Effectiveness of essential oils against dual-species biofilm of Listeria monocytogenes and Pseudomonas fluorescens in a Ricotta-based model system.

Biofilms represent an evolutionary form of life, which translates from life in free-living cells to a community lifestyle. In natural habitats, biofilms are a multispecies complex, where synergies or antagonisms can be established. For example, Listeria monocytogenes and Pseudomonas fluorescens are associated with a dual-species biofilm that is widespread in dairy plants. In food plants, multiple strategies are devised to control biofilms, including natural compounds such as essential oils (EOs). In this respect, this study evaluated the effectiveness of Thymbra capitata (L.) Cav. (TEO) and Cinnamomum zeylanicum (CEO) against a dual-species biofilm of L. monocytogenes and P. fluorescens, mimicking dairy process conditions. Based on Minimum Inhibitory Concentrations results, the EOs concentration (10 µL/mL) was chosen for the antibiofilm assay at 12°C on polystyrene (PS), and stainless-steel surfaces for 168 h, using a Ricotta-based model system as culture medium. Biofilm biomass was assessed by crystal violet staining, and the planktonic and sessile cells were quantified in terms of Log CFU/cm2. Results showed that CEO displayed the greatest antibiofilm activity, reducing significantly (P<0.05) P. fluorescens and L. monocytogenes sessile cells of about 2.5 and 2.8 Log CFU/cm2 after 72 h, respectively. However, L. monocytogenes gained the protection of P. fluorescens, evading CEO treatment and showing a minimal sessile cell reduction of 0.7 Log CFU/cm2 after 72 h. Considering the outcome of this study, CEO might have promising perspectives for applications in dairy facilities.

The Multifaceted Relationship between the COVID-19 Pandemic and the Food System.

The SARS-CoV-2 pandemic is being questioned for its possible food transmission, due to several reports of the virus on food, outbreaks developed in food companies, as well as its origins linked to the wet market of Wuhan, China. The purpose of this review is to analyze the scientific evidence gathered so far on the relationship between food and the pandemic, considering all aspects of the food system that can be involved. The collected data indicate that there is no evidence that foods represent a risk for the transmission of SARS-CoV-2. In fact, even if the virus can persist on food surfaces, there are currently no proven cases of infection from food. Moreover, the pandemic showed to have deeply influenced the eating habits of consumers and their purchasing methods, but also to have enhanced food waste and poverty. Another important finding is the role of meat processing plants as suitable environments for the onset of outbreaks. Lessons learned from the pandemic include the correct management of spaces, food hygiene education for both food workers and common people, the enhancement of alternative commercial channels, the reorganization of food activities, in particular wet markets, and intensive farming, following correct hygiene practices. All these outcomes lead to another crucial lesson, which is the importance of the resilience of the food system. These lessons should be assimilated to deal with the present pandemic and possible future emergencies. Future research directions include further investigation of the factors linked to the food system that can favor the emergence of viruses, and of innovative technologies that can reduce viral transmission.

An overview of the natural antimicrobial alternatives for sheep meat preservation.

Sheep meat is consumed and appreciated all over the world for its nutritional value and flavor. However, this meat is very perishable and easily subjected to the action of both spoilage and pathogenic microorganisms. For this reason, in combination with cold storage, effective preservation techniques are required. There is increasing interest in the application of natural antimicrobials, such as essential oils, extracts, spices, and by-products of the food industry. This review analyses the studies on natural antimicrobials in sheep meat and sheep meat products and gathers evidence about the encouraging results achieved on the reduction and/or elimination of spoilage and pathogenic microorganisms. The use of these natural antimicrobial alternatives might open up important perspectives for industrial application, considering that this specific meat is often traded over long distances. In fact, on the basis of scientific literature, natural antimicrobials can be considered a sustainable and affordable alternative to extend the shelf life of sheep meat and guarantee its safety, although many factors need to be further investigated, such as the sensory impact, potential toxicity, and economic aspects. For all these issues, investigated in some of the studies reviewed here, it is fundamental to obtain the antimicrobial effect with the minimum amount of effective substance to avoid sensory modifications, toxic effects, and unbearable costs. This study sets foundations for the possible direction of future studies, which will contribute to identify effective solutions for industrial applications of natural antimicrobials in the sheep meat industry.

