Question

Which among the following statements are true?
(A). Probiotics should be acid tolerant.
(B). Probiotics should be safe and non-pathogenic.
(C). All probiotic strains are Gram-positive.
(D). Probiotic strains should have strong adhesion capacity in the gastro-intestinal tract.
Choose the correct answer from the options given below:

• A. (A), (B) and (D) only.
• B. (A) and (B)
• C. (A) only
• D. (A), (B), (C) and (D)

Hint:

While lactic acid bacteria are Gram-positive, the existence of the famous Gram-negative probiotic Escherichia coli Nissle 1917 disproves statement (C).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
To be effective, probiotic microorganisms must survive transit through the upper digestive tract and successfully colonize the host's intestine.

Step 2: Detailed Explanation:
Let us evaluate each criterion for a strain to be classified as a probiotic:

• (A) Acid Tolerance: True. Probiotic strains must withstand the highly acidic environment of the stomach (\(\text{pH } 1.5\text{ to }3.0\)) and bile salts in the duodenum to reach the intestines alive.

• (B) Safe and non-pathogenic: True. They must be safe for consumption (Generally Recognized as Safe - GRAS status) and must not carry transmissible antibiotic resistance genes or virulence factors.

• (C) All probiotic strains are Gram-positive: False. While the most common probiotics belong to Gram-positive genera like Lactobacillus and Bifidobacterium, there are highly effective Gram-negative probiotic strains, such as Escherichia coli Nissle 1917.

• (D) Strong adhesion capacity: True. Adhering to the mucosal lining of the gastrointestinal tract allows the probiotic strains to colonize, compete with pathogens, and modulate the host's immune system effectively.
Thus, statements (A), (B), and (D) are true, while (C) is false.

Step 3: Final Answer
The true statements regarding probiotics are (A), (B), and (D) only.