Aspergillus fumigatus in a tulip bulb. (Illustration by Whitney Mathiesen and Andrea Piazza)
That pile of dirt you buy at the hardware store may contain more than just dirt, according to a new study from the University of Georgia.
A new study from the University of Georgia has found that commercially available compost, soil and flower bulbs contain high levels of multidrug-resistant bacteria.
Aspergillus fumigatus is a widespread fungus that grows in soil, but also poses serious health risks to humans if inhaled. People with weakened immune systems are particularly susceptible to this opportunistic fungus, and infection with multidrug-resistant strains has a near 100% mortality rate.
Marin T. Brewer (Photo by Andrew Davis Tucker/UGA)
“I don't think it's deadly to tulips, but it could be,” said Marin Brewer, lead author of the study and a professor in the College of Agricultural and Environmental Sciences at the University of Georgia.
“Gardening is a lovely stress-relieving hobby,” Brewer said, “but I worry that some people may not be aware of the potential health risks of working with compost and flower bulbs.”
Among these people are those with chronic obstructive pulmonary disease (also known as COPD), cystic fibrosis, type 2 diabetes, HIV/AIDS, and even COVID-19. Cancer patients and those taking immunosuppressants are also at risk of infection.
And studies are showing that more people than ever before are at risk of developing fungal infections.
Aspergillus fumigatus poses a major public health threat
The World Health Organization recently named Aspergillus fumigatus one of the most significant fungal threats facing the world.
Aspergillus fumigatus infects more than 2 million people worldwide each year.
Aspergillosis, caused by a fungus, is one of the most common causes of death in immunocompromised patients. Recent studies have shown that approximately 8 out of 10 patients with invasive aspergillosis die.
Our findings suggest that a single bag of compost could contain tens of thousands of strains of resistant bacteria.” —Marin Brewer, College of Agricultural and Environmental Sciences
Although less common, this bacteria can also pose a threat to people with healthy immune systems.
Known as aspergilloma, the fungus can form masses in the lungs. Some healthy people have few or no symptoms and the infection goes away on its own, but some people with aspergilloma may need antifungal medication or surgery to stop the infection from spreading.
The problem is that treatments for human patients rely on the same mechanisms to fight fungi as those used in agriculture — and they're becoming less effective.
Multi-drug resistant bacteria found in soil, fertilizer-based compost and flower bulbs
The researchers took samples of compost, soil, flower bulbs, and a variety of food products sold at big box stores between 2019 and 2021.
The study found more than 500 strains of Aspergillus fumigatus in various brands of products, with 90% of the 525 samples found to be from flower bulbs, soil, compost and peanuts.
Most of the drug-resistant strains were found in soil, compost made from manure, and flower bulbs such as daffodils, dahlias, gladioli, and tulips.
“We found dozens of resistant strains in just one gram of compost,” Brewer says, “and based on our findings, a single bag of compost could potentially contain tens of thousands of resistant strains.”
How can gardeners protect themselves against the fungus?
Humans become infected by inhaling Aspergillus fumigatus spores.
The researchers strongly recommend that people with weakened immune systems take precautions when gardening and discuss potential risks with their doctor. Avid gardeners can also wear N-95 masks for some protection.
While the agriculture industry works to solve the problem, Brewer said he personally won't be planting flower bulbs in the meantime, and he probably won't use commercial compost either.
The study, published in the journal Applied Environmental Microbiology, was co-authored by Caroline Wang, Natalie Miller, Douglas Vines, Paul M. Severn and Michelle Momany from the University of Georgia's Fungal Biology Group and the Department of Plant Pathology and Plant Biology.
