Reducing their natural signals: How sneaky germs hide from ants

Not only humans are social, ants are too. Group members are taking care of sick ones by providing collective hygiene measures. This presents germs with a task. They must circumvent the immunity of an individual ant and avoid the group's healthcare. A new study now published in Nature Ecology & Evolution reveals that germs develop a sneaky way to escape the ant colony's defense systems by reducing their detection cues.

Pathogens are disease-causing organisms. By natural selection, they develop evading mechanisms to outsmart the host's immune system and to get the upper hand. One way to support the immune system and fight back is medical intervention. However, this can lead to unwanted adaptions of pathogens as seen in antibiotic-resistant bacteria. Another strategy is social intervention. Some social groups like ants are trying to fight infection with "social immunity," the collective hygiene and health care measures to avoid spreading throughout the community. If and how pathogens can respond to this kind of group behavior, is still unknown.

The latest study by Professor Sylvia Cremer and her research team at the Institute of Science and Technology Austria (ISTA) shows the extraordinary effects of these kinds of host-parasite interactions. Together, with chemical ecologists at the University of Würzburg in Germany, the scientists took a close look at social ants, to see how pathogenic fungi respond to their hosts' social care intervention during infection. The results reveal that fungi reduce their chemical detection signals to outplay social immunity. The study is published today in Nature Ecology & Evolution.

More spores but less grooming

"Fungi infect the ants from the body surface and grow inside, but nestmates groom off many of the spores before they can even cause internal infection," explains Barbara Milutinović, one of the lead authors, former postdoc in the Cremer Group and now Marie Curie Sklodowska Fellow at Ruđer Bošković Institute in Croatia. The scientists set up an experiment where Argentine ants (Linepithemahumile) were infected with pathogenic Metarhizium fungi either in the absence or presence of caregiving colony members. "We found that the fungi fundamentally changed in response to the ant workers' caregiving," Milutinović continues. Over ten infection cycles, fungi which experienced grooming nestmate ants boosted their spore production compared to fungi accompanied by only individual ants. "Producing more spores will help the fungus counteract the spore-removal by helping nestmates. Yet, we were surprised to see that the ants showed less grooming against the spores," Sylvia Cremer adds. "This suggests, that the spores have become more difficult to detect by the ants."

Fungi lose their typical chemical profile

To check why ant workers had difficulties sensing fungi and to analyze possible fungal detection cues, the scientists teamed up with a chemical ecologist from the University of Würzburg. Local Professor Thomas Schmitt explains: "The fungi, that adapted to social hosts were perceived less strongly, due to a strong reduction of a fungi-specific compound called ergosterol." Ergosterol is an essential membrane compound, that all fungi have. By exposing the ants to pure fungal ergosterol or the slightly different non-fungal vertebrate equivalent, the researchers showed, that only the fungal compound induced intense grooming. Milutinović summarizes: "This demonstrates that fungal pathogens react to the presence of caregiving ants by reducing their characteristic fungal signals. They are no longer recognized as a disease threat and can escape the social immunity of the colony."

Read more at Science Daily

Ultrashort-pulse lasers kill bacterial superbugs, spores

Life-threatening bacteria are becoming ever more resistant to antibiotics, making the search for alternatives to antibiotics an increasingly urgent challenge. For certain applications, one alternative may be a special type of laser.

Researchers at Washington University School of Medicine in St. Louis have found that lasers that emit ultrashort pulses of light can kill multidrug-resistant bacteria and hardy bacterial spores. The findings, available online in the Journal of Biophotonics, open up the possibility of using such lasers to destroy bacteria that are hard to kill by other means. The researchers previously have shown that such lasers don't damage human cells, making it possible to envision using the lasers to sterilize wounds or disinfect blood products.

"The ultrashort-pulse laser technology uniquely inactivates pathogens while preserving human proteins and cells," said first author Shaw-Wei (David) Tsen, MD, PhD, an instructor of radiology at Washington University's Mallinckrodt Institute of Radiology (MIR). "Imagine if, prior to closing a surgical wound, we could scan a laser beam across the site and further reduce the chances of infection. I can see this technology being used soon to disinfect biological products in vitro, and even to treat bloodstream infections in the future by putting patients on dialysis and passing the blood through a laser treatment device."

Tsen and senior author Samuel Achilefu, PhD, the Michel M. Ter-Pogossian Professor of Radiology and director of MIR's Biophotonics Research Center, have been exploring the germicidal properties of ultrashort-pulse lasers for years. They have shown that such lasers can inactivate viruses and ordinary bacteria without harming human cells. In the new study, conducted in collaboration with Shelley Haydel, PhD, a professor of microbiology at Arizona State University, they extended their exploration to antibiotic-resistant bacteria and bacterial spores.

The researchers trained their lasers on multidrug-resistant Staphylococcus aureus (MRSA), which causes infections of the skin, lungs and other organs, and extended spectrum beta-lactamase-producing Escherichia coli (E. coli), which cause urinary tract infections, diarrhea and wound infections. Apart from their shared ability to make people miserable, MRSA and E. coli are very different types of bacteria, representing two distant branches of the bacterial kingdom. The researchers also looked at spores of the bacterium Bacillus cereus, which causes food poisoning and food spoilage. Bacillus spores can withstand boiling and cooking.

In all cases, the lasers killed more than 99.9% of the target organisms, reducing their numbers by more than 1,000 times.

Viruses and bacteria contain densely packed protein structures that can be excited by an ultrashort-pulse laser. The laser kills by causing these protein structures to vibrate until some of their molecular bonds break. The broken ends quickly reattach to whatever they can find, which in many cases is not what they had been attached to before. The result is a mess of incorrect linkages inside and between proteins, and that mess causes normal protein function in microorganisms to grind to a halt.

"We previously published a paper in which we showed that the laser power matters," Tsen said. "At a certain laser power, we're inactivating viruses. As you increase the power, you start inactivating bacteria. But it takes even higher power than that, and we're talking orders of magnitude, to start killing human cells. So there is a therapeutic window where we can tune the laser parameters such that we can kill pathogens without affecting the human cells."

Heat, radiation and chemicals such as bleach are effective at sterilizing objects, but most are too damaging to be used on people or biological products. By inactivating all kinds of bacteria and viruses without damaging cells, ultrashort-pulse lasers could provide a new approach to making blood products and other biological products safer.

Read more at Science Daily