How to Make Penicillin at Home

The mold used to make penicillin grows on rotting fruit and bread.
The mold used to make penicillin grows on rotting fruit and bread. carenas1, Getty Images

Penicillin is a powerful antibiotic that is effective against Gram-positive 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 is fairly complicated, yet it's easy to grow Penicillium mold and possible to make penicillin at home.

How to Grow Penicillium Mold

Penicillium mold colonies are blue-gray to blue-green and have a white border.
Penicillium mold colonies are blue-gray to blue-green and have a white border. Sinhyu, Getty Images

Chances are good you've grown Penicillium mold accidentally. 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. However, if you use bread, use a homemade version because most packaged bread contains an antifungal agent that may defeat your efforts.

Penicillium Versus Aspergillus

Under a microscope, Penicillium has a characteristic fan shape.
Under a microscope, Penicillium has a characteristic fan shape. Dr_Microbe, Getty Images

Once you've got moldy bread or produce, you need to identify Penicillium. There are actually several species of Penicillium. Not all of them produce penicillin. Some are used to add flavor to cheese and sausage and 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).

A 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 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. Penicillium is more blue. Depending on the stage of growth, appearance alone may not be enough.

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.

Getting Penicillin from Mold

A lemon is a good substrate for growing Penicillium mold.
A lemon is a good substrate for growing Penicillium mold. ozgurkeser, Getty Images

​The ancient Egyptians simply took moldy bread and applied it to a wound as an antibiotic. However, they also made eyeliner out of toxic antimony and lead. You can do better.

You can grow a relatively pure culture of the Penicillium mold growing on the bread or fruit.

  1. Sterilize a container and lid either using a pressure cooker or by baking it in a 315 °F oven for an hour.
  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 steeping the mold in hot water to make tea.
Rather than purifying penicillin, some people recommend steeping the mold in hot water to make tea. krungchingpixs, Getty Images

 Now you've got a culture of Penicillium. What do you do with it?

You could 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 contains dilute penicillin.

Yet, you don't actually need to purify penicillin. The mold itself is not toxic*, so further purification doesn't impact effectiveness.

If you opt against purification, you could:

  • Just eat the mold. Yum!
  • Make a tea by mixing in a bit of moldy bread or fruit into 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 nutrient broth. Add the bandage and let mold grow on it, to apply 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 by testing it on a bacterial culture.
You can test homemade penicillin by testing it on a bacterial culture. Sinhyu, Getty Images

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 bacterial death is not proof you isolated penicillin. Molds produce other antibiotics, too.

References

  • Andrew Jackson Moyer, Method for Production of Penicillin, United States Patent Office, US Patent 2,442,141, filed 11 May 1945, issued 25 March 1948.
  • Fleming A. (1929). "On the antibacterial action of cultures of a penicillium, with special reference to their use in the isolation of B. influenzæ". British Journal of Experimental Pathology. 10 (31): 226–236.
  • Gonzalez-Estrada, A; Radojicic, C (May 2015). "Penicillin allergy: A practical guide for clinicians". Cleveland Clinic journal of medicine82 (5): 295–300.
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Helmenstine, Anne Marie, Ph.D. "How to Make Penicillin at Home." ThoughtCo, Feb. 2, 2018, thoughtco.com/how-to-make-penicillin-at-home-4158232. Helmenstine, Anne Marie, Ph.D. (2018, February 2). How to Make Penicillin at Home. Retrieved from https://www.thoughtco.com/how-to-make-penicillin-at-home-4158232 Helmenstine, Anne Marie, Ph.D. "How to Make Penicillin at Home." ThoughtCo. https://www.thoughtco.com/how-to-make-penicillin-at-home-4158232 (accessed April 26, 2018).