Daniel R Shelton

Agricultural Research Service, Kerrville, Texas, United States

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Publications (103)231.75 Total impact

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    ABSTRACT: Biofilm formation on abiotic surfaces in fresh produce processing facilities may play a role in foodborne outbreaks by providing protective microniches for pathogenic bacteria. Our previous study showed that a strain of Ralstonia insidiosa isolated from a fresh produce processing plant could enhance the incorporation of E. coli O15:H7 in biofilms under various environmental conditions. These results raised the concern that R. insidiosa might have the ability to incorporate other foodborne pathogens and promote their survival and growth in biofilms. To test this hypothesis, 6 strains of Shiga toxin producing E. coli, 2 strains of Salmonella, and 6 strains of Listeria monocytogenes were examined for dual-species biofilm formation with R. insidiosa. A significant increase in biomass formation was observed in 7 of the 14 R. insidiosa-pathogen combinations, while significantly enhanced incorporation of pathogenic cells into biofilms was seen in 12 of the 14 R. insidiosa-pathogen combinations. The synergistic interactions between R. insidiosa and the tested foodborne pathogens seemed dependent on intimate cellular contact between the two strains. Overall, this study showed that R. insidiosa could enhance the incorporation of biofilms of different types of foodborne pathogenic bacteria and should be considered a bridging bacterium for biofilm formation in various food processing environments.
    No preview · Article · Jan 2016
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    ABSTRACT: The presence of antibiotic-resistant bacteria in environmental surface waters has gained recent attention. Wastewater and drinking water distribution systems are known to disseminate antibiotic-resistant bacteria, with the biofilms that form on the inner-surfaces of the pipeline as a hot spot for proliferation and gene exchange. Pipe-based irrigation systems that utilize surface waters may contribute to the dissemination of antibiotic-resistant bacteria in a similar manner. We conducted irrigation events at a perennial stream on a weekly basis for 1 month, and the concentrations of total heterotrophic bacteria, total coliforms, and fecal coliforms, as well as the concentrations of these bacterial groups that were resistant to ampicillin and tetracycline, were monitored at the intake water. Prior to each of the latter three events, residual pipe water was sampled and 6-in. sections of pipeline (coupons) were detached from the system, and biofilm from the inner-wall was removed and analyzed for total protein content and the above bacteria. Isolates of biofilm-associated bacteria were screened for resistance to a panel of seven antibiotics, representing five antibiotic classes. All of the monitored bacteria grew substantially in the residual water between irrigation events, and the biomass of the biofilm steadily increased from week to week. The percentages of biofilm-associated isolates that were resistant to antibiotics on the panel sometimes increased between events. Multiple-drug resistance was observed for all bacterial groups, most often for fecal coliforms, and the distributions of the numbers of antibiotics that the total coliforms and fecal coliforms were resistant to were subject to change from week to week. Results from this study highlight irrigation waters as a potential source for antibiotic-resistant bacteria, which can subsequently become incorporated into and proliferate within irrigation pipe-based biofilms.
    Full-text · Article · Jan 2016 · Environmental Monitoring and Assessment
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    ABSTRACT: The rainfall-induced release of pathogens and microbial indicators from land-applied manure and their subsequent removal with runoff and infiltration precedes the impairment of surface and groundwater resources. It has been assumed that rainfall intensity and changes in intensity during rainfall do not affect microbial removal when expressed as a function of rainfall depth. The objective of this work was to test this assumption by measuring the removal of Escherichia coli, enterococci, total coliforms, and chloride ion from dairy manure applied in soil boxes containing fescue, under 3, 6, and 9cmh(-1) of rainfall. Runoff and leachate were collected at increasing time intervals during rainfall, and post-rainfall soil samples were taken at 0, 2, 5, and 10cm depths. Three kinetic-based models were fitted to the data on manure-constituent removal with runoff. Rainfall intensity appeared to have positive effects on rainwater partitioning to runoff, and removal with this effluent type occurred in two stages. While rainfall intensity generally did not impact the parameters of runoff-removal models, it had significant, inverse effects on the numbers of bacteria remaining in soil after rainfall. As rainfall intensity and soil profile depth increased, the numbers of indicator bacteria tended to decrease. The cumulative removal of E. coli from manure exceeded that of enterococci, especially in the form of removal with infiltration. This work may be used to improve the parameterization of models for bacteria removal with runoff and to advance estimations of depths of bacteria removal with infiltration, both of which are critical to risk assessment of microbial fate and transport in the environment.
