What factors are needed for bacterial growth?

Bacteria generally occur in three morphologically distinct forms: round or spheroidal, rodlike and spiral. 

Bacteria are single celled organisms that can cause foodborne illness in two ways: They can infect foods themselves, by their presence in the food as they feed on it. They can produced toxins, which can make food hazardous, as they breakdown.

It is important to note that bacteria, though very small relative to man are much larger than viruses yet smaller than yeast or molds.

Bacteria, under good condition, can grow and divide quickly – each cell dividing into two approximately every 20 minutes.

Good conditions for bacterial growth require
Food – especially high protein
Acidity – neutral to low acid
Temperatures
Oxygen
Moisture

When one or more of these factor is present in a food product, creating the conditions for bacterial growth, that food product is a potentially hazardous food.

Food 
Food is required by bacteria, not only as a source of energy but also for manufacturing protoplasm and structural materials. Bacterial growth is accomplished through the synthesis of cellular components and energy.

The necessary nutrients for this process are derived from immediate environment of a microbial cell and, if the cell is growing in a food, it supplies the nutrients.

Bacteria differ greatly in their nutritional requirements but certain elements in food are essential and growth is impossible in their absence.

Potential hazardous foods therefore include meats; poultry; fish; soy-based foods; eggs; milk and milk products; cooked pasta, rice, potatoes, or beans; garlic oil mixture; raw fruits and vegetables; and raw seeds and sprouts.

Acidity 
The pH of a food has profound effect on the growth and viability of microbial cells. Each species has an optimum and arrange of pH for growth.

In general, molds and yeast are able to grow at lower pH levels than do bacteria and Gram-negative bacteria are more sensitive to low pH than are Gram-positive bacteria.

Temperature
Temperature is a factor of profound importance since temperature has marked influence on the rates of all chemical reactions linked to the processes of growth.

Moisture 
Water account for some 80-90% of the total weight of living cells and all organisms, require it for growth. Organisms vary tremendously in their water requirement but, generally bacteria need more than fungi.

The moisture available to the bacterial is referred to as water activity and abbreviated Aw.

Oxygen 
The oxidation-reduction potential of a microbial growth substrate is an indication of its relative oxidizing or reducing potential.

To a large extent, this parameter determines of bacteria that will survive and/or prosper in the presence and absence of air.
What factors are needed for bacterial growth?