Question

Which of the following Gram-positive bacterium shows Aesculin hydrolysis?
A. Enterococcus species
B. Listeria species
C. Mycobacterium species
D. Lactobacillus fermentum
E. Streptococcus thermophilus
Choose the correct answer from the options given below:

• A. A, B and D only
• B. A, B, and C only
• C. A, B, and E only
• D. C, D, and E only

Hint:

Bile Esculin test positivity is the classic hallmark for Enterococcus and Listeria species. Use this association to rule out options lacking both A and B.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Aesculin hydrolysis is a biochemical test used to differentiate various groups of Gram-positive bacteria.
Bacteria possessing the enzyme aesculinase hydrolyze aesculin into aesculetin and glucose.
Aesculetin then reacts with ferric ions in the medium to form a dark brown or black complex.

Step 2: Detailed Explanation:
Let us evaluate each organism's ability to hydrolyze aesculin:
- A. Enterococcus species: This is a defining characteristic of Group D streptococci and Enterococcus species, which actively hydrolyze aesculin even in the presence of bile salts (Bile Aesculin Agar positive). (True)
- B. Listeria species: Listeria monocytogenes and other Listeria species are well-known for their rapid hydrolysis of aesculin, which is a key identification criterion on selective media such as Oxford or PALCAM agar. (True)
- C. Mycobacterium species: While some mycobacteria can slowly degrade various glycosides, they are not typically classified as standard rapid aesculin-hydrolyzing Gram-positive bacteria in routine diagnostic schemes. (False)
- D. Lactobacillus fermentum: Certain heterofermentative lactobacilli, including strains of Lactobacillus fermentum, possess glycosidases capable of hydrolyzing aesculin. (True)
- E. Streptococcus thermophilus: This species is typically negative for aesculin hydrolysis, which helps distinguish it from other lactic streptococci and enterococci. (False)
Thus, the correct combination representing active aesculin hydrolysis is A, B, and D.

Step 3: Final Answer
The correct option is (A).