Antibiotic origins: Bacitracin (a peptide antibiotic with activity similar in outcome to penicillin on cell wall assembly) is produced by which microorganism?

Introduction / Context:
Bacitracin inhibits peptidoglycan synthesis by interfering with bactoprenol recycling, leading to bactericidal effects on Gram-positive bacteria. Knowing its producer supports understanding natural product discovery.

Given Data / Assumptions:

• We must match bacitracin to its natural producer.
• Options include bacilli, actinomycete, and a mold.

Concept / Approach:
Bacitracin was first isolated from a Bacillus species; industrial production typically uses Bacillus licheniformis (and sometimes Bacillus subtilis). Other options correspond to unrelated products (e.g., erythromycin from S. erythreus).

Step-by-Step Solution:
Identify bacitracin as a Bacillus peptide antibiotic. Recall the industrial producer: B. licheniformis. Select the correct organism.

Verification / Alternative check:
Monographs on peptide antibiotics list B. licheniformis as the standard producer strain.

Why Other Options Are Wrong:

• B. polymyxa: associated with polymyxins, not bacitracin.
• S. erythreus: erythromycin.
• Aspergillus fumigatus: filamentous fungus; not a bacitracin source.

Common Pitfalls:
Mixing up Bacillus-derived peptide antibiotics (polymyxins vs. bacitracin).

Final Answer:
Bacillus licheniformis