Penicillin antibiotic is obtained from

Antibiotics are chemical substances produced by living microorganisms — bacteria or fungi — that inhibit or kill other microorganisms. Penicillin, the first antibiotic ever discovered, belongs to the beta-lactam class and is naturally produced by a specific group of fungi called molds.

In 1928, Alexander Fleming observed that a mold contaminating one of his bacterial culture plates had killed the surrounding bacterial colonies. That mold was identified as a species of the fungal genus Penicillium, which naturally secretes penicillin as a defensive antimicrobial chemical. Because fungi produce it naturally, penicillin is extracted and industrially manufactured from fungal (mold) cultures.

Ruling out the other offered sources:

• Algae are photosynthetic, chlorophyll-bearing organisms; while some algae and cyanobacteria are studied for other antimicrobial compounds, no alga is documented as producing penicillin itself, and none is an industrial source of the drug.

• Bacteria are more typically the organisms antibiotics act against; a few other antibiotics (e.g., streptomycin) do come from soil bacteria, but this particular compound is not bacterial.

• Blue-green algae (cyanobacteria) are photosynthetic microbes; while some cyanobacteria are studied for other antimicrobial or peptide compounds, none is documented as a source of penicillin, and none is an industrial producer of the drug.

The molds (fungi) that secrete this compound are therefore its correct biological source.