The purpose of this study was to induce an oxidative-stress adaptation in Listeria monocytogenes Bug600 (serotype 1/2a) and F1057 (serotype 4b) by pre-exposing to sublethal H2O2 and alkali-stress either singly or sequentially. Our findings show that the sequential pre-exposure of cells to pH 9 for 30 min treatment followed by 50 ppm H2O2 for 30 min at 37°C yielded the highest oxidative-stress resistant phenotypes of L. monocytogenes Bug600 and F1057. The sublethal H2O2 and sublethal alkali-stress induced oxidative-stress adaptations were completely reversible within 60 min at 37°C in the absence of such sublethal stress. However, the oxidative-stress adaptation induced at 37°C was stable at 4°C over a 24 h test period in both L. monocytogenes Bug600 and F1057. Future studies will focus on the potential cross-resistance of oxidative-stress adapted L. monocytogenes serotypes 1/2a and 4b to commonly used disinfectants and GRAS antimicrobials.

No description available.

Stormwater runoff is a major environmental concern, particularly in urban environments. Trends in managing stormwater have evolved (and continue to evolve) from a quantity only approach into a sustainable approach, which integrates quantity, quality, the environment, and aesthetics. Best management practices (BMPs) and Low Impact Development (LID) are two well-documented techniques capable of managing to sustainable standards. There are a number of stormwater models available to design professionals today. However, there are few which integrate site-scale BMP/LID analysis in a simplified fashion. The purpose of this study is to determine if there is a demand in the design profession for simplified stormwater modeling tools to help designers make informed decisions about integrating BMP/LID strategies into site plans. A Web-based questionnaire was administered to a group of design professionals to determine their knowledge of BMPs and their technological needs and preferences in meeting stormwater goals and requirements.

Listeria monocytogenes is a deadly, Gram-positive foodborne pathogen that is ubiquitous in the environment. The bacterium expresses a number of virulence and stress adaptation proteins that support its pathogenic capabilities. Two-dimensional gel electrophoresis (2-DE) was used to map L. monocytogenes surface proteins, which play a central role in virulence, and to examine protein expression by L. monocytogenes grown on ready-to-eat meat, an important source of Listeria infections. A novel method for solubilization of surface proteins from L. monocytogenes for 2-DE was developed. Additionally, the unique proteome expressed by L. monocytogenes grown on a meat matrix was uncovered. The developed solubilization method will facilitate efforts to identify and routinely compare surface proteins of Listeria by 2-DE. Furthermore, the 2-DE database of proteins expressed by L. monocytogenes grown on a meat matrix will allow further understanding of the interactions of Listeria with its food environment that influence its ability to cause disease.

Post process application of antimicrobials is one method to control recontamination of Listeria monocytogenes on cooked RTE meat products. This study evaluated the antilisterial effect of externally applied solutions of nisin, buffered solution of sodium citrate supplemented with sodium diacetate (SCSD) and a combined solution of the two antimicrobials on commercial beef frankfurters formulated without antimicrobials. Autoclaved frankfurters were inoculated (104 -105 CFU/g), dipped (5 min, 25 ± 2°C) in treatments consisting of 2000; 4000;or 6000 IU/ml nisin, and buffered solutions of 2.5; 3.0; or 3.5% SCSD (Study I), and 6000 IU/ml nisin followed by 3.5% SCSD, or 3.5% SCSD followed by 6000 IU/ml nisin, or a combined solution containing both 6000 IU/ml nisin and 3.5% SCSD(Study II). Treated hot dogs were vacuum packaged and stored at 4 and 10°C. L. monocytogenes counts were determined on Modified Oxford Agar on 0, 14, 28, and 42 days at 4°C and 0, 4, 8, 12, 16, and 20 days at 10°C. Nisin (6000 IU/ml) initially reduced L. monocytogenes population by 2.1 and 2.5 logs (at 4 and 10°C, respectively on day 0), buffered SCSD (3.5%) by 1.1 and 0.2 logs (at 4 and 10°C, respectively on day 0) and the combined solution by 1.7 and 2.0 logs (at 4 and 10°C, respectively on day 0). The combined solution was the most effective treatment compared to nisin and buffered SCSD, used in sequence or alone, since it inhibited the growth of L. monocytogenes during 28 days at 4°C. The buffered SCSD was effective against L. monocytogenes at 4°C but not at 10°C. Further research is needed to investigate the effectiveness of buffered SCSD with other antimicrobials. The results of this study may be useful for further research on combinations of antimicrobials.

No description available.

