Introductory Microbiology

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Batch culture

• Growth of microorganisms in a limited volume of liquid medium is generally termed as a batch culture. The growth of bacteria in a culture medium in which conditions for balanced growth are favourable, changes in cell mass can be related to three or four phases, i.e., lag phase, log phase, stationary phase and death or autolytic phase.

  Ø  In lag phase, there is no increase in the number of viable cells. However, cell growth occurs as indicated by the increase in cell mass. During this period cell increase in size as a result of extensive macromolecular synthesis. This period represents a period of active growth without cell division and the cells prepare for cell division.
  Ø  In the log phase, the cell population increases logorithmically and the cells divide at the maximum rate permitted by the composition of the medium and environmental conditions. The growth rate can be expressed in terms of the number of cell divisions that occur per hour or unit time.
  Ø  In the stationary phase, the total number of viable cells remain constant. In fact the stationary phase is reached when the viable cell number does not increase.
  Ø  In death phase or phase of decline, is characterized by an exponential decrease in the number of viable cells. The phase of decline generally seen in bacteria.
• Some bacteria such as the sporulating bacteria may form endospores as they reach the stationary phase of growth and these would be resistant to lysis or death. In such cases the number of viable cells will remain constant after attaining the stationary phase and phase of decline may not be seen.
   

  

Typical Growth Curve of Bacteria in Culture