How to Make Penicillin at Home

The mold used to make penicillin grows on rotting fruit and bread

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Penicillin is a powerful antibiotic that is effective against bacteria. The drug comes from the Penicillium mold, most commonly the species P. chrysogenum. The discovery of penicillin and a method of purifying it earned Alexander Fleming, Ernst Chain, and Howard Florey the 1945 Nobel Prize in Physiology or Medicine. Modern purification and mass production of penicillin are fairly complicated, but it's easy to grow Penicillium mold and make penicillin at home.

How to Grow Penicillium Mold

Penicillium mold colonies are blue-gray to blue-green and have a white border

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Chances are good you've already grown Penicillium mold on accident, as it readily grows on bread and fruit. Fleming's initial culture grew on a cantaloupe. Many people prefer to leave oranges or lemons in the crisper of the refrigerator until mold develops. You can also dampen bread, seal it in a plastic bag, and wait for mold to grow. However, if you choose to use bread, use a homemade version because most packaged bread contains an antifungal agent that may defeat your efforts.

Penicillium vs. Aspergillus

Under a microscope, Penicillium has a characteristic fan shape

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Once you've got moldy bread or produce, you need to identify Penicillium. There are actually several species of this mold, and not all of them produce penicillin. Some are used to add flavor to cheese and sausage and to deter spoilage. There are also other types of mold that resemble Penicillium.

A Penicillium colony starts out gray or white, turns blue, and finally changes to blue-green. It typically develops a white outer ring (which you won't see if mold completely overtakes your specimen).

Another type of mold that resembles Penicillium is Aspergillus. Aspergillus species may be green, gray, or black. Some strains of Aspergillus have commercial value, such as for fermenting sake and producing citric acid. However, others cause disease or produce lethal toxins such as aflatoxin. You do not want to accidentally purify one of these.

How do you tell Penicillium and Aspergillus apart? If you see two cultures side by side, Aspergillus looks fuzzier than Penicillium, and Penicillium is bluer. Depending on the stage of growth, though, appearance alone may not be enough to distinguish the two.

The best way to identify Penicillium is to view it under magnification. Penicillium is branched, like a fan. Aspergillus is straight, like a long stalk with a fuzzy ball at the end.

Extracting Penicillin from Mold

A lemon is a good substrate for growing Penicillium mold

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​To exploit the medicinal powers of Penicillium, the ancient Egyptians simply took moldy bread and applied it to wounds as an antibiotic. However, they also made eyeliner out of toxic antimony and lead. You can do better.

By following these steps, you can grow a relatively pure culture of the Penicillium mold on a piece of fruit or bread:

  1. Sterilize a container and lid either using a pressure cooker or by baking it in an oven for one hour at 315 degrees Fahrenheit.
  2. Sterilize (as much as possible) fresh growth media for the mold. For example, you could boil an intact lemon, bake damp bread, or disinfect fruit with alcohol.
  3. Add the bread or fruit to the container, place a piece of mold onto the surface, and close the jar. Nothing will be truly sterile, but the mold will have the advantage and should out-compete other microorganisms.
  4. Allow a few days for the mold to grow. Keep the culture out of direct sunlight. Penicillium produces penicillin when the colony matures and comes under stress. The mold is most useful when it reaches the blue-green stage.

Should You Purify the Penicillin?

Rather than purifying penicillin, some people recommend drinking it as tea

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Now you've got a culture of Penicillium. How do you extract the penicillin?

One way is to add a weak acid (citric acid, cream of tartar, vitamin C) and water to the mold, mix it up, filter it through a coffee filter, and collect the liquid. The liquid will contain diluted penicillin.

You don't actually need to purify the penicillin, though. The mold itself is not toxic,* so further purification will not alter its effectiveness.

If you opt against purification, you can:

  • Eat the mold.
  • Make a tea by mixing a bit of moldy bread or fruit in warm water.
  • Make lemon curd (if you're using moldy lemons).
  • Make an antibiotic bandage by putting a bit of the mold from this culture into a nutrient broth. Add the bandage and let mold grow on it, then apply the bandage to a wound.

*Some people are allergic to mold. Some strains of Penicillium produce mycotoxins, neurotoxins, or carcinogens. While the mold itself might not be a problem, the compounds it releases may or may not be dangerous.

Alternatives to Making Penicillin

You can test homemade penicillin on a bacterial culture

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Taking homemade penicillin is risky. There's a good chance a do-it-yourself version could be ineffective or make a bad situation worse. In a dire situation, safer natural antibiotics include garlic, oil of oregano, and honey.

In the event of a true emergency, with no doctors or prescriptions in sight, you'd be much better off taking your chances with penicillin for fish, found in the aquarium section of a pet store. Still, it's good to know where penicillin comes from and how to make it. Just don't try your homemade concoction on people unless civilization ends.

What you can do is test homemade penicillin on bacteria. This is a great project for high school biology or college microbiology. Culture bacteria onto a plate (a swab from your mouth is a good source of Gram-positive bacteria) and add a drop of homemade penicillin to the plate. If the penicillin works, bacteria will die within the circle affected by the drop. Be aware, though, that bacterial death is not proof that you isolated penicillin. Molds produce other antibiotics, too.

Sources

  • Brown, Kevin. "Penicillin Man: Alexander Fleming and the Antibiotic Revolution." The History Press, 2013.
  • Fleming, Alexander. “Antibacterial Action in Cultures of Penicillium, With Special Reference to Their Use in Isolation of Bacillus Influenzas.” The American Journal of the Medical Sciences, vol. 180, no. 3, 1930, p. 449.
  • Gonzalez-Estrada, A., and C. Radojicic. “Penicillin Allergy: A Practical Guide for Clinicians.” Cleveland Clinic Journal of Medicine, vol. 82, no. 5, 2015, pp. 295–300.