Michael P Doyle

University of Georgia, Атина, Georgia, United States

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Publications (250)652.49 Total impact

  • Dong Chen · Tong Zhao · Michael P. Doyle ·
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    ABSTRACT: The development of single- and mixed-species biofilms formed by Escherichia coli O157:H7 and Salmonella was observed, and the antimicrobial effectiveness of levulinic acid (LVA) plus sodium dodecyl sulfate (SDS) on the cells in single- and dual-species biofilms was determined. Biofilm-forming ability of single- and mixed-species cultures was observed by crystal violet staining and their resistance to levulinic acid plus SDS was determined by enumeration. Fluorescent protein-labeled E. coli O157:H7 and Salmonella were constructed and the bacterial composition of the biofilms after treatment with levulinic acid plus SDS was visualized by confocal laser scanning microscopy (CLSM). E. coli O157:H7 and Salmonella were antagonistic to each other, being more sensitive to levulinic acid plus SDS in mixed-species biofilms. Images captured by CLSM revealed that E. coli O157:H7 and Salmonella were distributed evenly in the single- and dual-species biofilms, and confirmed that the combination of levulinic acid and SDS was effective in inactivating bacterial cells in biofilms. Results revealed that levulinic acid with SDS may be used as a potential biofilm control intervention.
    Food Control 11/2015; 57. DOI:10.1016/j.foodcont.2015.04.006 · 2.81 Impact Factor
  • Marilyn C. Erickson · Li M. Ma · Michael P. Doyle ·
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    ABSTRACT: Shelf life of fish packaged under modified atmosphere (MA) is extended, but within the United States, commercial application of MA with impermeable packaging films is restricted due to concerns that botulinum toxin production would precede spoilage when contaminated fish are held at abusive storage temperatures. Use of semipermeable packaging films has been advocated; however, previous studies are inconclusive in determining the oxygen transmission rate (OTR) of a film that is needed to achieve an acceptable margin of safety (i.e., toxin production occurs only after spoilage). This study was conducted to determine the influence of OTR (target OTRs of 3 to 15,000) on the development of spoilage volatiles and toxin in salmon inoculated with type E Clostridium botulinum and subjected to air, vacuum, or 75:25 CO2:N2 MA and storage temperatures of 4, 8, 12, or 16°C. The most dominant headspace volatile peak that was prod°Ced during spoilage of samples at 4, 8 or 12°C was a peak, having a Kovats retention index (KI) of 753, and at which external standards of 2-or 3-methyl 1-butanol also eluted. Under anaerobic conditions, both the aerobic microbial populations and the size of the KI 753 spoilage peak were less in inoculated samples compared with uninoculated samples. C. botulinum-inoculated samples that were stored at 12 or 16°C under conditions favorable for anaerobic growth were also characterized by a KI 688 peak. Using a previously developed model that related the percentage of elderly consumers who would prepare a sample having the KI 753 spoilage peak of a specific size, it was determined that for salmon packaged with 3 or 3,000 OTR films under any atmosphere and stored at 12 or 16°C, 2 to 61% of the consumers could potentially prepare toxin-contaminated samples. Hence, when abusive storage conditions are suspected, the fish should not be consumed.
    Journal of food protection 11/2015; 78(11):2006-2018. DOI:10.4315/0362-028X.JFP-15-004 · 1.85 Impact Factor
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    ABSTRACT: The objective of this study was to determine Salmonella numbers on retail raw chicken carcasses in Guatemala and to phenotypically characterize the isolates (serotyping and antibiotic susceptibility). In total, 300 chicken carcasses were collected from seven departments in Guatemala. Salmonella numbers were determined using the most-probable-number method following the U. S. Department of Agriculture's Food Safety and Inspection Service protocol. In total, 103 isolates were obtained, all of which were tested for antibiotic susceptibility, whereas 46 isolates were serotyped. Overall, Salmonella prevalence and mean number (mean log most probable number per carcass) was 34.3% and 2.3 (95% confidence interval: 2.1 to 2.5), respectively. Significant differences (P < 0.05) in Salmonella prevalence were found by storage condition (refrigerated or ambient temperature), market type (wet markets, supermarkets, and independent poultry stores), chicken production system (integrated or nonintegrated production company), and chicken skin color (white or yellow). Chickens produced by integrated companies had lower Salmonella numbers (P < 0.05) than nonintegrated companies, and white-skin carcasses had lower numbers (P < 0.05) than yellow-skin carcasses. Among 13 different Salmonella serovars identified, Paratyphi B (34.8%) was most prevalent, followed by Heidelberg (16.3%) and Derby (11.6%). Of all the Salmonella isolates, 59.2% were resistant to one to three antibiotics and 13.6% to four or more antibiotics. Among all the serovars obtained, Salmonella Paratyphi B and Heidelberg were the most resistant to the antibiotics tested. Salmonella levels and antibiotic resistant profiles among isolates from raw poultry at the retail market level were high relative to other reports from North and South America. These data can be used by Guatemalan stakeholders to develop risk assessment models and support further research opportunities to control transmission of Salmonella spp. and antibiotic-resistant isolates from chicken meat to humans.
