While examining the prevalence of listeria in agricultural soil throughout the U.S., Cornell University food scientists have stumbled upon five previously unknown and novel relatives of the bacteria.
The discovery, researchers said, will help food facilities identify potential growth niches that until now, may have been overlooked – thus improving food safety.
“This research increases the set of listeria species monitored in food production environments,” said lead author Catharine R. Carlin, a doctoral student in food science. “Expanding the knowledge base to understand the diversity of listeria will save the commercial food world confusion and errors, as well as prevent contamination, explain false positives and thwart foodborne outbreaks.”
One of the novel species, L. immobilis, lacked motility, or the ability to move. Listeria move a lot. Among scientists, motility was thought to be common among listeria closely related to L. monocytogenes, a well-known foodborne pathogen – and used as a key test in listeria detection methods. This discovery effectively calls for a rewrite of the standard identification protocols issued by food safety regulators, Carlin said.
As listeria species are often found co-existing in environments that support the growth of L. monocytogenes, food facilities will monitor for all listeria species to verify their sanitation practices.
“This paper describes some unique characteristics of listeria species that are closely related to listeria monocytogenes, which will be important from an evolutionary perspective and from a practical standpoint for the food industry,” said co-author Martin Wiedmann, the professor in food safety and food science. “Likely, some tests will need to be re-evaluated.”
Understanding the different listeria species is key to comprehending their similarities. “This will help us to get better about identifying listeria monocytogenes,” Wiedmann said, “and not misidentifying it as something else.”
Bob Whitaker, Ph.D., chief science and technology officer for Produce Marketing Association (PMA), writes that because it provides inherently healthy, nutritious foods, the fresh produce industry is uniquely positioned to help solve the nation’s obesity epidemic. To do so, consumers must have confidence in the safety of the fresh fruits, vegetables, and nuts they eat and feed their families.
A green row celery field is watered and sprayed by irrigation equipment in the Salinas Valley, California USA
Following a large and deadly outbreak of foodborne illness linked to fresh spinach in 2006, the U.S. produce industry couldn’t wait for government or other direction. After finding significant knowledge gaps and a lack of data needed to build risk- and science-based produce safety programs, the industry created the Center for Produce Safety (CPS) in 2007.
CPS works to identify produce safety hazards, then funds research that develops that data as well as potential science-based solutions that the produce supply chain can use to manage those hazards. While two foodborne illness outbreaks in the first half of 2018 associated with leafy greens demonstrate the industry still has challenges to meet, CPS has grown into a unique public-private partnership that moves most of the research it funds from concept to real-world answers in about a year.
Each June, CPS hosts a symposium to report its latest research results to industry, policy makers, regulators, academia, and other produce safety stakeholders. Key learnings from the 2017 symposium have just been released on topics including water quality, cross-contamination, and prevention. A few highlights from those key learnings are summarized here, and for the full details, you can download the Key Learnings report from CPS’s website.
Know Your Water (we were doing that in 2002, long before youtube existed)
Irrigation water is a potentially significant contamination hazard for fresh produce while it is still in the field. While CPS research has revealed many learnings about agricultural water safety in its 10 years, many questions still remain. Meanwhile, the U.S. Food and Drug Administration (FDA)’s proposed Food Safety Modernization Act (FSMA) water testing requirements—which offers some challenges for producers in specific production regions—recently raised even more questions.
New CPS research illustrates the risks of irrigating with “tail water” from runoff collection ponds. With water becoming a precious resource in drought-stricken areas, the objective was to learn if tail water might be recovered and used for irrigation. We learned that differences among pond sites—for example, water sources, climate, ag management practices—can strongly influence the chemistry and microbiology of the water. Further, water pH can influence disinfection treatment strategies.
CPS research continues to investigate tools for irrigation water testing, looking specifically at sample volumes, and searching for better water quality indicators and indexing organisms including harnessing next-generation DNA sequencing. Following a CPS-organized colloquium on ag water testing in late 2017, FDA subsequently announced it would revisit FSMA’s ag water requirements, and postponed compliance.
Bottom line, CPS research demonstrates that growers must thoroughly understand their irrigation water before they can accurately assess cross-contamination risk. CPS’s findings clearly point to the need to take a systems approach, to understand and control the entire water system to help achieve produce safety. Long term, this may mean prioritizing research into ag water disinfection systems to better manage contamination hazards that can also operate at rates needed for field production. Cross-Contamination Can Happen across the Supply Chain
While conceptually and anecdotally the fresh produce industry knows that food safety is a supply chain responsibility, research is needed that documents the role of the entire supply chain to keep fresh produce clean and safe from field to fork. At the 2017 CPS Research Symposium, research reports were presented focusing on cross-contamination risks from the packinghouse to retail store display.
