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ARS Study Aims to Enhance Traceability During Foodborne Outbreak Investigations

Findings from ARS scientists at the U.S. Meat Animal Research Center (USMARC) in Clay Center, Nebraska, could help enhance the abilities of regulatory agencies to trace Escherichia coli O157:H7 bacteria back to their source during foodborne outbreaks by better identifying strains through their DNA. The team of scientists analyzed samples collected from the Center's closed cattle feedlot from 1997 to 2019 and studied the genomes of the various E. coli O157:H7 strains and subtypes. They identified four unique clades within the specific bacteria population they studied. (Clades are a group of organisms that share specific characteristics.) Even though all clades shared a portion of their genetic composition, each clade also contained unique elements called mobile elements that may or may not be shared. Interpretation of these mobile elements' role during an outbreak investigation could help identify relatedness between human and environmental isolates of the E. coli bacteria. Results from this and future studies will continue to build information for rapid, more accurate traceback during outbreak investigations.

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Low-temperature electron micrograph of a cluster of oblong-shaped E. coli bacteria.

Fall Seasonal Effects Connected to E. coli O157:H7 Outbreaks in Bagged Romaine

ARS scientists have begun to uncover details underlying a pattern of seasonal E. coli O157:H7 outbreaks linked to bagged romaine lettuce. That E. coli O157:H7 infection outbreaks connected to romaine are more frequently associated with lettuce commercially grown and harvested at the end of the growing seasons in California and Arizona has been recognized for several years. Although contamination of lettuce products is rare, between 1998 and 2019, 36 outbreaks that traced back to lettuce were recorded by the Centers for Disease Control and Prevention. Most of these outbreaks involved romaine lettuce harvested in the fall on the California Central Coast such as in Salinas, and in late winter in Southern California and Arizona. These two states are the major lettuce growing areas in the United States with farm production valued at nearly $2.7 billion in 2021. One of the most significant findings of this study is that E. coli survived on average 5.6 times better in cold-stored packaged romaine harvested in the fall than on the same varieties harvested in late spring. They also found that among romaine varieties with longer and shorter shelf life in this study, the deterioration rate of the variety with long shelf life was significantly greater when harvested in the fall than in spring.

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ARS scientists have begun to unravel details that may underly a pattern of fall E. coli O157:H7 outbreaks linked to bagged romaine lettuce.

Scientist Evaluates Dietary Food Patterns for Healthy Adults Eating Dairy-Free Vegetarian or Vegan Diets

After assessing the current Healthy Vegetarian Dietary Pattern of the Dietary Guidelines for Americans (DGA), an ARS scientist has found it can be adapted for a dairy-free vegetarian or vegan diet while still meeting nutrient recommendations for non-pregnant and non-lactating healthy adults. The 2020-2025 DGA edition, issued by USDA and Health and Human Services, provides recommendations on healthy dietary patterns for all healthy individuals and delivers a customizable framework of healthy options that can be adapted for personal or cultural preferences. Still, it has been unclear if the Healthy Vegetarian Dietary Pattern can be adapted for an entirely plant-based diet without potential nutrition concerns. The study, completed by nutritionist Julie Hess at the ARS Grand Forks Human Nutrition Research Center, followed similar food pattern modeling procedures as the DGA Scientific Advisory Committee, to model an alternate egg-free and dairy-free vegetarian and a vegan dietary pattern that meets most nutrient recommendations for healthy adults [non-pregnant and non-lactating] consuming diets containing 1800, 2000, 2200 or 2400 calories. In the two models, the dairy food group was replaced with dairy-free nutrient-dense options included in the 2020-2025 DGA, which are fortified soy milk and soy yogurt. For the vegan model, eggs servings were replaced with equal proportions of vegetarian protein foods, including soy products, nuts and seeds, and beans, peas and lentils. The only nutrient that was below recommended levels in the dairy-free vegetarian and vegan diets was zinc for adult males. 

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Fruits and vegetables are essential parts of healthy diets for Americans in the Dietary Guidelines for Americans.