Unraveling the Antimicrobial Effectiveness of Coridothymus capitatus Hydrolate against Listeria monocytogenes in Environmental Conditions Encountered in Foods: An In Vitro Study.

The increased resistance of bacteria to antimicrobials, as well as the growing interest in innovative and sustainable alternatives to traditional food additives, are driving research towards the use of natural food preservatives. Among these, hydrolates (HYs) have gained attention as "mild" alternatives to conventional antimicrobial compounds. In this study, the response of L. monocytogenes ATCC 7644 exposed to increasing concentrations of Coridothymus capitatus HY (CHY) for 1 h at 37 °C was evaluated by means of Phenotype Microarray, modelling the kinetic data obtained by inoculating control and treated cells into GEN III microplates, after CHY removal. The results revealed differences concerning the growth dynamics in environmental conditions commonly encountered in food processing environments (different carbon sources, pH 6.0, pH 5.0, 1-8% NaCl). More specifically, for treated cells, the lag phase was extended, the growth rate was slowed down and, in most cases, the maximum concentration was diminished, suggesting the persistence of stress even after CHY removal. Confocal Laser Scanner Microscopy evidenced a diffuse aggregation and suffering of the treated cells, as a response to the stress encountered. In conclusion, the treatment with HY caused a stressing effect that persisted after its removal. The results suggest the potential of CHY application to control L. monocytogenes in food environments.

Thymus vulgaris L. essential oils from Emilia Romagna Apennines (Italy): phytochemical composition and antimicrobial activity on food-borne pathogens.

Between Modena and Bologna Apennines (Italy), several agricultural farms have recently been dedicated to the cultivation of autochthonous aromatic plants as primary cultivation or to complement other crops. In this study, the chemical composition of Thymus vulgaris L. essential oils (EOs) from this region was evaluated by means of gas-chromatographic analysis. Three different mulching techniques, in particular, soil coverage with grass, mulch with plastic film and with straw were investigated. The results highlighted that mulching techniques influenced the composition of the analysed EOs. All the EOs exerted good antimicrobial activity against clinical and food strains of the pathogen Listeria monocytogenes, with differences related to the composition. The EO obtained from plants covered with grass showed the best results, having MIC ≤ 2.5 µL/mL, and being able to inhibit also antibiotic-resistant strains, thus confirming that soil coverage with grass influences the composition and also the biological activity of Thymus vulgaris EO.

Combination of rosemary extract and buffered vinegar inhibits Pseudomonas and Shewanella growth in common carp (Cyprinus carpio).

BACKGROUND: Aquaculture is the fastest growing food-production sector, and common carp (Cyprinus carpio) is one of the most cultivated fish species in the world. Due to its intrinsic characteristics, fish meat is highly susceptible to microbiological spoilage. Pseudomonas and Shewanella are the primary and secondary occurring microbiota during storage of fish meat, with significant contribution to spoilage with the formation of hydrolytic enzymes (lipases and proteases). RESULTS: With in vitro testing, we show that rosemary extract (Inolens4), buffered vinegar and their combination (SyneROX) exhibit antimicrobial effects against P. fragi, P. psychrophila, S. putrefaciens and S. xiaemensis at concentrations of 3.13 and 1.56 mg mL-1 . The combination was the most effective in inhibiting growth of selected bacteria in food model, and production of lipases and proteases during 9 days at 5 °C. In situ testing of antimicrobial dip treatment of carp meat determined that aerobic mesophilic, total psychrotrophic, Pseudomonas and hydrogen sulfide producer counts were reduced in all treatments, with the most prominent influence being shown by the combination and buffered vinegar. CONCLUSIONS: Our study highlights the importance of a multilevel assessment of the antimicrobial potential of biopreservatives under conditions comparable to those of the selected food. Investigation with bacteria and food model provided coherent and consistent data for the evaluation of the antimicrobial potential for carp meat. Combination of buffered vinegar (as active antimicrobial) and rosemary extract, with well-known and researched antioxidant properties but low in situ antimicrobial activity, represents a good potential for combined effect in preservation of fish meat. © 2020 Society of Chemical Industry.