Why should the procedure for catalase test not be reversed?
There exists the possibility for the result of the test to be false positive. This fact occurs when the order of procedure is reversed or when red blood cells from blood agar are contaminated.
Hence, as a conclusion, if the procedure for catalase test is reversed, the results of the test can be false positive.
Catalase test is used to detect the existence of catalase enzyme, in order to differentiate Staphylococci from Streptococci bacteria. If the test is positive, then the staphylococcus species is identified, while if the test is negative, then streptococcus bacteria are detected.
Commonly, bacteria that contain catalase enzymes require oxygen, catalase converting H_2O_2 into O_2 and H_2O. The presence of staphylococcus species is shown by the bubble formation, that indicates the gas liberation, while the existence of streptococcus bacteria is indicated by no bubble formation.