24 results on '"Teresa M. Bergholz"'
Search Results
2. Vacuum steam treatment of soft wheat: Quality and reduction of Escherichia coli O121 and Salmonella Enteritidis PT30
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Senay Simsek, Teresa M. Bergholz, Sahar Malekmohammadi, and Jane Snelling
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Reduction (complexity) ,biology ,Chemistry ,Salmonella enteritidis ,Organic Chemistry ,Wheat flour ,Food science ,biology.organism_classification ,Food Science ,Escherichia coli O121 - Published
- 2020
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Catalog
3. Effect of Vacuum Steam Treatment of Hard Red Spring Wheat on Flour Quality and Reduction of Escherichia coli O121 and Salmonella Enteritidis PT 30
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Teresa M. Bergholz, Jae Ohm, Jane Snelling, Senay Simsek, and Sahar Malekmohammadi
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Salmonella ,Vacuum ,Food Handling ,Salmonella enteritidis ,Flour ,Colony Count, Microbial ,Wheat flour ,Thermal treatment ,medicine.disease_cause ,Microbiology ,medicine ,Food science ,Pathogen inactivation ,Triticum ,Escherichia coli O121 ,biology ,Chemistry ,food and beverages ,Contamination ,biology.organism_classification ,Steam ,Enterohemorrhagic Escherichia coli ,Food Microbiology ,Treatment time ,Food Science - Abstract
Recent outbreaks traced to contaminated flour have created a need in the milling industry for a process that reduces pathogens in wheat while maintaining its functional properties. Vacuum steam treatment is a promising technology for treatment of low-moisture foods. Traditional thermal treatment methods can compromise wheat functionality due to high temperatures; thus, maintaining the functional quality of the wheat protein was critical for this research. The objective of this study was to evaluate the effect of vacuum steam treatment of hard red spring (HRS) wheat kernels on final flour quality and the overall efficacy of vacuum stream treatment for reducing pathogens on HRS wheat kernels. HRS wheat samples were treated with steam under vacuum at 65, 70, 75, and 85°C for 4 and 8 min. Significant changes in dough and baked product functionality were observed for treatments at ≥70°C. Treatment time had no significant effect on the qualities evaluated. After determining that vacuum steam treatment at 65°C best preserved product quality, HRS wheat was inoculated with Escherichia coli O121 and Salmonella Enteritidis PT 30 and processed at 65°C for 0, 2, 4, 6, or 8 min. The treatments achieved a maximum average reduction of 3.57 ± 0.33 log CFU/g for E. coli O121 and 3.21 ± 0.27 log CFU/g for Salmonella. Vacuum steam treatment could be an effective pathogen inactivation method for the flour milling industry. HIGHLIGHTS more...
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- 2020
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4. Sustainable and eco-friendly poly (Lactic acid)/cellulose nanocrystal nanocomposite films for the preservation of oxygen-sensitive food
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Dangkamol Wongthanaroj, Lindsay A. Jessmore, Yawei Lin, Teresa M. Bergholz, Nicole M. Stark, Ronald C. Sabo, and Laurent M. Matuana
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Food Science - Published
- 2022
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5. Survival and Growth of Wild-Type and rpoS-Deficient Salmonella Newport Strains in Soil Extracts Prepared with Heat-Treated Poultry Pellets
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Esmond Nyarko, Patricia D. Millner, Manan Sharma, Rhodel Bradshaw, Teresa M. Bergholz, Manoj Shah, Deborah A. Neher, and Thomas R. Weicht
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Crops, Agricultural ,Salmonella ,Hot Temperature ,Food Contamination ,medicine.disease_cause ,complex mixtures ,Microbiology ,Poultry ,Soil ,03 medical and health sciences ,Nutrient ,medicine ,Animals ,Food science ,Pathogen ,Soil Microbiology ,030304 developmental biology ,0303 health sciences ,Strain (chemistry) ,030306 microbiology ,Chemistry ,Contamination ,Manure ,Soil conditioner ,rpoS ,Food Science - Abstract
Manure runoff can transfer pathogens to farmlands or to water sources, leading to subsequent contamination of produce. Untreated biological soil amendments, like manure, can be contaminated with foodborne pathogens, such as Salmonella Newport, which may lead to transfer of the pathogen to fruits or vegetables. Studies have reported the occurrence and survival of Salmonella in manure or manure slurries. However, data on the survival and growth of Salmonella Newport is lacking in matrices simulating runoff. We quantified the survival and growth of wild-type (WT) Salmonella Newport and rpoS-deficient (Δ rpoS) strains in sterile and nonsterile soil extracts prepared with (amended) or without (unamended) heat-treated poultry pellets at 25°C. Salmonella Newport WT and Δ rpoS populations reached a maximum cell density of 6 to 8 log CFU/mL in 24 to 30 h in amended and unamended soil extracts and remained in stationary phase for up to 4 days. Salmonella Newport in amended soil extracts exhibited a decreased lag phase (λ , 2.87 ± 1.01 h) and greater maximum cell densities ( Nmax, 6.84 ± 1.25 CFU/mL) compared with λ (20.10 ± 9.53 h) and Nmax (5.22 ± 0.82 CFU/mL) in unamended soil extracts. In amended soil extract, the Δ rpoS strain had no measurable λ , similar growth rates (μmax) compared with WT, and a lower Nmax compared with the WT strain. Unamended, nonsterile soil extracts did not support the growth of Salmonella Newport WT and led to a decline in populations for the Δ rpoS strain. Salmonella Newport had lower cell densities in nonsterile soil extracts (5.94 ± 0.95 CFU/mL) than it did in sterile soil extracts (6.66 ± 1.50 CFU/mL), potentially indicating competition for nutrients between indigenous microbes and Salmonella Newport. The most favorable growth conditions were provided by amended sterile and nonsterile soil extracts, followed by sterile, unamended soil extracts for both Salmonella Newport strains. Salmonella Newport may grow to greater densities in amended extracts, providing a route for increased Salmonella levels in the growing environments of produce. more...
