Effect of wine-based marinades on the behavior of Salmonella Typhimurium and background flora in beef fillets.

The aim of this study was to evaluate the wine-based marinades to control the survival of acid-adapted and non-adapted Salmonella Typhimurium and background flora of fresh beef stored aerobically or under modified atmosphere. Beef slices were inoculated with a 3-strain cocktail of acid-adapted or non-adapted Salmonella Typhimurium strains DT 193, 4/74 and DSM 554 and marinated by immersion in wine (W) or wine supplemented with 0.3% thyme essential oil (WEO), for 12h at 4°C. Marinated slices were then stored under air or modified atmosphere conditions at 5°C. S. Typhimurium and background flora were followed for a 19-day period of storage. S. Typhimurium individual strains were monitored by pulsed field gel electrophoresis. Marination with wine significantly (P<0.05) reduced the background flora compared to the control (non-marinated). Furthermore, immersion of fillets in W or WEO marinades for 12h significantly (P<0.05) reduced the levels of S. Typhimurium compared to the non-marinated (control) samples by 1.1 and 1.4logCFU/g or 2.0 and 1.9logCFU/g for acid-adapted and non-adapted cells, respectively. Acid-adapted cells were more susceptible (P<0.05) to the addition of thyme essential oil in the wine marinade. The epidemic multi-drug resistant DT 193, the 4/74 and DSM 554 strains survived marination (for both W and WEO) and were detected at about similar proportions as revealed by PFGE results. Present results indicate that wine-based marinades are efficient, from a safety and shelf life stand point, in reducing pathogen's levels as well as the background beef flora.

Transfer of foodborne pathogenic bacteria to non-inoculated beef fillets through meat mincing machine.

The aim of this study was to evaluate the transfer of pathogens population to non-inoculated beef fillets through meat mincing machine. In this regard, cocktails of mixed strain cultures of each Listeria monocytogenes, Salmonella enterica ser. Typhimurium and Escherichia coli O157:H7 were used for the inoculation of beef fillets. Three different initial inoculum sizes (3, 5, or 7 log CFU/g) were tested. The inoculated beef fillets passed through meat mincing machine and then, six non-inoculated beef fillets passed in sequence through the same mincing machine without sanitation. The population of each pathogen was measured. It was evident that, all non-inoculated beef fillets were contaminated through mincing with all pathogens, regardless the inoculum levels used. This observation can be used to cover knowledge gaps in risk assessments since indicates the potential of pathogen contamination and provides significant insights for the risk estimation related to cross-contamination, aiming thus to food safety enhancement.

Effect of Satureja thymbra essential oil on growth-no growth interfaces of Listeria monocytogenes Scott A and Salmonella Enteritidis PT4, at various temperatures, pH, and water activities.

Antimicrobial efficacy of Satureja thymbra essential oil against Listeria monocytogenes Scott A and Salmonella ser. Enteritidis PT4 was evaluated in vitro by modeling the growth boundaries at various temperatures, pH, and NaCl concentrations. Growth-no growth (turbidity) data were modeled by logistic polynomial regression. The concordance indices and the Hosmer- Lemeshow statistics of both logistic models indicated a good fit to the observed data. Salmonella Enteritidis was more sensitive at increasing salt content as compared with L. monocytogenes. On the other hand, pH changes had greater effect on growth initiation of L. monocytogenes than they had on growth initiation of Salmonella Enteritidis. Presence of essential oil up to 0.06% (vol/vol) had no or little effect on growth initiation of both microorganisms tested, while the concentration of 0.1% (vol/vol) essential oil exhibited great inhibition on growth initiation, especially when it was combined with increased salt content and low temperatures. The antimicrobial potency of S. thymbra essential oil was more pronounced when multiple hurdles were applied. Modeling the growth boundaries offers a useful tool to food microbiologists for assessing the antimicrobial activity in a range of food preservation conditions as compared with the conventional MIC determination.

Use of titanium dioxide (TiO2) photocatalysts as alternative means for Listeria monocytogenes biofilm disinfection in food processing.

The aim of this work was to study the photocatalytic activity of titanium dioxide (TiO(2)) against Listeria monocytogenes bacterial biofilm. Different TiO(2) nanostructured thin films were deposited on surfaces such as stainless steel and glass using the doctor-blade technique. All the surfaces were placed in test tubes containing Brain Heart (BH) broth and inoculated with L. monocytogenes. Test tubes were then incubated for 10 days at 16°C in order to allow biofilm development. After biofilm formation, the surfaces were illuminated by ultraviolet A light (UVA; wavelength of 315-400 nm). The quantification of biofilms was performed using the bead vortexing method, followed by agar plating and/or by conductance measurements (via the metabolic activity of biofilm cells). The presence of the TiO(2) nanoparticles resulted in a fastest log-reduction of bacterial biofilm compared to the control test. The biofilm of L. monocytogenes for the glass nanoparticle 1 (glass surface modified by 16% w/v TiO(2)) was found to have decreased by 3 log CFU/cm(2) after 90 min irradiation by UVA. The use of TiO(2) nanostructured photocatalysts as alternative means of disinfecting contaminated surfaces presents an intriguing case, which by further development may provide potent disinfecting solutions. Surface modification using nanostructured titania and UV irradiation is an innovative combination to enhance food safety and economizing time and money.

