The Antimicrobial and Antibiofilm Activity of Oregano Essential Oil against Enterococcus faecalis and Its Application in Chicken Breast

Activity and safety evaluation of natural preservatives

Synthetic preservatives are widely used in the food industry to control spoilage and growth of pathogenic microorganisms, inhibit lipid oxidation processes and extend the shelf life of food. However, synthetic preservatives have some side effects that can lead to poisoning, cancer and other degenerative diseases. With the improvement of living standards, people are developing safer natural preservatives to replace synthetic preservatives, including plant derived preservatives (polyphenols, essential oils, flavonoids), animal derived preservatives (lysozyme, antimicrobial peptide, chitosan) and microorganism derived preservatives (nisin, natamycin, ε-polylysine, phage). These natural preservatives exert antibacterial effects by disrupting microbial cell wall/membrane structures, interfering with DNA/RNA replication and transcription, and affecting protein synthesis and metabolism. This review summarizes the natural bioactive compounds (polyphenols, flavonoids and terpenoids, etc.) in these preservatives, their antioxidant and antibacterial activities, and safety evaluation in various products.

In Vitro Evaluation of Phytobiotic Mixture Antibacterial Potential against Enterococcus spp. Strains Isolated from Broiler Chicken

Enterococcus spp. are normal intestinal tract microflorae found in poultry. However, the last decades have shown that several species, e.g., Enterococcus cecorum, have become emerging pathogens in broilers and may cause numerous losses in flocks. In this study, two combinations (H1 and H2) of menthol, 1,8-cineol, linalool, methyl salicylate, γ-terpinene, p-cymene, trans-anethole, terpinen-4-ol and thymol were used in an in vitro model, analyzing its effectiveness against the strains E. cecorum, E. faecalis, E. faecium, E. hirae and E. gallinarum isolated from broiler chickens from industrial farms. To identify the isolated strains classical microbiological methods and VITEK 2 GP cards were used. Moreover for E. cecorum a PCR test was used.. Antibiotic sensitivity (MIC) tests were performed for all the strains. For the composition H1, the effective dilution for E. cecorum and E. hirae strains was 1:512, and for E. faecalis, E. faecium and E. gallinarum, 1:1024. The second mixture (H2) showed very similar results with an effectiveness at 1:512 for E. cecorum and E. hirae and 1:1024 for E. faecalis, E. faecium and E. gallinarum. The presented results suggest that the proposed composition is effective against selected strains of Enterococcus in an in vitro model, and its effect is comparable to classical antibiotics used to treat this pathogen in poultry. This may suggest that this product may also be effective in vivo and provide effective support in the management of enterococcosis in broiler chickens.

Antimicrobial Activity of Eugenol Against Bacillus cereus and Its Application in Skim Milk

Bacillus cereus is a foodborne pathogen widely distributed in the large-scale catering industry and produces spores. The study explored the antibacterial activity, potential mechanism of eugenol against B. cereus, and spores with germination rate. The minimum inhibitory concentration (MIC; 0.6 mg/mL) of eugenol to six B. cereus strains was compared with the control; B. cereus treated with eugenol had a longer lag phase. Eugenol at a concentration of more than 1/2MIC decreased viable B. cereus (∼5.7 log colony-forming unit [CFU]/mL) counts below detectable limits within 2 h, and eugenol of 3MIC reduced B. cereus (∼5.9 log CFU/mL) in skim milk below detectable limits within 30 min. The pH values of skim milk were unaffected by the addition of eugenol. The ΔE values below 2 show that the color variations of skim milk were not visible to the human eye. For sensory evaluation, eugenol did not significantly affect the color or structural integrity of the skim milk. It had a negative impact on the flavor and general sensory acceptance of the treated milk. Eugenol hyperpolarized B. cereus cell membrane, decreased intracellular ATP concentration, and increased intracellular reactive oxygen species contents and extracellular malondialdehyde contents, resulting in the cell membrane of B. cereus being damaged and permeabilized, and cell morphology being changed. In addition, according to the viable count, confocal laser scanning microscopy, and spore morphology changes, eugenol reduced the germination rate of B. cereus spores. These findings suggest that eugenol can be used as a new natural antibacterial agent to control B. cereus and spores in the food production chain.

Synergistic bactericidal mechanisms of RF energy simultaneously combined with cinnamon essential oil or epsilon-polylysine against Salmonella revealed at cellular and metabolic levels

Radio frequency (RF) heating and antimicrobials are considered to be effective methods for inactivating food pathogens. This study explored the bactericidal effects against Salmonella of RF heating combined with two kinds of natural antimicrobials possessing different hydrophobic properties and their synergistic bactericidal mechanisms. Results showed that RF heating caused sublethal damage to bacterial cells and enhanced the interaction of cells and antimicrobials, leading to synergistic bactericidal effects of the simultaneous combination of RF heating and antimicrobials. The combination of RF heating and ε-polylysine (ε-PL) further promoted cell morphological alteration, raised membrane permeability, intracellular adenosine triphosphate (ATP) leakage and intracellular reactive oxygen species (ROS) accumulation compared to individual treatment. The simultaneous combination of RF heating and cinnamon essential oil nanoemulsion (CEON) also further enhanced membrane permeability and ROS accumulation compared to individual treatment, but impacts were less than those in the combination of RF heating and ε-PL. The major synergistic bactericidal mechanism of RF heating and CEON was significantly inhibiting intracellular ATP synthesis. The untargeted metabolomics analysis revealed that the combined treatments enhanced disturbances to multiple intracellular metabolisms compared to individual treatment, thus leading to synergistic bactericidal effects against Salmonella. These results provide an in-depth understanding of the synergistic bactericidal mechanisms of the combination of RF heating and natural antimicrobials from cellular and metabolic levels.

