In vitro mechanism of antibacterial action of a citrus essential oil on an enterotoxigenic Escherichia coli and Lactobacillus rhamnosus

Efficacy of orange terpene against Escherichia coli biofilm on beef and food contact surfaces

Foodborne pathogen Escherichia coli frequently causes foodborne infections. In our study, we investigated the antibiofilm activity of orange terpene (OT) against E. coli biofilms on a food surface (beef) and different surfaces that come into touch with food, including stainless steel (SS), polyethylene terephthalate (PET), low-density polyethylene (LDPE), and rubber (SR). The study findings revealed that OT significantly (P < 0.05) eliminated 48-h-old biofilms from all food contact surfaces (SS: 2.09 log CFU/cm2, PET: 1.95 log CFU/cm2, LDPE: 1.94 log CFU/cm2, and SR: 1.4 log CFU/cm2). Additionally, on beef surfaces, OT at a minimum inhibitory concentration (MIC) of 0.13 % demonstrated the ability to inhibit biofilm development by approximately 1.5 log CFU/cm2 and reduced pre-formed biofilms by 2.02 log CFU/cm2. Our sensory evaluations showed that it had no adverse impacts on beef color and texture, although it slightly altered the natural odor of beef. Quantitative and qualitative assessments showed that OT has strong bactericidal actions on biofilm populations. It significantly altered cell surface hydrophobicity, reduced cellular ATP levels, and inhibited cell auto-aggregation in planktonic cells (P < 0.05). As a result, our findings emphasize the antibacterial potentiality of OT in reducing the biofilm of E. coli in the food sector.

Postharvest Quality of Citrus medica L. (cv Liscia-Diamante) Fruit Stored at Different Temperatures: Volatile Profile and Antimicrobial Activity of Essential Oils

Citron (Citrus medica L. cv. Liscia-diamante), cultivated in the "Riviera dei Cedri" (southern Italy), is mainly utilized in the production of candied fruit and essential oils (EOs). Up to now, no information regarding the effect of storage temperatures on citron has been reported. Here, citron samples, after harvesting, were stored at different temperatures (5, 10 and 20 °C at 70% relative humidity) for two weeks, and the main postharvest quality parameters were evaluated. Moreover, EOs extracted from the stored samples were chemically characterized to reveal changes in the volatiles profile and antimicrobial activity. The EOs presented monoterpene hydrocarbons (87.1 to 96.3% of the total oil profile) as the most abundant compounds, followed by oxygenated metabolites ranging from 9.7 to 3.1% of the total pattern. Postharvest quality traits showed a good retention of green peel color during storage at 5 °C, while EOs from samples stored for 7 and 14 days at 10 and 20 °C, respectively, showed the highest antimicrobial activity against most assayed strains. The results indicated storage at 10 °C for 7 days as the most suitable for the preservation of the postharvest quality of the fruit and the antimicrobial activity of the extracted EOs.

Essential Oils: Chemistry and Pharmacological Activities

In this review, we provide an overview of the current understanding of the main mechanisms of pharmacological action of essential oils and their components in various biological systems. A brief introduction on essential oil chemistry is presented to better understand the relationship of chemical aspects with the bioactivity of these products. Next, the antioxidant, anti-inflammatory, antitumor, and antimicrobial activities are discussed. The mechanisms of action against various types of viruses are also addressed. The data show that the multiplicity of pharmacological properties of essential oils occurs due to the chemical diversity in their composition and their ability to interfere with biological processes at cellular and multicellular levels via interaction with various biological targets. Therefore, these natural products can be a promising source for the development of new drugs.

Antibacterial activity of 2-hydroxy-4-methoxybenzaldehyde and its possible mechanism against Staphylococcus aureus

AIM

Staphylococcus aureus causes several complicated infections. Despite decades of research on developing new antimicrobials, methicillin-resistant S. aureus (MRSA) remains a global health problem. Hence, there is a dire need to identify potent natural antibacterial compounds as an alternative to antimicrobials. In this light, the present work divulges the antibacterial efficacy and the action mechanism of 2-hydroxy-4-methoxybenzaldehyde (HMB) isolated from Hemidesmus indicus against S. aureus.

METHODS AND RESULTS

Antimicrobial activity of HMB was assessed. HMB exhibited 1024 µg ml-1 as the minimum inhibitory concentration (MIC) and 2 × MIC as the minimum bactericidal concentration against S. aureus. The results were validated by spot assay, time kill, and growth curve analysis. In addition, HMB treatment increased the release of intracellular proteins and nucleic acid contents from MRSA. Additional experiments assessing the structural morphology of bacterial cells using SEM analysis, β-galactosidase enzyme activity, and the fluorescence intensities of propidium iodide and rhodamine123 dye divulged that the cell membrane as one of the targets of HMB to hinder S. aureus growth. Moreover, the mature biofilm eradication assay revealed that HMB dislodged nearly 80% of the preformed biofilms of MRSA at the tested concentrations. Further, HMB treatment was found to sensitize MRSA cells upon combining tetracycline treatment.