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. / Doctor of Philosophy / Tree fruit growers need information on pathogen behavior on harvest bag surfaces 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 E. coli (TVS353) or Salmonella strain cocktail or L. monocytogenes strain cocktail. All surfaces were air-dried and held for 90 d (E. coli), or 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 drying conditions (wet or visibly dry), 2 contact times (5 and 25 minutes), and 2 pressure scenarios (0.0 and 0.1kg/cm2). For Salmonella or L. monocytogenes trials, transfer was assessed for wet surfaces only and apples sat on surfaces for 5 minutes. For Obj. 3, harvest bags were inoculated with L. monocytogenes or Salmonella cocktails and exposed to different sanitizer treatments including 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. Canvas surfaces promoted better E. coli survival compared to cordura and nylon surfaces. Similarly, canvas materials also supported better L. monocytogenes and Salmonella survival compared to 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.

Various control methods used in the meat and poultry processing environment to mitigate listeriosis were evaluated using a dynamic in-plant Monte Carlo model. These control methods included food contact surface testing, sanitation, post-processing lethality treatment, and product formulation with microbial growth inhibitors. The dynamic in-plant model served as an input into the risk assessment model developed by the FDA and FSIS in 2003 which predicts the number of deaths and illnesses resulting from the use of each control method. The use of growth inhibitors combined with a post-processing lethality step was estimated to save over 200 more lives than the FSIS proposed minimum sampling standard. An analysis of data collected by the National Alliance for Food Safety and Security (NAFSS) found that retail-sliced deli meats have a greater prevalence and concentration of L. monocytogenes than prepackaged deli meats. Cross contamination at the retail level is suspected due to clustering of sample positives by store and the influence of sampling time of day on the prevalence of L. monocytogenes. The comparative risk of Listeria monocytogenes in retail sliced versus prepackaged deli meats was evaluated using a modified version of the 2003 FDA-FSIS risk assessment model which considered slicing location and the use of growth inhibitors. The comparative risk ratio for the number of deaths from retail-sliced versus prepackaged deli meats was found to be 9.1 and retail-sliced product with a growth inhibitor was found to be at greater risk for listeriosis than prepackaged product without growth inhibitor. / Master of Science

Log phase cells of Listeria monocytogenes Scott A were heat shocked in Trypticase Soy + 0.6% Yeast Extract broth at 40, 44, and 45°C for 3, 10 and 20 min at each temperature, followed by heating at 55â C for 50 minutes in order to determine an optimum heat shock response. Most heat shock temperatures significantly increased thermal resistance (p < 0.05). Increasing heat shock temperature and time allowed the organism to survive much longer at 50 to 65°C than nonheat shocked cells. The optimal heat shock condition was 45°C for 20 min where D-values at 55°C increased 2.3 fold in non-selective agar and 1.6 fold in selective agar in comparison to non-heat shocked cells. However, cells heat shocked at 48°C for 10 min gave more consistent results; these cells were heated at 50, 55, 60, and 65°C to determine a z-value. Although D-values notably increased due to heat shocking, z-values remained constant regardless of the plating medium. When aerobically heat shocked cells (45°C for 10 min) were plated on a non-selective or a selective medium, a 1.4x increase in D-value was observed when enumerated under strictly anaerobic conditions. Aerobically heat shocked cells (48°C for 10 min) added to shrimp samples retained the increased heat resistance at 55°C when enumerated on a nonselective medium compared to the non-heat shocked cells. Heat shocking conditions may be created in pasteurization or minimal thermal processing of foods allowing increased heat resistance of pathogenic and spoilage microorganisms. / Master of Science

Survival of Listeria monocytogenes in apple, orange, red grape, and white grape juice was evaluated. A six-strain cocktail of L. monocytogenes was used to inoculate (approx. 7 log cfu/ml) fruit juices, which were stored at 4, 10 and 24°C for up to 61 days. Inoculated red grape juice was stored for up to 5 hours only. Samples were withdrawn at appropriate intervals, neutralized with 1.0 N NaOH, serially diluted in 0.1% peptone water, and surface plated onto Tryptic Soy Agar + 0.6% Yeast Extract (TSAYE) and Modified Oxford Agar (MOX), followed by incubation at 32°C for 48 hours. When L. monocytogenes was no longer detected by direct plating, samples were enriched for L. monocytogenes using Listeria Enrichment Broth (LEB), followed by isolation on MOX. L. monocytogenes remained viable in white grape, apple, and orange juices for up to 12, 24 and 61 days, respectively. Over time, recovery of Listeria on TSAYE versus MOX was not significantly different (P>0.05), indicating that limited acid-injury developed during storage. The results of this study demonstrate the ability of L. monocytogenes to survive in apple, orange, and white grape juices during refrigerated and abusive storage conditions. Therefore, measures to prevent or eliminate L. monocytogenes in the fruit juice-processing environment are necessary to ensure the safety of juice products for public consumption. / Master of Science