Sophia Kathariou

The US Food and Drug Administration (FDA) has recognized Salmonella as one of the main causes of food-borne outbreaks associated with shell eggs and egg products. The FDA estimates that 79,000 cases of foodborne illness and 30 deaths each year are caused by eating eggs contaminated with Salmonella (USFDA, 2016a). Over 60% of salmonellosis cases due to contaminated eggs reported by the Centers for Disease Control and Prevention (CDC) have been attributed to Salmonella Enteritidis (SE) (Cao et al., 2009; Vaninni et al., 2009; CDC, 2013). Even though SE remains a leading serovar for egg-associated salmonellosis in the United States, several additional serovars including Typhimurium and Heidelberg also make major contributions (Chousalkar et al., 2018); in the past year a major outbreak involving serovar Braenderup caused illnesses in 10 states and prompted a massive recall of eggs (CDC, 2018). Besides the obvious food safety and public health implications, massive recalls of shell eggs due to frequent outbreaks (CDC, 2018; Food Safety News, 2016; USFDA, 2016b; USFDA, 2010) are accompanied by substantial economic losses to the industry. To reduce the incidence of such outbreaks, the FDA implemented a regulation which requires shell egg producers to take measures to prevent SE contamination of eggs (USFDA, 2009). Washing and disinfecting shell eggs using chemical sanitizers is a common practice to reduce organic load and inactivate pathogens from the exterior of the eggs. These chemical sanitizers may have undesirable consequences such as chemical residues, degradation of the cuticle, development of bacterial resistance, and adverse environmental impacts (Hutchison et al., 2003; Hutchison et al., 2004; Cao et al., 2009; Gole et al., 2014).| Developing novel methods that are less detrimental to the quality of eggs and to the environment, but are effective on pathogen inactivation, is essential. These novel methods should significantly reduce microbial load on eggs and provide protection from cross-contamination without raising safety concerns or causing changes in the integrity, cuticle coverage, and porosity of the egg shell. Recently, increased attention has been paid on novel pathogen inactivation strategies employing plasma, also referred to as the fourth state of matter. Plasma is ionized gas consisting of charged species, excited atoms and molecules, and high-energy photons (Niemira, 2012; Brandenburg et al., 2018; Pankaj et al., 2018; Keener, 2018). Plasma-activated water (PAW) is a novel sanitizer that is generated by exposing water to plasma in the presence of air at atmospheric pressure. The reactive nitrogen (RNS) and reactive oxygen species (ROS) in PAW have been shown to inactivate microbes on a variety of surfaces such as fresh produce (Ma et al., 2015; Xu et al., 2016, Joshi et al., 2018). However, no published data are available on the use and effectiveness of plasma-activated water (PAW) for egg washing. The application of this novel sanitizing procedure is particularly attractive because PAW is safe and environmentally friendly, does not leave potentially harmful residues, and may not adversely impact the outer shell integrity of eggs. In this proposal we will evaluate the use of PAW as a more effective and a less damaging alternative to the conventional methods for egg washing. We hypothesize that the reactive species in PAW will substantially inactivate Salmonella on the shell egg, while not being detrimental to the cuticle layer and the structural integrity of shell egg. Metastable reactive nitrogen and reactive oxygen species in PAW will provide antimicrobial effect without leaving any chemical residue. Keeping the cuticle layer intact will provide protection from bacterial migration through the pores in egg shells during storage and transport and thus increase the shelf-life of eggs. In the long term, PAW can serve as an environmentally friendly and effective sanitizer which can be prepared on site. Our specific objectives are to: 1) Assess the efficacy of PAW for inactivation of a pan

This project will assess the use of visible/natural light-activated carbon nanomaterials, specifically carbon ????????????????quantum??????????????? dots or carbon dots (????????????????CDots???????????????), for the highly efficient inactivation of persistent bacterial pathogens on model food contact surfaces under visible/natural light. The specific aims include: (1) To evaluate three selected CDots platforms for inactivating the persistent foodborne pathogens Listeria monocytogenes and Salmonella enterica, established on model food contact surfaces including stainless steel, polyvinyl chloride (PVC), and polyethylene (PE), and (2) Assess the efficacy of CDots for inactivation of these pathogens in mixed-species biofilms, and in the presence of organic material, on stainless steel, PVC and PE surfaces. The Kathariou laboratory will contribute to this project by culturing the bacterial pathogens in planktonic cultures and on biofilms established on different model food contact surfaces, i.e. stainless steel, PVC, and PE. Biofilms will be established and quantified following methods already established in the Kathariou laboratory. Pathogen inactivation will be monitored quantitatively via culture-based enumerations, live-dead staining and quantitative real-time PCR. The impact of CDots concentration, contact time, temperature, presence of other microbes (e.g. Pseudomonas spp., lactic acid bacteria, non-pathogenic Listeria spp.) in mixed-species biofilms, and organic material will be determined.

Listeria monocytogenes (LM) has been repeatedly linked to outbreaks involving fresh vegetables and fruit. In 2014, whole apples (Granny Smith and Gala) were for the first time implicated in a listeriosis outbreak involving both caramel and green apples. LM exhibits no or minimal growth on the surface of whole, intact apples, but can survive for impressive lengths of time and grow inside apples despite the low pH. The various attributes mediating LM survival on whole apples remain poorly understood, with a dearth of data on potential strain-specific differences in survival. Hence, the fate of LM on fresh apples as potentially impacted by both LM inoculum size and physiological state, and the variety of apple remain to be further characterized. Such information is critically needed to identify the risks posed by LM contamination of apples, and to adequately design and validate LM inactivation strategies. To address these important knowledge gaps, we will pursue the following objectives: Objective 1. Determine the fate of LM on apples of three different varieties, from three major apple-producing regions, under two different simulated commercial storage conditions. Objective 2. Characterize the potential impact of inoculum state on the fate of LM fate on apples. Objective 3. Characterize the relative strain fitness of various LM strains on apples. Objective 4. Assess the impact of waxing on the fate of LM on apples. The findings will provide data needed to guide the apple industry on conditions and processes that can minimize the food safety risk from LM in the apple supply.

Hurricane Florence made landfall on the North Carolina coast on September 14, 2018, and in the subsequent days several North Carolina communities received up to 35 inches of rain. Inland rivers did not crest until a week post-landfall, but the extent of cresting was unprecedented. The heavy rainfall and flooding can massively impact water quality and safety in flooded areas, especially via runoff from agricultural and industrial operations. We propose to analyze floodwater samples collected by the hydrology and civil engineering teams led by Ryan Emanuel and Angela Harris at North Carolina State University for prevalence of the human foodborne pathogens Salmonella, Listeria and Campylobacter. These pathogens will be also characterized for species designations and, in the case of Listeria, for serotypes. The data will complement those from the other team members who will monitor source-specific fecal indicators, Escherichia coli, and chemical contaminants in these samples.

Due to a number of food safety concerns with "low moisture foods" (LMF), there has been global recognition of the need to more rigorously consider and manage the microbiological hazards associated with these products. Various serotypes of Salmonella enterica have been the main pathogens involved in outbreaks due to LMF, but currently there are also concerns about the survival of Listeria monocytogenes in LMF such as dried fruits and tree nuts. Our hypothesis is that there will be changes in gene expression profiles of Salmonella and L. monocytogenes over time with storage in LMF, and that these changes will lead to changes in stress tolerance and virulence of the organisms. Such information will inform strategies to control and inactivate pathogens in LMF.