Facultative without oxygen. When oxygen is available,

Facultative anaerobic bacteria stand out from other bacteria because they can live with or without oxygen. Some of these anaerobes can also cause disease in humans.

Facultative Anaerobic Bacteria

Before we start describing facultative anaerobic bacteria, we should go over what the words ‘aerobic’ and ‘anaerobic’ mean. Aerobic means there is oxygen available to use. For example, when you are doing aerobic exercise, your heart is actively working to get oxygen to your cells. Anaerobic means an environment without oxygen.

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Bacteria can be classified based on how they use oxygen. Obligate aerobes are obligated to use oxygen, meaning they have to have oxygen in the environment in order to survive. Obligate anaerobes do not require oxygen, and many cannot even live in the presence of oxygen. Facultative anaerobes are the most versatile type of bacteria — they can live either with or without oxygen.

The Importance of Oxygen

Oxygen is important for respiration, which is how cells, like bacteria, turn food energy into a form of energy they can easily use.

This usable energy is called adenosine triphosphate, or ATP for short. ATP is like currency that the cell can spend readily to do work. Food must first be converted to ATP, just like your paycheck must first be converted to cash before you can go shopping.Facultative anaerobes grow best with oxygen. Aerobic respiration is very efficient at producing ATP, so this is ideal. However, when oxygen is unavailable, facultative anaerobes can still survive and grow — just not as well. Anaerobic respiration is much less efficient.

With oxygen, bacteria can make up to 38 molecules of ATP. Without oxygen, the bacteria can only make about 2 molecules of ATP. So, even though they are surviving, facultative anaerobes don’t grow as quickly in environments without oxygen.


There are many different facultative anaerobes, but the most interesting from a health standpoint are pathogens, or microbes that cause disease.

Bacteria species including Salmonella species, Shigella, and Escherichia coli (E. coli) are the most familiar examples of facultative anaerobes. All of these bacteria are associated with infection of the digestive system.Salmonella infections happen from eating contaminated food. Symptoms of Salmonella infection include vomiting, abdominal cramps, and diarrhea.

Most people can recover from ‘Salmonella’ infections easily; however, children and those with compromised immune systems may have more complications. While Salmonella infections are common, with over 1.5 million occurring each year, deaths are very rare.Shigella is another pathogen that infects the digestive system. It primarily attacks the intestines, causing bloody diarrhea, fever, and abdominal pain. It is passed through feces, which can happen in daycare settings, hospitals, or under unsanitary conditions.

Most cases of shigellosis, or Shigella infection, are mild and don’t need treatment. Proper hand washing is a simple, effective way to prevent the spread of Shigella.Unlike the other bacteria mentioned, E.

coli can infect other parts of the body besides the digestive tract. E. coli is a normal bacteria that lives in your intestines.

It helps make vitamins for you and digest your food. However, when E. coli moves to another part of your body, such as your stomach, an open wound, or your urinary tract, it becomes far less friendly. If eaten, pathogenic E. coli strains can cause severe vomiting and bloody diarrhea. While most cases are mild, some can be quite serious. If not treated properly, this can result in severe dehydration and death.

Lesson Summary

Facultative anaerobes are among the most versatile bacteria, due to their ability to live either with or without oxygen. When oxygen is available, they are able to efficiently produce ATP and grow quickly. Without oxygen, they can perform fermentation to produce enough ATP to continue living and growing. Some facultative anaerobic bacteria are pathogens. Salmonella, Shigella, and E. coli all attack the digestive tract, causing vomiting and diarrhea. While incredibly unpleasant, these infections don’t tend to be life threatening.


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