Michel Gautier

Agrocampus Ouest, Roazhon, Brittany, France

Are you Michel Gautier?

Claim your profile

Publications (44)94.35 Total impact

  • [Show abstract] [Hide abstract]
    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.
    Biochimica et biophysica acta. 01/2015;
  • [Show abstract] [Hide abstract]
    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.Practical ApplicationThis study provides new insights on the bacterial contamination of industrial liquid egg white and represents the starting point for the control of spoilage issues in the sector of chilled egg-based desserts potentially hosting egg white bacterial contaminants.
    Journal of Food Science 01/2015; · 1.78 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Very strong lysozyme affinity for LPS makes its insertion possible into a LPS monolayer.•The polysaccharide moieties of LPS are essential for lysozyme insertion.•Lysozyme interaction with LPS causes a slight reorganization of the LPS monolayer.•Dry-heated lysozyme has a stronger affinity for LPS than native lysozyme.•Dry-heated lysozyme causes more radical reorganization of the LPS monolayer.
    Biochimica et Biophysica Acta (BBA) - Biomembranes 01/2015; 1848(1). · 3.43 Impact Factor
  • [Show abstract] [Hide abstract]
    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.
    Journal of Microbiological Methods 12/2014; · 2.10 Impact Factor
  • [Show abstract] [Hide abstract]
    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.
    Journal of food protection 06/2014; 77(6):955-62. · 1.80 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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.
    PLoS ONE 03/2014; 9(3):e91549. · 3.53 Impact Factor
  • [Show abstract] [Hide abstract]
    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.
    Journal of Applied Microbiology 02/2014; · 2.39 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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.
    Journal of Agricultural and Food Chemistry 01/2014; · 3.11 Impact Factor
  • Source
  • Source
    [Show abstract] [Hide abstract]
    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.
    PLoS ONE 12/2013; 8(12):e81315. · 3.53 Impact Factor
  • [Show abstract] [Hide abstract]
    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.
    Foodborne Pathogens and Disease 11/2013; · 2.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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.
    Journal of Agricultural and Food Chemistry 09/2013; · 3.11 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Bacterial membranes are often thought to be the main targets of the antimicrobial activity of egg white. In order to test this hypothesis, the state of the membranes of Escherichia coli K-12 cells during either bactericidal (45°C) or bacteriostatic (30°C) incubation in egg white at natural alkaline pH was studied by biochemical methods. Namely, the permeability of the outer membrane was evaluated through its ability to incorporate a hydrophobic fluorescent probe (1-N-phenylnaphthylamine), and the permeability of the cytoplasmic membrane was evaluated through the release of a specific intracellular enzyme (β-galactosidase). The bacteria were observed by atomic force microscopy in order to support the biochemical results. At 45°C, the outer membrane of E. coli K-12 incorporated the hydrophobic probe, suggesting that it was disrupted. In addition, the cytoplasmic β-galactosidase was released at this temperature. The atomic force microscopy analysis revealed the formation of spheroplasts, which provided further evidence of the cell wall disruption and a progressive release of cellular contents. At 30°C, biochemical and micrographic experiments confirmed that membrane integrity was preserved. These techniques provide a useful approach for studying the mechanisms of bacterial cell death in egg white.
    Journal of food protection 09/2013; 76(9):1523-9. · 1.80 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Bacillus cereus is widespread pathogen. It is widely distributed in several environments such as soil and plants and is commonly isolated from food and additives. In this study we analyzed 18 foodborne B. cereus strains isolated in Morocco from food samples (milk and dairy products, rice salade and spices), in order to investigate the genetic diversity (assessed by PFGE and ERIC-PCR). The food samples were collected from hotels (n=38), restaurants (n=32) and private companies (n=26) in several cities in Morocco. The results obtained in this study confirmed the diversity of B. cereus strains. The results showed that PFGE analysis has good discriminatory power but it is long to implement, which promotes the use of ERIC-PCR as a complementary tool for molecular typing. However, additional studies involving