    Journal of food protection 09/2015; 9(september 15):642-1650(9). DOI:10.4315/0362-028X.JFP-15-117 · 1.85 Impact Factor
  • Cathy Webb · Marilyn Erickson · Lindsey Davey · Michael Doyle ·

    06/2015; 5(2):231-244. DOI:10.3390/agriculture5020231
  • Cathy C. Webb · Marilyn C. Erickson · Lindsey E. Davey · Michael P. Doyle ·
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    ABSTRACT: Freshly harvested Eastern variety cantaloupes (Cucumis melo L. var. reticulatus cv. Athena) were subjected to three different harvest and wash treatments to examine conditions under which the efficacy of the sanitizer, levulinic acid (LV) plus sodium dodecyl sulfate (SDS), could be enhanced to reduce Salmonella contamination. In treatment set one, cantaloupes were spot inoculated with Salmonella enterica serovar Poona (prepared from solid or liquid media cultures) before or after a 1-min dip treatment in LV (2.5, 5.0, 7.5, or 10%) and 2.5% SDS. S. Poona initial populations on rind tissue (4.26-5.04 log CFU/sample) were reduced to detection by enrichment culture when cantaloupes were subsequently exposed to any of the LV/SDS solutions. When S. Poona was introduced after cantaloupes had been dip-treated, greater decreases in pathogen populations at the stem scar were observed when cantaloupes were treated with increasing concentrations of LV. In treatment set two, the response of S. Poona dip-treated with 5% LV/2.5% SDS was compared to a simulated commercial dump tank treatment incorporating 200ppm chlorine as well as a two-stage treatment employing both the chlorine tank and LV/SDS dip treatments. S. Poona levels (log CFU/sample or # positive by enrichment culture/# analyzed) after treatments were 5.25, 3.07, 7/10, 5/10 (stem scar) and 3.90, 25/40, 28/40, 20/40 (rind) for non-treated, chlorine tank, LV/SDS dip, and tank plus dip treatments, respectively. In treatment set three, freshly harvested cantaloupes were first treated in the field using a needle-free stem scar injection (200μl, 7.5% LV/1.0% SDS, 60psi) and a cantaloupe spray (30ml, 7.5% LV/0.5% SDS). Cantaloupe stem scar and rind tissue were then spot-inoculated with S. Poona using either a liquid or soil-based medium followed by a simulated dump tank treatment incorporating either 200ppm chlorine or 5% LV/2% SDS. S. Poona inoculated on field-treated cantaloupe rind decreased by 4.7 and 5.31 (liquid) and 3.27 and 3.36 (soil) log CFU/sample after simulated chlorine and LV/SDS tank treatments, respectively. In the case of stem scar tissue, S. Poona populations exhibited a 1.0 log greater reduction when cantaloupes were treated with LV/SDS compared to chlorine in the dump tank (P<0.05). Based on this study, application of multiple hurdles is warranted, as additional decreases in S. Poona populations were obtained when cantaloupes were subjected to a chlorine dump tank followed by a LV/SDS dip treatment. Copyright © 2015 Elsevier B.V. All rights reserved.
