Question

Given below are two statements:
Statement (I): Lysozyme is present in cow milk in considerable amounts but is absent in human milk.
Statement (II): Gram negative bacteria are generally more resistant to lysozyme than Gram positive bacteria.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

Remember the comparative concentrations of lysozyme in milk:
- Human milk = Very High ($\approx 3,000\times$ more than bovine milk).
- Cow milk = Trace/Negligible.
Also, remember that the outer membrane of Gram-negative bacteria acts as a shield against hydrophilic molecules and large enzymes like lysozyme.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Lysozyme is an important bioactive enzyme found in various secretions, including tears, saliva, and milk.
It serves as an innate antimicrobial agent by enzymatically hydrolyzing the $\beta$-1,4-glycosidic bonds between N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG) in the peptidoglycan layer of bacterial cell walls.
Detailed Explanation:
Let us analyze Statement (I): "Lysozyme is present in cow milk in considerable amounts but is absent in human milk."
This statement is scientifically inaccurate.
Human milk actually contains an exceptionally high concentration of lysozyme, ranging from $30\text{ mg}$ to $40\text{ mg}$ per $100\text{ mL}$.
This high level provides crucial immunoprotective benefits to breastfed infants.
In contrast, bovine (cow) milk contains only trace amounts of lysozyme, typically around $0.013\text{ mg}$ per $100\text{ mL}$, which is roughly 3,000 times less than the concentration found in human milk.
Therefore, Statement (I) is incorrect as it reverses the biological reality.
Now let us analyze Statement (II): "Gram negative bacteria are generally more resistant to lysozyme than Gram positive bacteria."
This statement is correct.
Gram-positive bacteria have a thick, exposed outer peptidoglycan cell wall, making them highly susceptible to direct enzymatic degradation by lysozyme.
In contrast, Gram-negative bacteria possess an outer lipopolysaccharide membrane that surrounds their thin peptidoglycan layer.
This outer membrane acts as a physical barrier that prevents large enzymes like lysozyme from reaching the target peptidoglycan layer.
Consequently, Gram-negative bacteria are inherently much more resistant to lysozyme unless their outer membrane is first destabilized by agents like EDTA or lactoferrin.

Step 2: Final Answer:
Statement (I) is incorrect, but Statement (II) is correct.