Bacteria can be divided into following types on the basis of use of oxygen: Aerobic: which require oxygen for their growth they can be: a. Obligate Aerobic: survive only if oxygen is present example; Mycobacterium tuberculosis. b. Microaerophile: That require lower amount of oxygen i.e. 2 to 10% example; Helicobacter pylori. 2. Anaerobic bacteria; which do not require oxygen for their growth they can be; a. Obligate Anaerobic; which are harmed by presence of oxygen , they can not survive in presence of oxygen. Example: Clostridium tetani, C. perfringens. b. Facultative anaerobic bacteria; can grow without oxygen, but use oxygen if it is available to produce energy.