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- 2019
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6. Fate of Salmonella and Enterohemorrhagic Escherichia coli on Wheat Grain
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Senay Simsek, Teresa M. Bergholz, and Jessica R. Lauer
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Serotype ,Salmonella ,Veterinary medicine ,Inoculation ,Flour ,Wheat flour ,food and beverages ,Outbreak ,Biology ,medicine.disease_cause ,Shelf life ,biology.organism_classification ,Escherichia coli O157 ,Microbiology ,Salmonella enterica ,Enterohemorrhagic Escherichia coli ,medicine ,Food Microbiology ,Escherichia coli ,Triticum ,Food Science - Abstract
Wheat flour has been connected to outbreaks of foodborne illnesses with increased frequency in recent years, specifically, outbreaks involving Salmonella enterica and enterohemorrhagic Escherichia coli (EHEC). However, there is little information regarding the survival of these pathogens on wheat grain during long-term storage in a low-moisture environment. This study aims to evaluate the long-term survival of these enteric pathogens on wheat grain over the course of a year. Hard red spring wheat was inoculated with strains of four serovars of Salmonella (Enteritidis, Agona, Tennessee, and Montevideo) and six serotypes of EHEC (O157:H7, O26:H11, O121:H19, O45:NM, O111:H8, and O103:H2) in triplicate, sealed in Mylar bags to maintain the water activity, and stored at room temperature (22 ± 1°C). The survival of each pathogen was evaluated by plating onto differential media. Viable counts of strains from all four serovars of Salmonella (Enteritidis, Agona, Tennessee, and Montevideo) were detected on wheat grain stored at room temperature (22 ± 1°C) for the duration of the study (52 weeks). Viable counts of strains from EHEC serotypes O45:NM, O111:H8, and O26:H11 were only detected for 44 weeks, and strains from serotypes O157:H7, O121:H19, and O103:H2 were only detected for 40 weeks until they passed below the limit of detection (2.0 log CFU/g). The D-values were found to be significantly different between Salmonella and EHEC (adjusted P ≤ 0.05) with Salmonella D-values ranging from 22.9 ± 2.2 weeks to 25.2 ± 1.0 weeks and EHEC D-values ranging from 11.4 ± 0.6 weeks to 13.1 ± 1.8 weeks. There were no significant differences among the four Salmonella strains or among the six EHEC strains (adjusted P > 0.05). These observations highlight the wide range of survival capabilities of enteric pathogens in a low-moisture environment and confirm these pathogens are a food safety concern when considering the long shelf life of wheat grain and its products. HIGHLIGHTS more...
- Published
- 2021
7. Microbial and Chemical Shelf-Life of Vacuum Steam-Pasteurized Whole Flaxseed and Milled Flaxseed
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Clifford Hall, Manoj Shah, Luiz Gustavo Conde Lima, Bridget E. Eklund, and Teresa M. Bergholz
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0301 basic medicine ,Pasteurization ,Health benefits ,Shelf life ,medicine.disease_cause ,complex mixtures ,law.invention ,03 medical and health sciences ,chemistry.chemical_compound ,0404 agricultural biotechnology ,law ,Mold ,medicine ,Peroxide value ,Food science ,Water content ,chemistry.chemical_classification ,030109 nutrition & dietetics ,food and beverages ,Fatty acid ,04 agricultural and veterinary sciences ,040401 food science ,humanities ,Secoisolariciresinol diglucoside ,chemistry ,Food Science - Abstract
Flaxseed is an oilseed with many health benefits. Flaxseed may be consumed raw or in processed form. In the raw form, there is a potential for microbial contamination. Several pasteurization methods have been used to reduce microbial contamination. However, such treatments may affect chemical properties of foods. In this study, vacuum steam‐pasteurization was conducted on whole flaxseed and milled flaxseed using 4 different conditions (3 min at 75 °C, 3 min at 90 °C, 9 min at 90 °C, and 3 min at 105 °C). Microbial and chemical shelf‐life was monitored for 28 wk (36 wk for aerobic plate counts). Significant reduction (P < 0.05) in microbial counts (total aerobic plate counts, and yeast and mold counts) occurred after pasteurization and during storage of both whole flaxseed and milled flaxseed. Although both the moisture content and aw increased after pasteurization, they were similar to the unpasteurized samples during storage. Peroxide value, free fatty acid, headspace volatiles, fatty acid profiles, oil content, and secoisolariciresinol diglucoside (SDG) content were chemical indices measured. Only small changes were observed in the chemical indices after vacuum steam‐pasteurization for both pasteurized whole flaxseed and milled flaxseed as compared to the unpasteurized flaxseed at most instances. Vacuum steam‐pasteurization can be used as a safe alternative for the microbial reduction of low‐moisture products, such as flaxseed, without significantly affecting chemical stability. PRACTICAL APPLICATION: Vacuum steam‐pasteurization can be effectively used for the treatment of whole flaxseed and milled flaxseed to reduce spoilage microorganisms, such as total aerobes and yeasts and molds. In addition, this pasteurization method had minimal effects on several chemical shelf‐life parameters with positive impact on SDG of the processed flaxseed. more...
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- 2018
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8. Efficacy of vacuum steam pasteurization for inactivation of Salmonella PT 30, Escherichia coli O157:H7 and Enterococcus faecium on low moisture foods
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Teresa M. Bergholz, Manoj Shah, Julie S. Sherwood, Gladys Asa, and Kari Graber
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0301 basic medicine ,Salmonella ,Hot Temperature ,Time Factors ,Vacuum ,Water activity ,Enterococcus faecium ,030106 microbiology ,Colony Count, Microbial ,Pasteurization ,Escherichia coli O157 ,medicine.disease_cause ,complex mixtures ,Microbiology ,law.invention ,03 medical and health sciences ,0404 agricultural biotechnology ,law ,medicine ,Food microbiology ,Food science ,Moisture ,biology ,Chemistry ,food and beverages ,04 agricultural and veterinary sciences ,General Medicine ,Contamination ,biology.organism_classification ,040401 food science ,Sunflower ,Steam ,Seeds ,Food Microbiology ,Food Science - Abstract
Low moisture foods such as nuts, spices, and seeds have been implicated in several outbreaks due to Salmonella or E. coli O157:H7 contamination. Such foods may be consumed raw, and can be used as ingredients in other food products. While numerous thermal inactivation studies have been conducted for Salmonella on nuts, studies on other seeds and grains are minimal. Product water activity can influence the thermal resistance of pathogens, where thermal resistance increases as water activity decreases, leading to a requirement for higher temperatures and longer exposure times to achieve significant reduction of pathogen numbers. Vacuum steam pasteurization uses steam under vacuum, which can be operated at temperatures above and below 100°C. The objective of this study was to determine the efficacy of vacuum steam pasteurization for inactivation of pathogens on whole flaxseed, quinoa, sunflower kernels, milled flaxseed and whole black peppercorns. The use of E. faecium as a potential surrogate for Salmonella and E. coli O157:H7 in vacuum steam pasteurization was also evaluated. Pasteurization for 1min at 75°C yielded average log reductions of 5.48±1.22, 5.71±0.40 and 5.23±0.61 on flaxseed, 4.29±0.92, 5.89±0.26 and 2.39±0.83 on quinoa, and 4.01±0.74, 5.40±0.83 and 2.99±0.92 on sunflower kernels for Salmonella PT 30, E. coli O157:H7 and E. faecium, respectively. Similarly, on milled flaxseed and black peppercorns average log reductions of 3.02±0.79 and 6.10±0.64CFU/g were observed for Salmonella PT 30 after 1min of treatment at 75°C but, on average, >6.0 log reductions were observed after pasteurization at 85°C. Our data demonstrate that vacuum steam pasteurization can be effectively used to reduce pathogens on these low moisture foods at temperature as low as 75 and 85°C, and that E. faecium may be used as a potential surrogate for Salmonella PT 30 and E. coli O157:H7. more...
