Ants make their own ant-ibiotic for infected wounds

Although humans may think we are alone in creating antibiotics, there is a species of ant that secretes an especially powerful one—no pharma lab required.

The Matabele ants (Megaponera analis) of sub-Saharan Africa eat only termites. Unfortunately, the fierce mandibles of termite soldiers cause injuries that, if infected, can turn fatal. Ants back at the nest rush to the injured and can tell which wounds are infected. They then secrete an antibiotic for them.

An international team of researchers observed these ants closely and analyzed their antibiotic secretion. They found it can reduce mortality by about 90 percent in injured ants and that the ants can identify chemical changes that result from infected wounds, focusing treatment on those that need it most.

Risk of infection

To see how Matabele ants carry out their treatment, researchers experimentally injured two groups of worker ants, exposing one group to soil while the other group was sterilized with saline solution.

It only took two hours for injured ants exposed to soil to show thoracic bacterial loads 10 times higher than sterile ants. They became a hundred times higher after 11 hours. A microbiome analysis of infected ants revealed growing populations of pathogenic bacteria that included Pseudomonas aeruginosa, which can cause pneumonia and meningitis in humans.

Both sterile and infected ants were then either kept in isolation (with sterile and infected insects isolated separately) or returned to their colony (together). The colony was then filmed for 24 hours.

During the observation period, the scientists saw uninjured workers using their mouthparts to clean the wound. They would then apply a secretion from the metapleural gland in the back of their thorax. To do this, they either used their legs to gather the secretion from their own metapleural gland, transferring it to their mouthparts before applying it to the wound, or take it directly from the gland of the injured ant with their mouthparts and apply it to the wound. Although this behavior has been documented before in ants, what surprised the research team the most was that the Matabele ants can diagnose infections.

“Remarkably, workers were able to discriminate between infected and sterile ants,” they said in a study recently published in Nature Communications. “[Metapleural gland] secretions were deposited significantly more often on wounds of infected than sterile ants between 10 and 12 hours after infection.”

Literally life or death

But how can Matabele ants tell that a wound is infected? They were seen initially treating all wounds, which the researchers thought was to prevent infection, but later, there was a chemical change in infected wounds that they could detect.

Ants are already known to communicate using cuticular hydrocarbons, which are pheromones used to mark colony members according to their role and/or to recognize each other outside of the nest. Sterile and infected patients had similar pheromone profiles until around 11 hours after injury. After that, the pheromone profile of infected ants changed drastically, suggesting that they were using pheromone signaling to indicate infection.

The researchers found that 18 pheromone-related genes were differentially active in infected ants compared to sterile ants 11 hours after exposure to pathogenic bacteria. Since it takes some time for these changes in gene activity to produce altered levels of pheromones, this explains why the response to infection is somewhat delayed.

While previous studies had found metapleural gland secretions to have antimicrobial properties in other species of ants, they turned out to be especially effective in Matabele ants. The substance is made of over a hundred compounds, many of which have antibiotic properties.

Tests for pathogenic bacteria in the wounds post-treatment showed that the secretion reduced Pseudomonas growth by over 25 percent. This is impressive, as Pseudomonas is infamous for having developed antibiotic resistance repeatedly.

Could something derived from this ant-ibiotic ever be applied to humans? Maybe.

“The targeted treatment with antimicrobial compounds was extremely effective in preventing lethal bacterial infections by [Pseudomonas],” the researchers said in the same study. “This could potentially lead to promising new medical compounds to cure infections in human societies.”

If anything, fewer people may squash an ant with their shoe after knowing that these often aggravating insects may someday save our lives.

Nature Communications, 2023.  DOI: 10.1038/s41467-023-43885-w