Cordyceps Sterilization: How to Kill “The Last of Us” Parasite

In HBO’s recent adaptation of “The Last of Us,” a popular action-adventure video game, life as we know it is upended by a parasitic fungus that transforms its human hosts into zombies. The culprit? Cordyceps, a real-life genus of fungus which is best known for infecting insects (most famously ants) in much the same manner — but without the world-ending consequences.

Fortunately for us, though the fungus is real, the probability of it mutating to the degree it does in the show is not. As Charissa de Bekker, professor of biology at Utrecht University, explained to Vox: “We don’t see the fungi specialists just jumping from one ant species to another, let alone from an ant species to another insect. Spreading from ant to human is just such a big jump.”

But if we suspend our disbelief for just a moment, the question arises: How could we kill the fungus if we had to? Or for that matter, any fungus? When it comes to destroying fungi, the most effective method depends on the type. Read on to learn more about different methods for eliminating fungal cells, cordyceps, and how sterilization plays a role in fungus research.

What Are Cordyceps?

As a whole, cordyceps is a genus of fungus that includes hundreds of species worldwide. While many of these species are entomopathogenic — or lethal to insects — cordyceps may offer certain health benefits for humans. In fact, these mushrooms have been a staple in traditional Chinese medicine for centuries.

However, it’s the way in which these fungi — particularly Ophiocordyceps unilateralis — take over their insect hosts that caught the attention of the “The Last of Us” creators. Similar to other parasites, O. unilateralis absorbs its victims’ nutrients before filling their bodies with the spores it uses to reproduce. Then, in a feat of mind control, the fungus compels the host insect to climb to a high height where it stays until the spores are ready to be released.

Sterilization Needs for Parasitic Fungus Research

There’s a lot we’re still learning about cordyceps, including how it asserts control over its host, and in order to fully understand it — and any other type of fungus, for that matter — it’s important to conduct research. In laboratory settings, sterilizing substrates used to grow fungal specimens is a key step in ensuring successful studies. If certain substrates aren’t sterilized before use, it’s possible for foreign bacteria and spores to negatively impact fungal growth.

Here’s what you need to get your chosen substrate ready for fungus cultivation:

• The substrate: While more nutrient-rich options (e.g. manure, grain, soy hulls, etc.) must be sterilized prior to use, less nutritious types (e.g. straw, sawdust, cardboard) only require pasteurization. For cordyceps, grain is the preferred choice.
• Glassware: Since glass can tolerate the conditions that autoclaves create, glassware makes an excellent choice as a vessel for sterilized and pasteurized substrates alike.
• An autoclave: While it’s technically possible to sterilize substrates using a pressure cooker, they aren’t designed for this particular purpose, making autoclaves the more reliable option.

How to Treat Fungus-contaminated Goods

While some cleaning methods are effective when it comes to killing fungal cells, others are not, making these organisms — and their spores — difficult to destroy fully. In terms of the fungi you’re most likely to encounter as part of day-to-day life, molds are particularly susceptible to household cleaners such as white vinegar and diluted bleach or ammonia.

However, in high-stakes situations such as surgical environments where more harmful fungus species are potentially involved, simple cleanings aren’t sufficient. In these cases, the only reliable way of ensuring eradication of all fungal cells, including spores, is sterilization of contaminated tools, instruments, and devices.

Fungus and Steam Sterilization

Though a future in which the world is overrun by cordyceps-infected zombies is unlikely, funguses of all species are very much a part of our lives today. And sterilization plays an integral role in understanding and destroying harmful varieties.

To learn more about steam sterilization and how different autoclave cycles have an impact on the process, download a copy of our free eBook, The Definitive Guide to Steam Sterilization Cycles, today.