its about the environmental factors affecting the growth of microorganisms

1. WELWITCHIA HEALTH TRAINING CENTRE
CERTIFICATE IN HEALTH SCIENCES FOUNDATION
NQF LEVEL 4
COURSE: MICROBIOLOGY AND PARASITOLOGY FOUNDATIONS
(FMPY 1401)
UNIT 3: CONDITIONS FOR MICRO-ORGANISMS TO PRODUCE AND GROW
By L.Nambala

2. By the end of this unit, students should be
able to:
Describe the conditions for microbes to
produce and grow.
Classify microbes according to temperature
requirements.

3. Conditions for microbes to produce and grow
1. Moisture
 All micro-organisms in the vegetative state will require moisture for survival.
 They also require this moisture in order to extract nutrients.
 Their growth can then be controlled by regulating the moisture in the environment. This
factor is used in the preservation of certain foods; the drying of meat, fish and
vegetables in order to preserve the food stuff.
 Moisture is not however a requirement for micro-organisms which exist in the spore
state.

4. 2. Nutrients
 In this instance micro-organisms will require both inorganic and organic material
and the organic source will be proteins, carbohydrates and lipids.
 Included in the organic group will be vitamins which however are only required in
small quantities.
 The inorganic components will consist of various mineral salts such as iron,
copper, zinc etc. If there is a shortage of any of these then the micro-organisms will
not survive.

5. 3. Oxygen
 There are microbes which will only thrive in the presence of oxygen.
 Such microbes are referred to as aerobes.
 If oxygen is absolutely essential for their survival, then we say there are obligatory
aerobes.
 There are some microbes which are killed or inhibited by oxygen and they will only
survive in an environment devoid of oxygen.
 Such microbes are referred to as obligatory anaerobes.

6. 4. Temperature
 Micro-organisms thrive best at their optimum temperature. This enables the
physiological processes to function best at that particular temperature.
 Micro-organisms can be divided into three main groups based on their
temperature requirements and these are:
 Psychrophiles- Thrive best in temperatures ranging from -20 degrees Celsius to
+10 degrees Celsius.
 Mesophiles- A group to which most micro-organisms belong and it is in this group
that we have various pathogens. They thrive in temperatures between 20 degrees
Celsius to 45 degrees Celsius.
 Thermophiles- These prefer higher temperatures and survive best in temperatures
higher than 50 degrees Celsius.

7. 5. pH
 Each group of micro-organisms will function best at a
particular pH level.
 Some of them will function best when the environment is
likely acid.
 Others will prefer an alkaline medium while some will prefer a
pH environment which is neutral. Most bacteria grow between
pH 6.5 and 7.5.

8. 6. Osmotic pressure
 How successful the micro-organism thrives in the
environment which is always a liquid medium will depend on
the osmotic pressure.
 e.g. in a syrup or brine solution then the organism will have
fluid withdrawn from its body by the high osmotic pressure of
the liquid and therefore it will be unable to survive in such an
environment.
 This fact is utilized in preserving various food stuffs.

9. 7. Radiation
 The ultra violet radiation of sunlight is very effective in killing off various
micro-organisms especially those lacking pigmentation.
 The various radiations target the enzyme systems of the micro-organism
and also it’s DNA. Other forms of radiation will include X-rays, Gamma
rays, Alpha rays and Beta rays.
 Gamma rays have good penetration properties and this form of radiation
is being extensively used in the sterilization of tinned foods.
 Other factors which will harm micro-organisms include ultra- sonic
vibrations which will bring about the disintegration of micro-organisms
and ultra- sonic waves which will destroy organelles within the microbe.

10. 8. Toxic substances
 As the micro-organisms feed in the environment, they
produce various waste products and these waste products can
be toxic if they accumulate in large amounts and this will
adversely affect their growth.
 Sometimes however these toxic substances do not originate
from micro-organisms but they may occur in the environment
as a result of pollution.
 This in turn will also affect the growth of these microbes.

11. Self-help Assessment
 Identify conditions for microbes to produce and grow
 Differentiate between Mesophiles and Thermophiles

12. The end