How Climate Change is Elevating Foodborne Illness Risks in Fresh Produce
Recent research published in Applied and Environmental Microbiology, a journal of the American Society for Microbiology, shows that the risk of the foodborne illness from Salmonella enterica, which impacts 1.2 million people in the United States every year, is much much higher as a result of climate change. The infection most commonly spreads via contaminated fresh produce. While the effects of the illness are often mild, it can sometimes be life-threatening. According to the World Health Organization (WHO), “almost 1 in 10 people fall ill and 33 million of healthy life years are lost” due to foodborne illness.
Salmonella can survive in soil and water for long periods of time and researchers have found that Salmonella enterica takes advantage of the impact other organisms have on plant environments.
"It's not surprising that a host is altered by disease. What's interesting is how these changes affect other members of the bacteria community, in addition to the pathogen causing the disease. Furthermore, the impact of increased humidity on healthy plants also supported Salmonella's survival on plants, which would make climate change a food safety issue," said corresponding study author Jeri Barak, Ph.D., a professor in the Department of Plant Pathology, University of Wisconsin-Madison. "Controlling plant disease such as bacterial leaf spot of lettuce is also important for food safety. Climate change will increase the risk of foodborne illness from consumption of raw produce."
A major threat to the production of leafy greens is bacterial leaf spot caused by Xanthomonas hortorum pv. Vitians, which results in disease in nearly 400 plant hosts. The researchers aimed to determine if humidity levels or the timing of Salmonella's introduction during the progression of bacterial leaf spot influenced its fate. They chose to conduct experiments with lettuce with bacterial leaf spot and Salmonella. The experiments involved altering the timing of plant infections with X. vitians and the introduction of S. enterica in a water droplet on the leaf to simulate irrigation or splash dispersal from the ground.
The researchers also adjusted humidity levels and the duration between Salmonella introduction and measurement to assess its internal population. This internal Salmonella population refers to bacteria that have moved from the leaf surface to the interior, where they are protected from solar UV exposure and post-harvest sanitization treatments.
Ultimately, the researchers discovered that bacterial leaf spot caused by X. vitians can enhance Salmonella survival and internalization within romaine lettuce. The success of these bacterial leaf spot infections is dependent on the timing of Salmonella's arrival. If Salmonella arrives too early, the plant's defense mechanisms against the pathogen inhibit its growth and survival. Conversely, if it arrives too late, the plant’s disease-ridden environment also restricts Salmonella's growth. Additionally, high humidity and the water-soaking symptoms induced by X. vitians, exacerbated by climate change, further boost Salmonella’s growth in lettuce.
