Influence of temperature on biofilm formation by Listeria monocytogenes on various food-contact surfaces: relationship with motility and cell surface hydrophobicity

Aims:  To assess the ability of Listeria monocytogenes to form biofilm on different food-contact surfaces with regard to different temperatures, cellular hydrophobicity and motility.
Methods and Results:  Forty-four L. monocytogenes strains from food and food environment were tested for biofilm formation by crystal violet staining. Biofilm levels were significantly higher on glass at 4, 12 and 22°C, as compared with polystyrene and stainless steel. At 37°C, L. monocytogenes produced biofilm at significantly higher levels on glass and stainless steel, as compared with polystyrene. Hydrophobicity was significantly ( P  < 0·05) higher at 37°C than at 4, 12 and 22°C. Thirty (68·2%) of 44 strains tested showed swimming at 22°C and 4 (9·1%) of those were also motile at 12°C. No correlation was observed between swimming and biofilm production.
Conclusions:  L. monocytogenes can adhere to and form biofilms on food-processing surfaces. Biofilm formation is significantly influenced by temperature, probably modifying cell surface hydrophobicity.
Significance and Impacts of the Study:  Biofilm formation creates major problems in the food industry because it may represent an important source of food contamination. Our results are therefore important in finding ways to prevent contamination because they contribute to a better understanding on how L. monocytogenes can establish biofilms in food industry and therefore survive in the processing environment.     

Surfactin reduces the adhesion of food-borne pathogenic bacteria to solid surfaces

Aims:  To investigate the effect of the biosurfactants surfactin and rhamnolipids on the adhesion of the food pathogens Listeria monocytogenes , Enterobacter sakazakii and Salmonella Enteritidis to stainless steel and polypropylene surfaces.
Methods and Results:  Quantification of bacterial adhesion was performed using the crystal violet staining technique. Preconditioning of surfaces with surfactin caused a reduction on the number of adhered cells of Ent. sakazakii and L. monocytogenes on stainless steel. The most significant result was obtained with L. monocytogenes where number of adhered cells was reduced by 10² CFU cm⁻². On polypropylene, surfactin showed a significant decrease on the adhesion of all strains. The adsorption of surfactin on polystyrene also reduces the adhesion of L. monocytogenes and Salm. Enteritidis growing cells. For short contact periods using nongrowing cells or longer contact periods with growing cells, surfactin was able to delay bacterial adhesion.
Conclusions:  The prior adsorption of surfactin to solid surfaces contributes on reducing colonization of the pathogenic bacteria.
Significance and Impact of the Study:  This is the first work investigating the effect of surfactin on the adhesion of the food pathogens L. monocytogenes , Ent. sakazakii and Salm. Enteritidis to polypropylene and stainless steel surfaces.     

Adsorption of biosurfactant on solid surfaces and consequences regarding the bioadhesion of Listeria monocytogenes LO28

AIMS: The influence of biosurfactant compounds produced by a strain of Pseudomonas fluorescens on the adhesion of Listeria monocytogenes LO28 to polytetrafluoroethylene (PTFE) and AISI 304 stainless steel surfaces was investigated. METHODS AND RESULTS: The biosurfactant was produced according to a simple, novel technique based on cultivation on nutrient agar. Adhesion studies were performed using L. monocytogenes cells cultured at 20 or 37 degrees C. CONCLUSIONS: A substrate-dependent behaviour of the LO28 strain (larger number of cells adhering to stainless steel than to PTFE), and a significant reduction (< 90%) in microbial adhesion levels through the prior adsorption of biosurfactants on stainless steel surfaces, which can be related to a change in the electron-donor characteristics of this substratum, was demonstrated. SIGNIFICANCE AND IMPACT OF THE STUDY: The prior adsorption of biosurfactants on solid surfaces may constitute a new and effective means of combating the implantation of pathogenic micro-organisms in food processing plants.     

