Bacteria
constitute the largest form of life on earth. They are found everywhere; in bodies
of living or dead animals and plants, all forms of organic matter, in water,
dust, soil, and air. While some bacteria are useful to man, many are extremely harmful.
Those that are not usually harmful to man at the sites they inhibit are called Commensals, while harmful ones are called Pathogens. Knowledge of conditions
that affect bacteria growth is important in the maintenance of food hygiene.
Air and darkness
Bacteria
growth is affected by darkness or reduced light. Bright light slows down the
living or metabolic activities of bacteria. Also, most bacteria need air to survive
while some can metabolize in the absence of oxygen. Those that require oxygen
to live actively are called Aerobic bacteria (aerobes) e.g. Staphylococci and Salmonella,
while those that survive without oxygen are known as anaerobes. E.g. Clostridium
Botulinum and Clostridium Perfringens.
Food
Living
organisms require food substances to metabolize and give energy. Bacteria as
living organisms are by no means different. Incidentally, food spoilage or food
poisoning organisms thrive best on foods that are most often preferred by human
beings such as meat, eggs, milk, and their products. Therefor protein-based
foods are the most favorable media for bacteria metabolism provided that environmental
conditions are conducive.
PH (Acidity or
Alkalinity)
Bacteria
thrive actively at neutral PH of 7.0. Which is exactly the PH of the human
body. The implication is that the human body is a conducive environment for
bacterial growth.
Temperature
Each kind of bacterium has a peculiar temperature at which its activity is greatest (known as its optimum temperature). Bacteria can be grouped into three
based on three different temperature ranges in which they can survive or metabolize. They are
Mesophylls- they thrive at an optimum temperature of 37oC or 96.8oF (body temperature). They cause food poisoning and are responsible for food spoilage.
Psychrophilic bacteria grow below 20oC. Some cause food spoilage at temperature of the domestic refrigerator.
Thermophiles bacteria grow best at quite hot temperatures of up to 60oC (140oF). Thermophiles are prolific in food canning.
Mesophylls- they thrive at an optimum temperature of 37oC or 96.8oF (body temperature). They cause food poisoning and are responsible for food spoilage.
Psychrophilic bacteria grow below 20oC. Some cause food spoilage at temperature of the domestic refrigerator.
Thermophiles bacteria grow best at quite hot temperatures of up to 60oC (140oF). Thermophiles are prolific in food canning.
Time
Bacteria
multiply rapidly but still, they need certain time to grow sufficiently to
cause illness in man. Under ideal conditions one bacterium divides into two
every 20 to 30 minutes.
Moisture or water
Bacteria like all living
organisms need water for metabolism. Most cooked foods contain enough moisture
to stimulate bacteria growth. However, bacteria cannot multiply in dried or
dehydrated foods, rather they remain dormant till they gain moisture or that water
is added and they revive again. Similarly water has a higher concentration of
dissolved substances than the bacteria cytoplasm. Hence it causes water to flow out
of the bacteria by the principle of osmosis, as a result they get dehydrated. Based on the above principle, some foods are dried while salt and sugar are added as a food preservation method. However certain bacteria spores can remain dormant in dehydrated conditions but may revive to vegetative form when favorable conditions return. Foods that have high water content such as creams, sauces, jellies and custards are ideal for the growth of bacteria.