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- 2017
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9. Salmonella enterica in Soils Amended with Heat-Treated Poultry Pellets Survived Longer than Bacteria in Unamended Soils and More Readily Transferred to and Persisted on Spinach
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Patricia D. Millner, Manoj Shah, Teresa M. Bergholz, Eric T. Handy, Manan Sharma, Esmond Nyarko, Rhodel Bradshaw, and Cheryl East
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0303 health sciences ,Salmonella ,Ecology ,biology ,030306 microbiology ,food and beverages ,Soil classification ,biology.organism_classification ,medicine.disease_cause ,complex mixtures ,Applied Microbiology and Biotechnology ,Viable but nonculturable ,Soil conditioner ,03 medical and health sciences ,Horticulture ,Salmonella enterica ,Soil water ,Food Microbiology ,medicine ,Spinach ,rpoS ,030304 developmental biology ,Food Science ,Biotechnology - Abstract
Untreated biological soil amendments of animal origin (BSAAO) are commonly used as biological fertilizers but can harbor foodborne pathogens like Salmonella enterica, leading to potential transfer from soils to fruits and vegetables intended for human consumption. Heat-treated poultry pellets (HTPP) can provide produce growers with a slow-release fertilizer with a minimized risk of pathogen contamination. Little is known about the impact of HTPP-amended soil on the survival of Salmonella enterica. The contributions of RpoS and formation of viable but nonculturable cells to Salmonella survival in soils are also inadequately understood. We quantified the survival of Salmonella enterica subsp. enterica serovar Newport wild-type (WT) and rpoS-deficient (ΔrpoS mutant) strains in HTPP-amended and unamended soil with or without spinach plants over 91 days using culture and quantitative PCR methods with propidium monoazide (PMA-qPCR). Simulated “splash” transfer of S. Newport from soil to spinach was evaluated at 35 and 63 days postinoculation (dpi). The S. Newport WT and ΔrpoS mutant reached the limit of detection, 1.0 log CFU/g (dry weight), in unamended soil after 35 days, whereas 2 to 4 log CFU/g (dry weight) was observed for both WT and ΔrpoS mutant strains at 91 dpi in HTPP-amended soil. S. Newport levels in soils determined by PMA-qPCR and plate count methods were similar (P > 0.05). HTPP-amended soils supported higher levels of S. Newport transfer to and survival on spinach leaves for longer periods of time than did unamended soils (P more...
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- 2019
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10. Application of a Nonlinear Model to Transcript Levels of Upregulated Stress Response Gene ibpA in Stationary-Phase Salmonella enterica Subjected to Sublethal Heat Stress
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Bradley P. Marks, Laura M. Carroll, Teresa M. Bergholz, and Ian M. Hildebrandt
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0301 basic medicine ,Salmonella ,Hot Temperature ,030106 microbiology ,Colony Count, Microbial ,Biology ,medicine.disease_cause ,Microbiology ,03 medical and health sciences ,Downregulation and upregulation ,Heat shock protein ,medicine ,Thermal cycler ,Salmonella enterica ,biology.organism_classification ,Molecular biology ,Meat Products ,030104 developmental biology ,Real-time polymerase chain reaction ,Nonlinear Dynamics ,Chaperone (protein) ,biology.protein ,CLPB ,Food Science - Abstract
Sublethal heating, which can occur during slow cooking of meat products, is known to induce increased thermal resistance in Salmonella. However, very few studies have addressed the kinetics of this response. Although several recent studies have reported improved thermal inactivation models that include the effect of prior sublethal history on subsequent thermal resistance, none of these models were based on cellular-level responses to sublethal thermal stress. The goal of this study was to determine whether a nonlinear model could accurately portray the response of Salmonella to heat stress induced by prolonged exposure to sublethal temperatures. To accomplish this, stationary-phase Salmonella Montevideo cultures were subjected to various heating profiles (held at either 40 or 45°C for 0, 5, 10, 15, 30, 60, 90, 180, or 240 min) using a PCR thermal cycler. Differential plating on selective and nonselective media was used to confirm the presence of cellular injury. Reverse transcription quantitative PCR was used to screen the transcript levels of six heat stress-related genes to find candidate genes for nonlinear modeling. Injury was detected in populations of Salmonella held at 45°C for 30, 60, and 90 min and at 40°C for 0, 5, and 90 min (P0.05), whereas no significant injury was found at 180 and 240 min (P0.05). The transcript levels of ibpA, which codes for a small heat shock protein associated with the ClpB and DnaK-DnaJ-GrpE chaperone systems, showed the greatest increase relative to the transcript levels at 0 min, which was significant at 5, 10, 15, 30, 60, 90, and 180 min at 45°C and at 5, 10, 15, 30, 60, and 90 min at 40°C (P0.05). Using ibpA transcript levels as an indicator of adaptation to thermal stress, a nonlinear model for sublethal injury is proposed. The use of variables indicating the physiological state of the pathogen during stress has the potential to increase the accuracy of thermal inactivation models that must account for prolonged exposure to sublethal temperatures. more...
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- 2016
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11. Survival and thermal resistance among four Salmonella serovars inoculated onto flaxseeds
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Teresa M. Bergholz, Megan K. Townsend Ramsett, Sahar Malekmohammadi, and Manoj Shah
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Thermotolerance ,Serotype ,Salmonella ,Veterinary medicine ,Hot Temperature ,Vacuum ,Colony Count, Microbial ,Biology ,Serogroup ,medicine.disease_cause ,Microbiology ,03 medical and health sciences ,Species Specificity ,Flax ,medicine ,030304 developmental biology ,0303 health sciences ,Microbial Viability ,030306 microbiology ,Inoculation ,Water ,Steam ,Food Storage ,Food Microbiology ,Pasteurization ,Food Science - Abstract
Thermal resistance among Salmonella serovars has been shown to vary, however, such data are minimal for Salmonella inoculated onto low moisture foods. We evaluated survival and subsequent thermal resistance for 32 strains of Salmonella from four serovars (Agona, Enteritidis, Montevideo, and Tennessee) on flaxseed over 24 weeks. After inoculation, flaxseeds were adjusted to aw = 0.5 and stored at 22 °C. After 24 weeks at 22 °C, strains of serovar Agona had a significantly slower rate of reduction compared to those of Enteritidis and Montevideo (adj. p more...