    Full-text · Article · Sep 2015 · Science of The Total Environment
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    ABSTRACT: Microbial pathogens present a leading cause of impairment to rivers, bays, and estuaries in the United States, and agriculture is often viewed as the major contributor to such contamination. Microbial indicators and pathogens are released from landapplied animal manure during precipitation and irrigation events and are carried in overland and subsurface flow that can reach and contaminate surface waters and ground water used for human recreation and food production. Simulating the release and removal of manure-borne pathogens and indicator microorganisms is an essential component of microbial fate and transport modeling regarding food safety and water quality. Although microbial release controls the quantities of available pathogens and indicators that move toward human exposure, a literature review on this topic is lacking. This critical review on microbial release and subsequent removal from manure and animal waste application areas includes sections on microbial release processes and release-affecting factors, such as differences in the release of microbial species or groups; bacterial attachment in turbid suspensions; animal source; animal waste composition; waste aging; manure application method; manure treatment effect; rainfall intensity, duration, and energy; rainfall recurrence; dissolved salts and temperature; vegetation and soil; and spatial and temporal scale. Differences in microbial release from liquid and solid manures are illustrated, and the influential processes are discussed. Models used for simulating release and removal and current knowledge gaps are presented, and avenues for future research are suggested. © 2015 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.
    Full-text · Article · Sep 2015 · Journal of Environmental Quality
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    ABSTRACT: Understanding and quantifying microbial release from manure is a precondition to estimation and management of microbial water quality. The objectives of this work were to determine the effects of rainfall intensity and surface slope on the release of Escherichia coli, enterococci, total coliforms, and dissolved chloride from solid dairy manure, and to assess the performance of the one-parametric exponential model and the two-parametric Bradford-Schijven model when simulating the observed release. A controlled-intensity rainfall simulator induced one hour of release in runoff/leachate partitioning boxes at three rainfall intensities (30, 60, and 90 mm hr-1) and two surface slopes (5% and 20%). Bacterial concentrations in initial release were more than one order of magnitude lower than their starting concentrations in manure. As bacteria were released, they were partitioned into runoff and leachate at similar concentrations, but in different volumes, depending on slope. Bacterial release occurred in two stages that corresponded to mechanisms associated with release of manure liquid- and solid-phases. Parameters of the two models fitted to the bacterial release dependencies on rainfall depth were not significantly affected by rainfall intensity or slope. Based on two model performance tests, the Bradford-Schijven model is recommended for simulating bacterial release from solid manure.
    Full-text · Article · May 2015 · Environmental Science & Technology
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    M D Stocker · Y.A. Pachepsky · R L Hill · D R Shelton
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    ABSTRACT: Once released, manure-borne bacteria can enter runoff from interaction with the thin mixing zone near the soil surface. Objectives of this work were to document temporal changes in profile distributions of manure-borne E. coli and enterococci in the near-surface soil layers after simulated rainfalls, and to examine differences in survival of the two fecal indicator bacteria. Rainfall simulations were performed in triplicate on soil-filled boxes with grass cover and solid manure application for one hour with rainfall depths of 30, 60, and 90 mm. Soil samples were collected weekly from the depth ranges of 0-1, 1-2, 2-5, and 5-10 cm for one month. Rainfall intensity was found to have a significant impact on initial concentrations of fecal indicator bacteria in the soil. While total numbers of enterococci rapidly declined over time, E. coli populations experienced initial growth with concentration increases of 4, 10, and 25 times initial levels in rainfall depths of 30, 60, and 90 mm treatments, respectively. E. coli populations grew to the approximately the same level in all treatments. The 0-1 cm layer contained more indicator bacteria than layers beneath it, and survival of indicator bacteria was better in this layer with decimation times between 12 and 18 days after the first week growth. The proportion of bacteria in the 0-1 cm layer grew with time as the total number of bacteria in the 0-10 cm layer declined. Results of this work indicate the need to revisit the bacteria survival patterns that are assumed in water quality models. Copyright © 2015, American Society for Microbiology. All Rights Reserved.
