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The foodborne pathogen L.Monocytogenes can be effectively inhibited by acombination of nisin and modified atmosphere, and the shelf life of a product can be increased. In this study we propose to: <OL> <LI> Determine ATP hydrolysis and dissipation of Proton Motif Force(PMF) in listera <LI> Determine inhibition of listeria by combination of nisin, modified atmosphere and cold in liquid media and on the surface (agar plates) <LI> Determine efficiency of inhibition of listeria by combined hurdle technique in model food system (lettuce).
NON-TECHNICAL SUMMARY: Listeria is a harmful pathogen in food, and causes serious economic losses and health problems. Nisin and carbon dioxide enriched atmosphere are proposed as an efficient hurdle technology to inhibit the foodborne pathogen, Listeria, which has zero tolerance in ready-to-eat products. The effect of hurdle technology will be confirmed by evaluating the levels of cellular energy and integrity of the cell membrane. Cell energy and cell membrane integrity will be the significant signs of stress and damage cauased by antimicrobial treatment.
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APPROACH: The effectiveness of nisin and modified atmosphere against listeria will be determined as ATP hydrolysis and dissipation of PMF in the cells, as well as leakage of compounds from liposomes as a result of action of combined antimicrobial factors -- nisin and atmosphere composed of 10 percent carbon dioxide and 10 percent oxygen. In addition, we will study the effect of cold on the action of nisin and the modified atmosphere. We will also study the synergistic action of the combined factors (nisin, modified atmosphere and cold) on the growth of listeria cells in liquid media as well as on the surface (agar plates). Finally, we will show that nisin, modified atmosphere, and cold can inibit listeria on fresh produce, by using lettuce as a model food system.
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PROGRESS: 2002/03 TO 2005/03<BR>
With the assistance provided throughout this project, we were able to partially support one student. This resulted in the generating of data for understanding of the mechanisms underlying the susceptibility and resistance of a foodborne pathogen, Listeria monocytogenes to the natural antimicrobial nisin. We showed how adaptation to environmental factors can influence cell-antimicrobial interaction, resulting in the cell either having a higher sensitivity or a resistance to nisin. We also demonstrated (manuscript published) that although stress factors such as cold and a carbon dioxide enriched atmosphere cause morphological and physiological changes in the pathogen, these factors do not cause the appearance of VNC (viable but not culturable) cells, which are more resistant to preservatives and can survive in a nutrition limited environment for a long time in a dormant stage. Part of our project was dedicated to the elucidation of nisin's activity as a component of multiple hurdles, and resulted in a few manuscripts reporting nisin's enhanced activity in the presence of Zn lactate. Our effort on reviewing the current status of bacteriocins as food preservatives resulted in a paper which was recently reported to be in a group of the 1% highest referenced papers in the area since the date of its publication. This clearly the indicates significance of our effort on reviewing of the bacteriocins' safety for use in food preservation. One of our goals was to use the HATH-provided support to generate data which would allow us to study the controlled release of antimicrobials from a modified antimicrobial packaging material. Our goal was to understand the mechanism of the antimicrobial's release, and to understand how the pathogen responds to the instant addition of an antimicrobial, its slow delivery and to the combination of the two approaches. We achieved tremendous success in understanding the aspects of microbiological safety delivered by modified antimicrobial packaging that we modeled. As a clear recognition of the importance of our research, the resulting manuscript was published in the International Journal of Food Microbiology.
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IMPACT: 2002/03 TO 2005/03<BR>
CO2 would inhibit microbial growth but with higher risk of resistance development to nisin after adaptation. It is strongly suggested to use nisin and CO2 simultaneously to achieve synergistic effect. Parallel experiments using NR10 revealed similar results about the effects of the environmental factors. The underlying message is that the nisin resistant strain is more sensitive to additional stress factors than wild type because of the fitness cost posed by nisin. It is good news that even if nisin resistance were developed in L. monocytogenes, it could be controlled using another stress factor in combination with nisin.