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- 2020
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12. Optimization of combinations of bactericidal and bacteriostatic treatments to control Listeria monocytogenes on cold-smoked salmon
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Teresa M. Bergholz, Matthew J. Stasiewicz, Martin Wiedmann, Dillon Murray, Kathryn J. Boor, and Jihun Kang
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Meat ,Colony Count, Microbial ,Acetates ,Arginine ,medicine.disease_cause ,Microbiology ,chemistry.chemical_compound ,food ,Listeria monocytogenes ,Salmon ,Sodium diacetate ,Food Preservation ,medicine ,Animals ,Polylysine ,Food science ,Nisin ,health care economics and organizations ,Potassium lactate ,Chitosan ,General Medicine ,Antimicrobial ,food.food ,Anti-Bacterial Agents ,Smoked salmon ,chemistry ,Food Microbiology ,Brain heart infusion ,Salts ,Maximum Cell Density ,Food Science - Abstract
Contamination of cold-smoked salmon by Listeria monocytogenes is a major concern for the seafood industry. The objectives of this study were to (i) determine the most effective bactericidal treatment for L. monocytogenes on salmon and (ii) optimize bactericidal and bacteriostatic treatment combinations to identify cost-effective treatments against L. monocytogenes on salmon. L. monocytogenes challenge trials were conducted in brain heart infusion (BHI) and on salmon disks that were supplemented with bactericidal compounds nisin (NIS), lauric arginate (LAE), e-polylysine (EPL), and chitosan (CHIT). Subsequently, the most effective bactericidal compound was further tested by concurrent application of a blend of organic acid salts containing potassium lactate and sodium diacetate (PLSDA). L. monocytogenes populations were measured at 7 °C over 60 days, and initial cell density ( N 0 ), maximum initial log reduction ( N r ), lag phase (λ), maximum growth rate (μ max ), and maximum cell density ( N max ) over 60 days storage were estimated. Time to recover to initial cell density ( T initial ) was also compared for combinations of bactericidal and bacteriostatic treatments. Varying degrees of antimicrobial effects were observed with bactericidal compounds in BHI. However, when tested on salmon, only NIS significantly decreased initial L. monocytogenes populations by approximately 2 log CFU/g, and reduced N max by approximately 1.5 log CFU/g compared to untreated control (CTRL). N r achieved by the combined treatment of NIS and PLSDA was approximately 2 log CFU/g regardless of the presence of PLSDA, and a dose-dependent increase in N r was observed with increasing NIS concentrations. PLSDA alone or in combination with 20 ppm NIS was most effective at delaying growth of L. monocytogenes . The greatest reduction in N max was observed with the combination of 20 ppm NIS and PLSDA; N max was 3.1 log CFU/g lower compared to CTRL. Comparison of T initial indicated that PLSDA with NIS can effectively retard growth of L. monocytogenes to its initial level (following initial reduction) and offers a cost benefit over using high concentrations of NIS alone. In summary, the combined application of NIS (for a bactericidal effect) and PLSDA (for a bacteriostatic effect) proved to be an effective treatment option to reduce initial levels as well as minimize subsequent growth of L. monocytogenes throughout the expected shelf-life of cold-smoked salmon. more...
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- 2014
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13. Nisin Resistance of Listeria monocytogenes Is Increased by Exposure to Salt Stress and Is Mediated via LiaR
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Silin Tang, Martin Wiedmann, Teresa M. Bergholz, and Kathryn J. Boor
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Transcription, Genetic ,Microbial Sensitivity Tests ,Biology ,medicine.disease_cause ,Applied Microbiology and Biotechnology ,Microbiology ,chemistry.chemical_compound ,Listeria monocytogenes ,Osmotic Pressure ,Stress, Physiological ,Drug Resistance, Bacterial ,polycyclic compounds ,medicine ,Food microbiology ,Osmotic pressure ,Pathogen ,Nisin ,Ecology ,business.industry ,Gene Expression Profiling ,food and beverages ,Gene Expression Regulation, Bacterial ,biochemical phenomena, metabolism, and nutrition ,Antimicrobial ,Food safety ,Anti-Bacterial Agents ,Culture Media ,Response regulator ,chemistry ,Food Microbiology ,bacteria ,Salts ,business ,Gene Deletion ,Transcription Factors ,Food Science ,Biotechnology - Abstract
Growth of Listeria monocytogenes on refrigerated, ready-to-eat food is a significant food safety concern. Natural antimicrobials, such as nisin, can be used to control this pathogen on food, but little is known about how other food-related stresses may impact how the pathogen responds to these compounds. Prior work demonstrated that exposure of L. monocytogenes to salt stress at 7°C led to increased expression of genes involved in nisin resistance, including the response regulator liaR . We hypothesized that exposure to salt stress would increase subsequent resistance to nisin and that LiaR would contribute to increased nisin resistance. Isogenic deletion mutations in liaR were constructed in 7 strains of L. monocytogenes , and strains were exposed to 6% NaCl in brain heart infusion broth and then tested for resistance to nisin (2 mg/ml Nisaplin) at 7°C. For the wild-type strains, exposure to salt significantly increased subsequent nisin resistance ( P < 0.0001) over innate levels of resistance. Compared to the salt-induced nisin resistance of wild-type strains, Δ liaR strains were significantly more sensitive to nisin ( P < 0.001), indicating that induction of LiaFSR led to cross-protection of L. monocytogenes against subsequent inactivation by nisin. Transcript levels of LiaR-regulated genes were induced by salt stress, and lmo1746 and telA were found to contribute to LiaR-mediated salt-induced nisin resistance. These data suggest that environmental stresses similar to those on foods can influence the resistance of L. monocytogenes to antimicrobials such as nisin, and potential cross-protective effects should be considered when selecting and applying control measures for this pathogen on ready-to-eat foods. more...
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- 2013
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14. Transcriptomic and Phenotypic Analyses Identify Coregulated, Overlapping Regulons among PrfA, CtsR, HrcA, and the Alternative Sigma Factors σ B , σ C , σ H , and σ L in Listeria monocytogenes
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Soraya Chaturongakul, Yuewei Hu, Juliane Ollinger, Martin Wiedmann, Teresa M. Bergholz, Kathryn J. Boor, Sarita Raengpradub, Renato H. Orsi, and M. Elizabeth Palmer
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Genetics ,Regulation of gene expression ,Ecology ,Mutant ,Regulator ,Virulence ,Biology ,Applied Microbiology and Biotechnology ,Gene expression profiling ,Regulon ,Sigma factor ,Gene ,Food Science ,Biotechnology - Abstract
A set of seven Listeria monocytogenes 10403S mutant strains, each bearing an in-frame null mutation in a gene encoding a key regulatory protein, was used to characterize transcriptional networks in L. monocytogenes ; the seven regulatory proteins addressed include all four L. monocytogenes alternative sigma factors (σ B , σ C , σ H , and σ L ), the virulence gene regulator PrfA, and the heat shock-related negative regulators CtsR and HrcA. Whole-genome microarray analyses, used to identify regulons for each of these 7 transcriptional regulators, showed considerable overlap among regulons. Among 188 genes controlled by more than one regulator, 176 were coregulated by σ B , including 92 genes regulated by both σ B and σ H (with 18 of these genes coregulated by σ B , σ H , and at least one additional regulator) and 31 genes regulated by both σ B and σ L (with 10 of these genes coregulated by σ B , σ L , and at least one additional regulator). Comparative phenotypic characterization measuring acid resistance, heat resistance, intracellular growth in J774 cells, invasion into Caco-2 epithelial cells, and virulence in the guinea pig model indicated contributions of (i) σ B to acid resistance, (ii) CtsR to heat resistance, and (iii) PrfA, σ B , and CtsR to virulence-associated characteristics. Loss of the remaining transcriptional regulators (i.e., sigH , sigL , or sigC ) resulted in limited phenotypic consequences associated with stress survival and virulence. Identification of overlaps among the regulons provides strong evidence supporting the existence of complex regulatory networks that appear to provide the cell with regulatory redundancies, along with the ability to fine-tune gene expression in response to rapidly changing environmental conditions. more...