Anti-adhesive properties of fish tropomyosins

Aims:  We have recently found that preconditioning of stainless steel surfaces with an aqueous fish muscle extract can significantly impede bacterial adhesion. The purpose of this study was to identify and characterize the primary components associated with this bacteria-repelling effect.
Methods and Results:  The anti-adhesive activity was assayed against Escherchia coli K-12, and bacterial adhesion was quantified by crystal violet staining and sonication methods. Proteolytic digestion, elution and fractionation experiments revealed that the anti-adhesive activity of the extract was linked to the formation of a proteinaceous conditioning film composed primarily of fish tropomyosins. These fibrous proteins formed a considerable anti-adhesive conditioning layer on and reduced bacterial adhesion to several different materials including polystyrene, vinyl plastic, stainless steel and glass. The protein adsorption profiles obtained from the various materials did not differ significantly, but elution was often incomplete making minor qualitative/quantitative differences indiscernible.
Conclusions:  The data highlights the significance of protein conditioning films on bacterial adhesion and emphasizes the importance of substratum's physiochemical properties and exposure time with regards to protein adsorption/elution efficiency and subsequent bacterial adhesion.
Significance and Impact of the Study:  Fish tropomyosin-coatings could potentially offer a nontoxic and relatively inexpensive measure of reducing bacterial colonization of inert surfaces.     

Model systems allowing quantification of sensitivity to disinfectants and comparison of disinfectant susceptibility of persistent and presumed nonpersistent Listeria monocytogenes

Aims:  To determine if Listeria monocytogenes persistent strains differ from presumed nonpersistent strains in disinfection susceptibility and to examine the influence of attachment and NaCl on susceptibility.
Methods and Results:  Two model-systems that allowed quantitative inter-strain comparison of disinfectant sensitivity were developed. Persistent L. monocytogenes were not more tolerant to the disinfectants Incimaxx DES and Triquart SUPER than presumed nonpersistent isolates. When calibrating the systems with respect to presence of biological material and cell density, attached bacteria were as sensitive to disinfectants as were planktonic bacteria. Growth with 5% NaCl increased the tolerance of planktonic cells to Incimaxx DES. All strains of spot inoculated L. monocytogenes survived well 20 h of drying when protected by growth media and 5% NaCl, but were not protected by NaCl against disinfection.
Conclusions:  Persistent strains of L. monocytogenes are as susceptible to disinfectants as are presumed nonpersistent strains and attachment does not render the strains more tolerant to disinfectants. Growth with NaCl affected the susceptibility of the planktonic L. monocytogenes to Incimaxx DES and protected spot inoculated cells during drying.
Significance and Impact of the Study:  Attachment to surfaces does not per se offer protection to L. monocytogenes against disinfectants and disinfection tolerances do not appear to influence the ability of a strain to persist.     

Adhesion of food-borne bacteria to stainless steel is reduced by food conditioning films

Aims:  Preconditioning of stainless steel with aqueous cod muscle extract significantly impedes subsequent bacterial adhesion most likely due to repelling effects of fish tropomyosin. The purpose of this study was to determine if other food conditioning films decrease or enhance bacterial adhesion to stainless steel.
Methods and Results:  Attachment of Pseudomonas fluorescens AH2 to stainless steel coated with water-soluble coatings of animal origin was significantly reduced as compared with noncoated stainless steel or stainless steel coated with laboratory substrate or extracts of plant origin. Coating with animal extracts also decreases adhesion of other food-relevant bacteria. The manipulation of adhesion was not attributable to growth inhibitory effects. Chemical analysis revealed that the stainless steels were covered by homogenous layers of adsorbed proteins. The presence of tropomyocin was indicated by appearance of proteins with similar molecular weight based in sodium dodecyl sulfate–polyacrylamide gel electrophoresis, in several extracts that reduced adhesion but also extracts not containing this protein reduced bacterial adhesion, indicating that several molecular species may be involved in the phenomenon.
Conclusions:  It is a common perception that food materials facilitate bacterial adhesion to surfaces; however, this study demonstrates that aqueous coatings of food origin may actually reduce bacterial adhesion.
Significance and Impact of the Study:  Compounds from food extracts may potentially be used as nontoxic coatings to reduce bacterial attachment to inert surfaces.     

