Michel Gautier

Agrocampus Ouest, Roazhon, Brittany, France

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Publications (66)98.32 Total impact

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    ABSTRACT: Salmonella enterica serovar Enteritidis is the prevalent egg-product-related food-borne pathogen. The egg-contamination capacity of S. Enteritidis includes its exceptional survival capability within the harsh conditions provided by egg white. Egg white proteins, such as lysozyme and ovotransferrin, are well known to play important roles in defence against bacterial invaders. Indeed, several additional minor proteins and peptides have recently been found to play known or potential roles in protection against bacterial contamination. However, although such antibacterial proteins are well studied, little is known about their efficacy under the environmental conditions prevalent in egg white. Thus, the influence of factors such as temperature, alkalinity, nutrient restriction, viscosity and cooperative interactions on the activities of antibacterial proteins in egg white remains unclear. This review critically assesses the available evidence on the antimicrobial components of egg white. In addition, mechanisms employed by S. Enteritidis to resist egg white exposure are also considered along with various genetic studies that have shed light upon egg white resistance systems. We also consider how multiple, antibacterial proteins operate in association with specific environmental factors within egg white to generate a lethal protective cocktail that preserves sterility.
    No preview · Article · Jan 2016
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    ABSTRACT: Le comité d’organisation : Véronique Broussolle, UMR 408 SQPOV, INRA PACA Avignon Frédéric Carlin, UMR 408 SQPOV, INRA PACA Avignon Didier Lereclus, UMR 319 Micalis, INRA Jouy-en-Josas Christina Nielsen-Leroux, UMR 1319 Micalis, INRA Jouy-en-Josas Vincent Sanchis, UMR 1319 Micalis, INRA Jouy-en-Josas
    Full-text · Article · Jul 2015
  • Sophie Jan · Florence Baron · Michel Gautier
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    ABSTRACT: With 215 eggs consumed per person in 2013, France remains one of the largest consumers of eggs in the European Union. Over a third of this consumption is in the form of egg products. Egg products from ‘first processing’ are defined as resulting from the breaking of table eggs, giving rise to the recovery of whole egg or separated egg yolk and eggwhite, with the possible addition of salt, sugar and hydrocolloids. They are mainly delivered in the form of refrigerated liquid egg, but also as froze nor dried powder products. They are widely used for various food applications, suitable as ingredients for the food industry, artisans, and catering.Unlike shell eggs which are protected by the physic al barriers of the eggshell and the shell membranes and by the efficient antimicrobial activi ties of egg white, egg products are very sensitive from a microbiological point of view. That is the reason why a particular attention is paid to the microbial control of bacterial contamination alongthe different steps of egg processing. Liquid egg products are systematically pasteurized and storedat chilled temperatures. These processes allow controlling pathogenic bacteria, including Salmonella Enteritidis, which remains the main bacterium involved in foodborne diseases associated with egg and egg product consumption. However, the mild heat processes carried out for respecting the conformation of egg proteins are too low for eradicating heat-resistant bacteria, and particular ly when these bacteria present the specific ability to settle in the industrial equipment in the form of biofilms. In addition, psychrotrophy may represent an advantage for this flora to grow in the egg products, leading to spoilage events during storage, and particularly in the case of compromise d cold chain integrity. A focus will be made on this emerging flora which control would help reducing food wastes in the future.
    No preview · Article · May 2015
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    ABSTRACT: Lysozyme is mainly described active against Gram-positive bacteria, but is also efficient against some Gram-negative species. Especially, it was recently demonstrated that lysozyme disrupts Escherichia coli membranes. Moreover, dry-heating changes the physicochemical properties of the protein and increases the membrane activity of lysozyme. In order to elucidate the mode of insertion of lysozyme into the bacterial membrane, the interaction between lysozyme and a LPS monolayer mimicking the E. coli outer membrane has been investigated by tensiometry, ellipsometry, Brewster angle microscopy and atomic force microscopy. It was thus established that lysozyme has a high affinity for the LPS monolayer, and is able to insert into the latter as long as polysaccharide moieties are present, causing reorganization of the LPS monolayer. Dry-heating increases the lysozyme affinity for the LPS monolayer and its insertion capacity; the resulting reorganization of the LPS monolayer is different and more drastic than with the native protein.
