's growth and reaches a state of equilibrium. 
  4. Death:  The final phase occurs when the number of dead or dying bacterial cells begin to outnumber the new ones, either as a result of limited resources, waste production, or because of other changes in the environment around the bacteria. Bacteria will die off until there are few enough of them to survive on nearby resources, at which point they will start to cycle back to the first phase and begin the process all over again.
Scientists and doctors can use the basic knowledge of the metabolic events which are taking place in these phases to develop ways to combat bacterial growth: as bacteria are most vulnerable during the log phase, many antibiotics target metabolic processes in that phase in an attempt to stop the bacteria from growing.