Penicillin Cultivation

Part of Antibiotics

Growing penicillium mold is the first and most critical step in producing the antibiotic that transformed medicine. Before penicillin, a simple scratch could kill through infection. Cultivating the right mold strain and growing it under controlled conditions produces the raw material from which penicillin is extracted.

Why Penicillin Matters for Survival

Bacterial infections are the leading cause of death in any pre-antibiotic society. Wound infections, pneumonia, childbirth fever, urinary tract infections, and infected dental abscesses all kill reliably without antibiotics. Penicillin targets the most common killers — Staphylococcus, Streptococcus, and many gram-positive bacteria — and can be produced with surprisingly simple equipment.

The original discovery was accidental: Alexander Fleming noticed in 1928 that a mold contaminating a petri dish had killed surrounding bacteria. The mold was Penicillium notatum. By 1943, mass production saved thousands of wounded soldiers. You can replicate the essential steps with materials available in a rebuilding scenario.

Finding Penicillium Mold

Natural Sources

Penicillium species are everywhere. They are the blue-green molds that grow on:

Source	Species Likely Present	Penicillin Potential
Citrus fruits (oranges, lemons)	P. digitatum, P. italicum	Low — wrong species
Bread (especially rye)	P. chrysogenum (formerly P. notatum)	HIGH — best natural source
Blue cheese (Roquefort, Stilton)	P. roqueforti	Moderate — some strains produce penicillin
Decaying melons and cantaloupe	P. chrysogenum	HIGH — the famous Peoria cantaloupe strain
Soil, especially near compost	Various Penicillium	Variable — must test
Old leather, damp books	P. chrysogenum	Moderate

The Cantaloupe Connection

The most productive penicillin strain in history was found on a moldy cantaloupe at a market in Peoria, Illinois. Overripe melons and stone fruits in warm, humid conditions are excellent hunting grounds for high-yield strains.

Identification

Penicillium mold forms distinctive colonies:

• Color: Blue-green to gray-green on top, white or pale underneath
• Texture: Powdery or velvety surface (not slimy or fuzzy like other molds)
• Shape: Circular colonies with defined edges that radiate outward
• Smell: Musty, earthy odor — not strongly pungent
• Key distinguishing feature: Under any magnification, Penicillium shows a brush-like sporulation structure (the name comes from “penicillus,” Latin for paintbrush)

Not All Molds Are Safe

Black molds (Aspergillus niger, Stachybotrys) and red/orange molds can produce dangerous mycotoxins. Only work with blue-green molds that match Penicillium characteristics. If in doubt, discard and try another source.

Preparing Growth Medium

Penicillium needs nutrients to grow and produce penicillin. The production of penicillin is actually a stress response — the mold produces it when competing with bacteria for limited resources.

Simple Nutrient Broth

This is the easiest medium for liquid culture:

Ingredient	Amount per Liter	Purpose
Sugar (any type)	20-30 g (2-3 tablespoons)	Carbon source for energy
Cornsteep liquor or grain water	50-100 ml	Nitrogen source, amino acids
Lactose (milk sugar)	10-20 g if available	Slow-release carbon that boosts penicillin
Salt	2 g (half teaspoon)	Mineral nutrition
Boiled water	To 1 liter	Solvent

Cornsteep liquor substitute: Soak cracked corn in warm water for 24-48 hours. The resulting cloudy liquid is rich in amino acids and was the key ingredient that boosted penicillin yields 10-fold in early production. Alternatively, use water in which beans or lentils have been soaked overnight.

Solid Growth Medium

For initial isolation and strain selection, grow on solid surfaces:

1. Bread slices — moisten slightly, place in covered containers
2. Agar plates — if agar-agar (from seaweed) is available, dissolve 15 g per liter of nutrient broth, pour into shallow dishes, let solidify
3. Potato slices — boil potato, slice thin, place in covered dishes
4. Grain mash — cooked rice or wheat spread thin on plates

Sterilization

All media must be sterilized before inoculation to prevent contamination by unwanted bacteria and molds:

1. Boil liquid media for 30 minutes in covered containers.
2. For solid media, steam in a covered pot for 30 minutes (pressure cooking at 15 psi for 15 minutes is ideal if available).
3. Let cool to room temperature before adding mold — heat kills the culture.
4. Work in the cleanest environment available, ideally after wiping surfaces with alcohol or strong vinegar.