    Food and Public Health. 06/2013; 3(4):223-227.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The species Bacillus cereus, known for its ability to cause food borne disease, consists of a large variety of strains. An important property for discrimination of strains is their growth temperature range. Fifty-two strains of Bacillus cereus isolated from different sources of food (milk, dairy product, spices and rice salad) for two years were determined to be either mesophilic or psychrotrophic by growth at 6 °C and at 43° C on optimal agar medium. The strains were also screened by real time polymerase chain reaction to discriminate between mesophilic and psychrotrophic types. The result obtained allowed highlighting eight profiles. Thirty seven of the 52 strains were able to grow at 6°C, but only thirteen conformed to the new psychrotolerant species Bacillus weihenstephanensis. The presence of the gene components encoding production of enterotoxins Nhe, Hbl, EntT and a recently described cytotoxin K was determined by PCR. All the strains possessed genes for at least one of these toxins. The nhe genes were detected in a higher proportion than hbl genes. Haemolytic enterotoxin was detected in 71.1 per cent of the isolates. Results of this study indicate that there are intermediate forms between B. cereus and B. weihenstephanensis, these results might be of importance for gaining further understanding of the growth properties of B. weihenstephanensis and psychrotolerant B. cereus as well as their contribution to food poisoning. However, no relationship among haemolysis test, enterotoxin genes and growth temperatures of the strains was found.
    International Journal of Engineering Research and Applications. 06/2013; 3(3):964-970.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Abstract 1. The growth of Bacillus cereus group bacteria often limits the shelf-life of pasteurised liquid egg products and is also a putative toxin producer. This study was performed to better understand the route of contamination by B. cereus in egg products by studying the factors affecting eggshell contamination on-farm. 2. Eggs were collected in warm and cold seasons in 50 conventional laying farms in Western France. Egg surfaces were analysed for the presence of B. cereus group bacteria, environmental measurements were recorded and production practices were identified through a questionnaire filled out by the farmers. 3. A total of 44% of the farms were contaminated by mesophilic and 10% by psychrotrophic B. cereus group bacteria. No significant effect of the season was observed, whatever the thermal type. Several procedures were associated with reduced eggshell contamination by mesophilic bacteria, including the limitation of dust formation from manure and feeding and efficient disinfection of the silo, houses and the sanitary wall between houses. 4. The research highlights the need to promote prevention strategies, from farm to fork, for the control of eggshell and putative subsequent egg product contamination by B. cereus group bacteria.
    British Poultry Science 05/2013; · 1.15 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The species Bacillus cereus, known for its ability to cause food borne disease, consists of a large variety of strains. An important property for discrimination of strains is their growth temperature range. Fifty-two strains of Bacillus cereus isolated from different sources of food (milk, dairy product, spices and rice salad) for two years were determined to be either mesophilic or psychrotrophic by growth at 6 °C and at 43° C on optimal agar medium. The strains were also screened by real time polymerase chain reaction to discriminate between mesophilic and psychrotrophic types. The result obtained allowed highlighting eight profiles. Thirty seven of the 52 strains were able to grow at 6°C, but only thirteen conformed to the new psychrotolerant species Bacillus weihenstephanensis. The presence of the gene components encoding production of enterotoxins Nhe, Hbl, EntT and a recently described cytotoxin K was determined by PCR. All the strains possessed genes for at least one of these toxins. The nhe genes were detected in a higher proportion than hbl genes. Haemolytic enterotoxin was detected in 71.1 per cent of the isolates. Results of this study indicate that there are intermediate forms between B. cereus and B. weihenstephanensis, these results might be of importance for gaining further understanding of the growth properties of B. weihenstephanensis and psychrotolerant B. cereus as well as their contribution to food poisoning. However, no relationship among haemolysis test, enterotoxin genes and growth temperatures of the strains was found.
