Explain how the presence or absence of oxygen can affect bacterial growth.
In order for some bacteria to grow, they need oxygen. These bacteria are called "aerobic" or "aerobes." Aerobic bacteria need oxygen to yield energy for growth. Most spoilage bacteria, molds, and yeast require oxygen to grow.
Some bacteria grow in oxygen-free environments and are called "anaerobic" or "anaerobes." An example of a common anaerobic foodborne bacteria is the Clostridium species, such as Clostridium botulinum and Clostiridium perfringens.
Some bacteria are facultative which means that they can grow in either the presence or absence of oxygen. Most foodborne pathogens are facultative with the exception of the above-mentioned Clostridium.
Some are microaerophilic, meaning they grow in low concentrations of oxygen.