This document discusses 5 key factors that affect microbial growth: pH, moisture, nutrient content, oxygen, and light. Optimal pH and moisture levels vary between bacteria, yeasts, and molds. All microbes require nutrients like carbon, nitrogen, minerals, and sometimes vitamins or growth factors. The availability of oxygen and light also influence whether microbes can grow aerobically or anaerobically. Small changes in these conditions can significantly impact a microbe's growth rate.

1. Factors affecting microbial growth
PROF. VISHAKHA P. BORKAR
MUP’S COLLEGE OF PHARMACY, DEGAON

2. Factors affecting microbial growth
1. pH
2. Moisture
3. Nutrient Content
4. Oxygen
5. 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 + > Gram - >yeasts
> moulds

9. Nutrient content
• How easily are energy sources metabolized?
– sugar > alcohol > amino acids > complexmolecules
• How easily are nitrogen sources metabolized?
– amino acids > 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 absenceof
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.