    Full-text · Article · May 2015 · Applied and Environmental Microbiology
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    ABSTRACT: Biofilm-forming bacteria resident to food processing facilities are a food safety concern due to the potential of biofilms to harbor foodborne bacterial pathogens. When cultured together, Ralstonia insidiosa, a strong biofilm former frequently isolated from produce processing environments, has been shown to promote the incorporation of Escherichia coli O157:H7 into dual-species biofilms. In this study, interactions between E. coli O157:H7 and R. insidiosa were examined under different incubating conditions. Under static culture conditions, the incorporation of E. coli O157:H7 into biofilms with R. insidiosa was not significantly affected by either low incubating temperature (10°C) or by limited nutrient availability. Greater enhancement of E. coli O157:H7 incorporation in dual-species biofilms was observed by using a continuous culture system with limited nutrient availability. Under the continuous culture conditions used in this study, E coli O157:H7 cells showed a strong tendency of colocalizing with R. insidiosa on a glass surface at the early stage of biofilm formation. As the biofilms matured, E coli O157:H7 cells were mostly found at the bottom layer of the dual-species biofilms, suggesting an effective protection by R. insidiosa in the mature biofilms.
    Full-text · Article · Jan 2015 · Journal of food protection
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    ABSTRACT: Infiltration is important to modeling the overland transport of microorganisms in environmental waters. In watershed- and hillslope scale-models, infiltration is commonly described by simple equations relating infiltration rate to soil saturated conductivity and by empirical parameters defining changes in infiltration rate with soil water content. For the microbial transport model KINEROS2/STWIR used in this study, infiltration in unsaturated soil is accounted for by a net capillary drive parameter, G, in the Parlange equation. Scarce experimental data and multiple approaches for estimating parameter G introduce uncertainty, reducing reliability of overland water flow and microbial transport models. Our objectives were to evaluate reliability and robustness of three methods to estimate parameter G and associated accuracy and uncertainty in predicting runoff and fecal coliform (FC) transport. These methods include (i) KINEROS2 fitting to the experimental cumulative runoff data; (ii) estimating solely on soil texture; and (iii) estimating by individual pedotransfer functions (PTFs) and an ensemble of PTFs from basic soil properties. Results show that the most accurate prediction was obtained when the G parameter was fitted to the cumulative runoff. The KINEROS2-recommended parameter slightly overestimated the calibrated value of parameter G and yielded less accurate predictions of runoff, FC concentrations and total FC. The PTFs-estimated parameters systematically deviated from calibrated G values that caused high uncertainty in the KINEROS2/STWIR predictions. Averaging PTF estimates considerably improved model accuracy, reducing the uncertainty of runoff and FC concentration predictions. Overall, ensemble-based PTF estimation of the capillary drive can be efficient for simulations of runoff and bacteria overland transport when a single effective value is used across the study area.