In the packinghouse, CPS-funded research found that wash systems can effectively control cross-contamination on fruit, when proper system practices are implemented. Post-wash, CPS research involving fresh-cut mangos also demonstrated that maintaining the cold chain is critical to controlling pathogen populations. Across the cantaloupe supply chain, CPS studies show food contact surfaces—for example, foam padding—are potential points of cross-contamination. See the full 2017 Key Learnings report for details, as these brief descriptions only scratch the surface of this research.
CPS studies clearly demonstrate that food safety is a supply chain responsibility—a message that must be internalized from growers and packers to transporters, storages, and retailers to commercial, institutional, and home kitchens. While translating this research into reality will present engineering and operational challenges, our new understanding of produce safety demands it. Verifying Preventive Controls
The produce industry must know that its preventive controls are in fact effective. That said, validation can be tricky. If validation research doesn’t mimic the real world, industry ends up fooling itself about whether its food safety processes work—and the human consequences are real.
Numerous scientists presented research at the 2017 CPS Research Symposium that validates various preventive controls, from heat treating poultry litter to pasteurizing pistachios to validating chlorine levels in wash water systems. Some researchers effectively used nonpathogenic bacteria as a surrogate in their validation studies, while another is working to develop an avirulent salmonella surrogate, and another. Wang used actual Escherichia coliO157:H7 (albeit in a laboratory).
Importantly, CPS research finds that the physiological state of a pathogen or surrogate, and pathogen growth conditions themselves, are critically important to validation studies. Meanwhile, suitable surrogates have been identified for some applications, the search continues for many others.
The research findings described here are just some of the real world-applicable results to emerge from CPS’s research program. To learn more, download the 2017 and other annual Key Learnings reports from the CPS website > Resources > Key Learnings page at www.centerforproducesafety.org.
We were doing these videos in the early 2000s, long before youtube.com existed, and weren’t quite sure what to do with them. But we had fun.
That research is being conducted at the Malheur Experiment Station by Joy Waite-Cusic, assistant professor of Food Safety Systems at Oregon State University.
Onions in the research plot have been irrigated with water inoculated with E. coli, some to extreme highs, Waite-Cusic said. The E. coli was applied during the last irrigation. In the sample of onions taken from the plots, the majority of them did not test positive for the bacteria, Waite-Cusic said.
In one of the latest samplings, onions were harvested one afternoon, put in bags and tested the next morning. Only 16 out of 150 onions tested positive for E. coli, Waite-Cusic said, and this from rows where the irrigation water had been artificially inoculated with 100,000 colony-forming units of generic E. coli for 100 milliliters of water.
“The soil does a good job of filtering,” experiment station superintendent Clint Shock said.
Testing showed that there was less E. coli as the water moved from the furrow or drop tape through the soil to the onion bulb.
To date, of the 10 previously known species of Listeria, only two are pathogenic to humans; Listeria monocytogenes is the main cause of Listeriosis, which causes illness in hundreds – and death in nearly 250 – people each year in the United States through infected deli meats, seafood and produce.
The new study, published online March 5 in the International Journal of Systematic and Evolutionary Microbiology, suggests that all five new species are benign.
The research was part of a larger study led by researchers at Colorado State University and Cornell to examine the distribution of such foodborne pathogens as Listeria, E. coli and Salmonella in agricultural and natural environments. Samples were taken from fields, soil, ponds and streams in New York, Colorado and Florida.
“Doing studies on natural diversity in produce fields helps us develop better and more precise tests to make food safer,” said Martin Wiedmann, Cornell professor of food science and the paper’s senior author.
New research finds the pathogen E. coli O157:H7 lives about 30 days in soils from California’s Salinas Valley — 10 days more than in the state’s Imperial Valley or Yuma, Ariz.
Lower salinity in Salinas irrigation water is the main cause of the difference, said Mark Ibekwe, a microbiologist with the U.S. Department of Agriculture’s Agricultural Research Service in Riverside, Calif.
The results were based on laboratory-tested soil samples. Field studies of E. coli are typically limited to nonpathogenic varieties.
Increasing salinity in Salinas water would not be realistic or beneficial for leafy greens growers there, Ibekwe said. Nevertheless, the research underscores the importance of keeping new pathogens from entering the fields.
“You don’t want to introduce another variable into the farming environment that will ultimately cause adverse effects on the crops and result in lower yield,” Ibekwe said. “Because of how salinity will react with other factors there, we are not suggesting that.
“What we’re saying is that because we know there’s a longer survival in the Salinas area, we should be very, very careful in introducing pathogens from manure, poorly composted materials or any source at all into the farming environment,” he said.
