Using catalase-test to determine if Staphylo- or Streptococcus If the microscope clearly shows bacteria of cocci morphology but it is difficult to determine if they are Staphylo- or Streptococcus, are catalase tests a good way to differentiate between the two since Staphylococcus are positive and Streptococcus are negative? Are there any traps/exceptions? Thanks!

Generally yes: streptococci are catalase negative while staphylococci are catalase positive.

> [The catalase test is important in distinguishing streptococci (catalase-negative) [from] staphylococci which are catalase positive.](

> Unlike _Staphylococcus_ , all streptococci lack the enzyme catalase.

However, there are exceptions to every rule:

Catalase negative _Staphylococcus aureus_.

Catalase positive _Streptococcus sp._