Researchers at the University of Delaware have discovered a unique soil bacterium that boosts plant immunity in edible plants to fight off bacteria that can cause disease in humans. These soil bacteria, also known as plant growth promoting rhizobacteria (PGPR) are known in the field of plant science to increase plant immunity which helps fight off bacteria that cause disease in plants. This group of scientists have applied the same idea to use PGPR, sometimes referred to as “plant probiotics” to fight off foodborne bacteria that may get onto plants in the preharvest environment.
Edible plants, such as leafy greens, are the number one food commodity associated with foodborne illness. Plants can become contaminated with human pathogens in the preharvest environment through a variety of ways including intrusion of wild animals and insects as well as the use of contaminated irrigation water. These foods are also often eaten raw so there is no heat (kill step) used to inactivate any potential pathogens that may be present. Postharvest disinfection strategies are not always effective and it is essential that we include as many hurdles as possible, from farm to fork, in order to reduce the survival of these pathogens. Implementation of preharvest mitigation strategies to reduce the prevalence of pathogens is equally important.
In a previous study, it was demonstrated that a specific plant growth promoting rhizobacterium (PGPR), known as Bacillus subtilis UD1022 has been shown to trigger an induced systemic response (ISR) in plants and protect plants by infection with plant pathogens. This interaction caused small pores on the leaves of plants, known as stomata, to close, to prevent entry of the plant pathogen. It also increased the health of the plants and thus; increased the overall yield of the crop. Researchers at UD were able to demonstrate that UD1022 was able to induce stomata closure in the presence of human pathogens, including Salmonella and Listeria, on both lettuce and spinach. The results of this study indicate that this specific “plant probiotic” should able to prevent contamination by plant pathogens as well as by some human pathogens.
In addition, the authors of this study show that some human pathogens may also induce an immune response in plants. There are some plant pathogens that are able to cause infection in plants by hijacking the plant immune system to reopen plant stomata and enter the plants. For the first time, in this study the authors demonstrated that that Listeria behaves like a plant pathogen in that it is able to reopen plant stomata on lettuce. Similarly, Salmonella was able to reopen stomata on spinach as induce symptoms of disease in the plants. Other studies have also shown the ability of Salmonella to induce disease symptoms of plants. It is possible that in some cases human pathogens, such as Listeria or Salmonella species, may also have the ability to infect plants. It has been theorized by others that human pathogens may also use plants as a vector to get to their plant-eating host.
I am a postdoctoral researcher with interests in pre-harvest microbial food safety, nonthermal food processing technologies, zoonotic pathogens, and plant-microbe interactions. My current research projects involve the optimization of novel food processing technologies to reduce the number of foodborne pathogens on fresh produce. I am a food geek!