    International journal of food microbiology 05/2015; 207. DOI:10.1016/j.ijfoodmicro.2015.04.041 · 3.08 Impact Factor
  • Dong Chen · Tong Zhao · Michael P Doyle ·
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    ABSTRACT: The efficacy of levulinic acid (LVA) plus sodium dodecyl sulfate (SDS) to remove or inactivate Listeria monocytogenes, Salmonella Typhimurium, and Shiga toxin-producing Escherichia coli (STEC) in biofilms on the surface of stainless steel coupons was evaluated. Five- or six-strain mixtures (ca. 9.0logCFU/ml) of the three pathogens were separately inoculated on stainless steel coupons. After incubation at 21°C for 72h, the coupons were treated for 10min by different concentrations of LVA plus SDS (0.5% LVA+0.05% SDS, 1% LVA+0.1% SDS, and 3% LVA+2% SDS) and other commonly used sanitizers, including a commercial quaternary ammonium-based sanitizer (150ppm), lactic acid (3%), sodium hypochlorite (100ppm), and hydrogen peroxide (2%). The pathogens grew in the biofilms to ca. 8.6 to 9.3logCFU/coupon after 72h of incubation. The combined activity of LVA with SDS was bactericidal in biofilms for cells of the three pathogens evaluated, with the highest concentrations (3% LVA+2% SDS) providing the greatest log reduction. Microscopic images indicated that the cells were detached from the biofilm matrix and the integrity of cell envelopes were decreased after the treatment of LVA plus SDS. This study is conducive to better understanding the antimicrobial behavior of LVA plus SDS to the foodborne pathogens within biofilms. Copyright © 2015 Elsevier B.V. All rights reserved.
    International journal of food microbiology 04/2015; 207:1-7. DOI:10.1016/j.ijfoodmicro.2015.04.026 · 3.08 Impact Factor
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    ABSTRACT: During the past century, the microbiological safety of the U.S. food supply has improved; however, many foodborne illnesses and outbreaks occur annually. Hence, opportunities for the food industry to improve the safety of both domestic and imported food exist through the adoption of risk-based preventive measures. Challenging food safety issues that are on the horizon include demographic changes to a population whose immune system is more susceptible to foodborne and opportunistic pathogens, climate changes that will shift where food is produced, and consumers' preferences for raw and minimally processed foods. Increased environmental and product testing and anonymous data sharing by the food industry with the public health community would aid in identifying system weaknesses and enabling more targeted corrective and preventative actions. Clinicians will continue to play a major role in reducing foodborne illnesses by diagnosing and reporting cases and in helping to educate the consumer about food safety practices. © The Author 2015. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.
    Clinical Infectious Diseases 03/2015; 61(2). DOI:10.1093/cid/civ253 · 8.89 Impact Factor
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    ABSTRACT: During the early phases of aerobic composting of animal manures, pathogens are inactivated primarily from the accumulation of heat produced by indigenous microbial activity. When compost materials are not exposed to these lethal temperatures, the required holding time needed to obtain a pathogen-free product that may be applied to fields is unknown. Consequently, a series of studies examined whether the carbon amendment (wheat straw, peanut hulls, rice hulls, and pine needles) added to animal manures affected survival of either Salmonella or E. coli O157:H7 during storage of compost mixtures at sublethal temperatures (20 to 40°C). Pathogens consistently survived for longer periods of time in compost mixtures prepared with pine needles than compost mixtures prepared with either of the other three carbon amendments. Pathogen inactivation in wheat straw– or peanut hull–amended compost mixtures was dependent on the target pathogen, moisture level, and storage temperature. Moisture levels in wheat straw–amended compost mixtures stored at 40°C had no effect on inactivation of E. coli O157:H7. In contrast, wheat straw–amended mixtures stored at 30 to 35°C and equilibrated to suboptimal moisture contents (30 to 40%) were less effective for inactivating pathogens compared with drier (25% moisture) or moister (60% moisture) mixtures. In peanut hull–amended compost mixtures, inactivation of E. coli O157:H7 was affected minimally by moisture levels, whereas Salmonella survival increased as the moisture level was decreased. The different inactivation responses of Salmonella and E. coli O157:H7 in compost mixtures prepared with wheat straw or peanut hulls and equilibrated to different moisture levels suggest that there are different mechanisms for inactivation. Hence, developing reliable guidelines relying on time-temperature for holding of compost mixtures at sublethal temperatures will be challenging and, perhaps, not possible.
