Question

You have colonies growing on a culture and are going to identify them. First, you do a Gram stain and viewing it on 1000x magnification, you see Gram positive cocci, no predominating arrangement. What test should you do to determine if it a staphylococcus or a streptococcus

Answer 1

Answer: The test that's should be done to determine if it's a staphylococcus or a streptococcus is a BIOCHEMICAL TEST known as CATALASE TEST.

Explanation:

In the laboratory diagnosis of microbiology samples, GRAM STAINING technique is used to identify bacteria pathogens in specimens and cultures by their gram reactions. The bacteria may be either gram positive or gram negative.

Gram positive bacteria when views with ×100 oil immersion stains dark purple with crystal violet and are not decolorize by acetone or ethanol. Examples of gram positive bacteria include:

--> Staphylococcus

--> Streptococcus

--> Clostridium

--> Corynebacterium

Since a gram positive cocci was identified without a predominating arrangement, further biochemical test known as catalase test should be carried out to determine if the cocci is staphylococcus or a streptococcus.

CATALASE TEST is used to differentiate those bacteria that produce catalase enzyme such as staphylococcus from non- catalase producing bacteria such as streptococcus. Catalase acts as a catalyst in the breakdown of hydrogen peroxide to oxygen and water. An organism is tested for catalase production by bringing it into contact with hydrogen peroxide. Bubbles of oxygen are released if the organism is a catalase producer, therefore staphylococcus but if no bubbles are observed, it's a streptococcus.