Investigation into the effect of detergents on disinfectant susceptibility of attached Escherichia coli and Listeria monocytogenes

Aims:  Investigate the effect of detergent treatment on susceptibility of attached Escherichia coli and Listeria monocytogenes to subsequent disinfectant treatment.
Methods and Results:  Plate counts show that E. coli attached to stainless steel surfaces became significantly more susceptible to benzalkonium chloride (BAC) after treatment with sodium alkyl sulfate (SAS) and fatty alcohol ethoxylate (FAE). No change in susceptibility was observed with Sodium dodecyl sulfate (SDS). L. monocytogenes became significantly less susceptible to BAC after treatment with SAS and SDS yet no change in susceptibility was observed with FAE. Flow cytometry using the fluoresceine propidium iodide revealed significant increases in cell membrane permeability of both organisms by SAS and FAE, although the effect was much greater in E. coli . No change was observed with SDS. Hydrophobic interaction chromatography showed that both organisms became less hydrophobic following treatment with SAS and SDS but FAE had no effect.
Conclusions:  In E. coli, detergents that increase susceptibility to BAC increase membrane permeability. In L. monocytogenes, detergents that reduce susceptibility to BAC lower cell surface hydrophobicity.
Significance and Impact of the Study:  Detergents can influence the sensitivity of pathogenic food borne micro-organisms to BAC.     

Comparative evaluation of adhesion, surface properties, and surface protein composition of Listeria monocytogenes strains after cultivation at constant pH of 5 and 7

AIMS: To analyse the cellular mechanisms that influence Listeria monocytogenes adhesion onto inert surfaces under acidic growth conditions. METHODS AND RESULTS: The adhesion capability of all the strains was significantly reduced after cultivation at constant pH 5 than at constant pH 7 and the cell surface was significantly less hydrophobic at pH 5 than at 7. At pH 5, the analyses of surface protein composition revealed that the flagellin was downregulated for all strains, which was confirmed by the absence of flagella and the P60 protein was upregulated for L. monocytogenes EGD-e, X-Li-mo 500 and 111. The use of L. monocytogenes EGD mutants revealed that flagellin could be involved in the adhesion process, but not P60 protein. It was also observed that the hydrophobic character was not linked to the presence or the absence of flagellin or P60 protein at the cell surface of L. monocytogenes. CONCLUSIONS: The decrease of L. monocytogenes adhesion at pH 5 could be attributed to the downregulation of the flagellin synthesis under the acidic conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: Conservation of food product at pH 5 will delay bacterial adhesion and biofilm formation during food processing on inert surfaces when the product is contaminated with L. monocytogenes.     

Modelling the effect of the redox potential and pH of heating media on Listeria monocytogenes heat resistance

Aims:  Study the effect of redox potential and pH of the heating media on Listeria monocytogenes heat resistance and model its action at fixed temperature.
Methods and Results:  The heat resistance of Listeria monocytogenes at 58°C was studied in Brain Heart Infusion broth as a function of pH (from 5·0 to 7·0) and redox potential ( E _h7). The media redox was adjusted with nitrogen gas, potassium ferricyanide and dithiothreitol. A Weibull model was used to fit survival curves. The heat resistance parameter (δ_58°C) was estimated from each inactivation curve. A major effect of pH was observed. Bigelow model was used to describe the effect of redox potential on the apparent L. monocytogenes heat resistance. The highest δ_58°C values have been obtained at pH 7·0 and oxidizing conditions.
Conclusions:  The developed model indicates that the E _h7 has a significant effect and varied depending on the pH of the heating media. The z _redox values, calculated from δ_58°C allowed quantifying the influence of heating media redox potential on L. monocytogenes thermal inactivation.
Significance and Impact of the Study:  The obtained model shows the action of redox potential on L. monocytogenes thermal destruction and might be useful to take into account in food thermal processes.     

