George Nychas | Agricultural University of Athens (original) (raw)

Papers by George Nychas

Research paper thumbnail of Intra- and inter-species interactions within biofilms of important foodborne bacterial pathogens

Frontiers in Microbiology, 2015

A community-based sessile life style is the normal mode of growth and survival for many bacterial... more A community-based sessile life style is the normal mode of growth and survival for many bacterial species. Under such conditions, cell-to-cell interactions are inevitable and ultimately lead to the establishment of dense, complex and highly structured biofilm populations encapsulated in a self-produced extracellular matrix and capable of coordinated and collective behavior. Remarkably, in food processing environments, a variety of different bacteria may attach to surfaces, survive, grow, and form biofilms. Salmonella enterica, Listeria monocytogenes, Escherichia coli, and Staphylococcus aureus are important bacterial pathogens commonly implicated in outbreaks of foodborne diseases, while all are known to be able to create biofilms on both abiotic and biotic surfaces. Particularly challenging is the attempt to understand the complexity of inter-bacterial interactions that can be encountered in such unwanted consortia, such as competitive and cooperative ones, together with their impact on the final outcome of these communities (e.g., maturation, physiology, antimicrobial resistance, virulence, dispersal). In this review, up-to-date data on both the intra- and inter-species interactions encountered in biofilms of these pathogens are presented. A better understanding of these interactions, both at molecular and biophysical levels, could lead to novel intervention strategies for controlling pathogenic biofilm formation in food processing environments and thus improve food safety.

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Research paper thumbnail of The effect of the olive phenolic compound, oleuropein, on growth and enterotoxin B production by Staphylococcus aureus

The Journal of applied bacteriology, 1993

The presence of low concentrations (0.1% w/v) of oleuropein, a phenolic compound extracted from o... more The presence of low concentrations (0.1% w/v) of oleuropein, a phenolic compound extracted from olives, delayed the growth of Staphylococcus aureus in NZ amine A and brain heart infusion media modified by the addition of growth factors and glucose (NZA+ and BHI+), as indicated by changes in conductance, whilst higher concentrations (0.4-0.6% w/v) inhibited growth completely. Intermediate concentrations of oleuropein (0.2%) prevented growth in BHI+ but allowed growth to occur in NZA+ despite an extended lag phase (30 h). Concentrations of oleuropein > 0.2% inhibited growth and production of enterotoxin B in both types of media. Lower levels (0.1%) did not affect the final viable count and production of toxin in BHI+ but decreased the number of viable organisms and reduced the toxin production in NZA+ by eightfold. An increase in the concentration of oleuropein resulted in a decrease in the amount of glucose assimilated and consequently the amount of lactate produced. In addition, ...

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Research paper thumbnail of Staphylococcus aureus S-6: factors affecting its growth, enterotoxin B production and exoprotein formation

Journal of Applied Bacteriology, 1991

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Research paper thumbnail of Genotypic characterization of Brochothrix thermosphacta isolated during storage of minced pork under aerobic or modified atmosphere packaging conditions

Meat Science, 2012

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Research paper thumbnail of Modeling the Listeria monocytogenes survival/death curves using wavelet neural networks

The 2010 International Joint Conference on Neural Networks (IJCNN), 2010

Abstract The development of accurate models to describe and predict pressure inactivation kinetic... more Abstract The development of accurate models to describe and predict pressure inactivation kinetics of microorganisms is very beneficial to the food industry for optimization of process conditions. The need for “intelligent” methods to model highly nonlinear systems is long ...

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Research paper thumbnail of Effects of essential oil from mint ( Mentha piperita ) on Salmonella enteritidis and Listeria monocytogenes in model food systems at 4° and 10°C

Journal of Applied Bacteriology, 1995

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Research paper thumbnail of Modeling and predicting spoilage of cooked, cured meat products by multivariate analysis

Meat Science, 2007

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Research paper thumbnail of Rapid monitoring of the spoilage of minced beef stored under conventionally and active packaging conditions using Fourier transform infrared spectroscopy in tandem with chemometrics

Meat Science, 2009

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Research paper thumbnail of Microbial colonization of naturally black olives during fermentation and associated biochemical activities in the cover brine

Letters in Applied Microbiology, 2002

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Research paper thumbnail of Phenolic extract from olives: inhibition of Staphylococcus aureus

Letters in Applied Microbiology, 1990

... growth of Staph. aureus in static cultures was markedly influ-enced by the composition of the... more ... growth of Staph. aureus in static cultures was markedly influ-enced by the composition of the growth medium. NZA medium was invariably superior to BHI when judged by cell proliferation and protein secretion. In practice, the ...