    Full-text · Article · Jan 2015 · Biochimica et Biophysica Acta (BBA) - Biomembranes
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    ABSTRACT: Antimicrobial resistance is currently an important public health issue. The need for innovative antimicrobials is therefore growing. The ideal antimicrobial compound should limit antimicrobial resistance. Antimicrobial peptides or proteins such as hen egg white lysozymes are promising molecules that act on bacterial membranes. Hen egg white lysozymes have recently been identified as active on Gram-negative bacteria due to disruption of the outer and cytoplasmic membrane integrity. Furthermore, dry-heating (7days and 80°C) improves the membrane activity of lysozymes, resulting in higher antimicrobial activity. These in vivo findings suggest interactions between lysozymes and membrane lipids. This is consistent with the findings of several other authors who have shown lysozyme interaction with bacterial phospholipids such as phosphatidylglycerol and cardiolipin. However, until now, the interaction between lysozyme and bacterial cytoplasmic phospholipids has been in need of clarification. This study proposes the use of monolayer models with a realistic bacterial phospholipid composition in physiological conditions. The lysozyme/phospholipid interactions have been studied by surface pressure measurements, ellipsometry and atomic force microscopy. Native lysozyme has proved able to absorb and insert into a bacterial phospholipid monolayer, resulting in lipid packing reorganization, which in turn has lead to lateral cohesion modifications between phospholipids. Dry-heating of lysozymes has increased insertion capacity and ability to induce lipid packing modifications. These in vitro findings are then consistent with the increased membrane disruption potential of dry heated lysozyme in vivo compared to native lysozyme. Moreover, an eggPC monolayer study suggested that lysozyme/phospholipid interactions are specific to bacterial cytoplasmic membranes. Copyright © 2015. Published by Elsevier B.V.
    Full-text · Article · Jan 2015 · Biochimica et Biophysica Acta (BBA) - Biomembranes
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    ABSTRACT: As a 1st step, this study aimed at investigating the microbial quality of liquid egg white in a French egg processing company. Thirty raw and 33 pasteurized liquid egg white samples were analyzed. Pasteurization was globally found efficient on mesophilic contaminants (1.7 ± 1.6 and 0.8 ± 0.9 log CFU/mL in raw and pasteurized samples, respectively), including for the control of Salmonella. However,Gram-positive enterococci were still detected in the pasteurized samples. As a 2nd step, a representative bacterial collection was built for exploring the spoilage issue in egg-based chilled desserts. Custard cream was chosen as growth medium since this food is widely used for the production of French chilled desserts. All of the 166 isolates of the bacterial collection were shown to be able to grow and to induce spoilage of the custard cream at refrigeration temperature (10 °C). Several spoilage types were highlighted in the custard cream, on the basis of changes regarding pH, consistency, production of holes or gas. As a 3rd step, bacterial enzymatic activities were explored on custard cream-based agar media. The bacterial collection was reduced to 43 isolates, based on further selection regarding the genera and the spoilage types previously highlighted. Albeit to different degrees, all these isolates were able to produce proteases. A large part of these isolates also expressed lipolytic and amylolytic activities. This study emphasizes the need to control egg white contamination and especially with Gram-positive heat-resistant Enterococi, in order to guarantee the shelf life of egg-based chilled desserts.
    No preview · Article · Jan 2015 · Journal of Food Science
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    ABSTRACT: The objective of this study was to develop and evaluate a SYBR Green real-time PCR method for the specific detection of Salmonella spp using a novel target, the siiA gene. Primers specificity testing was done on a panel of 76 Salmonella strains and 32 non-Salmonella strains. The primers directed against the siiA gene amplified all Salmonella strains tested, while non-Salmonella strains were not amplified. The melting temperatures of the 107bp amplicons were consistently specific as they gave melting peaks around 75.5°C. The precision of the assay, based on intra and inter-run variations, was shown to be widely acceptable. In the second part of this study, 45 Salmonella strains were screened for the presence of 6 virulence-associated genes (sopB, cat2, safC, sefB and SC1248) located in several Salmonella Pathogenicity Islands (SPIs) and the spvC gene from the Salmonella virulence plasmid. The prevalence of these genes ranged from 51% to 100%. Variable virulence gene profiles were obtained even within the same serotype. Copyright © 2014. Published by Elsevier B.V.