Growth and reducing capacity of Listeria monocytogenes under different initial redox potential

Aims:  To determine the reducing capacity of Listeria monocytogenes and to highlight the effect of redox potential on its growth parameters.
Methods and Results:  The reducing capacity of L. monocytogenes was monitored in Brain Heart Infusion Broth media at different initial redox potential (Eh) and pH at 37°C. The effect of Eh obtained by gas flushing (air, N₂ and N₂-H₂) or by adding potassium ferricyanide and dithiotreitol in concentration from 1 to 10 mmol l⁻¹on L. monocytogenes growth parameters at pH 6·0, 7·0 and 8·0 was investigated. A total change of 539 mV (±44 mV) from an initial redox value of +330 ± 8 mV to a more negative potential in redox curves was observed resulting from L. monocytogenes growth at pH 7·0 at 37°C. A significant influence of pH and redox potential on L. monocytogenes lag phase of growth was shown ( P  < 0·05).
Conclusions:  Listeria monocytogenes exhibited longer lag phase in reducing conditions and at pH 6·0. The method used to modify the redox potential was shown to have no effect on growth parameters at pH 7·0.
Significance and Impact of the Study:  The provided information on the extending lag time and the possible delayed growth of this major pathogen in reducing conditions might be useful for its control in foods.     

Assessment of cell surface properties and adhesion potential of selected probiotic strains

Aim:  To evaluate the physicochemical cell surface and adhesive properties of selected probiotic strains for human use.
Methods and Results:  Probiotic strains, Bifidobacterium longum B6, Lactobacillus acidophilus ADH, Lactobacillus paracasei , Lactobacillus rhamnosus GG, Lactobacillus brevis , Lactobacillus casei , Leuconostoc mesenteroides and Pediococcus acidilactici were tested for the physicochemical properties of cell surfaces and the adhesion abilities against foodborne pathogens. Bif .  longum B6 (53·6%) and Lact .  rhamnosus GG (46·5%) showed the highest hydrophobicity, while the least affinity to xylene was observed in Ped .  acidilactici (10·4%). Bifidobacterium longum B6 showed the strongest coaggregation phenotype with Listeria monocytogenes (53·0%), Shigella boydii (42·0%) and Staphylococcus aureus (45·9%). Lactobacillus rhamnosus GG had the strong binding ability to Caco-2 cells and effectively inhibited the adhesion of L .  monocytogenes , Salmonella Typhimurium, Sh .  boydii and Staph .  aureus to Caco-2 cells. The hydrophobicity was highly correlated with coaggregative abilities and competitive inhibition, suggesting a good relationship between in vitro adhesion and in vivo colonization.
Conclusion:  The results suggest that Bif .  longum B6 and Lact .  rhamnosus GG can be candidate probiotics available for human consumption.
Significance and Impact of the Study:  Because the use of probiotic strains has been more concerned with their beneficial effects in the GI tract, it is essential to examine the potential of probiotic strains based on the physicochemical properties in terms of bacterial-binding and adhesion capabilities.     

Comparison of in vitro models to study bacterial adhesion to the intestinal epithelium