Disinfectant test against monoculture and mixed-culture biofilms composed of technological, spoilage and pathogenic bacteria: bactericidal effect of essential oil and hydrosol of Satureja thymbra and comparison with standard acid-base sanitizers.

AIMS: To assess the antimicrobial action of three natural-derived products (essential oil, decoction and hydrosol of Satureja thymbra) against biofilms, composed of useful, spoilage and pathogenic bacteria (formed as monoculture or/and mixed-culture), and to compare their efficiency with three standard acid and alkaline chemical disinfectants. METHODS AND RESULTS: Two acids (hydrochloric and lactic, pH 3), one alkali (sodium hydroxide, pH 11), the essential oil of S. thymbra (1% v/v) and the two by-products of the essential oil purification procedure (the decoction and the hydrosol fraction of essential oil, 100%), were tested against biofilms formed by five bacterial species, either as monospecies, or as mixed-culture of all species. The tested bacterial species were Staphylococcus simulans and Lactobacillus fermentum (useful technological bacteria), Pseudomonas putida (spoilage bacterium), Salmonella enterica and Listeria monocytogenes (pathogenic bacteria). Biofilms were left to be formed on stainless steel coupons for 5 days at 16 degrees C, before the application of disinfection treatments, for 60 and 180 min. The disinfection efficiency was evaluated by detaching the remaining viable biofilm cells and enumerating them by agar plating, as well as by automated conductance measurements (using Rapid Automated Bacterial Impedance Technique). Both these methods revealed that the essential oil and the hydrosol of S. thymbra exhibited a strong antimicrobial action against both monospecies and mixed-culture biofilms. Surprisingly, the efficiency of the other three acid-base disinfectants was not adequate, although a long antimicrobial treatment was applied (180 min). CONCLUSIONS: The essential oil of S. thymbra (1%), as well as its hydrosol fraction (100%), presents sufficient bactericidal effect on bacterial biofilms formed on stainless steel. SIGNIFICANCE AND IMPACT OF THE STUDY: Use of natural antimicrobial agents could provide alternative or supplemented ways for the disinfection of microbial-contaminated industrial surfaces.

A newly developed assay to study the minimum inhibitory concentration of Satureja spinosa essential oil.

AIMS: The minimum inhibitory concentration (MIC) of Satureja spinosa essential oil against Staphylococcus aureus, Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica, Salmonella serovar Enteritidis PT4 and Bacillus cereus was comparatively assessed with an established optical density method as well as a novel impedimetric method. METHODS AND RESULTS: The impedimetric analysis takes into account information of microbial growth, such as detection time, maximum conductance, and slope of the conductance curve. For each pathogen two levels of inoculation were studied, a high (10(5) CFU ml(-1)) and a low level (10(2) CFU ml(-1)). Non-linear regression analysis was used to fit the data using a modification of a previously published model, from which a more exact value can be obtained for the MIC. Both methods gave similar MICs as shown by t-test statistical analysis. Salm. Enteritidis seems to be the least sensitive to the action of S. spinosa essential oil followed by L. monocytogenes, E. coli, B.cereus and Staph. aureus. The MICs of low inoculum were lower than that of high inoculum. CONCLUSIONS: The new impedimetric assay of MIC of essential oils can be considered a reliable rapid method for screening antimicrobial effectiveness of natural additives. SIGNIFICANCE AND IMPACT OF THE STUDY: Determination of the minimum inhibitory concentration of an essential oil with the simple conductance technique and further study of the mode of action of its components is a good combination for obtaining additional knowledge for industrial application of such natural additives.

Survival of Escherichia coli O157:H7 during the fermentation of Spanish-style green table olives (conservolea variety) supplemented with different carbon sources.

Olives were supplemented with two different carbon sources (sucrose and glucose) at five different levels (0%, 0.1%, 0.3%, 0.5% and 1%) and the fermentation procedure was followed after inoculation with or without starter culture. Inhibition of Escherichia coli O157:H7 was evident in all fermentation procedures regardless of the treatment used. The pathogen numbers declined but did not die out during fermentation. It was evident that the rate of death was higher in samples supplemented with starter cultures compared to natural fermentation. The production of acids during fermentation seems to be the main factor that governs the behaviour of this pathogen under such stress conditions. The HPLC analysis revealed that lactate, formate and acetate were among the end-products during the fermentation of green olives.