- Published
- 2011
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15. Gene Expression Induced in Escherichia coli O157:H7 upon Exposure to Model Apple Juice
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Sivapriya Kailasan Vanaja, Thomas S. Whittam, and Teresa M. Bergholz
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Malus ,Virulence ,Pasteurization ,Biology ,Escherichia coli O157 ,medicine.disease_cause ,Applied Microbiology and Biotechnology ,Microbiology ,law.invention ,Beverages ,Stress, Physiological ,law ,Gene expression ,medicine ,Escherichia coli ,Pathogen ,Gene ,Oligonucleotide Array Sequence Analysis ,Ecology ,Escherichia coli Proteins ,Gene Expression Profiling ,Gene Expression Regulation, Bacterial ,biology.organism_classification ,Enterobacteriaceae ,Up-Regulation ,Food Microbiology ,Food Science ,Biotechnology - Abstract
Escherichia coli O157:H7 has caused serious outbreaks of food-borne illness via transmission in a variety of food vehicles, including unpasteurized apple juice, dried salami, and spinach. To understand how this pathogen responds to the multiple stresses of the food environment, we compared global transcription patterns before and after exposure to model apple juice. Transcriptomes of mid-exponential- and stationary-phase cells were evaluated after 10 min in model apple juice (pH 3.5) using microarrays probing 4,886 open reading frames. A total of 331 genes were significantly induced upon exposure of cells to model apple juice, including genes involved in the acid, osmotic, and oxidative stress responses as well as the envelope stress response. Acid and osmotic stress response genes, including asr, osmC, osmB , and osmY , were significantly induced in response to model apple juice. Multiple envelope stress responses were activated as evidenced by increased expression of CpxR and Rcs phosphorelay-controlled genes. Genes controlled by CpxR ( cpxP, degP , and htpX ) were significantly induced 2- to 15-fold upon exposure to apple juice. Inactivation of CpxRA resulted in a significant decrease in survival of O157:H7 in model apple juice compared to the isogenic parent strain. Of the 331 genes induced in model apple juice, 104 are O157-specific genes, including those encoding type three secretion effectors ( espJ, espB, espM2, espL3 , and espZ ). Elucidating the response of O157:H7 to acidic foods provides insight into how this pathogen is able to survive in food matrices and how exposure to foods influences subsequent transmission and virulence. more...
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- 2009
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16. Determination of Evolutionary Relationships of Outbreak-Associated Listeria monocytogenes Strains of Serotypes 1/2a and 1/2b by Whole-Genome Sequencing
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Michael Frace, Henk C. den Bakker, Benjamin J. Silk, Lee S. Katz, Teresa M. Bergholz, Zuzana Kucerova, Lavin A. Joseph, Kelly A. Jackson, Jessica L. Halpin, Joseph P. Gossack, Karen Xavier, Todd J. Ward, Maryann Turnsek, Cheryl L. Tarr, and Lori M. Gladney more...
- Subjects
0301 basic medicine ,Gene Transfer, Horizontal ,030106 microbiology ,Population ,Biology ,Serogroup ,Applied Microbiology and Biotechnology ,DNA sequencing ,Disease Outbreaks ,Evolution, Molecular ,03 medical and health sciences ,Genetic variation ,Humans ,Point Mutation ,Listeriosis ,Evolutionary and Genomic Microbiology ,Serotyping ,education ,Phylogeny ,Whole genome sequencing ,Genetics ,education.field_of_study ,Ecology ,Outbreak ,Genetic Variation ,Sequence Analysis, DNA ,Listeria monocytogenes ,Subtyping ,United States ,Genetic divergence ,Horizontal gene transfer ,Genome, Bacterial ,Food Science ,Biotechnology - Abstract
We used whole-genome sequencing to determine evolutionary relationships among 20 outbreak-associated clinical isolates of Listeria monocytogenes serotypes 1/2a and 1/2b. Isolates from 6 of 11 outbreaks fell outside the clonal groups or “epidemic clones” that have been previously associated with outbreaks, suggesting that epidemic potential may be widespread in L. monocytogenes and is not limited to the recognized epidemic clones. Pairwise comparisons between epidemiologically related isolates within clonal complexes showed that genome-level variation differed by 2 orders of magnitude between different comparisons, and the distribution of point mutations (core versus accessory genome) also varied. In addition, genetic divergence between one closely related pair of isolates from a single outbreak was driven primarily by changes in phage regions. The evolutionary analysis showed that the changes could be attributed to horizontal gene transfer; members of the diverse bacterial community found in the production facility could have served as the source of novel genetic material at some point in the production chain. The results raise the question of how to best utilize information contained within the accessory genome in outbreak investigations. The full magnitude and complexity of genetic changes revealed by genome sequencing could not be discerned from traditional subtyping methods, and the results demonstrate the challenges of interpreting genetic variation among isolates recovered from a single outbreak. Epidemiological information remains critical for proper interpretation of nucleotide and structural diversity among isolates recovered during outbreaks and will remain so until we understand more about how various population histories influence genetic variation. more...
