Sept. 4, 2024 – The world is getting hotter, and the air is getting more humid. And that is a perfect recipe for more people to get sick from food tainted with salmonella and other bacteria.
Jeri Barak, PhD, a professor in the Department of Plant Pathology at the University of Wisconsin-Madison, said that as climate change continues to affect our planet, there will be “more periods of time with high humidity,” leading to more frequent and numerous cases of bacteria-infected plants.
This can include the regular produce that you buy at your local grocery store. Of course, if produce is infected, why would we eat it? According to Barak, it isn’t easy to evade infection, and seemingly healthy plants found in stores could be hiding salmonella.
“Healthy plants can get water-congested” as intense rain events happen more often with climate change, she said. “Even though the plant’s healthy, salmonella can enter the plant’s apoplast – the interior of the leaf – where it’s protected from ultraviolet light.”
Barak led a study published in Applied and Environmental Microbiology that found the number of Americans who get sick from foodborne bacteria – already at 1.2 million a year – will increase due to climate change.
The data reported in the study – along with the study authors’ previous research – examines how plant disease and host infection by a plant pathogen can influence survival and persistence of salmonella on or in plants.
The study found that rising humidity levels – a result of a warmer atmosphere due to climate change – will increase the survivability of salmonella in raw produce. The study further found that high humidity could help other bacteria that live in the intestines of animals and humans – like E. coli and yersinia, along with salmonella – survive in crop fields and cause infection.
Salmonella Infection can cause diarrhea and stomach pains. The bacteria is in the intestinal tract of animals and is usually transmitted to humans through the consumption of food contaminated with animal feces.
With sudden infection, enough of the bacteria is able to overcome the defensive effects of your stomach acid and immune system. The bacteria invade and destroy the cells that line the intestinal tract, meaning the body can’t absorb water as well, and this causes stomach cramps. The water then leaves your body in the form of diarrhea.
Although the thought of salmonella may conjure images of raw, infected meat or chicken, the most common way to get infected is by eating contaminated fresh produce. Salmonella can also survive on many different agricultural crops and persist in the soil for long periods of time.
Creating the Perfect Environment for Plant Disease
Efforts to fight salmonella in the field or before food reaches consumers has been mixed.
Sterilization methods to stop the reproduction of germs include ultraviolet (UV) light, but because they are protected when they get inside the leaf, congested with water, UV won’t block them from growing.
A common threat against leafy green production is Xanthomonas hortorum pv. vitians, a bacteria that causes spots on lettuce, a disease that affects the quality and yield of lettuce. They can sometimes be seen as small dead spots on lettuce leaves a few days after infection, and these spots later combine into larger patches.
First described in 1918 after an outbreak in South Carolina lettuce fields, bacterial leaf spot threatens lettuce production worldwide. The last century has seen several outbreaks, prompting researchers to investigate and better understand the interaction between this pathogen and plants.
In this latest study, researchers tried to figure out whether salmonella’s ability to survive in produce is impacted by humidity or by the timing of bacterial leaf spot disease progress.
The researchers found that bacterial leaf spot infection can affect salmonella's success within the plant. If the bacterial leaf spot infection arrives too early, the plant’s defenses will limit salmonella’s spread. If the infection arrives too late, then the plant will have become so infected, salmonella doesn’t really have much of a place to grow and survive.
It's a fascinating, complex, and yet worrisome interplay between host and pathogen that threatens food security not just in the U.S., but worldwide.
Climate Change’s Impact on Food Security
Other commonly eaten foods around the world – notably rice – can be affected by climate change. Successful rice cultivation depends partly on its resistance to any potential bacterial disease that could affect the crop. As better environments for the increase in bacterial crop diseases arise around the world, production issues arise and growing conditions decline, leading to price hikes and supply shortages.
“Food prices could go up because of climate factors,” Barak said. “There’s less food available … some countries rely on imported food and the producing countries could decide not to export that food because they want to keep it for their own population.”
Areas where we once produced food may not be viable anymore due to climate change, especially in tropical or subtropical areas. The climate will be simply no longer be good for producing food, threatening food security.
Decreasing the Risk of Foodborne Illness
Higher rates of plant disease are a risk factor for contamination with human pathogens like salmonella.
Plants may be bred for resistance against these diseases.
“For the most part, we breed for resistance when the diseases are causing significant crop yield loss, but we’re talking one step beyond … a risk factor for foodborne illness,” Barak said. “Controlling food waste and breeding for plant resistance against plant pathogens could be a way to increase food safety.”
The farm industry often overuses antibiotics and chemicals against bacteria that contaminate food or animal feed. In doing so, bacteria may become resistant to antibiotics over time. This has begun to concern microbiologists and infectious disease specialists the world over, as new and safer solutions become urgently needed before all our usual weapons against bacteria – mainly antibiotics – become useless.
In fact, this has been noted for years now. Many in the microbiology field have warned against an antimicrobial resistance crisis – of which the misuse and overuse of antibiotics in animals and plants is a main driver. In theory, that could continue to get worse as climate change increases the risk of foodborne illness, creating the need for even more overuse of antimicrobials in our food production.
Though Barak said she has not yet seen any evidence of antibiotic-resistant strains among salmonella bacteria, she and her team analyzed data collected over the last 10 years by the CDC’s National Center for Emerging and Zoonotic Infectious Diseases. They focused on illness, hospitalization, and death from outbreaks of salmonella.
They found a “significant increase in hospitalizations for people that got sick when they consumed plant products,” vs. those who consumed meat products, she said. “Whether that's lettuce or nuts or seeds or alfalfa sprouts.”