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Research paper thumbnail of Antilisterial Properties of Marinades during Refrigerated Storage and Microwave Oven Reheating against Post-Cooking Inoculated Chicken Breast Meat

Journal of Food Science, 2013

This study evaluated growth of Listeria monocytogenes inoculated on cooked chicken meat with diff... more This study evaluated growth of Listeria monocytogenes inoculated on cooked chicken meat with different marinades and survival of the pathogen as affected by microwave oven reheating. During aerobic storage at 7 °C, on days 0, 1, 2, 4, and 7, samples were reheated by microwave oven (1100 W) for 45 or 90 s and analyzed microbiologically. L. monocytogenes counts on nonmarinated (control) samples increased (P < 0.05) from 2.7 ± 0.1 (day-0) to 6.9 ± 0.1 (day-7) log CFU/g during storage. Initial (day-0) pathogen counts of marinated samples were <0.5 log CFU/g lower than those of the control, irrespective of marinating treatment. At 7 d of storage, pathogen levels on samples marinated with tomato juice were not different (P ≥ 0.05; 6.9 ± 0.1 log CFU/g) from those of the control, whereas for samples treated with the remaining marinades, pathogen counts were 0.7 (soy sauce) to 2.0 (lemon juice) log CFU/g lower (P < 0.05) than those of the control. Microwave oven reheating reduced L. monocytogenes counts by 1.9 to 4.1 (45 s) and >2.4 to 5.0 (90 s) log CFU/g. With similar trends across different marinates, the high levels of L. monocytogenes survivors found after microwave reheating, especially after storage for more than 2 d, indicate that length of storage and reheating time need to be considered for safe consumption of leftover cooked chicken.

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Research paper thumbnail of A study of the minimum inhibitory concentration and mode of action of oregano essential oil, thymol and carvacrol

Journal of Applied Microbiology, 2001

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Research paper thumbnail of Microbiological and physicochemical changes in minced meats under carbon dioxide, nitrogen or air at 3°C

International Journal of Food Science & Technology, 2007

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Research paper thumbnail of Potential of multispectral imaging technology for rapid and non-destructive determination of the microbiological quality of beef filets during aerobic storage

International Journal of Food Microbiology, 2014

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Research paper thumbnail of Modelling Salmonella concentration throughout the pork supply chain by considering growth and survival in fluctuating conditions of temperature, pH and aw

International Journal of Food Microbiology, 2011

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Research paper thumbnail of Potential of a simple HPLC-based approach for the identification of the spoilage status of minced beef stored at various temperatures and packaging systems

International Journal of Food Microbiology, 2011

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Research paper thumbnail of Attachment and biofilm formation by Escherichia coli O157:H7 at different temperatures, on various food-contact surfaces encountered in beef processing

International Journal of Food Microbiology, 2011

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Research paper thumbnail of The effect of glucose supplementation on the spoilage microflora and chemical composition of minced beef stored aerobically or under a modified atmosphere at 4 °C

International Journal of Food Microbiology, 1996

Glucose was added to minced meat (pH 6.0) and stored under aerobic or a modified atmosphere (MA) ... more Glucose was added to minced meat (pH 6.0) and stored under aerobic or a modified atmosphere (MA) composed of 80% O2 and 20% CO2 to assess the effects of carbohydrate on the microbial association and the chemical properties of the meat. The type of packaging affected the size and the final composition of the microflora. The microbial composition of the mince without added glucose in air or MA, given in log10 cfu/g respectively, were pseudomonads (9.8 and 7.3), Brochothrix thermosphacta (8.5 and 8.1), lactic acid bacteria (8.8 and 8.7), Enterobacteriaceae (7.2 and 6.1) and yeasts (4.3 and 4.2). In mince supplemented with 0.2% (w/w) glucose, similar composition and numbers were observed. Glucose, glucose 6-phosphate and lactic acid were consumed at slower rates by the flora on meat stored under MA than by the flora on meat stored in air. The addition of glucose enhanced gluconate production by the flora on meat stored in air. D-lactic and acetic acid were produced in all samples stored under the MA.

