Question

Unable to grow at 45 C,but able to grow in 0.3% Methylene blue and capable of hydrolysing arginine is true for ______
______\.

• A. Leuconostoc
• B. Lactococcus
• C. Bifidobacterium
• D. Brevibacterium

Hint:

Arginine hydrolysis, growth in 0.3% methylene blue, and lack of growth at 45 $^\circ\text{C}$ are standard physiological keys used to differentiate mesophilic Lactococcus from other lactic acid bacteria.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The genus Lactococcus consists of mesophilic Gram-positive lactic acid bacteria that are widely used as starter cultures in cheese and butter manufacturing.
Lactococcus lactis species have specific physiological and biochemical characteristics that distinguish them from other lactic acid bacteria.

Step 2: Detailed Explanation:
Since they are mesophilic, they are unable to grow at high temperatures such as 45 $^\circ\text{C}$, which distinguishes them from thermophilic species like Streptococcus thermophilus or Lactobacillus helveticus.
However, they are highly robust and can grow in the presence of selective inhibitors, including 0.3% methylene blue.
Furthermore, many strains of Lactococcus lactis possess the arginine deiminase pathway, allowing them to hydrolyze the amino acid arginine to produce ammonia, carbon dioxide, and ornithine.
These combined physiological traits are used as diagnostic criteria for identifying the genus Lactococcus in dairy microbiology laboratories.

Step 3: Final Answer
The described physiological characteristics (no growth at 45 $^\circ\text{C}$, growth in 0.3% methylene blue, and arginine hydrolysis) are characteristic of the genus Lactococcus.