- Published
- 2016
17. Transcriptomic Analysis of the Adaptation of Listeria monocytogenes to Growth on Vacuum-Packed Cold Smoked Salmon
- Author
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Teresa M. Bergholz, Silin Tang, Kathryn J. Boor, Martin Wiedmann, Henk C. den Bakker, and Renato H. Orsi
- Subjects
Cobalamin biosynthesis ,Vacuum ,Food Contamination ,Biology ,medicine.disease_cause ,Applied Microbiology and Biotechnology ,Microbiology ,Transcriptome ,food ,Listeria monocytogenes ,Bacterial Proteins ,Salmon ,Food Preservation ,Fish Products ,medicine ,Animals ,Gene ,Ecology ,Strain (chemistry) ,Food preservation ,Food Packaging ,Adaptation, Physiological ,Fold change ,food.food ,Smoked salmon ,Food Microbiology ,Food Science ,Biotechnology - Abstract
The foodborne pathogen Listeria monocytogenes is able to survive and grow in ready-to-eat foods, in which it is likely to experience a number of environmental stresses due to refrigerated storage and the physicochemical properties of the food. Little is known about the specific molecular mechanisms underlying survival and growth of L. monocytogenes under different complex conditions on/in specific food matrices. Transcriptome sequencing (RNA-seq) was used to understand the transcriptional landscape of L. monocytogenes strain H7858 grown on cold smoked salmon (CSS; water phase salt, 4.65%; pH 6.1) relative to that in modified brain heart infusion broth (MBHIB; water phase salt, 4.65%; pH 6.1) at 7°C. Significant differential transcription of 149 genes was observed (false-discovery rate [FDR], L. monocytogenes were not significantly different between CSS and MBHIB, indicating that the transcriptomic differences reflect how L. monocytogenes is able to facilitate growth under these different conditions. Differential expression analysis and Gene Ontology enrichment analysis indicated that genes encoding proteins involved in cobalamin biosynthesis as well as ethanolamine and 1,2-propanediol utilization have significantly higher transcript levels in H7858 grown on CSS than in that grown in MBHIB. Our data identify specific transcriptional profiles of L. monocytogenes growing on vacuum-packaged CSS, which may provide targets for the development of novel and improved strategies to control L. monocytogenes growth on this ready-to-eat food. more...
- Published
- 2015
18. Contributions of σ(B) and PrfA to Listeria monocytogenes salt stress under food relevant conditions
- Author
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V.B. Ribeiro, Martin Wiedmann, Maria Teresa Destro, Kathryn J. Boor, Teresa M. Bergholz, Sana Mujahid, and Renato H. Orsi
- Subjects
Mutant ,Virulence ,Sigma Factor ,Biology ,medicine.disease_cause ,Real-Time Polymerase Chain Reaction ,Microbiology ,Hemolysis ,Article ,Time ,Cell wall ,Gentamicin protection assay ,Listeria monocytogenes ,Bacterial Proteins ,Stress, Physiological ,medicine ,Serotyping ,Gene ,Genetics ,Microarray analysis techniques ,Gene Expression Profiling ,General Medicine ,Gene Expression Regulation, Bacterial ,Regulon ,Food Microbiology ,Salts ,Food Science - Abstract
Listeria monocytogenes is well known to survive and grow under several stress conditions, including salt stress, which is important for growth in certain foods as well as for host infection. To characterize the contributions, to salt stress response, of transcriptional regulators important for stress response and virulence (i.e., σ(B) and PrfA), we analyzed three L. monocytogenes parent strains and isogenic mutants (ΔsigB, ΔprfA, and ΔsigBΔprfA), representing different serotypes and lineages, for their ability to grow, at 25 °C, in BHI with 1.9 M NaCl. With regard to growth rate, only the lineage IV strain presented a significant difference between the parent strain and both of its respective mutants lacking prfA (ΔprfA and ΔsigBΔprfA). Conversely, the lineage I and II parent strains showed significantly shorter lag phase in comparison to their respective ΔsigB mutant strains. Intestinal epithelial cell invasion assay and hemolytic activity assays showed a significant role for σ(B) in the former and for PrfA in the latter. To explore the mechanism that may contribute to the extended lag phase in the ΔsigB mutant strain and survival and growth of the parent strain upon salt shock, whole genome transcription profiling was performed to compare transcript levels between the lineage I, serotype 1/2b, parent strain and its isogenic ΔsigB mutant after 30 min of lag phase growth at 25 °C in the presence of 1.9 M NaCl (salt shock) without aeration. Microarray data showed significantly higher transcript levels for 173 genes in the parent strain as compared to the ΔsigB strain. Overall, 102 of the 173 σ(B) up-regulated genes had been identified in previous studies, indicating that 71 genes were newly identified as being up-regulated by σ(B) in this study. We hypothesize that, among these genes newly identified as σ(B) up-regulated, four genes (lmo2174, lmo0530, lmo0527 and lmo0529) may play a major role in response to salt stress. Lmo2174 contains domains that facilitate sensing and producing a transduction signal in the form of cyclic di-GMP, which may activate the enzymes Lmo0527, Lmo0529 and Lmo0530, which encode proteins similar to those responsible for synthesis of exopolysaccharides that may protect the cell by changing the cell wall structure during salt stress. Overall, our data showed that σ(B), but not PrfA, contributes to growth under salt stress. Moreover, we show that the σ(B) regulon of a L. monocytogenes lineage I strain challenged with salt shock includes salt stress-specific as well as previously unidentified σ(B) up-regulated genes. more...
- Published
- 2014
19. Efficacy of different antimicrobials on inhibition of Listeria monocytogenes growth in laboratory medium and on cold-smoked salmon
- Author
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Silin Tang, Teresa M. Bergholz, Martin Wiedmann, Kathryn J. Boor, and Matthew J. Stasiewicz
- Subjects
Colony Count, Microbial ,Biology ,Acetates ,medicine.disease_cause ,Microbiology ,chemistry.chemical_compound ,food ,Listeria monocytogenes ,Anti-Infective Agents ,Sodium diacetate ,Salmon ,Food Preservation ,medicine ,Animals ,Food science ,Nisin ,Potassium lactate ,Growth medium ,General Medicine ,Antimicrobial ,food.food ,Culture Media ,Smoked salmon ,Cold Temperature ,chemistry ,Brain heart infusion ,Food Microbiology ,Salts ,Food Science - Abstract
Listeria monocytogenes is of particular concern in cold-smoked fish products as it can survive curing and cold-smoking, and can subsequently grow from low numbers to potentially hazardous levels during refrigerated storage. The purpose of this study was to (i) quantify the effects of organic acids, nisin, and their combinations on controlling L. monocytogenes growth on cold-smoked salmon at refrigeration temperatures, (ii) identify synergistic interactions of binary combinations of these antimicrobials, and (iii) determine if results from laboratory growth media can predict antimicrobial efficacy on cold-smoked salmon. Strains representing the genetic diversity of L. monocytogenes lineages I and II were grown in brain heart infusion (BHI) broth as well as on the surface of commercially produced wet-cured, cold-smoked salmon slices at 7 °C. BHI broth and cold-smoked salmon were supplemented with sodium diacetate (SDA, 0.14% water phase (w.p.)), potassium lactate (PL, 2% w.p.), nisin (NI, 50 ppm), and binary combinations of inhibitors at the same levels. Cell densities of L. monocytogenes were measured over time and used to calculate growth parameters, including initial cell density ( N 0 ), lag phase (λ), maximum growth rate (μ max ), and maximum cell density ( N max ) for each antimicrobial treatment. N 0 was significantly lowered by addition of NI with a similar average reduction on salmon (2.02 ± 0.99 log(CFU/g)) and in BHI (1.51 ± 0.83 log(CFU/ml)). Among all antimicrobial treatments, the combination of PL and SDA led to the greatest increase in λ both on salmon (7.1 ± 3.6 days) and in BHI (9.7 ± 3.8 days) when compared to the controls. The combination of PL and SDA had synergistic effects on increasing λ and lowering N max both in BHI and on salmon. Among all the treatments tested, the combination of NI and PL led to the greatest reductions in N max on salmon. We observed positive correlations between the growth parameters obtained from BHI broth and cold-smoked salmon, indicating that growth of L. monocytogenes in broth, to some extent, qualitatively reflected characteristics of growth on cold-smoked salmon under antimicrobial stresses. Results from BHI could quantitatively predict the variability of growth parameters obtained from salmon for lineage II strains, but not for lineage I strains. Although results from laboratory growth medium may not provide exact predictions of antimicrobial efficacy on cold-smoked salmon, they could be used to rapidly identify effective combinations for further examination on cold-smoked salmon. more...