Aims:  To evaluate the adhesion ability of intestinal bacteria to different in vitro models of intestinal epithelia, and to estimate the suitability of these models and the type of interactions involved.
Methods and results:  The adhesion of probiotic ( Lactobacillus rhamnosus GG and Bifidobacterium animalis subsp . lactis Bb12), commensal ( B. animalis IATA-A2 and B. bifidum IATA-ES2) and potentially pathogenic bacteria ( E. coli and L. monocytogenes ) was determined. The adhesion models used were polycarbonate-well plates, with or without mucin, and different configurations of Caco-2 and/or HT29-MTX cell cultures. All bacteria adhered to wells without mucin (2·6–27·3%), the values being highly variable depending on the bacterial strain. Adhesion percentages of potentially probiotic bacteria to Caco-2 cultures were remarkably lower ( P  <   0·05) than those to mucin, and more similar to those of pathogenic strains. The lowest adhesion of different bacterial strains was detected on HT29-MTX (0·5–2·3%) cultures and Caco-2/HT29-MTX (0·6–3·2%) cocultures, while these values were increased in Caco-2 cultures plus mucin.
Conclusions:  The results suggested that bacterial strains exhibit different capacities to adhere to cellular components and several types of mucin present in different models, showing preferences for intestinal MUC2.
Significance and impact of the study:  The use of Caco-2 cells monolayer plus mucin (type II) better approaches the physiological characteristics of in vivo situation, providing a reliable and suitable in vitro model to evaluate bacterial adhesion.     

Adsorption, attachment and biofilm formation among isolates of Listeria monocytogenes using model conditions

Aims:  To determine whether isolates of Listeria monocytogenes differ in their ability to adsorb and form biofilms on a food-grade stainless steel surface.
Methods and Results:  Strains were assessed for their ability to adsorb to a test surface over a short time period. Although some differences in numbers of bound cells were found among the strains, there were no correlations between the degree of adsorption and either the serotype or source of the strain. The ability of each strain to form a biofilm when grown with the test surface was also assessed. With the exception of a single strain, all strains adhered as single cells and did not form biofilms. Significant differences in adherence levels were found among strains. Strains demonstrating enhanced attachment produced extracellular fibrils, whereas those which adhered poorly did not. A single strain formed a biofilm consisting of adhered single cells and aggregates of cells.
Conclusions:  Significant differences were found in the ability of various L. monocytogenes strains to attach to a test surface. In monoculture, the majority of strains did not form biofilms.
Significance and Impact of the Study:  Differences in attachment and biofilm formation among strains provide a basis to study these characteristics in L. monocytogenes .     

Physicochemical surface properties of five Listeria monocytogenes strains from a pork-processing environment in relation to serotypes, genotypes and growth temperature

Physicochemical surface properties, related to electrostatic, van der Waals and Lewis acid–base interactions, of five Listeria monocytogenes strains isolated from pork-processing environments were determined after two subcultures at 37 °C and a final culture at three temperatures: 37, 10 and 4 °C. Three strains (Lm1, Lm114 and Lm191) were genetically related while two were unrelated (Lm25 and Lm74) according to Apa I-macrorestriction and pulsed-field gel electrophoresis (PFGE) typing.
Listeria monocytogenes cell surfaces were generally negatively charged regardless of pH and tended to be hydrophilic due to a basic character. However, variable physicochemical surface properties of the five Listeria monocytogenes isolates were observed after growth at 37 °C. After growth at 10 °C, the three genetically related isolates exhibited similar surface properties and were slightly more hydrophilic and basic than the others. After growth at 4 °C, the five isolates displayed the same weak affinity for all kinds of solvents and low electrophoretic mobility values.
A sharp decrease of temperature and subsequent growth of various Listeria monocytogenes strains resulted in loss of the physicochemical surface property variability, which may suggest the role of common chill adaptation mechanisms affecting surface properties.     

