Introduction

Bacterial growth refers to increase in number of cells and dimension (preferentially increase in number of cells). Bacteria divides by binary fission where 1 cell divide into 2 cells, each then divide into 2 and so on doubling after each generation.

Generation time (gt) or doubling time:

The time required to double the number of cells present at the initial observation is gt. For most common pathogenic bacteria gt =15-20 minutes. However, Mycobacterium tuberculosis (slowest growing bacteria) have gt = 8-10 hours.

Growth requirements:

• Nutritional requirements: essential elements, mineral sources, organic growth factors.
• Favorable environment: water, oxygen, CO2, temperature, H+ concentration, light, osmotic pressure.

*Growth curve:

For the growth of bacteria, suitable culture media and suitable environment is required. When bacterial count in a growing culture medium is determined at certain intervals and plotted, the curve obtained is bacterial growth curve.

There are four phases in a bacterial growth curve- lag phase, log phase, stationary phase, decline phase.

1. Lag phase: It is adaptive or preparatory phase where necessary enzymes and metabolites are built. At the end of lag phase there is increase in size and increase metabolic activities (no increase in number).
2. Log phase: Bacteria grow and multiply exponentially due to favorable condition and sufficient nutrition and attain maximum number.

• Stationary phase: The nutrition supply exhaust and bacterial growth stops. There is neither increase nor decrease in number of cells.

1. Decline phase: There is exhaustion of nutrients, accumulation of toxic products and autolytic enzymes. Due to unfavorable condition, bacteria begins to die, few survive and undergo sporulation.