good expanation with digrams

1. 1
Factors Affecting
Microbial Growth

2. Factors Affecting Microbial Growth 2
FATTOM
Food
Acid
Temperature
Time
Oxygen
Moisture

3. Factors Affecting Microbial Growth 3
Food

4. Factors Affecting Microbial Growth 4
Food
 Nutrients needed by microorganisms include:
Carbon – carbon containing compounds are n
eeded as
 an energy source (ex. glucose)
 for building blocks.
Nitrogen
 needed for amino acids and nucleotides;
 some can synthesize all 20 amino acids;
 others have to have some provided in their
medium.

5. Factors Affecting Microbial Growth 5
Food
 Sulfur – needed for amino acids, coenzymes,
 Phosphorus – needed for ATP, phospholipids, and nu
cleotides
 Vitamins
 a vitamin is an organic substance that an organism
requires in small amounts and that is typically used
as a coenzyme;
 many bacteria make their own, but some are requir
ed in the medium;
 microbes living in the human intestine manufacture
vitamin K, needed for blood clotting, and some of t
he B vitamins, thus benefiting their host.
 Certain trace elements – ex. copper, iron, zinc, sodium
, chloride, potassium, calcium, etc.;
 often serve as cofactors in enzymatic reactions.

6. Factors Affecting Microbial Growth 6
Acid (pH)
 Measures alkalinity or acidity
 Most spoilage bacteria grow best near neutral
pH
 Most bacteria grow between pH 6.5-7.5
 Molds and yeasts grow between pH 5 and 6
 Most bacteria produce organic acids as they
grow and metabolize
 Buffers

7. Factors Affecting Microbial Growth 7
Effects of acids on organisms
 enzyme activity affected
 proteins, DNA, other molecules denatured
 longer lag, less rapid growth

8. Factors Affecting Microbial Growth 8
Classification
of microbes
according
to tolerance
of pH
extremes

9. Factors Affecting Microbial Growth 9
Typical growth rates of different types of
microorganisms as affected by pH

10. Factors Affecting Microbial Growth 10
Limits of pH for growth of
pathogens

11. Factors Affecting Microbial Growth 11
T
Temperature
emperature

12. Factors Affecting Microbial Growth 12
T
Temperature
emperature
Type of
microorganism
Growth Range Optimum
Psychrophiles -10 - 20°C 10 - 15°C
Psychrotrophs 0 - 30°C 20 - 25°C
Mesophiles 10 - 50°C 36 - 38°C
Thermophiles 40 - 72°C 55 - 65°C
Thermodurics 35 - 80°C 45 - 55°C

13. Factors Affecting Microbial Growth 13
Temperature
effects
on growth
rate.

14. Factors Affecting Microbial Growth 14
Typical growth rates of different types of
microorganisms in response to temperature

15. Factors Affecting Microbial Growth 15
Food spoilage temperature

16. Factors Affecting Microbial Growth 16
Time
 Not more than 2-4
hours at temperature
danger (growth) zone

17. Factors Affecting Microbial Growth 17
Oxygen
 Poisonous at high concentrations
 Often combined with hydrogen to form
water
 Microorganisms have variation in need to
metabolize oxygen

18. Factors Affecting Microbial Growth 18
Oxygen
Type of Organism Description Oxygen Level Example
Obligate aerobe With O2 20% B.subtilis
Obligate anaerobe Without O2 0% C. botulinum
Facultative anaerobe With/without O2 0-20% E.coli
Microaerophiles With O2 2-10% Campylobacter
Aerotolerant With/without O2 0-20%

19. Factors Affecting Microbial Growth 19
Oxygen and Growth
Obligate aerobic
anaerobes
facultative
aerobes
Microaerophiles
Aerotolerant
anaerobes

20. Factors Affecting Microbial Growth 20
Oxygen Requirements: The Shake Tube

21. Factors Affecting Microbial Growth 21
Moisture
 Types of water
Bound water – not available for
microorganisms
Free water – available for microorganisms
 Water activity
Amount of free water
Potentially hazardous – 0.97-0.99
Lowest Aw to prevent bacterial growth: 0.85

22. Factors Affecting Microbial Growth 22
Effects of low water levels
longer lag, slower growth
impaired transport
loss of membrane fluidity

23. Factors Affecting Microbial Growth 23
Approximate Aw values of selected food categories

24. Factors Affecting Microbial Growth 24
Approximate Aw values of selected food categories

25. Factors Affecting Microbial Growth 25
Addendum: Osmotic Pressure
 High osmotic pressures remove necessary water
from the cell
 Plasmolysis – shrinkage of the cell’s plasma
membrane
 Growth of cell is inhibited as the plasma
membrane pulls away from the cell wall
 Served as the basis of food preservation
methods using salt and sugar

26. Factors Affecting Microbial Growth 26
Plasmolysis

27. Factors Affecting Microbial Growth 27
Osmotic Pressure
 Halophiles
Can withstand high salt concentration
Obligate – require high salt concentrations
(30%)
Facultative – do not require high salt
concentration, but can survive high salt
concentrations (2-15%)

28. Factors Affecting Microbial Growth 28
Classification
of microbes
according
to salinity
tolerances.