    No preview · Article · Dec 2014 · Journal of Microbiological Methods
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    ABSTRACT: The reduction of wastes due to food spoilage may help save food resources among the current worldwide food production. Industrial egg products, obtained after egg breaking, recovery and pasteurisation of the internal egg components, are used in a wide range of food, including chilled egg- and milk-based food particularly susceptible to microbial spoilage due to their low cooking temperatures. One of the main bacteria involved in the spoilage of pasteurized egg and dairy products belongs to the spore-former B. cereus group. Several members of this group may lead to food spoilage due to their enzymatic activities, even at low temperatures. However, the risk of spoilage has mainly been assessed by targeting enzymatic activities in dairy products or in vegetables foods that do not require chilled storage.In order to consider more accurately the food spoilage issue at both optimal and low temperatures, this work proposes to characterize the enzymatic potential of a collection of 68 strains of the B. cereus group, coming from pasteurized liquid egg products collected in the French egg breaking industry at two consecutive seasons. An egg-based medium was designed, allowing the kinetic characterisation of bacterial lipases and proteases at optimal and refrigeration temperatures. The results contribute to further investigate a comprehensive bacterial collection that was already characterised for its cold adaptation, its ability to grow in whole egg at higher levels than in optimum laboratory medium, to colonize the industrial surfaces, and to induce phase, texture and colour shifts of whole egg.This study contributes to the search for early markers that could help the producers of pasteurized liquid egg and dairy products to better assess the microbial quality of their products for their orientation towards specific applications.
    No preview · Article · Sep 2014
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    ABSTRACT: The consumption of chilled dairy desserts is increasing in the European Union. The famous French “île flottante”, consisting in a foam of egg white floating on a custard cream, represents a highly nutritive medium for bacterial growth and for the expression of enzymes susceptible to affect the food shelf-life at chilled temperatures. To avoid such issues, the suppliers may either adjust the processes of heat-treatment -but this means of control is limited due to the high heat-sensitivity of egg proteins- or incorporate food additives. However, there is an increasing consumer demand for natural products without preservatives. The present study aims at better controlling the spoilage events by fully characterising the bacterial biodiversity and spoilage potential during cold storage.Sixty-five spoiled desserts delivered by two companies were analysed for their (i) sensorial characteristics and (ii) bacterial counts and 16S rDNA sequencing. Five hundred sixty-six isolates were further studied through an in vivo (in pure custard cream) spoilage test at 10°C. An in vitro (in a custard cream-based medium) test allowed assaying the expression of proteases (10°C) and growth (6°C). The expression of lipases was assayed on PCA tributyrin agar (10°C).The spoilage mainly concerned the custard cream part of the dessert, exhibiting high bacterial counts (> 6 log UFC/mL), pH decrease, thickening, coagulation and appearance of off-odours. Eighty bacterial genera were identified, mainly corresponding to Gram positive bacteria. The contamination by the Bacillus cereus group concerned 80% of the spoiled desserts. Fifty-seven and 8% of the recovered isolates expressed proteolytic and lipolytic activities at 10°C. Thirty four percents was able to grow at 6°C in the in vitro test. A statistical analysis of the whole data highlighted various correlations between the type of bacterium, its growth and enzymatic potentials at low temperature, and the spoilage characteristics of the dessert.