    Journal of food protection 02/2015; 78(2):248-55. DOI:10.4315/0362-028X.JFP-14-289 · 1.85 Impact Factor
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    ABSTRACT: Heat is the primary mechanism by which aerobic composting inactivates zoonotic bacterial pathogens residing within animal manures, but at sublethal temperatures, the time necessary to hold the compost materials to ensure pathogen inactivation is uncertain. To determine the influence of the type of nitrogen amendment on inactivation of Salmonella, Listeria monocytogenes, and Escherichia coli O157:H7 in compost mixtures stored at sublethal temperatures, specific variables investigated in these studies included the animal source of the manure, the initial carbon/nitrogen (C:N) ratio of the compost mixture, and the age of the manure. Salmonella and L. monocytogenes were both inactivated more rapidly in chicken and swine compost mixtures stored at 20°C when formulated to an initial C:N ratio of 20:1 compared with 40:1, whereas a C:N ratio did not have an effect on inactivation of these pathogens in cow compost mixtures. Pathogen inactivation was related to the elevated pH of the samples that likely arises from ammonia produced by the indigenous microflora in the compost mixtures. Indigenous microbial activity was reduced when compost mixtures were stored at 30°C and drier conditions (
    Journal of food protection 02/2015; 78(2):302-10. DOI:10.4315/0362-028X.JFP-14-288 · 1.85 Impact Factor
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    Marilyn C Erickson · Jean Liao · Xiuping Jiang · Michael P Doyle ·
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    ABSTRACT: Two separate studies were conducted to address the condition and the type of feedstocks used during composting of dairy manure. In each study, physical (temperature), chemical (ammonia, volatile acids, and pH), and biological (Salmonella, Listeria monocytogenes, and Escherichia coli O157:H7) parameters were monitored during composting in bioreactors to assess the degree to which they were affected by the experimental variables and, ultimately, the ability of the chemical and physical parameters to predict the fate of pathogens during composting. Compost mixtures that contained either aged dairy manure or pine needles had reduced heat generation; therefore, pathogen reduction took longer than if fresh manure or carbon amendments of wheat straw or peanut hulls were used. Based on regression models derived from these results, ammonia concentration, in addition to heat, were the primary factors affecting the degree of pathogen inactivation in compost mixtures formulated to an initial carbon-nitrogen (C:N) ratio of 40:1, whereas, the pH of the compost mixture along with the amount of heat exposure were most influential in compost mixtures formulated to an initial C:N ratio of 30:1. Further studies are needed to validate these models so that additional criteria in addition to time and temperature can be used to evaluate the microbiological safety of composted manures.
    Journal of food protection 11/2014; 77(11):1911-8. DOI:10.4315/0362-028X.JFP-14-194 · 1.85 Impact Factor
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    ABSTRACT: Abstract Escherichia coli O157:H7 has been the causative agent of many outbreaks associated with leafy green produce consumption. Elucidating the mechanism by which contamination occurs requires monitoring interactions between the pathogen and the plant under typical production conditions. Intentional introduction of virulent strains into fields is not an acceptable practice. As an alternative, attenuated strains of natural isolates have been used as surrogates of the virulent strains; however, the attachment properties and environmental stabilities of these attenuated isolates may differ from the unattenuated outbreak strains. In this study, the Shiga toxin (stx1, stx2, and/or stx2c) genes as well as the eae gene encoding intimin of two E. coli O157:H7 outbreak isolates, F4546 (1997 alfalfa sprout) and K4492 (2006 lettuce), were deleted. Individual gene deletions were confirmed by polymerase chain reaction (PCR) and DNA sequencing. The mutant strains did not produce Shiga toxin. The growth kinetics of these mutant strains under nutrient-rich and minimal conditions were identical to those of their wild-type strains. Attachment to the surface of lettuce leaves was comparable between wild-type/mutant pairs F4546/MD46 and K4492/MD47. Adherence to soil particles was also comparable between the virulent and surrogate pairs, although the F4546/MD46 pair exhibited statistically greater attachment than the K4492/MD47 pair (p≤0.05). Wild-type and mutant pairs F4546/MD46 and K4492/MD47 inoculated into wet or dry soils had statistically similar survival rates over the 7-day storage period at 20°C. A plasmid, pGFPuv, containing green fluorescent protein was transformed into each of the mutant strains, allowing for ease of identification and detection of surrogate strains on plant material or soil. These pGFPuv-containing surrogate strains will enable the investigation of pathogen interaction with plants and soil in the farm production environment where the virulent pathogen cannot be used.
