Question

4.Explain one way you can perform the oxidase test.

a.Name a bacterial species that will test negative for this test.

Answer 1

ANS: 4 - oxidase test is a biochemical test use to perform for identification of bacteria. we can perform this test by using a reagent named as N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) or N,N-dimethyl-p-phenylenediamine (DMPD). this reagent mainly used on the bacteria containing cytochrome c oxidase as a terminal enzymes in electron transport system which is present in cytochrome c act as a substrate. as we know that cytochromes are iron containing hemoproteins and acts as a last link in the chain of aerobic respiration transferring electron (H+) to oxygen in formation of watrer molecule.

Now when we do any oxidase test we are actually adding this reagent TMPD and in bacteria containg this protein cytochrome c will pick an electron from this reagent and get convert into cytochrome reductase ( carrying that elctron ) and give this electron to cytochrome C oxidase which ultimaeltly complete that cycle and as the electron get tranfer this cycle goes on .In this process TMPD tranfers an electron to cytochrome C transforming transfer it into TMPD radical which is purple in colour. an dthis indication of colour represents that the bacteria is an aerobic bacteria which produces oxygen and water as its final product.

ANS: a) Enterobacteriaceae family of Gram-negative, facultatively anaerobic,shows oxidase test as negative as electron transport system is not present in these becteria so no production of oxygen and water takes place and reagent will not produce any radical and no change in colour takes place.

E.coli is a gram-negative and anaerobic becteria which wil givw a negative result of oxidase test.