    IJERA. 05/2013; 3(3):964-970.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A direct, label-free immunosensor was designed for the rapid detection and quantification of staphylococcal enterotoxin A (SEA) in buffered solutions using quartz crystal microbalance with dissipation (QCM-D) as transduction method. The sensing layer including the anti-SEA antibody was constructed by chemisorption of a self-assembled monolayer of cysteamine on the gold electrodes placed over the quartz crystal sensor followed by activation of the surface amino groups with the rigid homobifunctional cross-linker 1,4-phenylene diisothiocyanate (PDITC) and covalent linking of binding protein (protein A or protein G). Four anti-SEA antibodies (two of which from commercial source) have been selected to set up the most sensitive detection device. With the optimized sensing layer, a standard curve for the direct assay of SEA was established from QCM-D responses within a working range of 50-1000 or 2000 ngml(-1) with a detection limit of 20 ngml(-1). The total time for analysis was 15 min. Using a sandwich type assay, the response was ca. twice higher and consequently the lowest measurable concentration dropped down to 7 ngml(-1) for a total assay time of 25 min.
    Biosensors & Bioelectronics 08/2011; 29(1):140-4. · 6.45 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The aim of the present study was (i) to type, by genotypic and phenotypic methods, a collection of psychrotrophic bacteria belonging to the Bacillus cereus group collected in a farm and in 6 egg breaking industries during a period covering a warm and a cold season, and (ii) to characterize the egg product spoilage (growth in liquid whole egg) and the sanitary risk potential (cytotoxic activity on Caco-2 cells and adhesion on stainless steel) of each isolate of the collection. The investigation of specific psychrotrophic and mesophilic signatures together with the study of ability to grow at 6 °C and/or at 43 °C on optimal agar medium allowed highlighting twelve profiles, the major one corresponding to the species Bacillus weihenstephanensis (46.2% of the collection). The diversity of the profiles depended on the season and on the origin of the isolates. In terms of food spoilage, all the isolates were able to grow at the same level in liquid whole egg and in optimal medium, even at low temperature. Under the same conditions, the cytotoxic activity depended on the isolate, the medium and the temperature. At 10 °C, no isolate was cytotoxic at 10 °C in liquid whole egg and only one, belonging to the Bacillus weihenstephansensis species, in the optimal medium. All the isolates were able to adhere on stainless steel at various levels, from 2.6±0.2 log cfu/cm(2) to 4.9±0.1 log cfu/cm(2). A large majority (80.8%) was strongly adhering and could lead to the formation of biofilms in industrial equipments.
    Food Microbiology 04/2011; 28(2):261-5. · 3.37 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The mechanism of egg white antimicrobial activity involves specific molecules and environmental factors. However, it is difficult to compare the data from the literature because of the use of various bacterial strains and incubation conditions. The aim of our study was to determine the effect of temperature, pH, inoculum size, and egg white protein concentration on egg white antimicrobial activity and to investigate the putative interactions among these factors by conducting a complete factorial design analysis. The behavior of Salmonella Enteritidis and Escherichia coli was studied after precultivation in tryptic soy broth and Luria-Bertani broth, respectively, using three different egg white protein concentrations (0, 10, and 100%), five temperatures (37, 40, 42, 45, and 48°C), two pHs (7.8 and 9.3), and six inoculum levels (3 to 8 log CFU/ml). The essential role of temperature was identified. An inverse relationship was observed between bacterial growth and an increase in temperature. The role of egg white proteins was clearly demonstrated. In the absence of egg white proteins, bacterial growth occurred under most incubation conditions, whereas the presence of 10 and 100% protein produced bacteriostatic or bactericidal effects. The interaction between temperature and protein concentration was significant. At the highest tested temperatures, proteins were less involved in the bactericidal effect. Bacterial destruction was higher at pH 9.3 than at pH 7.8. Under our experimental conditions, Salmonella Enteritidis was more resistant to inactivation by egg white than was E. coli.
    Journal of food protection 01/2011; 74(1):24-31. · 1.80 Impact Factor