Mirobial Growth, Lecture 2-Revised WPR 2016
Mirobial Growth, Lecture 2-Revised WPR 2016
Mirobial Growth, Lecture 2-Revised WPR 2016
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MICROBIAL GROWTH
L Nuraida, WP Rahayu and HD Kusumaningrum
Learning Outcomes
1. Students are able to explain microbial growth in
general
2. Students are able to explain microbial growth,
kinetics, growth curve, and growth measurements
3. Students are able to determine the kinetics of
microbial growth
4. Students are able to calculate the rate of microbial
growth Department of Food Science and Technology
Bogor Agricultural University
LN
Microbial Growth
• Growth
– increase in the number of microbial cells
– increase in microbial mass
• Growth rate
– change in cell number or mass per unit time
• Generation
– interval for formation of two cells from one
• Generation time (doubling time)
– time required for formation of two cells
– vary widely among organisms
Department of Food Science and Technology
Bogor Agricultural University
LN
Microbial Growth
Bacterial division
10 1048576
Department of Food Science and Technology
Bogor Agricultural University
LN
Microbial Growth
Parameter
• Exponential Growth
– the number of cell increases by a constant factor
during each unit time period
– the rate of increase in the cell number is slow initially
but increases at an ever faster rate
– explosive increase in cell numbers
• Growth data are plotted on an arithmetic scale
– log10 value or semi-logarithmic graph
–k = 0.693 µ or µ = k/0.693
Department of Food Science and Technology
µ = number of doubling per h or growth rate
Bogor Agricultural University
LN
Microbial Growth Kinetic
– Ln X - ln Xo = kt
– log X - log Xo = kt/2.303
– log X - log Xo = 0.693 µ t/2.303
– log X - log Xo = 0.301 µ t
• µ = (log Xt - log Xo)/0.301 t
• where µ = number of doubling per h or
growth rate
• Lag Phase
– when a microbial population is inoculated into a fresh
medium, growth usually does not begin immediately, but
only after a period of time
– lag is not seen when an exponentially growing culture is
inoculated into the same medium and the same conditions
– observed when a population is transferred from a rich
culture medium to a poorer one
• the cells must have complete complement of enzymes
Department of Food Science and Technology
Bogor Agricultural University
LN
Microbial Growth Curve
• Stationary Phase
– A single bacterial cell weight 1/1012 g
• If a single bacterium having generation time of
20 min. and continues to grow exponentially for 48 h.
– A single cell produces a population weighed
about 4 000 times the weight of the earth !!!!!
– But it never happens
– exponential growth ceases:
• essential nutrient of the culture used up
• some waste product of the microorganisms builds up
in the medium to an inhibitory level
Department of Food Science and Technology
Bogor Agricultural University
LN
Microbial Growth Curve
• Stationary Phase
– no net decrease or increase in cell number
– no growth occurs
– But, many cell functions may continue,
including energy metabolism and biosynthesis
– certain microorganisms produce secondary
metabolites such as toxins, antibiotics
• Death Phase
– total count (measured by direct microscopic count)
may remain constant
• In some cases death is accompanied by cell lysis
leading to decrease in the DMC
– viable count slowly decrease
• Measure:
– changes in number of cells or
– weight of cell mass
– turbidity of cell suspension
• Methods:
– Total cell count (DMC)
– Viable count
– Cell mass
– Turbidity
Department of Food Science and Technology
Bogor Agricultural University
LN
Measurement of Microbial Growth
Total count (DMC)
tedious but quick way of estimating microbial cell number
Viable Count
determine the number of cells in the sample capable of
Methods:
Spread plate
Pour plate
• Cell Mass
– Net weight measurement
• centrifuging the cells and weighing the pellet
• dry weight obtained by drying the centrifuge mass, usually
by placing it overnight at 100 – 105 oC
– dry weight usually 10-15 % of wet weight
• filtration of culture media on a membrane filter, the filter
is oven dried.
– Turbidity measurement
• expressed as unit absorbance
• used widely to follow the rate of growth of the culture
Thank You