- Published
- 2012
20. Effect of curing method and freeze-thawing on subsequent growth of Listeria monocytogenes on cold-smoked salmon
- Author
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Kathryn J. Boor, Siyun Wang, Teresa M. Bergholz, Rui Hai Liu, Martin Wiedmann, Jihun Kang, and Silin Tang
- Subjects
Curing (food preservation) ,Time Factors ,Water activity ,Food Handling ,Colony Count, Microbial ,Food Contamination ,Biology ,medicine.disease_cause ,Microbiology ,chemistry.chemical_compound ,food ,Listeria monocytogenes ,Salmon ,Food Preservation ,medicine ,Animals ,Humans ,Food science ,Pathogen ,Inoculation ,Consumer Behavior ,biology.organism_classification ,food.food ,Lactic acid ,Smoked salmon ,Cold Temperature ,Kinetics ,chemistry ,Seafood ,Consumer Product Safety ,Taste ,Salts ,Bacteria ,Food Science - Abstract
The presence of the foodborne pathogen Listeria monocytogenes on cold-smoked salmon is a major concern for the seafood industry. Understanding processing and postprocessing handling factors that affect the ability of this pathogen to grow on cold-smoked salmon is critical for developing effective control strategies. In this study, we investigated the effect of curing method and freeze-thawing of cold-smoked salmon on (i) physicochemical properties and (ii) subsequent growth of genetically diverse strains of L. monocytogenes (inoculated after freeze-thawing) and endogenous lactic acid bacteria. The majority of the measured physicochemical properties were unaffected by freezing and thawing. Overall, wet-cured cold-smoked salmon had higher pH, water activity, and moisture, as well as lower fat, water-phase salt, and phenolic content compared with dry-cured cold-smoked salmon. The curing method and freeze-thawing did not affect growth of endogenous lactic acid bacteria. Freeze-thawing cold-smoked salmon prior to inoculation led to pronounced growth of L. monocytogenes at 7°C. The increase in cell density between days 0 and 30 was significantly (P = 0.0078) greater for cold-smoked salmon that was frozen and thawed prior to inoculation compared with nonfrozen cold-smoked salmon. On dry-cured, freeze-thawed cold-smoked salmon, L. monocytogenes had a lag phase ranging from 3.7 ± 0.1 to 11.2 ± 1.4 days compared with salmon that was wet cured and freeze-thawed, on which L. monocytogenes began to grow within 24 h. Variation in growth among L. monocytogenes strains was also observed, indicating the significance of assessing multiple strains. Further efforts to understand the impact of processing and postprocessing handling steps of cold-smoked salmon on the growth of genetically diverse L. monocytogenes will contribute to improved challenge study designs and data. This, in turn, will likely lead to more reliable and unbiased risk assessments and control measures. more...
- Published
- 2012
21. Listeria monocytogenes shows temperature-dependent and -independent responses to salt stress, including responses that induce cross-protection against other stresses
- Author
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Teresa M. Bergholz, Martin Wiedmann, Barbara M. Bowen, and Kathryn J. Boor
- Subjects
Osmotic shock ,Antiporter ,Sodium ,chemistry.chemical_element ,Sigma Factor ,Biology ,medicine.disease_cause ,Applied Microbiology and Biotechnology ,Microbiology ,Transcriptome ,chemistry.chemical_compound ,Listeria monocytogenes ,Bacterial Proteins ,Osmotic Pressure ,Stress, Physiological ,medicine ,Osmotic pressure ,Ecology ,Strain (chemistry) ,Gene Expression Profiling ,Temperature ,Membrane Transport Proteins ,Hydrogen Peroxide ,Up-Regulation ,chemistry ,Food Microbiology ,Salts ,Peptidoglycan ,Food Science ,Biotechnology - Abstract
The food-borne pathogen Listeria monocytogenes experiences osmotic stress in many habitats, including foods and the gastrointestinal tract of the host. During transmission, L. monocytogenes is likely to experience osmotic stress at different temperatures and may adapt to osmotic stress in a temperature-dependent manner. To understand the impact of temperature on the responses this pathogen uses to adapt to osmotic stress, we assessed genome-wide changes in the L. monocytogenes H7858 transcriptome during short-term and long-term adaptation to salt stress at 7°C and 37°C. At both temperatures, the short-term response to salt stress included increased transcript levels of sigB and SigB-regulated genes, as well as mrpABCDEFG , encoding a sodium/proton antiporter. This antiporter was found to play a role in adaptation to salt stress at both temperatures; Δ mrpABCDEFG had a significantly longer lag phase than the parent strain in BHI plus 6% NaCl at 7°C and 37°C. The short-term adaptation to salt stress at 7°C included increased transcript levels of two genes encoding carboxypeptidases that modify peptidoglycan. These carboxypeptidases play a role in the short-term adaptation to salt stress only at 7°C, where the deletion mutants had significantly different lag phases than the parent strain. Changes in the transcriptome at both temperatures suggested that exposure to salt stress could provide cross-protection to other stresses, including peroxide stress. Short-term exposure to salt stress significantly increased H 2 O 2 resistance at both temperatures. These results provide information for the development of knowledge-based intervention methods against this pathogen, as well as provide insight into potential mechanisms of cross-protection. more...
