Antibiotic production by Brevibacillus (Bacillus) brevis — This organism is exploited commercially to produce which of the following peptide antibiotics?

Introduction / Context:
Bacillus brevis (now Brevibacillus brevis) is historically important in antibiotic discovery. It produces several membrane-active peptides used as topical agents and research tools. Recognizing these products aids in linking microbial taxonomy to natural product chemistry.

Given Data / Assumptions:

• Tyrothricin is a mixture of tyrocidines and gramicidins.
• Gramicidin A and tyrocidin are classic products from B. brevis.
• The question asks whether one or all apply.

Concept / Approach:
Since B. brevis produces both gramicidin (notably gramicidin A) and tyrocidin, and tyrothricin refers to the combined preparation, the most inclusive correct choice is “all of the above.”

Step-by-Step Solution:

Verification / Alternative check:
Classic antibiotic catalogs and microbiology texts attribute these peptides to B. brevis.

Why Other Options Are Wrong:
They are not wrong individually, but each is incomplete relative to the full set the organism produces.

Common Pitfalls:
Confusing tyrothricin with bacitracin; bacitracin is from B. subtilis group, whereas tyrothricin is the B. brevis mixture of tyrocidin and gramicidin.

Final Answer:
all of the above