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Research paper thumbnail of Behavior of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Typhimurium in teewurst, a raw spreadable sausage

International Journal of Food Microbiology, 2009

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Research paper thumbnail of Field evaluation of the application of time temperature integrators for monitoring fish quality in the chill chain

International Journal of Food Microbiology, 2005

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Research paper thumbnail of Intra- and inter-species interactions within biofilms of important foodborne bacterial pathogens

Frontiers in Microbiology, 2015

A community-based sessile life style is the normal mode of growth and survival for many bacterial... more A community-based sessile life style is the normal mode of growth and survival for many bacterial species. Under such conditions, cell-to-cell interactions are inevitable and ultimately lead to the establishment of dense, complex and highly structured biofilm populations encapsulated in a self-produced extracellular matrix and capable of coordinated and collective behavior. Remarkably, in food processing environments, a variety of different bacteria may attach to surfaces, survive, grow, and form biofilms. Salmonella enterica, Listeria monocytogenes, Escherichia coli, and Staphylococcus aureus are important bacterial pathogens commonly implicated in outbreaks of foodborne diseases, while all are known to be able to create biofilms on both abiotic and biotic surfaces. Particularly challenging is the attempt to understand the complexity of inter-bacterial interactions that can be encountered in such unwanted consortia, such as competitive and cooperative ones, together with their impact on the final outcome of these communities (e.g., maturation, physiology, antimicrobial resistance, virulence, dispersal). In this review, up-to-date data on both the intra- and inter-species interactions encountered in biofilms of these pathogens are presented. A better understanding of these interactions, both at molecular and biophysical levels, could lead to novel intervention strategies for controlling pathogenic biofilm formation in food processing environments and thus improve food safety.

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Research paper thumbnail of The effect of the olive phenolic compound, oleuropein, on growth and enterotoxin B production by Staphylococcus aureus

The Journal of applied bacteriology, 1993

The presence of low concentrations (0.1% w/v) of oleuropein, a phenolic compound extracted from o... more The presence of low concentrations (0.1% w/v) of oleuropein, a phenolic compound extracted from olives, delayed the growth of Staphylococcus aureus in NZ amine A and brain heart infusion media modified by the addition of growth factors and glucose (NZA+ and BHI+), as indicated by changes in conductance, whilst higher concentrations (0.4-0.6% w/v) inhibited growth completely. Intermediate concentrations of oleuropein (0.2%) prevented growth in BHI+ but allowed growth to occur in NZA+ despite an extended lag phase (30 h). Concentrations of oleuropein > 0.2% inhibited growth and production of enterotoxin B in both types of media. Lower levels (0.1%) did not affect the final viable count and production of toxin in BHI+ but decreased the number of viable organisms and reduced the toxin production in NZA+ by eightfold. An increase in the concentration of oleuropein resulted in a decrease in the amount of glucose assimilated and consequently the amount of lactate produced. In addition, ...

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Research paper thumbnail of Staphylococcus aureus S-6: factors affecting its growth, enterotoxin B production and exoprotein formation

Journal of Applied Bacteriology, 1991

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Research paper thumbnail of Genotypic characterization of Brochothrix thermosphacta isolated during storage of minced pork under aerobic or modified atmosphere packaging conditions

Meat Science, 2012

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Modeling the Listeria monocytogenes survival/death curves using wavelet neural networks

The 2010 International Joint Conference on Neural Networks (IJCNN), 2010

Abstract The development of accurate models to describe and predict pressure inactivation kinetic... more Abstract The development of accurate models to describe and predict pressure inactivation kinetics of microorganisms is very beneficial to the food industry for optimization of process conditions. The need for “intelligent” methods to model highly nonlinear systems is long ...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Effects of essential oil from mint ( Mentha piperita ) on Salmonella enteritidis and Listeria monocytogenes in model food systems at 4° and 10°C

Journal of Applied Bacteriology, 1995

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Modeling and predicting spoilage of cooked, cured meat products by multivariate analysis

Meat Science, 2007

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Rapid monitoring of the spoilage of minced beef stored under conventionally and active packaging conditions using Fourier transform infrared spectroscopy in tandem with chemometrics

Meat Science, 2009

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Microbial colonization of naturally black olives during fermentation and associated biochemical activities in the cover brine

Letters in Applied Microbiology, 2002

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Phenolic extract from olives: inhibition of Staphylococcus aureus

Letters in Applied Microbiology, 1990

... growth of Staph. aureus in static cultures was markedly influ-enced by the composition of the... more ... growth of Staph. aureus in static cultures was markedly influ-enced by the composition of the growth medium. NZA medium was invariably superior to BHI when judged by cell proliferation and protein secretion. In practice, the ...