Inoculation and Growing

Starting a Culture

1. Transfer a small amount of blue-green mold from your source to the sterilized medium using a sterilized needle, wire, or wooden splinter (flame the tip until red, let cool).
2. For liquid culture (broth), drop a tiny fragment of mold into the flask and swirl gently.
3. For solid culture, touch the sterilized tool to the mold colony, then touch it to the center of the plate.
4. Cover loosely — the mold needs air exchange but not exposure to environmental contaminants. Cotton plugs for flask openings, or loosely fitting lids for plates.

Optimal Growth Conditions

Parameter	Optimal Range	Notes
Temperature	20-25 degrees C (68-77 degrees F)	Room temperature; too warm favors bacteria
Humidity	70-80%	Moist but not wet
Light	Dim to dark	Direct sunlight inhibits growth
Air	Needs oxygen	Do not seal containers airtight
pH	5.0-6.0 (slightly acidic)	Add small amount of vinegar if needed
Time for colony growth	5-7 days	Patience is essential
Time for penicillin production	7-14 days	Peaks around day 10-12 in liquid culture

Temperature Matters Enormously

Above 30 degrees C, Penicillium grows poorly and penicillin production drops to near zero. In hot climates, culture in the coolest available space — a cellar, cave, or north-facing room. Evaporative cooling (wet cloth over the container) can help.

Scaling Up Liquid Culture

For useful quantities of penicillin, you need liters of broth, not milliliters:

1. Start small — grow a strong culture in a 500 ml flask.
2. Transfer 50 ml of the actively growing broth to a fresh 2-liter container of sterilized medium.
3. Aerate — penicillin production increases dramatically with oxygen. Gently swirl or shake containers twice daily. In a more sophisticated setup, bubble air through the broth using a hand bellows connected to a tube with a cotton filter.
4. Maintain for 10-14 days. The broth turns yellow-brown as penicillin accumulates.
5. Harvest when the liquid is distinctly yellow and the mold mat on the surface is thick and beginning to produce spores (dusty surface).

Strain Selection and Improvement

Not all Penicillium colonies produce the same amount of penicillin. Some produce almost none.

Testing for Antibiotic Activity

1. Prepare a plate of nutrient agar.
2. Spread bacteria across the surface (bacteria from an infected wound, or culture from raw meat juice left at room temperature).
3. Place a small piece of the mold colony or a drop of culture broth in the center.
4. Incubate at room temperature for 24-48 hours.
5. Look for a clear zone (zone of inhibition) around the mold where bacteria cannot grow.
6. Larger clear zone = more potent penicillin producer. Select this strain for your production cultures.

Maintaining Good Strains

Once you find a productive strain:

• Subculture regularly — transfer to fresh medium every 2-3 weeks to keep it vigorous.
• Keep backup cultures — maintain at least 3 separate cultures in case one becomes contaminated.
• Store spores — scrape dry spores from mature colonies onto clean, dry paper. Fold and store in a cool, dry place. Spores remain viable for months to years.
• Avoid contamination — if bacterial colonies (glossy, smooth, often smelly) appear in your mold cultures, discard and restart from a clean backup.

Common Mistakes

1. Using the wrong mold — not all blue-green molds produce penicillin. Always test with bacteria to confirm antibiotic activity before investing in large-scale production.
2. Overheating the culture — temperatures above 30 degrees C dramatically reduce penicillin output even if the mold appears healthy.
3. Sealing containers airtight — Penicillium needs oxygen. Airtight containers lead to poor growth and negligible penicillin production.
4. Harvesting too early — penicillin concentration peaks at 10-14 days. Harvesting at 5 days yields a fraction of the potential.
5. Poor sterilization of medium — bacterial contamination overgrows the slower-growing mold and consumes the nutrients first.

Summary

Penicillin Cultivation — At a Glance

• Source Penicillium from moldy bread, cantaloupe, or blue cheese — look for blue-green, powdery colonies
• Grow in nutrient broth (sugar + cornsteep liquor/grain water + salt) sterilized by boiling
• Maintain at 20-25 degrees C in dim light with loose covers for air exchange
• Penicillin production peaks at 10-14 days — harvest when broth turns distinctly yellow
• Test every strain’s antibiotic activity with a zone-of-inhibition test before scaling up
• Keep backup cultures and stored spores to protect your best-producing strain
• Aerate liquid cultures by swirling or bubbling filtered air to boost yields significantly