    Foodborne Pathogens and Disease 09/2014; 11(11). DOI:10.1089/fpd.2014.1798 · 1.91 Impact Factor
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    M C Erickson · J Liao · L Ma · X Jiang · M P Doyle ·
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    ABSTRACT: Reduction of enteric pathogens in animal manures before field application is essential for mitigating the risk of foodborne illness associated with produce. Aerobic composting of manures has been advocated as an effective treatment for reducing pathogen populations, and heat is a major factor contributing to pathogen inactivation. This study was initiated to determine the potential contribution of both thermal and nonthermal (pH, volatile acids, and ammonia) factors to pathogen inactivation during aerobic composting in bioreactors for mixtures containing manure from various sources (dairy, chicken, and swine). The test mixtures were formulated with an initial moisture content of 60% and a C:N ratio of 20:1, using straw and cottonseed meal as amendments. Mixtures were then inoculated with Salmonella and Listeria monocytogenes labeled with green fluorescent protein at initial populations of ca. 107 CFU/g. Three replicate trials of each treatment were conducted. Temperatures within the bioreactors were recorded at 30-min intervals, and duplicate samples were withdrawn daily from two sampling locations within the bioreactor. Significant regression models were derived relating decreases in pathogen populations to the degree of heat generated in the mixture (cumulative heat) and the pH of the mixture on the day before the pathogen losses were calculated (P < 0.0002). Although pathogens in swine manure compost mixtures were inactivated by the third day of composting, very little heat was generated in these mixtures, which were characterized by significantly higher levels of volatile acids compared with the other two compost mixtures. Therefore, volatile acids could help achieve pathogen inactivation when temperatures are too low such as when heat is lost too quickly at the surface of static compost piles or during winter composting.
    Journal of food protection 09/2014; 77(9):1512-1518. DOI:10.4315/0362-028X.JFP-14-111 · 1.85 Impact Factor
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    ABSTRACT: The objective of this study was to determine Salmonella counts, serotypes, and antimicrobial resistance profiles in retail raw chicken meat in the People's Republic of China. Salmonella counts were determined according to the most-probable-number (MPN) method for 300 whole chicken carcasses. These samples were collected from large, small, and wet (open) markets in Guangdong, Shaanxi, and Sichuan provinces. Salmonella isolates were serotyped and tested for antimicrobial susceptibility. Of the 300 chicken carcasses, 43.3% were positive for Salmonella, with an overall mean of 1.7 log MPN per carcass (95% confidence interval, 1.6 to 1.8 log MPN per carcass). No significant differences (P > 0.05) were detected for storage temperature (i.e., chilled, frozen, or ambient), market type (large, small, or wet), province, or location (capital or noncapital city). Seventy-eight serotypes were identified among the 1,094 Salmonella isolates. The top five most common Salmonella serotypes on raw chicken carcasses were Enteritidis (19.2%), Indiana (15.2%), Typhimurium (14.6%), Agona (7.1%), and Thompson (6.6%). Salmonella isolates (n = 779) were most frequently resistant to sulfisoxazole (74.1%) and tetracycline (71.1%) and least resistant to ceftriaxone (22.5%) and cefoxitin (19%). Only 4% of the isolates were susceptible to all 15 antimicrobial agents, 45% were resistant to 1 to 5 agents, 29% were resistant to 6 to 10 agents, and 22% were resistant to 11 to 15 agents. Our findings revealed that Salmonella contamination was common in retail raw poultry in China, and the counts on contaminated carcasses were mostly low. Salmonella isolates were diverse in their serotype distribution and antimicrobial susceptibility profiles, with more than half of the isolates resistant to more than five antimicrobial agents. These data may be used in risk assessment models to reduce the transmission of Salmonella via chicken meat to humans in China.
