Bacterial growth

Bacterial growth

1. Bacterial Growth

2. Bacterial Growth
•Increase in number of cells, not cell size
•One cell becomes colony of millions of cells

3. Bacterial division

4. Generation Time
•Time required for cell to divide/for population
to double.
•Average for bacteria is 1-3 hours
•E. coli generation time = 20 min
–20 generations (7 hours), 1 cell becomes 1 million
cells!

6. Standard Growth Curve

7. Standard Growth Curve
Lag phase – making new enzymes in response to new medium.
The length of lag phase depend upon
a.Type of bacteria.
b.Better the medium, shorter the lag phase.
c.The phase of culture from which inoculation is taken.
d.Size or volume of inoculum.
e.Environmental factors like temperature.
Log phase – Logarithmic (Exponential) phase: In logarithmic
phase the bacterial cell start dividing and their number
increase by geometric progression with time.
During this period…
a.Bacteria have high rate of metabolism
b.Bacteria are more sensitive to antibiotics and radiation during
this period.

8. Stationary phase – nutrients becoming limiting or waste
products becoming toxic.
death rate = division rate
In stationary phase after some time a stage comes when rate of
multiplication and death becomes almost equal. It may be
due to:
a.Depletion of nutrients.
b.Accumulation of toxic products and sporulation may occur
during this stage.
Death or Decline phase – In decline (death) phase, death
exceeds division. During this phase population decreases due
to death of cells. The factors responsible are:
a.Nutritional exhaustion
b.Toxic accumulation
c.Autolysinenzymes

9. Measuring Growth
•Dilution Plating
•Turbidity analysis using spectrophotometer
•Direct count with hemacytometer
•Optical detection – Coulter Counter

10. Measuring Bacterial Growth
Serial Dilutions
Direct Measurements of Microbial Growth
Plate counts: Perform serial dilutions of a sample

11. Standard Plate Count
Inoculate Petri
plates from
serial dilutions
2 methods:
Pour Plate
Spread Plate

12. •After incubation, count colonies on plates that have
25-250 colonies (CFUs)

13. Turbidity

14. Electronic Counting

15. Direct Microscopic Count

17. Direct Microscopic Count

18. Factors Affecting Growth

19. Environmental Factors
1. pH: measure of [H
+
]
each organism has a pH range and a pH optimum.
acidophiles – optimum in pH range 1-4
alkalophiles – optimum in pH range 8.5-11

lactic acid bacteria – 4-7
Thiobacillus thiooxidans – 2.2-2.8
Fungi – 4-6
Internal pH regulated by BUFFERS and near neutral
adjusted with ion pumps
Human blood and tissues has pH 7.2+0.2

20. pH and Microbial growth
•The acidity or alkalinity of an environment can greatly affect
microbial growth.
•Most organisms grow best between pH 6 and 8, but some
organisms have evolved to grow best at low or high pH. The
internal pH of a cell must stay relatively close to neutral even
though the external pH is highly acidic or basic.
–Acidophiles : organisms that grow best at low pH
(Helicobacter pylori, Thiobacillus thiooxidans )
–Alkaliphiles : organisms that grow best at high pH (Vibrio
cholera)
–Most of pathogenic bacteria are neutrophiles.

22. 2.Temperature
•Minimum Temperature: Temperature below which growth
ceases, or lowest temperature at which microbes will grow.
•Optimum Temperature: Temperature at which its growth
rate is the fastest.
•Maximum Temperature: Temperature above which growth
ceases, or highest temperature at which microbes will
grow.

–Psychrophiles, Mesophiles and Thermophiles

23. •
–Midrange temperature.
–Found in warm-blooded animals and in terrestrial and aquatic
environments in temperate and tropical latitudes.
•
–Cold temperature optima
–Most extreme representatives inhabit permanently cold
environments.
•
–Growth temperature optimum between 45ºC and 80ºC .
•Hyperthermophiles
–Optimum greater than 80°C.
–These organisms inhabit hot environments including boiling hot
springs, as well as undersea hydrothermal vents that can have
temperatures in excess of 100ºC.

24. Classification of Microorganisms by Temperature Requirements

25. 3. Salt Concentration
•Halophiles: have evolved to grow best at reduced water
potential, and some extreme halophiles e.g. Halobacterium
even require high levels of salts for growth.
•Halotolerant: can tolerate some reduction in the water
activity of their environment but generally grow best in the
absence of the added solute e.g. Staphylococcus aureus.
•Xerophiles: are able to grow in very dry
environments.

26. Salt Concentration
•Halophiles

27. Oxygen Requirements
•Aerobes: use oxygen in metabolism; obligate.
•Microaerophiles: require oxygen (also
obligate), but in small amounts.
•Anaerobes: grow without oxygen