    Full-text · Article · Nov 2014 · Journal of Hydrology
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    M D Stocker · Y A Pachepsky · D R Shelton
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    ABSTRACT: Modeling inactivation of indicator microorganisms is a necessary component of microbial water quality forecast and management recommendations. The linear semi-logarithmic (LSL) model is commonly used to simulate the dependencies of bacterial concentrations in waters on time. There were indications that assumption of the semi-logarithmic linearity may not be accurate enough in waters. The objective of this work was to compare performance of the LSL and the two-parametric Weibull inactivation models with data on survival of indicator organism in various types of water from a representative database of 167 laboratory experiments. The Weibull model was preferred in >99% of all cases when the root mean squared errors and Nash-Sutcliffe statistics were compared. Comparison of corrected Akaike statistic values gave the preference to the Weibull model in only 35% of cases. This was caused by (i) a small number of experimental points on some inactivation curves, (ii) closeness of the shape parameter of the Weibull equation to one, and (iii) piecewise log-linear inactivation dynamic that could be well described by neither of the two models compared. Based on the Akaike test, the Weibull model was favored in agricultural, lake, and pristine waters, whereas the LSL model was preferred for groundwater, wastewater, rivers, and marine waters. The decimal reduction time parameter of both the LSL and Weibull models exhibited an Arrhenius-type dependence on temperature. Overall, the existing inactivation data indicate that the application of the Weibull model can improve the predictive capabilities of microbial water quality modeling. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.
    Full-text · Article · Sep 2014 · Journal of Environmental Quality
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    ABSTRACT: As sediments increasingly become recognized as reservoirs of indicator and pathogen microorganisms, an understanding of the persistence of indicator organisms becomes important for assessment and predictions of microbial water quality. The objective of this work was to observe the response of water column and sediment coliform populations to the change in nutrient concentrations in the water column. Survival experiments were conducted in flow-through chambers containing sandy sediments. Bovine feces were collected fresh and introduced into sediment. Sixteen days later, the same fecal material was autoclaved and diluted to provide three levels - 1×, 0.5×, and 0.1× of nutrient concentrations - spike in water column. Total coliforms, Escherichia coli, and total aerobic heterotrophic bacterial concentrations were monitored in water and sediment. Bacteria responded to the nutrient spike with initial growth both in the water column and in sediment. The response of bacterial concentrations in water column was nonlinear, with no significant changes at 0.1 and .5× spikes, but a substantial change at 1× spike. Bacteria in sediment responded to the spikes at all added nutrient levels. Coliform inactivation rates both in sediment and in water after the initial growth occurred, were not significantly different from the inactivation rates before spike. These results indicate that introduction of nutrients into the water column results in nonlinear response of E. coli concentrations both in water and in sediments, followed by the inactivation with the same rate as before introduction of nutrients.
    Full-text · Article · Apr 2014 · Water Research
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    Y. A Pachepsky · R. A Blaustein · G Whelan · D. R. Shelton
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    ABSTRACT: Unlabelled: The objective of this study was to compare dependency of survival rates on temperature for indicator organisms Escherichia coli and Enterococcus and the pathogen Salmonella in surface waters. A database of 86 survival datasets from peer-reviewed papers on inactivation of E. coli, Salmonella and Enterococcus in marine waters and of E. coli and Salmonella in lake waters was assembled. The Q10 model was used to express temperature effect on survival rates obtained from linear sections of semi-logarithmic survival graphs. Available data were insufficient to establish differences in survival rates and temperature dependencies for marine waters where values of Q10 = 3 and a survival rate of 0·7 day(-1) could be applied. The Q10 values in lake waters were substantially lower in marine waters, and Salmonella inactivation in lake water was, on average, twice as fast as E. coli; data on E. coli substantially outnumber data on Enterococcus and Salmonella. The relative increase in inactivation with increase in temperature is higher in marine waters than lake water, and differences in inactivation between Salmonella and E. coli at a given temperature were significant in lake water but not in marine waters. Significance and impact of the study: Microbiological quality of surface waters is of paramount importance for public health. The novelty of this work is using a large compendium of published data to develop the first comparison of temperature effects on survival of the pathogen Salmonella and water quality indicator micro-organisms Escherichia coli and Enterococcus in natural waters. The existing relatively large body of knowledge on E. coli survival appears to be useful to assess the effect of temperature on survival of Salmonella. Moreover, results of this work constitute an essential input in models to support environmental management decisions on the use of surface water sources in agriculture, aquaculture and recreation.