    Journal of food protection 06/2014; 77(6):894-902. DOI:10.4315/0362-028X.JFP-13-439 · 1.85 Impact Factor
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    ABSTRACT: Preharvest internalization of Escherichia coli O157:H7 into the roots of leafy greens is a food safety risk because the pathogen may be systemically transported to edible portions of the plant. In this study, both abiotic (degree of soil moisture) and biotic (E. coli O157:H7 exposure, presence of Shiga toxin genes, and type of leafy green) factors were examined to determine their potential effects on pathogen internalization into roots of leafy greens. Using field soil that should have an active indigenous microbial community, internalized populations in lettuce roots were 0.8 to 1.6 log CFU/g after exposure to soil containing E. coli O157:H7 at 5.6 to 6.1 log CFU/g. Internalization of E. coli O157:H7 into leafy green plant roots was higher when E. coli O157:H7 populations in soil were increased to 7 or 8 log CFU/g or when the soil was saturated with water. No differences were noted in the extent to which internalization of E. coli O157:H7 occurred in spinach, lettuce, or parsley roots; however, in saturated soil, maximum levels in parsley occurred later than did those in spinach or lettuce. Translocation of E. coli O157:H7 from roots to leaves was rare; therefore, decreases observed in root populations over time were likely the result of inactivation within the plant tissue. Shiga toxin-negative (nontoxigenic) E. coli O157:H7 isolates were more stable than were virulent isolates in soil, but the degree of internalization of E. coli O157:H7 into roots did not differ between isolate type. Therefore, these nontoxigenic isolates could be used as surrogates for virulent isolates in field trials involving internalization.
    Journal of food protection 06/2014; 77(6):872-9. DOI:10.4315/0362-028X.JFP-13-432 · 1.85 Impact Factor
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    ABSTRACT: In the past decade, leafy greens have been implicated in several outbreaks of foodborne illness, and research has focused on contamination during preharvest operations. Concerns have been raised that internalization of pathogens into the edible tissue occurs where postharvest chemical interventions would be ineffective. This study was initiated to measure the degree and fate of Escherichia coli O157:H7 internalized in the phyllosphere tissue of leafy greens when spray conditions, inoculum level, and type of leafy green were varied. Two spraying treatments were applied: (i) spraying individual spinach or lettuce leaves on plants once with a high dose (7 to 8 log CFU/ml) of E. coli O157:H7 and (ii) spraying spinach, lettuce, or parsley plants repeatedly (once per minute) with a low dose (2.7 to 4.2 log CFU/ml) of E. coli O157:H7 over a 10- to 20-min period. With the high-dose spray protocol, no significant differences in the prevalence of internalization occurred between Shiga toxin-negative E. coli O157:H7 isolates and virulent isolates (P > 0.05), implying that the Shiga toxin virulence factors did not influence internalization or the subsequent fate of those populations under these test conditions. Significantly greater internalization of E. coli O157:H7 occurred in spinach leaves compared with lettuce leaves when leaves were sprayed once with the high-dose inoculum (P < 0.05), whereas internalization was not observed in lettuce leaves but continued to be observed in spinach and parsley leaves following repeated spraying of the low-dose inoculum. Based on these results, it is surmised that a moisture film was generated when spraying was repeated and this film assisted in the mobilization of pathogen cells to plant apertures, such as stomata. E. coli O157:H7 cells that were internalized into spinach tissue using a low-dose repeat-spray protocol were temporary residents because they were not detected 2 days later, suggesting that plant-microbe interactions may be responsible.