- Published
- 2012
22. The Transcriptional Response of Listeria monocytogenes during Adaptation to Growth on Lactate and Diacetate Includes Synergistic Changes That Increase Fermentative Acetoin Production▿†
- Author
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Martin Wiedmann, Teresa M. Bergholz, and Matthew J. Stasiewicz
- Subjects
Sodium Acetate ,Transcription, Genetic ,Biology ,Acetates ,medicine.disease_cause ,Applied Microbiology and Biotechnology ,Microbiology ,chemistry.chemical_compound ,Listeria monocytogenes ,Sodium diacetate ,Osmotic Pressure ,medicine ,Lactic Acid ,Cation Transport Proteins ,Potassium lactate ,chemistry.chemical_classification ,Ecology ,Acetoin ,Cold-Shock Response ,Vitamin K 2 ,Hydrogen-Ion Concentration ,Adaptation, Physiological ,Carbon ,Lactic acid ,Culture Media ,chemistry ,Biochemistry ,Fermentation ,Brain heart infusion ,Food Microbiology ,ATP-Binding Cassette Transporters ,Energy Metabolism ,Sodium acetate ,Acids ,Food Science ,Biotechnology ,Organic acid - Abstract
The organic acids lactate and diacetate are commonly used in combination in ready-to-eat foods because they show synergistic ability to inhibit the growth of Listeria monocytogenes . Full-genome microarrays were used to investigate the synergistic transcriptomic responses of two L. monocytogenes strains, H7858 (serotype 4b) and F6854 (serotype 1/2a), to these two organic acids under conditions representing osmotic and cold stress encountered in foods. Strains were exposed to brain heart infusion (BHI) broth at 7°C with 4.65% water-phase (w.p.) NaCl at pH 6.1 with (i) 2% w.p. potassium lactate, (ii) 0.14% w.p. sodium diacetate, (iii) the combination of both at the same levels, or (iv) no organic acids as a control. RNA was extracted 8 h after exposure, during lag phase, to capture gene transcription changes during adaptation to the organic acid stress. Significant differential transcription of 1,041 genes in H7858 and 640 genes in F6854 was observed in at least one pair of the 4 different treatments. The effects of combined treatment with lactate and diacetate included (i) synergistic transcription differences for 474 and 209 genes in H7858 and F6854, respectively, (ii) differential transcription of genes encoding cation transporters and ABC transporters of metals, and (iii) altered metabolism, including induction of a nutrient-limiting stress response, reduction of menaquinone biosynthesis, and a shift from fermentative production of acetate and lactate to energetically less favorable, neutral acetoin. These data suggest that additional treatments that interfere with cellular energy generation processes could more efficiently inhibit the growth of L. monocytogenes . more...
- Published
- 2011
23. Salt stress phenotypes in Listeria monocytogenes vary by genetic lineage and temperature
- Author
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Teresa M. Bergholz, Henk C. den Bakker, Kathryn J. Boor, Esther D. Fortes, and Martin Wiedmann
- Subjects
Lineage (genetic) ,Osmotic shock ,Colony Count, Microbial ,Biology ,Sodium Chloride ,medicine.disease_cause ,Applied Microbiology and Biotechnology ,Microbiology ,Evolution, Molecular ,Listeria monocytogenes ,Phylogenetics ,Stress, Physiological ,Genotype ,medicine ,Humans ,Gene ,Phylogenetic tree ,Reverse Transcriptase Polymerase Chain Reaction ,Temperature ,Gene Expression Regulation, Bacterial ,Original Articles ,Phenotype ,Genes, Bacterial ,Animal Science and Zoology ,Food Science - Abstract
Listeria monocytogenes can survive and grow under wide-ranging environmental stress conditions encountered both in foods and in the host. The ability of certain L. monocytogenes subtypes to thrive under stress conditions present in specific niches was hypothesized to reflect genetic characteristics and phenotypic capabilities conserved among strains within a subtype. To quantify variations in salt stress phenotypes among 40 strains selected to represent the diversity of the three major L. monocytogenes genetic lineages and to determine if salt stress phenotypes were associated with genetic relatedness, we measured growth under salt stress at both 7°C and 37°C. At 7°C, in brain–heart infusion with 6% NaCl, average growth rates among the lineages were similar. A comparison of doubling times after exposure to salt stress at 7°C or 37°C indicated that growth at 7°C provided crossprotection to subsequent salt stress for strains in lineages I and II. At 37°C, in brain–heart infusion with 6% NaCl, lineage I and III strains grew significantly faster (p more...
- Published
- 2010
24. The Combination of Lactate and Diacetate Synergistically Reduces Cold Growth in Brain Heart Infusion Broth across Listeria monocytogenes Lineages
- Author
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Teresa M. Bergholz, Matthew J. Stasiewicz, and Martin Wiedmann
- Subjects
Colony Count, Microbial ,Food Contamination ,Biology ,Acetates ,medicine.disease_cause ,Microbiology ,chemistry.chemical_compound ,Listeria monocytogenes ,Sodium diacetate ,Refrigeration ,Salmon ,Food Preservation ,medicine ,Animals ,Humans ,Food science ,Potassium lactate ,Phylogeny ,chemistry.chemical_classification ,Food preservation ,Environmental factor ,Drug Synergism ,biology.organism_classification ,Lactic acid ,Anti-Bacterial Agents ,Kinetics ,chemistry ,Seafood ,Consumer Product Safety ,Food Microbiology ,Food Preservatives ,Lactates ,Monte Carlo Method ,Bacteria ,Food Science ,Organic acid - Abstract
Combinations of organic acids are often used in ready-to-eat foods to control the growth of Listeria monocytogenes during refrigerated storage. The purpose of this study was to quantitatively assess synergy between two organic acid growth inhibitors under conditions similar to those present in cold-smoked salmon, and to assess the effect of evolutionary lineage on response to those growth inhibitors. Thirteen strains of L. monocytogenes, representing lineages I and II, were grown at 7 degrees C in broth at pH 6.1 and 4.65% water-phase NaCl, which was supplemented with 2% potassium lactate, 0.14% sodium diacetate, or the combination of both at the same levels. Our data suggest that lineages adapt similarly to these inhibitors, as the only significant growth parameter difference between lineages was a minor effect (+/- 0.16 day, P = 0.0499) on lag phase (lambda). For all strains, lactate significantly extended lambda, from 2.6 +/- 0.4 to 3.8 +/- 0.5 days (P < 0.001), and lowered the maximum growth rate (mu(max)) from 0.54 +/- 0.06 to 0.49 +/- 0.04 log(CFU/ml)/day (P < 0.001), compared with the control. Diacetate was ineffective alone, but in combination with lactate, synergistically increased lambda to 6.6 +/- 1.6 days (P < 0.001) and decreased mu(max) to 0.34 +/- 0.05 log(CFU/ml)/day (P < 0.001). Monte Carlo simulations provided further evidence for synergy between diacetate and lactate by predicting signficantly slower growth to nominal endpoints for the combination of inhibitors. This study shows potassium lactate and sodium diacetate have significant synergistic effects on both lambda and mu(max) of L. monocytogenes at refrigeration temperature in broth, and justifies combining these inhibitors, at effective levels, in food product formulations. more...
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