Question

aeruginosa 4. Which families of organisms are differentiated by the Oxidase test? What reagent is used to test for Oxidase? 5. Which families of organisms are differentiated by the Catalase test? What is a positive test for catalase? 6. What substrate is used to test for the presence of the Coagulase enzyme? What does Coagulase do for a bacteria that has it?

Answer 1

Answer 4. The oxidase test is used to ascertain the presence of  the cytochrome oxidase enzyme containing microorganism. This test is employed for the differentiation of Moraxella, Campylobacter, Neisseria and Pasteurella species (oxidase positive). It is a main test  to differentiate between pseudomonadaceae (Oxidase positive) and Enterobactericeae (Oxidase negative). 1% tetra-methyl-p-phenylenediamine dihydrochloride (TMPD) reagent is used to test for oxidase, act as electron donor for oxidase enzyme.

Answer 5. The catalase test is used to differentiate  between gram positive cocci ( Staphylococcus, which are catalase positive) and gram negative cocci (streptococcus and enterococcus, which are catalase negative).

The catalase positive microorganism produce catalase enzyme which breaks down the harmful by products hydrogen peroxide thereby producing bubbles indicating catalase positive microorganism, if there is no bubbles are produced by the microorganism then microorganism is catalase negative and do not produce catalase.

Answer 6. There are two types of coagulase tests- slide and tube coagulase and both the test are used to detect enzymes that convert the fibrinogen into fibrin. Substrates used for this test are rabbit or sheep pooled plasma.

The enzyme coagulase is tightly adherent to the bacterial surface and surround its surface with fibrin on contact with blood. This fibrin coat protects the bacteria from phagocytosis and renders the bacteria more virulent and safeguard from host defences.