methods of bacterial growth measurement

1. METHODS OF BACTERIAL GROWTH
MEASUREMENT
DEPARTMENT OF VETERINARY
MICROBIOLOGY
PRESENTED BY :- DR. PUSHPENDRA BAGHEL
ROLL NO. :- M-6470

2. METHODS FOR BACTERIAL GROWTH
MEASUREMENT
 In Microbiology, Growth is defined as a process of –
Increase in number of microorganisms by Asexual method
OR
Increase in cell mass
OR
Increase in cell activity.
( Here, growth refers to population growth, rather than growth of
individual cells.)

3. MEASURMENT OF BACTERIAL GROWTH
1. DETERMINATION OF
CELL MASS.
2. DETERMINATION OF
CELL ACTIVITY.
3. DETERMINATION OF
CELL NUMBER.

4. CELL MASS
DIRECT
METHOD
PHYSICAL
DRY
WEIGHT
WET
WEIGHT
CHEMICAL
MEASURMENT OF
CELLULAR
COMPONENT
INDIRECT
METHOD
METABOLIC
ACTIVITY
RATE OF
PRODUCTION OF
METABOLIC
PRODUCT
TURBIDITY
SPECTRO-
PHOTOMETER

5. DRY WEIGHT ANALYSIS
 In this method, at first, the sample is centrifuged
 Than the resulting cell pellet is filtered and then it is weighed.
ADVANTAGES:
 It is a easy and rapid method.
 It is the only way to determine growth of filamentous bacteria.
DISADVANTAGES:
 Cumbersome and not very accurate.
 Does not give distinction between cell number and cell mass.
 It cannot distinguish between live and dead cells.

6. MESURMENT OF CELL NITROGEN
 As the microbes (bacteria) grow, there is an increase in the protein concentration
(i.e. nitrogen concentration) in the cell.
 Around 14% dry weight of bacterial cell is nitrogen.
 Thus, cell mass can be subjected to quantitative chemical analysis methods to
determine total nitrogen that can be correlated to growth.
 This method is useful in determining the effect of nutrients or antimetabolites
upon the protein synthesis of growing culture.
LIMITATIONS:
 It can be performed only on samples free from all other sources of nitrogen.
 It is applicable for concentrated solutions only.

7. MEASURMENT OF METABOLIC ACTIVITY
 Another Indirect method of estimating bacterial mass is measuring the metabolic
activity of the population ( for example – acid production or oxygen
consumption, nutrient utilization, waste production, pH etc).
 The assumption is that the amount of acid produced or oxygen consumed under
specific conditions and during a fixed period of time is proportional to the
magnitude of bacterial populations.
 Admittedly, the measurement of acid or any other end product is a very indirect
approach to the measurement of growth and is applicable only in special
circumstances.

8. TURBIDOMETRIC METHOD
 Rapid cell mass determination is possible using Turbidometry method.
 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
present and indirectly relates to cell number.
 One visible characteristic of growing bacterial culture is the increase in
cloudiness of the medium (turbidity).
 A Spectrophotometer is used to determine turbidity by measuring the
amount of light that passed through a suspension of cells.
 More cells = More turbidity; More turbidity = Less light passing through
the suspension.
 However, the culture to be measured must be dense enough to register
some turbidity on the instrument.

9.  LIMITATIONS:
 It doesn’t give the value of cell mass but the number has to be calculated
by plotting calibration curve between mass and optical density.

10. TURBIDOMETRIC METHOD