Effect of Vapor-Phase Oregano Essential Oil on Resistant Candida Species Biofilms: Mechanisms of Action

Vulvovaginal candidiasis (VVC) is one of the most prevalent vaginal infectious diseases. The increasing incidence of drug-resistant Candida strains and the limited therapeutic options make the discovery of effective alternative therapies fundamental. Essential oils (EOs) have been suggested as a promising alternative, and interestingly, vapor-phase essential oils (VP-EOs) present more advantages than their direct application. Thus, this study aims to evaluate the effect of oregano VP-EO (VP-OEO) on biofilms of antifungal-resistant vaginal isolates of Candida species (Candida albicans and Candida glabrata) and determine its mode of action. CFU, membrane integrity, and metabolic activity were evaluated. Furthermore, a reconstituted vaginal epithelium was used to mimic vaginal conditions and evaluate the effect of VP-OEO on Candida species infection, analyzed by DNA quantification, microscopy, and lactate dehydrogenase activity. The results revealed high VP-OEO antifungal activity. There was a significant reduction (>4 log CFU) in Candida species biofilms. Furthermore, the results show that the mechanisms of action of VP-OEO are related to membrane integrity and metabolic activity. The epithelium model confirms the effectiveness of VP-OEO. This study suggests that VP-EO can be considered a first approach for the development of an alternative form of VVC treatment. IMPORTANCE This work presents a new approach to the application of essential oils, exposure to the vapor phase, which can be considered a first approach for the development of a complementary or alternative form of vulvovaginal candidiasis (VVC) treatment. VVC is a significant infection caused by Candida species and remains a common disease that affects millions of women every year. The great difficulty in treating VVC and the extremely limited effective therapeutic options make the development of alternative treatments crucial. In this scope, this study aims to contribute to the development of effective, inexpensive, and nontoxic strategies for the prevention and treatment of this infectious disease, based on natural products. Moreover, this new approach has several advantages for women, such as lower costs, easy access, an easier mode of application, avoidance of skin contact, and, therefore, fewer negative impacts on women's health.

Biofilm Formation Capacity and Presence of Virulence Determinants among Enterococcus Species from Milk and Raw Milk Cheeses

Bacterial biofilm is one of the major hazards facing the food industry. Biofilm-forming ability is one of the most important virulence properties of enterococci. The genus Enterococcus includes pathogenic, spoilage, and pro-technological bacteria. The presence of enterococci in milk and dairy products is usually associated with inadequate hygiene practices. The study examined the isolates' capacity for biofilm formation and identification of the genetic determinants of its formation among 85 Enterococcus strains isolated from raw milk (n = 49) and soft-ripened cheeses made from unpasteurized milk (n = 36). E. faecalis and E. faecium were the dominant species. The obtained results showed that 41.4% isolates from milk and 50.0% isolates from cheeses were able to form biofilm. All of the isolates analyzed had at least one of the studied genes. As regards the isolates from raw milk, the most prevalent gene was the gelE (85.6%), followed by the asa1 (66.7%). None of the isolates from cheeses showed the presence of cylA and sprE. The most prevalent gene among the strains from this source was the epbC (94.4%), followed by the gelE (88.9%). In isolates from both sources, the presence of proteins from the Fsr group was noted the least frequently. Nevertheless, results showed that were no significant differences between the biofilm-producing Enterococcus spp. and non-biofilm-producing isolates in term of occurrences of tested virulence genes. The ability to produce a biofilm by enterococci isolated from raw milk or ready-to-eat products emphasizes the need for continuous monitoring of the mechanisms of microbial adhesion.

Application of the Hurdle Technology Concept to the Fresh Za'atar (Origanum syriacum) Preservation

Oregano (Origanum syriacum) is popularly called za’atar in the Middle East region. It is widely used in the Mediterranean diet as an aromatic herb. This study aimed to evaluate the preservation effect of natural additives, vacuum packaging, and refrigeration on the quality traits of fresh oregano. In total, 132 fresh oregano samples were formulated and split into 4 groups (n = 33) labeled group A (100% fresh oregano leaves, Control), group B (fresh oregano 63.2%, 15% fresh onion, 20% oil, 1.8% salt), group C (fresh oregano 61.91%, 15% fresh Allium cepa, 20% oil, 1.8% salt, 1.29% sumac), and group D (fresh oregano 59.2%, 15% fresh Allium cepa, 20% corn oil, 1.8% salt, 4% lactic acid, ultimate pH 4.4). Different quality traits such as color index (L*a*b*), microbiological analysis (total aerobic, anaerobic, and psychrotrophic bacteria and yeasts and molds), and sensory features (taste, flavor, appearance, saltiness, and overall acceptance) were assessed during the storage period (42 days) for all groups. Our study showed that the addition of lactic acid (group D) exhibited a strong preservation effect against aerobic and anaerobic bacteria. In this context, group D had significantly lower aerobic and anaerobic bacterial counts (5.12 vs. 6.7, 6, and 6.7 log (cfu/g); p < 0.05) and (4.75 vs. 6.6, 6.1, 6.77 (cfu/g); p < 0.05) than group A, B, and C; respectively. Group D exhibited significantly (p < 0.05) lower psychrotrophic bacterial count (3.6 log (cfu/g)) during the whole period of storage compared with control. Group B had a lower redness index (a*) (−3.3 vs. −1.8, −1.65, −1.23; p < 0.05) than groups A, C, and D; respectively. In conclusion, our study showed that there is a possibility of improving the preservation of oregano (Origanum syriacum) by using lactic acid and sumac combined with vacuum packaging under refrigeration conditions.