Interactions of Salmonella enterica with lettuce leaves

Aims:  To investigate the interactions of Salmonella enterica with abiotic and plant surfaces and their effect on the tolerance of the pathogen to various stressors.
Methods and Results:  Salmonella strains were tested for their ability to form biofilm in various growth media using a polystyrene plate model. Strong biofilm producers were found to attach better to intact Romaine lettuce leaf tissue compared to weak producers. Confocal microscopy and viable count studies revealed preferential attachment of Salmonella to cut-regions of the leaf after 2 h at 25°C, but not for 18 h at 4°C. Storage of intact lettuce pieces contaminated with Salmonella for 9 days at 4°C resulted only in small changes in population size. Exposure of lettuce-associated Salmonella cells to acidic conditions (pH 3·0) revealed increased tolerance of the attached vs planktonic bacteria.
Conclusions:  Biofilm formation on polystyrene may provide a suitable model to predict the initial interaction of Salmonella with cut Romaine lettuce leaves. Association of the pathogen with lettuce leaves facilitates its persistence during storage and enhances its acid tolerance.
Significance and Impact of the Study:  Understanding the interactions between foodborne pathogens and lettuce might be useful in developing new approaches to prevent fresh produce-associated outbreaks.     

Antimicrobial mortar surfaces for the improvement of hygienic conditions

Aims:  To evaluate the effectiveness of various antimicrobial mortar formulations in inhibiting the growth of a selection of pathogens of environmental and hygienic concern.
Methods and Results:  Mortar prisms containing triclosan-incorporated fibres or different concentrations of silver copper zeolites were incubated with Escherichia coli , Listeria monocytogenes , Salmonella enterica or Staphylococcus aureus at 4 or 20°C for 24 h. From plate counting, a substantial bactericidal effect (>4 log units) could only be observed for the mortar specimens containing more than 3% zeolites on cement weight base, the effect being more pronounced at 20°C compared to 4°C. No inhibitory effect could be observed for mortar specimens containing antimicrobial fibres. Adenosinetriphosphate (ATP) measurements allowed for a rapid indication of the occurrence of antimicrobial activity.
Conclusions:  In order to obtain a bactericidal effect on mortar surfaces, concentrations of silver copper zeolites of more then 3% are required.
Significance and Impact of the Study:  To our knowledge, this is the first study in which the effectiveness of various antimicrobial mortar mixtures towards the inhibition of pathogens has been evaluated in a quantitative way. Antimicrobial concrete mixtures can be used for the improvement of the hygienic conditions in a variety of environments.     

The differential adherence capabilities of two Listeria monocytogenes strains in monoculture and multispecies biofilms as a function of temperature

AIMS: To determine the differential adherence capabilities at three different temperatures of Listeria monocytogenes Scott A, a clinical food pathogen, and L. monocytogenes FM876, a persistent strain from a milk-processing environment, to stainless steel. METHODS AND RESULTS: Differential adherence was investigated by submerging stainless steel coupons in both 48-h Listeria monocultures and mixed cultures additionally containing Staphylococcus xylosus DP5H and Pseudomonas fragi ATCC 4973. Immunofluorescent microscopy and image analysis techniques were utilized to identify and quantify the L. monocytogenes cells adhering to the steel at 4 degrees C, 18 degrees C and 30 degrees C. The monoculture biofilms consistently contained greater L. monocytogenes numbers than the multispecies biofilms, with the persistent strain FM876 showing significantly greater adherence than strain Scott A. Optimum adherence occurred at 18 degrees C in monoculture biofilms. CONCLUSION: L. monocytogenes strains exhibit differential, temperature-dependent, adherence to stainless steel. SIGNIFICANCE AND IMPACT OF THE STUDY: These results demonstrate temperature dependent biofilm adherence and support previous findings that persistent strains exhibit increased adherence capability.     

Characterization of probiotic carnobacteria isolated from rainbow trout (Oncorhynchus mykiss) intestine