Diets High in Fiber Associated with Less Antibiotic Resistance in Gut Bacteria

Healthy adults who eat a diverse diet with at least 8-10 grams of soluble fiber a day have fewer antibiotic-resistant microbes in their gut, according to a study published by ARS scientists and their colleagues. These results lead directly to the idea that modifying the diet has the potential to be a new weapon in the fight against antimicrobial resistance, and they aren't talking about eating an exotic diet either, but a diverse diet, adequate in fiber, that some Americans already eat. The researchers found regularly eating a diet with higher levels of fiber and lower levels of protein, especially from beef and pork, was significantly correlated with lower levels of antimicrobial resistance genes (ARG) among their gut microbes. Those with the lowest levels of ARG in their gut microbiomes also had a greater abundance of strict anaerobic microbes, which are bacteria that do not thrive when oxygen is present and are a hallmark of a healthy gut with low inflammation. Bacterial species in the family Clostridiaceae were the most numerous anaerobes found.

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Healthy adults eating a diverse diet with at least 8-10 grams of soluble fiber a day have fewer antibiotic-resistant microbes in their guts.

Boosting the Nutritional Bounty of Carrots and Onions

A team coordinated by Philipp Simon, research leader of the ARS Vegetable Crops Research Unit in Madison, Wisconsin, is leveraging the latest genomics tools and techniques to identify specific gene or gene regions that can increase the levels of beta carotene, anthocyanin and other phytonutrients in carrots and onions. Onions and garlic are also rich in phytonutrients such as thiosulfinates and fructan. Thiosulfinates give allium species their pungent aroma and flavor. Cutting or crushing onion and garlic bulbs releases the thiosulfinates and exposure to air causes their breakdown into secondary compounds called organosulfates. There is some evidence dietary sources of organosulfates help minimize the risk of heart disease, stroke and some forms of cancer. Fructan, a carbohydrate-storing polymer, is also of interest for its health-promoting potential in the human body (though some individuals are sensitive to it and may experience bloating among other symptoms). Onions are second only to wheat as a leading source of fructan, which the body cannot digest but which helps nourish populations of beneficial intestinal bacteria. 

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Carrots that reflect almost all colors of the rainbow.

Distinguished Nutrition Scientist Alice H. Lichtenstein Honored as 2022 ARS W.O. Atwater Memorial Lecturer

"Nutrition Information/MisinformationWho's Right? Who Gets to Decide?" was the title of the 2022 Agricultural Research Service W.O. Atwater Memorial Lecture, presented by nutrition scientist Alice H. Lichtenstein on June 15 at Nutrition 2022, the annual meeting of the American Society for Nutrition. "Food and nutrition information comes at the public from many sources and in many forms. Frequent discordance within this plethora of information has undermined people's trust in the scientific community and this in turn has impeded public health efforts to improve diet quality. Our challenge is to come together to engage in productive discussions on how best to communicate the most accurate and timely food and nutrition information available, that will ultimately lead to improved overall diet quality for all," Lichtenstein said in her Lecture. Lichtenstein's laboratory was among the first to document the detrimental effects of partially hydrogenated (trans) fat on blood lipids. This work helped lay the foundation for the labeling and subsequent banning of partially hydrogenated fat by the U.S. Food and Drug Administration. She currently is the Stanley N. Gershoff Professor of Nutrition Science and Policy at the Friedman School, at Tufts University. She also holds appointments as Professor of Medicine at Tufts Medical Center and Director of the Cardiovascular Nutrition Laboratory and Senior Scientist at the Jean Mayer USDA Human Nutrition Research Center on Aging.

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Alice H. Lichtenstein is the 2022 W.O. Atwater Memorial Lecturer.

Obesity and Metabolism Research Unit Physiologist Named to ARS Science Hall of Fame

Lindsay H. Allen, a research physiologist with the Obesity and Metabolism Research Unit at the ARS Western Human Nutrition Research Center in Davis, California, has been inducted into the ARS Hall of Fame. Allen was honored for her outstanding and sustained contributions leading to a better understanding of micronutrient deficiencies, particularly vitamin B12, which is only available from animal food sources. In some instances, Allen's findings reversed long-held scientific dogma. In the case of vitamin B12, for example, her research showed that a deficiency of this micronutrient isn't solely limited to strict vegetarians, but is also widespread in men, women and children who consume inadequate amounts of animal-source foods such as fish, meat, poultry milk and eggs. This deficiency also extends to low-income population groups. Allen's research also showed that consumers could be deficient in a suite of micronutrients because of poor dietary quality. Based on those findings, she helped to devise micronutrient supplement formulations for infants and pregnant women that were adopted by the United Nations Children's Fund (UNICEF) , which are used globally with notable beneficial impacts on maternal and infant health.

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Lindsay H. Allen.