Growth Curve of Bacteria SlideShare

Growth curve of bacteria SlideShare

1. Growth Curve of Bacteria Food Microbiology By Sayanta Mitra

2. What is Bacterial Growth Curve ? Bacterial growth curve is a curve on a graph that shows the changes in number of a bacterial population over time in a culture. Important points : Not increase in size it means increase in number , increase in population. Depends on favourable condition ( eg – temperature, pH, nutrients etc)

3. This graphical representation is for heterotrophic bacteria; that means that type of bacteria who takes their food or nutrients from other sources. The growth Curve of bacteria occurs in a geometric or exponential manner. (Means with each division cycle or generation one cell gives rise to 2 cells, then 4 cells, then 8, then 16, then 32 and so on) The time require for formation one single generation is called generation time (G) .

4. Phases of Bacterial Growth Curve It has been determined that in a closed system or batch culture (no food added, no wastes removed) bacteria will grow in a predictable pattern, resulting in the growth curve. This curve consists four distinct phases: Lag phase Exponential or log phase Stationery phase
Death phase

5. Lag Phase : Newly inoculated bacteria are adopting the new environment. So this phase is also called preparatory phase . The bacteria required the period of time between the introduction of a microorganism into a new culture medium and the time it begins to increase exponentially, this period is called lag period . A small group of cells that are placed in a rich nutrient medium, synthesize proteins and other necessary molecules. These cells increase in size , but no cell division occurs in the phase.

6. Log Phase : This is the time when the cells are dividing by binary fission and doubling in numbers after each generation time. The division of the bacteria is in logarithmic or exponential way. So this phase is also called exponential phase . In case of pathogenic bacteria our body try to kill them, as they increase in number. As a result symptoms appear at this phase.

7. Stationery Phase : Lack of food, nutrients and accumulation of wate products, hence growth slow down. Reproduction rate = Death rate. The stationary phase lasts as long until there are no nutrients left and also there is too much accumulation of waste.

8. Death Phase : Acute shortage of available food. Increase the secretion of toxins. Number of living cells decreases exponentially. Death rate >> Reproduction rate. Ultimately the bacteria disappear completely from that place.