Aims:  To characterize two probiotic carnobacterial isolates, Carnobacterium maltaromaticum (B26) and C. divergens (B33), derived from rainbow trout ( Oncorhynchus mykiss ) intestine.
Methods and Results:  Both cultures, which were able to colonize the fish gut mucosal layer, comprised nonsporogenous, nonmotile, Gram-positive, catalase and oxidase-negative rods. The growth of both carnobacteria occurred between 0 and 37°C, in 0–10% (w/v) NaCl and at pH 5–10. Specifically, strain B26 grew in nutrient broth supplemented with 15% (w/v) NaCl. The most abundant cellular fatty acid of both cultures was 9-octadecenoic acid (18 : 1 n -9) (B26 = 52·6%; B33 = 40·6%), which was characteristic of Carnobacterium . Both cultures were inhibitory to Aeromonas salmonicida , Aer. hydrophila , Streptococcus iniae and Vibrio anguillarum , and strain B33 inhibited Listeria monocytogenes . Both carnobacteria, which did not contain plasmids, produced inhibitory compounds against Gram-positive and Gram-negative bacteria.
Conclusions:  Both probiotic cultures, B26 and B33, had unique phenotypic characteristics and showed a broad spectrum of antibiotic resistance against varying pathogenic bacteria.
Significance and Impact of the Study:  The results of this study contribute to new information and significance of carnobacterial species.     

Effectiveness of cell-adsorbed bacteriocin produced by Lactobacillus curvatus CWBI-B28 and selected essential oils to control Listeria monocytogenes in pork meat during cold storage

Aims:  To study the effectiveness of a combination of cell-adsorbed bacteriocin (CAB; a suspension of producer cells on which maximum bacteriocin has been immobilized by pH adjustments) of a Lactobacillus curvatus strain with oregano or savory essential oil to control Listeria monocytogenes in pork meat at 4°C.
Methods and Results:  The antimicrobial activity of the CAB and six different essential oils was tested by the well diffusion assay against L. monocytogenes M, Escherichia coli 10536 and Salmonella serotype Typhi CWBI-H1. The anti- Listeria activity of the CAB and oregano or savory essential oils was also investigated in pork meat. The results of the well diffusion assay showed that CAB was only inhibitory to L. monocytogenes while savory and oregano essential oils were the most active against the three indicator bacteria. In pork meat, Listeria counts have declined from c. 10² CFU g⁻¹ to below the detectable limit during the first week of storage in samples treated with CAB or oregano essential oil and in those treated with CAB combined with oregano or savory essential oil. However, the counts of L. monocytogenes have increased after the third week of storage in all samples with the exception of those treated with the combination of CAB and oregano essential oil. The combination of CAB with savory essential oil resulted in a 2-week delay of the growth rebound compared with samples treated with CAB alone.
Conclusions:  Addition of oregano or savory essential oil exhibited a synergistic effect with CAB to control L. monocytogenes in pork meat during storage at 4°C.
Significance and Impact of the Study:  The combination of CAB with oregano or savory essential oil may be effectively used in meat industry to enhance the safety and stability of meat products.     

Listeria monocytogenes LO28: surface physicochemical properties and ability to form biofilms at different temperatures and growth phases

The surface physicochemical properties of Listeria monocytogenes LO28 under different conditions (temperature and growth phase) were determined by use of microelectrophoresis and microbial adhesion to solvents. The effect of these parameters on adhesion and biofilm formation by L. monocytogenes LO28 on hydrophilic (stainless steel) and hydrophobic (polytetrafluoroethylene [PTFE]) surfaces was assessed. The bacterial cells were always negatively charged and possessed hydrophilic surface properties, which were negatively correlated with growth temperature. The colonization of the two surfaces, monitored by scanning electron microscopy, epifluorescence microscopy, and cell enumeration, showed that the strain had a great capacity to colonize both surfaces whatever the incubation temperature. However, biofilm formation was faster on the hydrophilic substratum. After 5 days at 37 or 20 degrees C, the biofilm structure was composed of aggregates with a three-dimensional shape, but significant detachment took place on PTFE at 37 degrees C. At 8 degrees C, only a bacterial monolayer was visible on stainless steel, while no growth was observed on PTFE. The growth phase of bacteria used to inoculate surfaces had a significant effect only in some cases during the first steps of biofilm formation. The surface physicochemical properties of the strain are correlated with adhesion and surface colonization.