Question

This question has two parts: Catalase test Questions and Oxidase test Questions:

What can you learn about a microbe by doing the catalase test?How do you conduct the catalase test? What does a positive catalase test look like and what does a negative test look like?

Oxidase test Questions:

What can you learn about a microbe by doing the oxidase test and how do you conduct the oxidase test?What does a positive oxidase test look like and what does a negative oxidase test look like?

Answer 1

Question A.

Answer. By performing catalase test it can be inferred that

(i) That microbe contain catalase enzyme or not.

(ii) The microbe be categorised as gram positive (Catalase +) or gram negative bacteria ( catalase -)

(iii) It can be used to differentiate aerotolerant strains of Clostridium, which are catalase negative, from Bacillus species, which are positive.

(iV) Semiquantitative catalase test can be used in identification of Mycobacterium tuberculosis.

Method :

1. Transfer a small amount of bacterial colony to a surface of clean, dry glass slide using a loop or sterile wooden stick
2. Place a drop of 3% H₂O₂ on to the slide and mix.

Result

1. A positive result is the rapid evolution of oxygen (within 5-10 sec.) as evidenced by bubbling.
2. A negative result is no bubbles or only a few scattered bubbles.

Question (B )

Use of Oxidase test

• Oxidase test is used to identify bacteria that produce cytochrome c oxidase.
• Microbes can be further classified as aerobic , anaerobic or facultative anaerobe.

Method

1. Take a filter paper soaked with the substrate tetramethyl-p-phenylenediamine dihydrochloride
2. Moisten the paper with a sterile distilled water
3. Pick the colony to be tested with wooden or platinum loop and smear in the filter paper
4. Observe inoculated area of paper for a color change to deep blue or purple within 10-30 seconds

Result

1. Positive: Development of dark purple color (indophenols) within 10 seconds
2. Negative: Absence of color