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Research paper thumbnail of Antilisterial Properties of Marinades during Refrigerated Storage and Microwave Oven Reheating against Post-Cooking Inoculated Chicken Breast Meat

Journal of Food Science, 2013

This study evaluated growth of Listeria monocytogenes inoculated on cooked chicken meat with diff... more This study evaluated growth of Listeria monocytogenes inoculated on cooked chicken meat with different marinades and survival of the pathogen as affected by microwave oven reheating. During aerobic storage at 7 °C, on days 0, 1, 2, 4, and 7, samples were reheated by microwave oven (1100 W) for 45 or 90 s and analyzed microbiologically. L. monocytogenes counts on nonmarinated (control) samples increased (P < 0.05) from 2.7 ± 0.1 (day-0) to 6.9 ± 0.1 (day-7) log CFU/g during storage. Initial (day-0) pathogen counts of marinated samples were <0.5 log CFU/g lower than those of the control, irrespective of marinating treatment. At 7 d of storage, pathogen levels on samples marinated with tomato juice were not different (P ≥ 0.05; 6.9 ± 0.1 log CFU/g) from those of the control, whereas for samples treated with the remaining marinades, pathogen counts were 0.7 (soy sauce) to 2.0 (lemon juice) log CFU/g lower (P < 0.05) than those of the control. Microwave oven reheating reduced L. monocytogenes counts by 1.9 to 4.1 (45 s) and >2.4 to 5.0 (90 s) log CFU/g. With similar trends across different marinates, the high levels of L. monocytogenes survivors found after microwave reheating, especially after storage for more than 2 d, indicate that length of storage and reheating time need to be considered for safe consumption of leftover cooked chicken.

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Research paper thumbnail of A study of the minimum inhibitory concentration and mode of action of oregano essential oil, thymol and carvacrol

Journal of Applied Microbiology, 2001

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Microbiological and physicochemical changes in minced meats under carbon dioxide, nitrogen or air at 3°C

International Journal of Food Science & Technology, 2007

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Research paper thumbnail of Potential of multispectral imaging technology for rapid and non-destructive determination of the microbiological quality of beef filets during aerobic storage

International Journal of Food Microbiology, 2014

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Modelling Salmonella concentration throughout the pork supply chain by considering growth and survival in fluctuating conditions of temperature, pH and aw

International Journal of Food Microbiology, 2011

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Potential of a simple HPLC-based approach for the identification of the spoilage status of minced beef stored at various temperatures and packaging systems

International Journal of Food Microbiology, 2011

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Attachment and biofilm formation by Escherichia coli O157:H7 at different temperatures, on various food-contact surfaces encountered in beef processing

International Journal of Food Microbiology, 2011

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The effect of glucose supplementation on the spoilage microflora and chemical composition of minced beef stored aerobically or under a modified atmosphere at 4 °C

International Journal of Food Microbiology, 1996

Glucose was added to minced meat (pH 6.0) and stored under aerobic or a modified atmosphere (MA) ... more Glucose was added to minced meat (pH 6.0) and stored under aerobic or a modified atmosphere (MA) composed of 80% O2 and 20% CO2 to assess the effects of carbohydrate on the microbial association and the chemical properties of the meat. The type of packaging affected the size and the final composition of the microflora. The microbial composition of the mince without added glucose in air or MA, given in log10 cfu/g respectively, were pseudomonads (9.8 and 7.3), Brochothrix thermosphacta (8.5 and 8.1), lactic acid bacteria (8.8 and 8.7), Enterobacteriaceae (7.2 and 6.1) and yeasts (4.3 and 4.2). In mince supplemented with 0.2% (w/w) glucose, similar composition and numbers were observed. Glucose, glucose 6-phosphate and lactic acid were consumed at slower rates by the flora on meat stored under MA than by the flora on meat stored in air. The addition of glucose enhanced gluconate production by the flora on meat stored in air. D-lactic and acetic acid were produced in all samples stored under the MA.

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Research paper thumbnail of Behavior of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Typhimurium in teewurst, a raw spreadable sausage

International Journal of Food Microbiology, 2009

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Field evaluation of the application of time temperature integrators for monitoring fish quality in the chill chain

International Journal of Food Microbiology, 2005

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