It is an organism or aerobes that requires oxygen to survive and grow in the environment. There are 4 categories of aerobes.

1. Obligate Aerobes – need oxygen to grow. In a process known as cellular respiration, these organisms use oxygen to oxidize substrates (for example sugars and fats) and generate energy
2. Facultative Aerobes – use oxygen if it is available, but also have anaerobic methods of energy production.
3. Microaerophilic –require oxygen for energy production, but are harmed by atmospheric concentrations of oxygen (21% O2).
4. Aerotolerant – do not use oxygen but are not harmed by it.