Newswise — When left out on the counter for too long, a loaf of bread grows mold. That mold is a common type of filamentous fungi, a microorganism that grows in thread-like structures that can ruin baked goods.
But filamentous fungi can pose a much larger problem than just moldy toast. They can cause crop blights and harm human health, particularly by infecting immunocompromised people in hospitals. There are very few classes of antifungal treatments available, and, like bacteria and viruses, fungi are constantly adapting and developing resistances. The potential pathogens are also emerging and thriving in new locations.
In a study published in the Journal of Microbiological Methods, researchers from Lawrence Livermore National Laboratory (LLNL) combined and refined two established techniques into one new method to effectively screen chemicals for their ability to kill filamentous fungi. This advancement enables identification of new antifungal treatments and drugs.
“We have lots of assays that we can use for various chemicals to try and understand whether they’re antibacterial, but we don’t have a lot of good assays to figure out whether filamentous fungi are susceptible to a certain chemical,” said LLNL scientist and lead author Salustra Urbin. “Our method could be a wonderful tool for that. It doesn’t require a lot of sophisticated equipment, so it could be widely used.”
The team was initially interested in exploring the antifungal activity of algae extracts that inhibited fungal growth in previous work, but they needed a tailored method.
“We needed a way to understand if those extracts could affect these medically relevant filamentous fungi,” said Urbin. “But we looked, and we couldn’t find a test. So, we created a test.”
“Standardized assays exist for Aspergillus fungi, but no other filamentous strains have established methods,” said Annette LaBauve, LLNL scientist and co-author. “Our method aims to fill this gap in the field.”
The test, called the Disk diffusion Assay for Filamentous Fungi Susceptibility to antifungals, or DAFFS, exploits the technique normally used to test antibacterials. In that case, bacterial culture is spread in a thin layer across an entire Petri dish. Small disks containing antibacterial chemicals are placed on top and scientists watch to see if the bacteria or yeasts are unable to grow around those disks. But filamentous fungi are different and often more challenging to work with.
“If we place a thin layer of fungi on the on the plate, it will immediately just grow up and take over, like a little forest,” said LLNL scientist and co-author Hailey Casey. “It doesn’t grow in the same way as bacteria. Spores jump everywhere. It just goes crazy.”
To counteract this, the authors only deposited the fungi in a singular spot in the middle of the dish. Because fungi grow somewhat symmetrically outward, they observed as it grew toward and then avoided disks with effective antifungals.
The researchers also made use of a standardized Aspergillus test to hone the nutrients in the DAFFS growth medium. That nutrient level is key because the fungal growth needs to be slow enough to discern sensitivity to antifungals. While the Aspergillus test is currently only a standardized method for one type of fungi, DAFFS could be established and standardized as a powerful test for many filamentous fungal strains.
Now that they have the antifungal testing technology, the team aims to revisit their algae extracts. They hope to identify new antifungal treatments and enable other groups to do the same.
“In a world with increased globalization and adaptive, resistant fungi, filamentous fungi are an important group of emerging human pathogens with few antifungal treatment options,” said LLNL scientist and co-author Carolyn Fisher. “But the natural world still contains so much chemical diversity that has yet to be explored. We hope to find new chemicals that can be used as therapeutics against known and emerging pathogens.”
This work was part of a Laboratory Directed Research and Development project, “Antimicrobials for Multidrug-resistant Infections for Bioresilience Advancement”.
