Location: Produce Safety and Microbiology Research
2022 Annual Report
Accomplishments
1. Seasonality of E. coli O157:H7 survival and microbiome in cold-stored fresh-cut lettuce. Outbreaks of Escherichia coli O157:H7 (EcO157) linked to romaine lettuce grown on the Central West Coast of California are more prevalent in the fall, and the cause of these seasonal trends is unknown. These outbreaks have greatly impacted the California lettuce industry, which is valued at over $2 billion annually. ARS researchers in Albany and Salinas, California, in collaboration with scientists at the Food and Drug Administration, discovered that EcO157 survives better on cold-stored fresh-cut romaine harvested in the fall than in the spring, and that the lettuce microbiome also has seasonality. This points to seasonal properties of lettuce and/or its microbiome, or interaction thereof, as factors in the seasonal behavior of EcO157 in this commodity. The results open a new branch of inquiry for the identification of plant traits and microbiome components that may be used in plant breeding or manipulated in order to suppress enhanced EcO157 survival in fall fresh-cut romaine. These findings led to a scientific publication, a press release picked up by numerous national and international outlets including Associated Press, and consultations by, and talks to, the leafy greens industry.
2. Virulence gene patterns in Listeria monocytogenes strains native to Central California coastal waters. Over half of the fatalities resulting from bacterial foodborne illness are caused by Listeria monocytogenes and increasing numbers of outbreaks and product recalls are due to contaminated produce. In a collaboration between ARS researchers in Albany, California, and Food and Drug Administration (FDA) researchers in College Park, Maryland, the genomes of over 1,200 isolates of L. monocytogenes isolated from surface waters along the Central California coastal region were sequenced and characterized. All the isolates contained core L. monocytogenes virulence genes in Listeria Pathogenicity Island 1 (LIPI-1), which allows the strains to cause listeriosis. Pathogenicity islands LIPI-3 and LIPI-4, which are found in strains that cause neurological illness and higher mortality, were intact in 73% and 63%, respectively, of the isolates. These findings have led to continued collaborations between ARS and FDA to define risk factors for environmental strains of L. monocytogenes. This information is needed for risk assessments and modelers of foodborne pathogens in the vicinity of agricultural production.
3. Identification of Salmonella serovars present in Central California coast surface waters. Salmonella is one of the leading causes of foodborne illness world-wide and produce-related outbreaks have been sourced to tomatoes, cucumbers, peppers, onions, and leafy greens. ARS researchers in Albany, California, undertook a five-year survey of surface waters along the Central California coastal agricultural region and determined a 56% prevalence of Salmonella in lakes, ponds, streams, and rivers. Sixteen of the 24 most common serovars detected in the region are among the Top 20 serovars reported to cause the most human salmonellosis in the United States, and some serovars had location and seasonal bias. These findings have resulted in multiple collaborations with government and academic institutions to describe types of Salmonella present in water and in the environment. This information is needed for risk assessments and modelers of foodborne pathogens in the vicinity of agricultural production.
4. Identification of novel molecular targets for detection of hypervirulent STEC strains. Shiga toxin producing Escherichia coli (STEC) is estimated to cause 2.8 million cases of acute illnesses globally each year. Strains of STEC vary greatly in pathogenicity; thus, genetic markers of hyper-virulent strains are critically needed for rapid detection and risk assessment. ARS researchers in Albany, California, systematically examined over 300 E. coli virulence genes in a large number of STEC strains isolated from various environmental samples collected in a major leafy greens production region in California and identified a list of genes that are important for STEC pathogenesis. New molecular targets were discovered to assess virulence potential of STEC isolates. The study provided additional molecular targets to develop a systematic approach for STEC detection, which improves the sensitivity of detection and the accuracy in developing risk assessment models.
5. A rapid and sensitive method to remove assay inhibitors in elutes from produce. Fruit and vegetable-related human norovirus outbreaks are becoming prevalent worldwide. Detection of human noroviruses in food samples has been a challenge due to the assay inhibitors present in washings from fruits and vegetables. ARS researchers in Albany, California, developed an easy method to remove these inhibitors using bentonite-coated activated carbon. The method was applied for detection of human noroviruses as well as surrogates spiked onto fruits and vegetables. The average detection limits of these viruses were reduced by approximately 10 to 100 fold. The method developed is a rapid, sensitive method to remove inhibitors and has the potential to be used to detect low numbers of food-borne viruses in produce.
Review Publications
Leonard, S., Simko, I., Mammel, M., Richter, T., Brandl, M. 2021. Seasonality, shelf life and storage atmosphere are main drivers of the microbiome and E. coli O157:H7 colonization of post-harvest lettuce cultivated in a major production area in California. Environmental Microbiome. 16. Article 25. https://doi.org/10.1186/s40793-021-00393-y.
Gorski, L.A., Cooley, M.B., Oryang, D., Carychao, D.K., Nguyen, K., Luo, Y., Weinstein, L., Brown, E., Allard, M., Mandrell, R., Chen, Y. 2022. Prevalence and clonal diversity of over 1,200 Listeria monocytogenes isolates collected from public access waters near produce production areas on the central California coast during 2011 to 2016. Applied and Environmental Microbiology. 88(8). Article e00357.22. https://doi.org/10.1128/aem.00357-22.
Carter, M.Q., Laniohan, N.S., Lo, C., Chain, P.G. 2022. Comparative genomics applied to systematically assess pathogenicity potential in Shiga toxin-producing Escherichia coli O145:H28. Microorganisms. 10(5). Article 866. https://doi.org/10.3390/microorganisms10050866.
Wang, N., Pan, G., Guan, S., Rong, S., Wang, D., Gao, Z., Tian, P., Li, Q. 2022. A broad-range disposable electrochemical biosensor based on screen-printed carbon electrodes for detection of human noroviruses. Frontiers in Bioengineering and Biotechnology. 10. Article 845660. https://doi.org/10.3389/fbioe.2022.845660.
Zhang, Z., Liu, D., Zhang, Z., Tian, P., Li, S., Wu, Q., Wang, D., Tian, Z. 2021. Complete genome sequence of GII.9 norovirus. Archives of Virology. 167:249-253. https://doi.org/10.1007/s00705-021-05257-x.
Gorski, L.A., Liang, A.S., Walker, S., Carychao, D.K., Aviles Noriega, A., Mandrell, R., Cooley, M.B. 2022. Salmonella enterica serovar diversity, distribution, and prevalence in public-access waters from a central California coastal leafy green-growing region from 2011 to 2016. Applied and Environmental Microbiology. 88(3). Article e01834-21. https://doi.org/10.1128/aem.01834-21.
George, A.S., Brandl, M. 2021. Plant bioactive compounds as an intrinsic and sustainable tool to enhance the microbial safety of crops. Microorganisms. 9(12). Article 2485. https://doi.org/10.3390/microorganisms9122485.