    No preview · Article · Sep 2014
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    ABSTRACT: Although egg white is known as expressing efficient antimicrobial properties under physiological conditions, little is known on the microbial quality of industrial egg white. This issue is of great importance when egg white enters into the composition of highly perishable products, such as chilled egg-based desserts. Due to the high thermo-sensitivity of its constitutive proteins, liquid egg white is stabilized at low heat-treating times and temperatures (2 to 6 min at 55°C to 57°C in France). The remaining of heat-resisting bacteria may shorten the shelf-life of the desserts, with damaging health and economical consequences. The objective of this study was to investigate the microbial quality of raw and pasteurized liquid egg white products collected in a French company at two consecutive warm and cold seasons. A total of 63 samples were analyzed, including 30 raw and 33 pasteurized (at 57°C for 6 min) liquid egg white products. The level and type of bacterial contamination was evaluated by pour-plating in PCA (incubation for 24h at 30°C under aerobic conditions) and 16SrDNA sequencing of the colonies. The average counts were fairly low and a broad range of population was highlighted from one sample to another, namely 1.7 ± 1.6 log CFU/mL
    No preview · Article · Jul 2014
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    ABSTRACT: Antibiotic resistance causes public health problems and stimulates research for novelantimicrobials. Particular attention is given to molecules that limit drug resistancedevelopment.1Hen egg white lysozyme acting on the bacterial cell envelope through itsphysico-chemical properties is thus a good candidate.2,3However, its antimicrobial effectcaused by membrane permeabilization on Gram-negative bacteria remains limited. But somephysico-chemical modifications of the lysozyme can modify its membrane activity, increasinglysozyme antimicrobial properties against E. coli ; dry-heating is able to induce suchmodifications. 4 Especially, we previously highlighted that native (N-L) and dry-heatedlysozyme (DH-L) disrupt the outer membrane of E. coli , but in different ways.3,4 The mode of insertion into the bacterial outer membrane and molecular interactions remains unknown.This was thus investigated using an E. coli lipopolysaccharide monolayer (LPSM) membranemodel, mimicking the outer leaflet of the bacterial outer membrane. The interactions betweenlysozyme and LPSM were studied by tensiometry, ellipsometry, atomic force microscopy(AFM) and Brewster angle microscopy (BAM). Both N-L and DH-L are able to insert into aLPSM. As expected, electrostatic interactions between the negatively charged LPSM and bothpositively charged forms of lysozyme were observed. Furthermore, we could establish that N-L and DH-L insertion into the LPSM depends on the presence of the polysaccharide moieties.These polysaccharide chains might increase the space between the lipid headgroups, enablinglysozyme insertion. Moreover, dry-heating increases the lysozyme affinity for the LPSM.Microscopic observations (BAM and AFM) show that the LPSM reorganizes and reorients inthe presence of DH-L, in contrast to N-L. Dry-heating thus improves the lysozyme insertion,which might explain the increased activity on the outer membrane of E. coli , resulting in ahigher antimicrobial effec
    No preview · Article · Jun 2014
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    ABSTRACT: Bacillus cereus group bacteria are opportunistically pathogenic spore-forming microorganisms well known in the sector of pasteurized food products because of their involvement in spoilage events. In the sector of egg product processing, these bacteria may lead to important economic losses. It seemed then relevant to study their behavior in egg white, a widely used egg product usually recognized as developing different levels of antimicrobial activities depending on the environmental conditions. A strong bactericidal effect (decrease in the bacterial population of 6.1 ± 0.2 log CFU/ml) was observed for 68 B. cereus group isolates, independently incubated at 30°C in egg white at pH 9.3 (natural egg white pH). To determine which components could explain such a strong bactericidal effect, an experimental strategy was carried out, based on egg white fractionation by ultrafiltration and by anion-exchange liquid chromatography. The role of the protein fraction was thus demonstrated, and subsequent nano-liquid chromatography-tandem mass spectrometry analyses allowed identification of ovotransferrin as a major protein involved. The strong bactericidal effect was confirmed in the presence of commercial ovotransferrin. Such a bactericidal effect (i.e., a decrease in the bacterial population through cell death) had never been described because ovotransferrin is known for its bacteriostatic effect (i.e., inhibition of growth) due to its ability to chelate iron. Surprisingly, the addition of iron did not reverse the bactericidal effect of ovotransferrin under alkaline conditions (pH 9.3), whereas it completely reversed this effect at pH 7.3. Ovotransferrin was shown to provoke a perturbation of the electrochemical potential of the cytoplasmic membrane. A membrane disturbance mechanism could, hence, be involved, leading to the lysis of B. cereus group bacteria incubated in egg white.
