Question

1. What is the clinical importance of the Catalase test?

2. How can you deternine if a microbe is using an oxidative or fermentative metabolism?

3. Explain aerotolerant anaerobe microorganisms.

Answer 1

1. Catalase is an enzyme that is present in most living organisms that respire using oxygen. It is an enzyme that converts hydrogen peroxide to water and oxygen and protects the living being from oxidative damage caused by the by-products of aerobic respiration. Catalase test has a clinical significance in differentiating between infection of organisms that are utilizes oxygen for respiration and those which do not. For example the test can differentiate between staphylococcus which is catalase positive and streptococcus which is catalase negative. Also it can differentiate between clostridium species which are catalase negative and bacillus strains which are catalase positive.

2. Microbes can be identified for their choice of metabolism by oxidation-fermentation (OF) test which is also known as two tube procedure. In this method two tubes are taken and inoculated with same strain in OF medium which contains peptone, NaCl, glucose, tryptophan and bromophenol blue ( as indicator). One of the tube is covered with paraffin to assure anaerobic conditions. The microbes either use tryptophan and turns colour dark blue due to alkaline reaction or utilizes glucose and produce acid which forms yellow colour.

Oxidation is indicated when yellow colour appears in open tube only whereas fermentation is indicated when both tubes show yellow colour.

3. Aerotolerant anaerobic microbes are those that perform anerobic respiration in presence or absence of oxygen. They are insensitive to the presence of oxygen and can protect themselves from reactive oxygen species. They form ATP only by fermentation. Example- lactobacilli