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Friday, October 13, 2017

Measurement of Microbial growth by turbidometric method

Objective:
To find the generation time of given organism by turbidity method.
Principle:
Turbidometric method is the rapid, sensitive and useful technique to measure the growth of microbes. Turbidometry is based on the fact that microbial cells scatter light striking them. Since the microbial cells in a population are of roughly constant size, the amount of scattering is directly proportional to the biomass of cells and indirectly related to cell number. One visible characteristic of growing bacterial culture is the increase in turbidity (cloudiness) of the medium.  When the concentration of bacteria increasing, the medium appears slightly cloudy or turbid. Further increase in concentration results in greater turbidity. When a beam of light is passed through a turbid culture, the amount of light transmitted is measured, Greater the turbidity, lesser would be the transmission of light through medium. Thus, light will be transmitted in inverse proportion to the number of bacteria. Turbidity can be measured using spectrophotometer.

Materials required:
-Nutrient broth
- 10- 12 hrs old broth culture
-Spectrophotometer
-Cuvette

Procedure:
-  Prepare and take 50ml of nutrient broth in sterile flask.
- Then this broth is inoculated with 1 ml of overnight bacterial culture and places it in incubator.
- The 0th hour reading take by using spectrophotometer and the culture is again keep it in incubator.
- The flask is removing from incubator for a particular interval time (30 min.) and the sample is transfer aseptically to the cuvette using sterile pipette for observe the reading.
- The optical density reading in spectrophotometer is at 620nm.
- The reading will be tabulated and plotted the graph by OD value in Y-axis and incubation time in X -axis.  

Determination of generation time:
-Select the 2 points on the optical density scale that represents doubling the turbidity.
 The generation time is to be determine by using the formula
 Gt = t (OD2) –t(OD1)
Result:


The generation time of ­­­_______cells found to ­­­­­________ min/hr.


Peptone Broth Composition:

Peptone    20g
Sodium chloride    5g

Distilled water   1000ml

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