    No preview · Article · Jun 2014 · Journal of food protection
  • Florence Baron · Michel Gautier · Sophie Jan
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    ABSTRACT: Quatrième Edition du Congrès Maghrébin sur les Toxi-infections alimentaires "Sécurité sanitaire des aliments face aux mutations sociétales et à la mondialisation" Fès (Maroc) - 16-18 Avril 2014 Le Maroc accueille du 16 au 18 Avril 2014 à la ville de Fès, la quatrième édition du Congrès Maghrébin sur les Toxi-infections alimentaires sous le thème : «Sécurité sanitaire des aliments face aux mutations sociétales et à la mondialisation». Deux ateliers en marge du congrès sont organisés les 15 et 16 Avril 2014 sous les thèmes : 1) Analyse critique des principes, des étapes de mise en place et de l’audit du système HACCP dans les établissements de produits alimentaires et 2) Microbiologie Prévisionnelle.
    No preview · Article · Apr 2014
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    ABSTRACT: Bovine abortion of unknown infectious etiology still remains a major economic problem. Thus, we investigated whether Brucella spp., Listeria monocytogenes, Salmonella spp., Campylobacter spp. and Coxiella burnetii are associated with abortion and/or stillbirth in Tunisian dairy cattle. Using a pan-Chlamydiales PCR, we also investigated the role of Chlamydiaceae, Waddlia chondrophila, Parachlamydia acanthamoebae and other members of the Chlamydiales order in this setting. Veterinary samples taken from mid to late-term abortions from twenty dairy herds were tested. From a total of 150 abortion cases collected, infectious agents were detected by PCR in 73 (48.66%) cases, 13 (8.66%) of which represented co-infections with two infectious agents. Detected pathogens include Brucella spp (31.3%), Chlamydiaceae (4.66%), Waddlia chondrophila (8%), Parachlamydia acanthamoebae (5.33%), Listeria monocytogenes (4.66%) and Salmonella spp. (3.33%). In contrast, Campylobacter spp. and Coxiella burnetii DNA were not detected among the investigated veterinary samples. This demonstrates that different bacterial agents may cause bovine abortion in Tunisia. This is the first report suggesting the role of Parachlamydia acanthamoebae in bovine abortion in Africa. Further studies with a larger number of samples are necessary to confirm whether this emerging pathogen is directly linked to abortion in cattle.
    Full-text · Article · Mar 2014 · PLoS ONE
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    ABSTRACT: To evaluate the food safety and spoilage risks associated with psychrotrophic Bacillus cereus group bacteria for the egg product industry, and to search for relevant risk markers. A collection of 68 psychrotrophic B. cereus group isolates, coming from pasteurized liquid whole egg products, was analyzed through a principal component analysis (PCA) regarding their spoilage and food safety risk potentials. The principal component analysis showed a clear differentiation between two groups within the collection, one half of the isolates representing a safety risk and the other half a spoilage risk. Relevant risk markers were highlighted by PCA, i.e. (i) for the food safety risk, the presence of the specific 16S rDNA-1m genetic signature and the ability to grow at 43°C on solid medium; and (ii) for the spoilage risk, the presence of the cspA genetic signature. This work represents a first step in the development of new diagnostic technologies for the assessment of the microbiological quality of foods likely to be contaminated with psychrotrophic B. cereus group bacteria. This article is protected by copyright. All rights reserved.