When is organic ever safer? It’s a production standard.
The story about Organic Italian olives is a timely reminder that if Clostridium botulinim, the bacteria that causes botulism, makes it as far as a jar packed with oil and not much oxygen, it can flourish.
"It’s the perfect environment for botulinum to grow," says Eric Johnson, a professor of microbiology at the University of Wisconsin-Madison.
Johnson said the case reminded him of an outbreak in the 1980s, which was caused by chopped garlic packed in oil. "Garlic is from the soil, so it has spores of botulinum in it.” The oil floats on top of the jar and seals out air, leaving water to collect at the bottom, where it acts like a Petri dish for botulism.
After the outbreak in chopped garlic, the FDA told garlic processors add phosphoric acid. The higher acid level thwarts bacterial growth. Another strategy used by big commercial processors is a "bot cook," which involves cooking foods at high temperatures under pressure to wipe out spores.
C. Claiborne Ray of the New York Times asks, when a virulent strain of E. coli from manure contaminates produce, how do farmers clean the soil in their fields?
“Farmers commonly rely on environmental conditions over time to inactivate the pathogenic E. coli,” said Randy W. Worobo, associate professor of food microbiology at Cornell University.
The disease-causing bacteria may come from the feces of deer, sheep, cattle or other warm-blooded mammals, including humans, Dr. Worobo said. Generic E. coli are normal inhabitants of the lower intestine. Pathogenic forms have acquired virulence genes that produce substances like enterotoxins, which cause intestinal illness, and adhesins, which allow for binding to intestinal cells in the hosts.
“It is not a common contaminant of fecal material,” Dr. Worobo said, “but if the host becomes infected with a pathogenic E. coli strain, it can cause illness in the host and be shed in the fecal material along with generic nonpathogenic E. coli.”
Over time, the pathogenic E. coli are inactivated by exposure to the sun; desiccation; poor nutrient conditions; temperature extremes; and competing soil microbes. To hasten the die-off, farmers may turn the soil, evenly distributing the microbes and making sure they are exposed to these conditions.
To keep the microbes out of land used for food production, Dr. Worobo said, farmers rely on animal barriers and specific practices for handling compost and manure.
I keep meaning to start my seedlings for the garden, which I should have done weeks ago. But it has been unseasonably cold and, after four years in Kansas, I’m liking the warmer weather. So bring it on. ‘Tis the season. And maybe I’ll get motivated.
Eurosurveillance reports today that three cases of Legionnaires’ disease caused by Legionella longbeachae Sg 1 associated with potting compost have been reported in Scotland between 2008 and 2009. The exact method of transmission is still not fully understood as Legionnaires’ disease is thought to be acquired by droplet inhalation. The linked cases associated with compost exposure call for an introduction of compost labelling, as is already in place in other countries where L. longbeachae outbreaks have been reported.
It has been reported that various Legionella strains have been isolated from different types of potting soils including peat. In Australia, where cases and outbreaks of L. longbeachae have been reported, the standards for composts, soil conditioners and mulches provide clear guidance to commercial producers of compost on how to process organic materials into compost in a safe and effective way. These standards also include requirements for labelling bags and promoting safe and healthy gardening practices. Public health advice includes the risk of Legionnaires’ disease following exposure to compost or potting soil.
The cases reported here emphasize the need for a voluntary use in the UK of an industry-agreed warning label for potting soil, as the risk of Legionnaires’ disease associated with compost is now clearly identified.
When a bucket in one of his five bathrooms is full, he empties it in the compost pile in his backyard in rural Pennsylvania. Eventually he takes the resulting soil and spreads it over his vegetable garden as fertilizer.
"It’s an alternative sanitation system," says Jenkins, "where there is no waste." His 255-page Humanure Handbook: A Guide to Composting Human Manure is in its third edition and has been translated into five languages, but it has only recently begun to catch on. His message? Human manure, when properly managed, is odorless. His audience? Ecologically committed city dwellers who are looking to do more for the earth than just sort their trash or ride a bike to work.
Night soil is rumored to be used in the production of fresh veggies , especially for upscale restaurants, in many large cities.
I’ll stick with riding my bike to work, and thank engineers for sewage treatment.
The person who died is believed to have contracted the illness overseas, while four others in Canterbury are thought to have become infected since September through contact with potting mix.
Legionnaires’ Disease is a pneumonia caused by Legionella bacteria that are commonly found in water and soils, including potting mix and compost.
Dr Ramon Pink, Medical Officer of Health for Canterbury, said recommendations for handling and warnings were printed on most bags of potting mix.
"It is very important to take care to avoid inhaling the dust when opening and handling the potting mix. Bags should be carefully opened in a well-ventilated area, preferably outdoors, and away from the face."