Browsing by Author "Weller, Daniel Lowell"

Now showing 1 - 3 of 3
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    Evaluating Risks and Mitigation Measures for Foodborne Pathogens on Harvest Bags
    Ayuk Etaka, Cyril Nsom (Virginia Tech, 2024-06-07)
    Tree fruit growers need information on pathogen dynamics following harvest bags contamination to determine effective sanitation interventions for decontaminating these surfaces. Therefore, the objectives of this research were (i) to determine the survival of generic E. coli, Salmonella, and L. monocytogenes on different harvest bag materials (ii) to quantify the transfer of generic E. coli, Salmonella, and L. monocytogenes from different harvest bag materials to fresh unwaxed apples and (iii) to determine the efficacy of different sanitizers for decontaminating different harvest bag materials. For Obj. 1, harvest bag materials were inoculated with rifampicin-resistant (80ppm; R) E. coli (TVS353) or Salmonella strain cocktail or L. monocytogenes strain cocktail. All surfaces were air-dried and held at 22 °C and either 30 or 80% relative humidity for 90 d (E. coli), or at 22 °C and 55% relative humidity (RH) for 21 d (L. monocytogenes and Salmonella). For Obj. 2, harvest bag materials were inoculated with E. coli (TVS353) or Salmonella strain cocktail or L. monocytogenes strain cocktail and air dried as previously mentioned. For E. coli trials, bacterial transfer to unwaxed 'Red Delicious' apples was assessed for 2 inoculum dry times (1 or 4 h), 2 contact times (5 or 25 minutes), and 2 pressure scenarios (0.0 or 0.1kg/cm2). For Salmonella or L. monocytogenes trials, transfer was assessed for 1 inoculum dry time (1 h), and 1 contact time (5 minutes). For Obj. 3, coupons were inoculated with L. monocytogenes or Salmonella cocktails and were air-dried. Following inoculation, coupons were exposed to different sanitizer treatments: chlorine, peroxyacetic acid (PAA), isopropyl alcohol with quaternary ammonium compounds (IPAQuats), steam, and water. Regression models were fitted, and Tukey's post hoc test was performed at P<0.05. E. coli exhibited survival for extended durations at 30 % than at 80% RH. In addition, E. coli survived at higher concentrations on canvas surfaces than on cordura and nylon surfaces. Generally, E. coli survived for more than 21 d across all surfaces and exhibited a triphasic die-off pattern. Similarly, L. monocytogenes and Salmonella exhibited die-off in phases with an initial rapid die-off followed by more gradual die-off rates up to 21 d. Canvas materials also promoted better L. monocytogenes and Salmonella survival than cordura surfaces. Contact time did not significantly impact the transfer of E. coli from harvest bag surfaces to apples (P=0.55). However, pressure, inoculum dry time and material type significantly impacted the transfer of E. coli to 'Red Delicious' apples (P≤0.03). The transfer rates of Salmonella did not differ between canvas and cordura surfaces (P=0.46). However, cordura transferred L. monocytogenes at significantly higher rates than canvas surfaces (P<0.001). Of the sanitizer treatments that were used on L. monocytogenes or Salmonella inoculated surfaces, IPAQuats was the most effective achieving over 4.5 log CFU/coupon reduction on both canvas and cordura surfaces. Our studies demonstrated that bacteria could survive for over 21 d under different conditions and could transfer from contaminated harvest bag surfaces to apples underlining the importance of cleaning and sanitizing harvest bags with sanitizers like IPAQuats.
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    Factors Influencing The Ecology and Epidemiology of Microbial Indicators and Foodborne Pathogens In Surface Waters and Development of Risk Mitigations
    Murphy, Claire Margaret (Virginia Tech, 2023-04-25)
    Foodborne outbreaks have continued to be associated with produce contamination originating from on-farm sources, such as soil or agricultural water. Additionally, the heterogeneity of the pre-harvest environment complicates the development of universal strategies for managing produce safety risks. Understanding the ecology and epidemiology of foodborne pathogens and fecal indicator bacteria (FIB) by growing regions, sample types, scale of analysis, and detection method is essential for developing targeted mitigation strategies. This dissertation utilized quantitative research methods and statistical modeling to examine the impact of sampling method, spatial, temporal, meteorological, and physicochemical factors on pathogen prevalence and FIB levels. Key findings highlight that the drivers of prevalence differ between pathogens and were influenced by sample type, scale, and region.. The variations in associations emphasize that risk varies by space and time. Therefore, results support regional and scale-dependent food safety standards and guidance documents for controlling hazards to minimize risk. Additionally, the method used for pathogen detection influences prevalence highlighting the need for standard methods since methodological differences confound comparisons across studies. Furthermore, since agricultural water quality is an important food safety priority, this dissertation aimed to determine the efficacy of chemical antimicrobial sanitizers against Salmonella in pre-harvest agricultural water. Results demonstrated that certain sanitizer treatments and conditions can significantly reduce Salmonella populations in preharvest agricultural water sources and thus may serve as a risk reduction option when used correctly.
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    Trends in the Incidence of Culture-Confirmed Human Salmonellosis Reported in Virginia During 2012-2022
    Yates, Caroline Renea (Virginia Tech, 2024-08-20)
    Recognizing that Salmonella is a leading cause of bacterial foodborne illness in the United States (US), the US government established disease reduction goals for salmonellosis incidence. Surveillance data are used to monitor progress toward these goals, and to characterize salmonellosis epidemiology (e.g., specific serotype causing disease, model national and regional trends in incidence). This study used data from 11,411 culture-confirmed salmonellosis cases among Virginia residents reported to Virginia Department of Health during 2012-2022 to characterize salmonellosis epidemiology in Virginia using incidence rate ratios (IRRs) and a negative binomial Bayesian splines model. Trends were modelled separately for salmonellosis overall and for individual sub-types at the state level. State-level modelled incidence ranged between 10.9-12.9 (per 100,000 people); the lowest and highest reported incidence occurred in 2020 and 2019, respectively. During the COVID-19 pandemic, incidence appears to have decreased; incidence has not returned to pre-pandemic levels. According to the splines model, there was a substantial decrease in state-level culture-confirmed salmonellosis incidence in 2021 compared to 2018, which is consistent with trends nationally. Of the187 total Salmonella serotypes reported in Virginia during 2012-2022, 64% of culture-confirmed cases were attributable to six serotypes: Typhimurium/I 4,[5],12:i:- (20%), Enteritidis (18%), Newport (11%), and Javiana (8%), Bareilly (4%), and Braenderup (4%). The incidence of illnesses to specific attributable serotypes appeared to change between 2012 and 2022 with some serotypes decreasing in incidence (e.g., the incidence of S. Typhimurium/I 4,[5],12:i:-) and others increasing (e.g., S. Braenderup). Opposing serotype-specific trends may be contributing to the apparent stability in overall salmonellosis incidence in Virginia during 2012 through 2022. Some serotypes had an overall high reported incidence across all months, while others had distinct peaks in incidence during summer months (June-August). Similar to national trends, children <4 years old had the highest reported incidence of all age groups across all serotypes, indicating that reducing incidence in this population should be prioritized for achieving the desired reduction in salmonellosis incidence. Analyses using whole genome sequencing data indicated that within each of the 6 most common serotypes, most isolates represented 1-3 subtypes. Overall, our analyses indicate that trends in reported culture-confirmed salmonellosis incidence in Virginia are largely consistent with national trends and support the use of analyses of salmonellosis incidence at the subtype level to inform intervention efforts to address incidence of infections caused by specific serotypes.