Factors affecting microbial growth

1
Factors affecting microbial growth
2
Factors affecting microbial growth

• pH
• Moisture
• Nutrient Content
• Oxygen
• Light

3
pH

• Most spoilage bacteria grow best near neutral pH
•  Pathogenic bacteria even more narrow in
  tolerance range of near neutral
•  Yeast and moulds have much greater tolerance to
  acidic (lower) pH

4
pH

• The optimum pH range is usually quite narrow so
  that small changes in the pH can have large
  effects on the growth rate of the organism

5
pH

• Effects of acids on organisms
• energy required to maintain cell's internal pH
• enzyme activity affected
• proteins, DNA, other molecules denatured
• longer lag, less rapid growth

6
Moisture

• Microbes must have a supply of of water available
• Bacteria most restricted, then yeasts, then
  moulds
• Organisms tolerant of low water levels
• halophilic bacteria osmophilic yeasts
• xerophilic molds

7
Moisture

• Effects of low water levels
• longer lag, slower growth
• impaired transport
• loss of membrane fluidity

8
Nutrient content

• Required by all organisms water, carbon,
  nitrogen, minerals
• Organic growth factors needed to varying degrees
  
• Gram gt Gram - gt yeasts gt moulds

9
Nutrient content

• How easily are energy sources metabolized?
• sugar gt alcohol gt amino acids gt complex molecules
  
• How easily are nitrogen sources metabolized?
• amino acids gt proteins
• B vitamins required by many bacteria

10
Oxygen

• Obligate aerobes, e.g. Mycobacterium, will grow
  only in presence of free oxygen

11
Oxygen

• Facultative anaerobes, e.g. Saccharomyces (yeast)
  will grow in the absence of oxygen, but more
  slowly than if oxygen were present.

12
Oxygen

• Obligate anaerobes, e.g. Clostridium will grow
  only in absence of oxygen which is toxic to them

13
Light

• Essential for photoautotrophs.
• As well as its intensity its wavelength may be
  significant.