    Full-text · Article · Apr 2014 · Letters in Applied Microbiology
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    Full-text · Article · Jan 2014
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    ABSTRACT: Spinach plants were irrigated biweekly with water containing 2.1 log CFU Salmonella/100 ml water (the maximum Escherichia coli MPN recommended by the Leafy Greens Marketing Agreement; LGMA), or 4.1 CFU Salmonella/100 ml water to determine Salmonella persistence on spinach leaves. Green Fluorescent protein expressing Salmonella were undetectable by most-probable number (MPN) at 24 h and 7 days following each irrigation event. This study indicates that Salmonella are unlikely to persist on spinach leaves when irrigation water is contaminated at a level below the LGMA standards. In a parallel study, persistence of Salmonella isolated from poultry or produce was compared following biweekly irrigation of spinach plants with water containing 6 log CFU Salmonella/100 ml. Produce Salmonella isolates formed greater biofilms on polystyrene, polycarbonate and stainless steel surfaces and persisted at significantly higher numbers on spinach leaves than those Salmonella from poultry origin during 35 days study. Poultry Salmonella isolates were undetectable (<1 log CFU/g) on spinach plants 7 days following each irrigation event when assayed by direct plating. This study indicates that Salmonella persistence on spinach leaves is affected by the source of contamination and the biofilm forming ability of the strain.
    No preview · Article · Dec 2013 · Food Microbiology
  • Nancy T Liu · Xiangwu Nou · Alan M Lefcourt · Daniel R Shelton · Y Martin Lo
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    ABSTRACT: Biofilm formation is a mechanism adapted by many microorganisms that enhances the survival in stressful environments. In food processing facilities, foodborne bacterial pathogens, which many are poor biofilm formers, could potentially take advantage of this protective mechanism by interacting with other strong biofilm producers. The objective of this study was to determine the influence of bacteria native to fresh produce processing environments on the incorporation of Escherichia coli O157:H7 in biofilms. Bacteria strains representing 13 Gram-negative species isolated from two fresh produce processing facilities in a previous study were tested for forming dual-species biofilms with E. coli O157:H7. Strong biofilm producing strains of Burkholderia caryophylli and Ralstonia insidiosa exhibited 180% and 63% increase in biofilm biomass, and significant thickening of the biofilms (B. caryophylli not tested), when co-cultured with E. coli O157:H7. E. coli O157:H7 populations increased by approximately 1 log in dual-species biofilms formed with B. caryophylli or R. insidiosa. While only a subset of environmental isolates with strong biofilm formation abilities increased the presence of E. coli O157:H7 in biofilms, all tested E. coli O157:H7 exhibited higher incorporation in dual-species biofilms with R. insidiosa. These observations support the notion that E. coli O157:H7 and specific strong biofilm producing bacteria interact synergistically in biofilm formation, and suggest a route for increased survival potential of E. coli O157:H7 in fresh produce processing environments.
    No preview · Article · Nov 2013 · International journal of food microbiology
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    ABSTRACT: Microbial quality of irrigation water attracts substantial attention due to the increased incidence of gastrointestinal illness caused by contaminated produce. Little is known about the changes in microbial quality of water during its delivery to crops. Studies were conducted to compare the biofilm formation and changes in microbial water quality in aluminum and PVC irrigation pipes. Irrigation events were conducted weekly and sections of irrigation pipe (coupons) analyzed for total protein, for total and fecal coliform bacteria, and for Escherichia coli. Coliform and E. coil concentrations along with nitrate, orthophosphate, and total organic carbon were monitored in the intake surface water, output irrigation water, and measured in residual standing water in pipes just prior to each irrigation event. Proteins accumulated to a greater extent in aluminum-associated biofilms than in plastic-associated biofilms. Numbers of total coliforms associated with aluminum coupons increased with time while numbers of total coliforms associated with plastic coupons fluctuated. Nitrates disappeared in standing water after one week in aluminum pipes and remained present in plastic. No detectable E. coil remained in standing water in both types of pipe. There was a high probability that coliform concentrations in output irrigation water were different from the intake concentrations in plastic pipes but not in aluminum pipes. Further research is required to evaluate how pipe material may affect the potential of biofilms in irrigation distribution systems to serve as reservoirs of pathogens that can be disseminated to crops during irrigation. Published by Elsevier B.V.
