The catalase test determines whether bacteria are able to use oxygen as a terminal electron acceptor in respiration. If a type of bacteria contains catalase, it is able to use oxygen, and the colony bubbles when exposed to hydrogen peroxide.
Catalase is an enzyme produced by certain bacteria to protect themselves from the byproducts of oxygen metabolism, according to Michigan State University. The catalase test identifies aerobic or facultative anaerobic bacteria using hydrogen peroxide as a reactant. In a lab setting, the catalase test often determines whether a type of bacteria is Staphylococcus, which is able to use oxygen, or Streptococcus, which can not use oxygen.
In the protocol for this lab, a solution of 3 percent hydrogen peroxide is dropped onto a clean glass slide. A sterile wooden applicator swabs the bacteria, which are then immersed in the peroxide on the slide. If the colony bubbles immediately, the bacteria contain catalase. If no bubbles appear, the bacteria is not able to use oxygen as an electron acceptor. Bubbling occurs because the catalase breaks down the peroxide into both water and oxygen gas. Bacteria that do not contain catalase are usually anaerobes, but may be facultative anaerobes that only ferment.