Multidrug-resistant fungi found in commercial soil, compost, flower bulbs

That pile of soil you bought at the home improvement store may contain more than just dirt, according to new research from the University of Georgia.

A new UGA study found high levels of multidrug-resistant fungi in commercially available compost, soil and flower bulbs.

Aspergillus fumigatus is a widespread fungus that thrives in soil. But it also poses a serious risk to human health if inhaled. People with compromised immune systems are particularly vulnerable to the opportunistic fungus, facing a near 100% fatality rate if infected with a multidrug-resistant strain.

"People don't think of tulips as deadly, but they could be," said Marin Brewer, lead author of the study and a professor in UGA's College of Agricultural and Environmental Sciences.

"Gardening is a nice, stress-relieving hobby," Brewer said. "But I'm nervous for people who may not be aware that working with compost and flower bulbs could pose a risk to their health."

Those people include individuals with chronic obstructive pulmonary disease (also known as COPD), cystic fibrosis, Type 2 diabetes, HIV/AIDS and even COVID-19. Cancer patients and anyone taking immunosuppressant drugs are also vulnerable.

And research shows more people are at risk of developing fungal infections than before.

Aspergillus fumigatus poses a critical public health threat

The World Health Organization recently named Aspergillus fumigatus as one of the most critical fungal threats facing the world.

Aspergillus fumigatus infects more than 2 million people annually worldwide.

Aspergillosis, the disease caused by the fungus, is one of the most frequent causes of death in immunocompromised patients. About eight out of every 10 invasive aspergillosis patients die, according to a recent study.

Based on our findings, there could be tens of thousands of potentially resistant strains in one bag of compost." -Marin Brewer, College of Agricultural & Environmental Sciences

Although less common, the fungus can even pose a threat to individuals with healthy immune systems.

Known as aspergillomas, the fungus can create a clump on the lung. While some healthy individuals may clear the infection on their own with minimal to no symptoms, other aspergilloma patients require antifungal medications or surgery to stop the infection from spreading.

The problem is that the treatments for human patients rely on the same mechanisms to fight the fungi as those used in agricultural settings. And they're becoming less effective.

Multidrug-resistant fungi found in soil, manure-based compost, flower bulbs

The researchers sampled products including compost, soil, flower bulbs and a variety of food products sold at big box retail stores from 2019 through 2021.

The study found more than 500 strains of Aspergillus fumigatus in the products, which included an assortment of different brands. Of the 525 samples, 90% were found in flower bulbs, soil, compost and peanuts.

Most of the drug-resistant strains of fungi were found in soil, compost made from manure and flower bulbs, including daffodils, dahlias, gladioli and tulips.

"We found dozens of strains of resistant fungi in just 1 gram of compost," Brewer said. "Based on our findings, there could be tens of thousands of potentially resistant strains in one bag of compost."

How can gardeners keep themselves safe from fungus?

People are infected with Aspergillus fumigatus by inhaling the fungi's spores.

The researchers highly recommend individuals with compromised immune systems take precautions when gardening and discuss the potential risks with their physicians. Devoted gardeners can also wear N-95 masks to provide some protection.

The agricultural industry is working to address the problem, but in the meantime Brewer said she personally won't be planting flower bulbs. And she'll probably pass on using commercial compost too.

Published in Applied and Environmental Microbiology, the study was co-authored by Caroline Wang, Natalie Miller, Douglas Vines, Paul M. Severns and Michelle Momany, of UGA's Fungal Biology Group and UGA's Departments of Plant Pathology and Plant Biology.