What are the key conditions for bacterial growth?

Answer : Bacteria can live in hotter and colder temperatures than humans, but they do best in a warm, moist, protein-rich environment that is pH neutral or slightly acidic. There are exceptions, however. Some bacteria thrive in extreme heat or cold, while others can survive under highly acidic or extremely salty conditions. 

There are four things that can impact the growth of bacteria. These are: temperatures, moisture, oxygen, and a particular pH. 

 Many factors affect bacterial growth but the most important ones are:

1. Water -- Bacteria need water to dissolve the food they use for energy and growth. Water allows the food to get into the cells, is used for the many chemical reactions necessary for life and growth, and allows waste products to escape.
2. Food/Nutrients -- All bacteria require energy to live and grow. Energy sources such as sugars, starch, protein, fats and other compounds provide the nutrients.
3. Oxygen -- Some bacteria require oxygen to grow (aerobes) while others can grow only in the absence of oxygen (anaerobes). However, many bacteria grow under either condition and they are facultative anaerobes.
4. Temperature -- Bacteria in general are capable of growing over a wide range of temperatures and are usually classified according to the temperature at which they grow. Psychrotrophic bacteria are those that are capable of growing at 32°F - 45°F but their optimum is from 68°F to 86°F. They cause spoilage in foods stored under refrigeration. Several pathogenic bacteria are psychotrophic -- Yersinia and Listeria. Mesophilic bacteria. Most bacteria are capable of growing at 60°F - 110°F and belong in this group. Most pathogenic bacteria grow at these temperatures. Thermophilic bacteria. These microorganisms grow at higher temperatures such as 110°F - 150°F. Temperature is the most widely used method of controlling bacterial growth. Bacteria grow slowly at temperatures below 45°F and thermal destruction occurs at temperatures above 140°F. But in the temperature danger zone -- between 40°F and 140°F -- many bacteria are not controlled.
5. pH -- pH is a measure of acid or alkali in a product. It is indicated on a scale from 0 to 14, with seven being neutral. If the pH value is below 7, the food is classified as acid; if it is above 7, the food is classified as alkaline. Most bacteria grow well at neutral pH, but many can reproduce in a pH range from 4.5 - 10.0.