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Giaouris E.,University of Aegean | Heir E.,Nofima Materials AS | Hebraud M.,French National Institute for Agricultural Research | Chorianopoulos N.,Veterinary Research Institute of Athens | And 7 more authors.
Meat Science

Attachment of potential spoilage and pathogenic bacteria to food contact surfaces and the subsequent biofilm formation represent serious challenges to the meat industry, since these may lead to cross-contamination of the products, resulting in lowered-shelf life and transmission of diseases. In meat processing environments, microorganisms are sometimes associated to surfaces in complex multispecies communities, while bacterial interactions have been shown to play a key role in cell attachment and detachment from biofilms, as well as in the resistance of biofilm community members against antimicrobial treatments. Disinfection of food contact surfaces in such environments is a challenging task, aggravated by the great antimicrobial resistance of biofilm associated bacteria. In recent years, several alternative novel methods, such as essential oils and bacteriophages, have been successfully tested as an alternative means for the disinfection of microbial-contaminated food contact surfaces. In this review, all these aspects of biofilm formation in meat processing environments are discussed from a microbial meat-quality and safety perspective. © 2013 Elsevier Ltd. Source

Giaouris E.,University of Aegean | Chorianopoulos N.,Veterinary Research Institute of Athens | Nychas G.-J.,Agricultural University of Athens
Food Research International

The abilities of Listeria monocytogenes to adapt to stress and also to attach to surfaces are believed to contribute to its persistence in food processing environments. In this study, the possible influence of acid adaptation of L. monocytogenes cells during their planktonic growth on their subsequent resistance against 3 different natural disinfection treatments (0.05% lactic acid, 1% essential oil or 100% hydrosol of S. thymbra) upon their attachment to stainless steel (SS) was evaluated by simultaneously using the bead vortexing technique and a conductance method. Prior to disinfection, both nonadapted and acid-adapted stationary phase bacteria were left to attach to SS coupons statically incubated for 10. days into Brain Heart Infusion (BHI) broth under 3 different temperatures (5, 16 or 30. °C). Results revealed that both essential oil and hydrosol presented sufficient bactericidal activity against all formed sessile populations, always resulting in counts following disinfection below the plate counting detection limit. However, the conductance method, able to detect metabolically active sessile bacteria unable to be recovered by the bead vortexing, revealed the positive influence of previously acquired acid adaptation on disinfection resistance of attached cells against these plant extracts. A similar effect of acid adaptation was also evident for lactic acid disinfection. © 2014 Elsevier Ltd. Source

Giaouris E.,University of Aegean | Chorianopoulos N.,Veterinary Research Institute of Athens | Nychas G.-J.,Agricultural University of Athens
International Journal of Food Microbiology

This study aimed to evaluate the possible impact of acid adaptation of Listeria monocytogenes cells on their attachment to stainless steel (SS) during long-term incubation under either low or moderate temperature conditions and on the subsequent recalcitrance of attached cells to lethal acid treatments. Initially, nonadapted or acid-adapted stationary phase L. monocytogenes cells were used to inoculate (ca. 108CFU/ml) brain-heart infusion (BHI) broth in test tubes containing vertically placed SS coupons. Incubation was carried out at either 5 or 30°C for up to 15days, under static conditions. On the 5th, 10th and 15th days of incubation, attached cells were subjected to lethal acid treatments by exposing them, for either 6 or 60min, to pH2, adjusted with either hydrochloric or lactic acid. Following the acid treatments, remaining viable cells were detached (through strong vortexing with glass beads) and enumerated by agar plating, and also indirectly quantified by conductance measurements via their metabolic activity. Results obtained from both quantification techniques, employed here in parallel, revealed that although the numbers of attached cells for nonadapted and acid-adapted ones were similar, the latter were found to present significantly (p<0.05) increased recalcitrance to all the acid treatments for both incubation temperatures and all sampling days. In addition and regardless of acid adaptation, when long (60min) acid treatments were applied, conductance measurements revealed that the weak organic lactic acid exhibited significantly (p<0.05) stronger antilisterial activity compared to the strong inorganic hydrochloric acid (at the same pH value of 2). To conclude, present results show that acid adaptation of L. monocytogenes cells during their planktonic growth is conserved even after 15days of incubation under both low and moderate temperature conditions, and results in the increased recalcitrance of their sessile population to otherwise lethal acid treatments. This "stress hardening" should be severely taken into account when acidic decontamination interventions are used to kill attached to equipment surfaces cells of this important pathogenic bacterium. © 2013 Elsevier B.V. Source

Nisiotou A.,Wine Institute | Chorianopoulos N.G.,Veterinary Research Institute of Athens | Gounadaki A.,Agricultural University of Athens | Panagou E.Z.,Agricultural University of Athens | Nychas G.-J.E.,Agricultural University of Athens
International Journal of Food Microbiology

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 12. h 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 12. h significantly (P<. 0.05) reduced the levels of S. Typhimurium compared to the non-marinated (control) samples by 1.1 and 1.4. log. CFU/g or 2.0 and 1.9. log. CFU/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. © 2013 Elsevier B.V. Source

Giaouris E.,University of Aegean | Chorianopoulos N.,Veterinary Research Institute of Athens | Doulgeraki A.,University of Aegean | Doulgeraki A.,Agricultural University of Athens | Nychas G.-J.,Agricultural University of Athens

Biofilm formation is a phenomenon occurring almost wherever microorganisms and surfaces exist in close proximity. This study aimed to evaluate the possible influence of bacterial interactions on the ability of Listeria monocytogenes and Pseudomonas putida to develop a dual-species biofilm community on stainless steel (SS), as well as on the subsequent resistance of their sessile cells to benzalkonium chloride (BC) used in inadequate (sub-lethal) concentration (50 ppm). The possible progressive adaptability of mixed-culture biofilms to BC was also investigated. To accomplish these, 3 strains per species were left to develop mixed-culture biofilms on SS coupons, incubated in daily renewable growth medium for a total period of 10 days, under either mono- or dual-species conditions. Each day, biofilm cells were exposed to disinfection treatment. Results revealed that the simultaneous presence of L. monocytogenes strongly increased the resistance of P. putida biofilm cells to BC, while culture conditions (mono-/dual-species) did not seem to significantly influence the resistance of L. monocytogenes biofilm cells. BC mainly killed L. monocytogenes cells when this was applied against the dual-species sessile community during the whole incubation period, despite the fact that from the 2nd day this community was mainly composed (>90%) of P. putida cells. No obvious adaptation to BC was observed in either L. monocytogenes or P. putida biofilm cells. Pulsed field gel electrophoresis (PFGE) analysis showed that the different strains behaved differently with regard to biofilm formation and antimicrobial resistance. Such knowledge on the physiological behavior of mixed-culture biofilms could provide the information necessary to control their formation. © 2013 GIAOURIS et al. Source

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