    No preview · Article · Nov 2013 · Agricultural Water Management
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    ABSTRACT: Release of manure components is an important element of modeling applications in environmental water quality. The scarcity of experimental data and the multiplicity of the approaches for modeling release kinetics of the manure components introduce uncertainty and reduce reliability of overland flow and contaminant transport models. The goal of this study was to estimate release parameters for different manure components and provide input for KINEROS2/STWIR model developed for pathogen risk assessment associated with livestock operations. The objectives of this work were to evaluate reliability and robustness of the manure release parameters estimated based on individual and grouped release kinetics of soluble, particulate and combination of particulate and soluble materials from surface applied manure. The parameters of Bradford–Schijven model were evaluated from the experimental data on release of chloride, water-extractable phosphate-P, total bioactive P, organic carbon, enterococci and E. coli from surface applied manure measured in the runoff-box and runoff-plot experiments. The results showed that release of different manure components from surface applied manure can be reliably predicted with just a single set of parameters characterizing the kinetics of manure mass release. We demonstrated that the manure release parameters could be estimated more reliably when the model fit was performed using data for different manure components pooled together, while the model fit to a single release curve produced correlated parameters. The model parameters appeared to be robust and transferable from the calibration to validation datasets without any or with only minor losses of the model accuracy.
    No preview · Article · Aug 2013 · Ecological Modelling
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    ABSTRACT: Representative food contact and nonfood contact surfaces in two mid-sized, fresh-cut processing facilities were sampled for microbiological analyses after routine daily sanitization. Mesophilic and psychrotrophic bacteria on the sampled surfaces were isolated by plating on nonselective bacterial media. Alternatively, bacteria were isolated after an incubation period that allowed the formation of heterogeneous biofilms on stainless steel beads. Of over 1,000 tested isolates, most were capable of forming biofilms, with approximately 30 % being strong or moderate biofilm formers. Selected isolates (117) were subjected to species identification by using the Biolog Gen III microbial identification system. They distributed among 23 genera, which included soil bacteria, plant-related bacteria, coliforms, and opportunistic plant- or human-pathogenic bacteria. The most commonly identified bacteria species were Pseudomonas fluorescens, Rahnella aquatilis, and Ralstonia insidiosa. The high prevalence of R. insidiosa, a strong biofilm former, and P. fluorescens, a moderate biofilm former, suggests that they were established residents in the sampled plants. These results suggest that native microflora capable of forming biofilms are widely distributed in fresh-produce processing environments.
    No preview · Article · May 2013 · Journal of food protection
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    ABSTRACT: Escherichia coli is the leading indicator of microbial contamination of natural waters, and so its in-stream fate and transport needs to be understood to eventually minimize surface water contamination by microorganisms. To better understand mechanisms of E. coli release and transport from soil sediment in a creek the artificial high-water flow events were created by releasing 60-80 m(3) of city water on a tarp-covered stream bank in four equal allotments in July 2008, 2009 and 2010. A conservative tracer difluorobenzoic acid (DFBA) was added to the released water in 2009 and 2010. Water flow rate, E. coli and DFBA concentrations as well as water turbidity were monitored with automated samplers at three in-stream weirs. A one-dimensional model was applied to simulate water flow, and E. coli and DFBA transport during these experiments. The Saint-Venant equations were used to calculate water depth and discharge while a stream solute transport model accounted for release of bacteria by shear stress from bottom sediments, advection-dispersion, and exchange with transient storage (TS). Reach-specific model parameters were estimated by evaluating observed time series of flow rates and concentrations of DFBA and E. coli at all three weir stations. Observed DFBA and E. coli breakthrough curves (BTC) exhibited long tails after the water pulse and tracer peaks had passed indicating that transient storage (TS) might be an important element of the in-stream transport process. Comparison of simulated and measured E. coli concentrations indicated that significant release of E. coli continued when water flow returned to the base level after the water pulse passed and bottom shear stress was small. The mechanism of bacteria continuing release from sediment could be the erosive boundary layer exchange enhanced by changes in biofilm properties by erosion and sloughing detachment.