    Full-text · Article · Feb 2014 · Journal of Applied Microbiology
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    ABSTRACT: For food as well as for medical applications, there is a growing interest for novel and natural antimicrobial molecules. Lysozyme is a promising candidate for the development of such molecules. This protein is largely studied and known for its muramidase activity against Gram-positive bacteria, but it also shows antimicrobial activity against Gram-negative bacteria, especially when previously modified. In this study, the activity of dry-heated lysozyme (DH-L) against E. coli has been investigated and compared to that of native lysozyme (N-L). Whereas N-L only delays bacterial growth, DH-L causes an early stage population decrease. The accompanying membrane permeabilization suggests that DH-L induces either larger pores or more pores in the outer membrane as compared to N-L, as well as more ion channels in the inner membrane. The strong morphological modifications observed by optical microscopy and AFM when E. coli cells are treated with DH-L are consistent with the suggested disturbances of membrane integrity. The higher hydrophobicity, surface-activity and positive charge induced by dry-heating would be responsible of the increased activity of DH-L on the E. coli membranes.
    Full-text · Article · Jan 2014 · Journal of Agricultural and Food Chemistry
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    Full-text · Dataset · Dec 2013
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    ABSTRACT: All over the world, the incidence of Salmonella spp contamination on different food sources like broilers, clams and cow milk has increased rapidly in recent years. The multifaceted properties of Salomnella serovars allow the microorganism to grow and multiply in various food matrices, even under adverse conditions. Therefore, methods are needed to detect and trace this pathogen along the entire food supply network. In the present work, PFGE and ERIC-PCR were used to subtype 45 Salmonella isolates belonging to different serovars and derived from different food origins. Among these isolates, S. Enteritidis and S. Kentucky were found to be the most predominant serovars. The Discrimination Index obtained by ERIC-PCR (0.85) was slightly below the acceptable confidence value. The best discriminatory ability was observed when PFGE typing method was used alone (DI = 0.94) or combined with ERIC-PCR (DI = 0.93). A wide variety of profiles was observed between the different serovars using PFGE or/and ERIC-PCR. This diversity is particularly important when the sample origins are varied and even within the same sampling origin.
    Full-text · Article · Dec 2013 · PLoS ONE
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    ABSTRACT: Abstract This article reports the prevalence and antibiotic resistance of the Bacillus cereus group isolated from different foods (milk and dairy products, spices, and rice salad) in Morocco. In total, 402 different food samples collected from 2008 to 2010 were analyzed by microbiological methods to isolate B. cereus. The strains were subjected to a polymerase chain reaction test in order to verify whether they belonged to the B. cereus group. Sixty-four of all isolates (15.9%) were found to be positive. Among the sources, B. cereus strains from milk and dairy products constituted the largest proportion of isolates (33/64; 51.6%) followed by spices (22/64; 34.4%) and salad with rice (9/64; 14.1%). The genetic diversity of the strains of B. cereus group was examined by pulsed-field gel electrophoresis (PFGE) of chromosomal DNA digested with SmaI. The enzyme restriction profiles showed a high degree of polymorphism among the strains. The results showed that PFGE analysis could reveal the genetic differences among B. cereus strains. Investigation of antibiotic-resistance profiles showed that isolates were resistant to ampicillin (98.4%), tetracycline (90.6%), oxacillin (100%), cefepime (100%), and penicillin (100%), and were susceptible to chloramphenicol (67.2%), erythromycin (84.4%), and gentamicin (100%). The results of this study indicated that B. cereus could be a significant etiological agent of food poisoning in Morocco because of its high prevalence. Also, we demonstrated that the majority of strains came from milk and dairy products. However, additional research involving cytotoxicity tests is needed to more evaluate this sanitary risk.
    No preview · Article · Nov 2013 · Foodborne Pathogens and Disease
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    ABSTRACT: Natural preservatives answer the consumer demand for long shelf-life foods, considering synthetic molecules are perceived as a health risk. Lysozyme is already used because of its muramidase activity against Gram-positive bacteria. It is also described active against some Gram-negative bacteria; membrane disruption would be involved, but the mechanism remains unknown. In the presently reported study, a spectrophotometric method using the mutant Escherichia coli ML-35p, has been adapted to investigate membrane disruption by lysozyme for long durations. Lysozyme rapidly increases the permeability of the outer membrane of E. coli due to large size pore formation. A direct delayed activity of lysozyme against the inner membrane is also demonstrated, but without evidence of perforations.
    Full-text · Article · Sep 2013 · Journal of Agricultural and Food Chemistry