    Journal of food protection 05/2014; 77(5):713-721. DOI:10.4315/0362-028X.JFP-13-357 · 1.85 Impact Factor
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    Dong Chen · Tong Zhao · Michael P Doyle ·
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    ABSTRACT: This study investigated the degree of cross-contamination between deli foods and slicers by Listeria monocytogenes, Salmonella, and Escherichia coli O157:H7, and their inactivation by levulinic acid (LA) plus sodium dodecyl sulfate (SDS) on slicers. The transfer rate of pathogens at 5 locations on the contaminated slicers (scenario I) and on food slices (scenario II) was determined. The antimicrobial efficacy of the LA + SDS sanitizers applied either as a liquid or as foam at three concentrations (0.5% LA + 0.05% SDS, 1% LA + 0.1% SDS, and 2% LA + 0.5% SDS) was determined for decontamination of the pathogens on the slicers at 21 °C. After slicing 10 slices, the pathogens recovered from slicer blades were significantly (P < 0.05) less than the recovery from some other contact locations (scenario I). With an initial inoculum at approximately 8.5 log CFU/blade, the populations of the pathogens transferred from blades to slices decreased logarithmically (R(2) > 0.9, scenario II). Contaminated slicer surfaces sprayed with 1% LA plus 0.1% SDS as a foam (45-55 psi) reduced within 1 min 6.0 to 8.0 log CFU/blade of the pathogens. Results revealed that cross-contamination can occur between deli foods and slicers. Also, LA-based sanitizer applied as foam can be a useful treatment to remove microbial contamination on the slicers.
    Food Microbiology 04/2014; 38:263-9. DOI:10.1016/j.fm.2013.10.004 · 3.33 Impact Factor
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    Tong Zhao · Ping Zhao · Dong Chen · Ravirajsinh Jadeja · Yen-Con Hung · Michael P Doyle ·
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    ABSTRACT: Studies were done at 21°C to determine the bactericidal activity of lactic acid, levulinic acid, and sodium dodecyl sulfate (SDS) applied individually and in combination on Shiga toxin-producing Escherichia coli (STEC) in pure culture and to compare the efficacy of lactic acid and levulinic acid plus SDS treatments applied by spray or immersion to inactivate STEC and Salmonella (10(7) CFU/cm(2)) on beef trim pieces (10 by 10 by 7.5 cm). Application of 3 % lactic acid for 2 min to pure cultures was shown to reduce E. coli O26:H11, O45:H2, O111:H8, O103:H2, O121:H2, O145:NM, and O157:H7 populations by 2.1, 0.4, 0.3, 1.4, 0.3, 2.1, and 1.7 log CFU/ml, respectively. Treatment with 0.5 % levulinic acid plus 0.05 % SDS for <1 min reduced the populations of all STEC strains to undetectable levels (>6 log/ml reduction). Beef surface temperature was found to affect the bactericidal activity of treatment with 3 % levulinic acid plus 2 % SDS (LV-SDS). Treating cold (4°C) beef trim with LV-SDS at 21, 62, or 81°C for 30 s reduced E. coli O157:H7 by 1.0, 1.1, or 1.4 log CFU/cm(2), respectively, whereas treating beef trim at 8°C with LV-SDS at 12°C for 0.1, 1, 3, or 5 min reduced E. coli O157:H7 by 1.4, 2.4, 2.5, or 3.3 log CFU/cm(2), respectively. Spray treatment of beef trim at 4°C with 5 % lactic acid only reduced the E. coli O157:H7 population by 1.3 log CFU/cm(2). Treating beef trim at 8°C with LV-SDS for 1, 2, or 3 min reduced Salmonella Typhimurium by 2.1, 2.6, and >5.0 log CFU/cm(2), respectively. Hand massaging the treated beef trim substantially reduced contamination of both pathogens, with no detectable E. coli O157:H7 or Salmonella Typhimurium (<5 CFU/cm(2)) on beef trim pieces treated with LV-SDS. Reduction of E. coli O157:H7 and Salmonella Typhimurium populations was enhanced, but bactericidal activity was affected by the meat temperature.