    Full-text · Article · Feb 2013 · Water Research
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    ABSTRACT: Microbiological quality of surface waters can be affected by microbial load in runoff from grazing lands. This effect, with other factors, depends on the survival of microorganisms in animal waste deposited on pastures. Since temperature is a leading environmental parameter affecting survival, it indirectly impacts water microbial quality. The Q(10) model is widely used to predict the effect of temperature on rates of biological processes, including survival. Objectives of this work were to (i) evaluate the applicability of the Q(10) model to Escherichia coli inactivation in bovine manure deposited on grazing land (i.e., cowpats) and (ii) identify explanatory variables for the previously reported E. coli survival dynamics in cowpats. Data utilized in this study include published results on E. coli concentrations in natural and repacked cowpats from research conducted the U.S. (Virginia and Maryland), New Zealand, and the United Kingdom. Inspection of the datasets led to conceptualizing E. coli survival (in cowpats) as a two-stage process, in which the initial stage was due to growth, inactivation or stationary state of the population and the second stage was the approximately first-order inactivation. Applying the Q(10) model to these datasets showed a remarkable similarity in inactivation rates, using the thermal time. The reference inactivation rate constant of 0.042 (thermal days)(-1) at 20°C gave a good approximation (R(2)=0.88) of all inactivation stage data with Q(10)=1.48. The reference inactivation rate constants in individual studies were no different from the one obtained by pooling all data (P<0.05). The rate of logarithm of the E. coli concentration change during the first stage depended on temperature. Duration of the first stage, prior to the first-order inactivation stage and the initial concentration of E. coli in cowpats, could not be predicted from available data. Diet and age are probable factors affecting these two parameters however, until their environmental and management predictors are known, microbial water quality modeling must treat them as a stochastic source of uncertainty in simulation results.
    No preview · Article · Jan 2013 · Environment international
  • YANG YANG · YAGUANG LUO · PATRICIA MILLNER · DANIEL SHELTON · XIANGWU NOU
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    ABSTRACT: Chlorine is widely used as a sanitizer in commercial fresh-cut produce wash operations. However, chlorine reacts rapidly with organic materials, leading to potential pathogen survival when chlorine concentration nears depletion. This study evaluated a new process aid, T128, for its capacity to enhance chlorine efficacy against Escherichia coli O157:H7 in solutions with high organic loads. Chlorine solutions were prepared with either T128 or citric acid (control) to adjust pH. Survival of E. coli O157:H7 was assayed during washing of increasing amounts of shredded lettuce, or addition of lettuce juice as organic load. The application of T128 significantly reduced survival of E. coli O157:H7 when free chlorine in solution decreased to levels approaching depletion. In the presence of T128, no pathogen survival was observed with the free chlorine concentration as low as 0.05 mg/L, while 0.4 mg/L free chlorine was required to kill pathogens in the absence of T128 in the wash solution. The foodborne illness outbreaks that plague the fresh-cut produce industry are a testament to the need for a more effective sanitizer to prevent pathogen survival and cross contamination in commercial produce wash systems with large influxes of organic matter. This paper reports the investigation of the effect of a new process aid, T128, on reducing the survival of E. coli O157:H7 in wash solutions in which chlorine is near depletion due to high organic load, and thus the potential to improve the safety margin of fresh-cut process control.
    No preview · Article · Dec 2012 · Journal of Food Processing and Preservation

Publication Stats

2k Citations
231.75 Total Impact Points

Institutions

  • 1999-2013
    • Agricultural Research Service
      Kerrville, Texas, United States
  • 2011
    • University of Illinois, Urbana-Champaign
      • Department of Food Science and Human Nutrition
      Urbana, Illinois, United States
  • 2009
    • Creatv MicroTech, Inc
      Maryland, United States
  • 1993-2005
    • Natural Resources Research Institute
      Silver Spring, Maryland, United States
  • 2001
    • Maryland Department Of Agriculture
      Annapolis, Maryland, United States