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Researchers in South à£à£Ö±²¥Ðã State University's Department of Dairy and Food Science are developing an innovative solution to defeat listeria and other foodborne pathogens. 

Listeriosis is a bacterial infection caused by the bacterium Listeria monocytogenes. The infection affects around 1,600 people annually in the United States (per the Centers for Disease Control and Prevention) and has a fatality rate between 20% and 30%. Those at greater risk include pregnant women, newborns, older adults and individuals with weakened immune systems.

This year, a listeria outbreak linked to contaminated supplement shakes caused issues across 21 states. According to the CDC and the Food and Drug Administration, 38 people fell ill, 37 were hospitalized and 12 died from to the widespread outbreak.

Preventing listeria outbreaks is especially important for food and dairy manufacturers as, without proper precautions, conditions can be ripe for the bacteria to persist inside food/ dairy plants. 

South à£à£Ö±²¥Ðã State University's Department of Dairy and Food Science has been conducting research on how to better control environmental listeria and other foodborne pathogens for nearly a decade. With the frequent outbreaks being reported on a year-to-year basis the need for more effective control methods is clear and SDSU professor Sanjeev Anand and his team of graduate and undergraduate students are homing in on a solution.

Listeria in food and dairy plants

Compared to other environmental foodborne pathogens, listeria has a few unique characteristics that create challenges for food and dairy manufacturers. Unlike many other pathogens, listeria is psychotropic and can grow in a wide range of temperatures including refrigeration temperature. It can also survive freezing temperatures for extended periods, making it a persistent threat in frozen foods. Environmental listeria is commonly associated with a wide variety of food-contact and non-food-contact surfaces including equipment and utensils, and hands and clothing. Considering the environmental conditions required in food and dairy manufacturing, these characteristics create opportunities for cross-contamination in food and dairy plants. While pasteurization kills listeria, postpasteurization contamination is the primary culprit for many listeria outbreaks. This is because the bacterium, which enters processing facilities through a variety of the aforementioned sources, will embed itself in difficult-to-clean areas, like drains and crevices. There, the bacteria will proliferate into fortress-like biofilms, which are difficult to clean and allow protection for the bacteria to survive for extended periods.

Frozen vegetables and fruits, ready-to-eat products, like ice cream and raw milk cheeses, are at a higher risk for listeria contamination.

Anand and his team believe they can solve this problem by developing a novel cleaning method that would prevent the bacteria from attaining the biofilm stage. By targeting certain genetic characteristics, the developed cleaning solution will prevent biofilms from forming, leading to a more effective control of environmental listeria.

Getting to this point has been a multiyear, step-by-step process for Anand and his team.

"It has been an interesting journey," Anand said.

First, the team worked to understand the different types of surfaces on which listeria will form biofilms. Clay, brick and concrete floors are widely used in dairy processing facilities, and Anand has found that adjusting the floor cleaning and sanitation regimen is one way to help mitigate biofilm formation.

The team also worked to understand the various factors influencing listeria persistence in dairy facilities. One of the key findings was the bacteria's ability to develop a sort of tolerance against disinfectants. Coupled with other environmental factors, sublethal levels of disinfectants applied to listeria biofilms gives the bacteria a tolerance to persist. This creates a long-term contamination risk for dairy manufacturers.

Genetic sequencing

Anand determined that a more thorough understanding of listeria was needed to create better, more effective control methods. Specifically, he wanted to know the genetic determinants that allowed the bacteria to persist in the manufacturing environment. In collaboration with professor Jose Gonzalez, SDSU's core research support facilities director, the research team began whole genome sequencing of the listeria isolates.

Whole genome sequencing is the process of determining the entire DNA sequence of an organism's genetic information. Using state-of-the-art technology in SDSU's Genomics Sequencing Facility, Anand was able to pinpoint the genetic traits that allow the bacteria to form biofilms, resist disinfectants and persist in dairy manufacturing facilities.

Antimicrobial peptides are small molecules that work as part of the immune response in organisms. These molecules have also shown promise in defeating bacteria by disrupting their cell membranes. Anand and his research team believe antimicrobial peptides can be used in cleaning solutions to prevent listeria from forming biofilms. Utilizing the genetic information derived from the genomic sequencing, the team is determining what peptide would be most effective against listeria.

As Anand notes, finding an effective antimicrobial peptide would be a "green" method for controlling listeria as it would not require harsh chemicals, disinfectants or antibiotics. He also notes this research, while focused on listeria, has broad applications in controlling other environmental pathogens.

"This is fundamental, frontline research on listeria that can be applied to other foodborne pathogens," Anand said. "We are developing more effective environmental control methods that can provide benefits beyond the dairy industry."

In the future, Anand and the research team will apply their research in commercial dairy plants.

Funding for this work is provided by the National Dairy Council, Dairy Management Inc. and the Midwest Dairy Association.