    Journal of food protection 04/2014; 77(4):528-37. DOI:10.4315/0362-028X.JFP-13-335 · 1.85 Impact Factor
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    ABSTRACT: Both growth chamber and field studies were conducted to investigate the potential for Escherichia coli O157:H7 to be internalized into leafy green tissue when seeds were germinated in contaminated soil. Internalized E. coli O157:H7 was detected by enrichment in both spinach (Spinacia oleracea L.) and lettuce (Lactuca sativa L.) seedlings when seeds were germinated within the growth chamber in autoclaved and nonautoclaved soil, respectively, contaminated with E. coli O157:H7 at 2.0 and 3.8 log CFU/g, respectively. Internalized E. coli O157:H7 populations could be detected by enumeration within leafy green tissues either by increasing the pathogen levels in the soil or by autoclaving the soil. Attempts to maximize the exposure of seed to E. coli O157:H7 by increasing the mobility of the microbe either through soil with a higher moisture content or through directly soaking the seeds in an E. coli O157:H7 inoculum did not increase the degree of internalization. Based on responses obtained in growth chamber studies, internalization of E. coli O157:H7 surrogates (natural isolates of Shiga toxin-negative E. coli O157:H7 or recombinant [stx- and eae-negative] outbreak strains of E. coli O157:H7) occurred to a slightly lesser degree than did internalization of the virulent outbreak strains of E. coli O157:H7. The apparent lack of internalized E. coli O157:H7 when spinach and lettuce were germinated from seed in contaminated soil (ca. 3 to 5 log CFU/g) in the field and the limited occurrence of surface contamination on the seedlings suggest that competition from indigenous soil bacteria and environmental stresses were greater in the field than in the growth chamber. On the rare occasion that soil contamination with E. coli O157:H7 exceeded 5 log CFU/g in a commercial field, this pathogen probably would not be internalized into germinating leafy greens and/or would not still be present at the time of harvest.
    Journal of food protection 02/2014; 77(2):189-96. DOI:10.4315/0362-028X.JFP-13-216 · 1.85 Impact Factor
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    ABSTRACT: The objective of this study was to determine Salmonella counts, serovars, and antimicrobial-resistant phenotypes on retail raw chicken carcasses in Colombia. A total of 301 chicken carcasses were collected from six departments (one city per department) in Colombia. Samples were analyzed for Salmonella counts using the most-probable-number method as recommended by the U.S. Department of Agriculture, Food Safety Inspection Service protocol. A total of 378 isolates (268 from our previous study) were serotyped and tested for antimicrobial susceptibility. The overall Salmonella count (mean log most probable number per carcass ± 95% confidence interval) and prevalence were 2.1 (2.0 to 2.3) and 37%, respectively. There were significant differences (P < 0.05) by Salmonella levels (i.e., counts and prevalence) by storage temperature (i.e., frozen, chilled, or ambient), retail store type (wet markets, supermarkets, and independent markets), and poultry company (chicken produced by integrated or nonintegrated company). Frozen chicken had the lowest Salmonella levels compared with chicken stored at other temperatures, chickens from wet markets had higher levels than those from other retail store types, and chicken produced by integrated companies had lower levels than nonintegrated companies. Thirty-one Salmonella serovars were identified among 378 isolates, with Salmonella Paratyphi B tartrate-positive (i.e., Salmonella Paratyphi B dT+) the most prevalent (44.7%), followed by Heidelberg (19%), Enteritidis (17.7%), Typhimurium (5.3%), and Anatum (2.1%). Of all the Salmonella isolates, 35.2% were resistant to 1 to 5 antimicrobial agents, 24.6% to 6 to 10, and 33.9% to 11 to 15. Among all the serovars obtained, Salmonella Paratyphi B dT+ and Salmonella Heidelberg were the most antimicrobial resistant. Salmonella prevalence was determined to be high, whereas cell numbers were relatively low. These data can be used in developing risk assessment models for preventing the transmission of Salmonella from chicken to humans in Colombia.
    Journal of food protection 02/2014; 77(2):227-35. DOI:10.4315/0362-028X.JFP-13-276 · 1.85 Impact Factor

Publication Stats

11k Citations
652.49 Total Impact Points


  • 1991-2015
    • University of Georgia
      • • Department of Food Science and Technology
      • • College of Agricultural and Environmental Sciences
      • • Department of Environmental Health Science
      • • College of Veterinary Medicine
      Атина, Georgia, United States
  • 2012
    • University of Texas Health Science Center at Houston
      • School of Dentistry
      Houston, TX, United States
  • 2006
    • Clemson University
      Clemson, South Carolina, United States
  • 2001-2002
    • The University of Arizona
      Tucson, Arizona, United States
    • Berry College
      Атина, Georgia, United States
  • 1997
    • University System of Georgia
      Atlanta, Georgia, United States
  • 1981-1993
    • University of Wisconsin–Madison
      • Muscle Biology Laboratory
      Madison, Wisconsin, United States