CONCLUSIONS

The present study suggests that HMB is a promising compound with antibacterial and antibiofilm activities and could act as a lead structure for developing new antibacterial drugs against MRSA.

Citrus essential oil: would it be feasible as antimicrobial in the bioethanol industry?

Essential oils (EOs) extracted from Citrus peels contain 85%-99% volatile components (a mixture of monoterpenes, sesquiterpenes, and their oxygenated derivatives) and 1%-15% non-volatile compounds. Citrus EOs have been long known for their antimicrobial properties, owing to which these EOs have a diverse range of applications. However, no studies have reported the applicability of Citrus EOs for the control of bacterial and yeast contaminants in the bioethanol industry. In this regard, the present review aimed to explore the feasibility of Citrus EOs in this industry. The Web of Science database was searched for reports that described the association of Citrus EOs with the most common microorganisms in the bioethanol industry to evaluate the efficacy of these EOs as antimicrobial agents in this context. The objective of the review was to suggest a novel antimicrobial that could replace sulfuric acid and antibiotics as the commonly used antimicrobial agents in the bioethanol industry. Citrus EOs exhibit antibacterial activity against Lactobacillus, which is the main bacterial genus that contaminates this fermentation process. The present report also confirms the selective action of these EOs on the contaminating yeasts and not/less on ethanol-producing yeast Saccharomyces cerevisiae, however further studies should be conducted to investigate the effects of Citrus EOs in yeast-bacterium co-culture.

Potential Applications of Essential Oils for Environmental Sanitization and Antimicrobial Treatment of Intensive Livestock Infections

The extensive use of antibiotics has contributed to the current antibiotic resistance crisis. Livestock infections of Salmonella spp, Clostridium spp. and E. coli antimicrobial-resistant bacteria represent a public threat to human and animal health. To reduce the incidence of these zoonoses, essential oils (EOs) could be effective antibiotic alternatives. This study aims at identifying EOs safe for use, effective both in complementary therapy and in the environmental sanitization of intensive farming. Natural products were chemo-characterized by gas chromatography. Three S. Typhimurium, three C. perfringens and four E. coli strains isolated from poultry and swine farms were used to assess the antimicrobial properties of nine EOs and a modified GR-OLI (mGR-OLI). The toxicity of the most effective ones (Cinnamomum zeylanicum, Cz; Origanum vulgare, Ov) was also evaluated on porcine spermatozoa and Galleria mellonella larvae. Cz, Ov and mGR-OLI showed the strongest antimicrobial activity; their volatile components were also able to significantly inhibit the growth of tested strains. In vitro, Ov toxicity was slightly lower than Cz, while it showed no toxicity on G. mellonella larvae. In conclusion, the study confirms the importance of evaluating natural products to consolidate the idea of safe EO applications in reducing and preventing intensive livestock infections.

Evaluation of the Membrane Damage Mechanism of Chlorogenic Acid against Yersinia enterocolitica and Enterobacter sakazakii and Its Application in the Preservation of Raw Pork and Skim Milk

Plant-derived antimicrobial agents have adequate antimicrobial effects on food-borne pathogens, which can be used as food preservatives. The purpose of this study was to evaluate the antibacterial mechanism of chlorogenic acid (CA) against Yersinia enterocolitica and Enterobacter sakazakii. The minimum inhibitory concentration (MIC) of CA was determined by employing the broth microdilution method. Then, the cell function and morphological changes of Y. enterocolitica and E. sakazakii treated with CA were characterized. Finally, the growth inhibition models of Y. enterocolitica in raw pork and E. sakazakii in skim milk were constructed through the response surface methodology. The results demonstrated that CA has a satisfactory inhibitory effect against Y. enterocolitica and E. sakazakii with a MIC of 2.5 mg/mL. In addition, CA inhibited the growth of Y. enterocolitica and E. sakazakii via cell membrane damage, such as depolarization of the cell membrane, reduction in intracellular adenosine triphosphate (ATP) and pH levels, and destruction of cell morphology. Moreover, CA reduced two log cycles of Y. enterocolitica in raw pork and E. sakazakii in skim milk at a certain temperature. According to the corresponding findings, CA has the potential to be developed as an effective preservative to control Y. enterocolitica and E. sakazakii-associated foodborne diseases.

Nutrients and bioactives in citrus fruits: Different citrus varieties, fruit parts, and growth stages

Citrus fruits are consumed in large quantities worldwide due to their attractive aromas and taste, as well as their high nutritional values and various health-promoting effects, which are due to their abundance of nutrients and bioactives. In addition to water, carbohydrates, vitamins, minerals, and dietary fibers are important nutrients in citrus, providing them with high nutritional values. Citrus fruits are also rich in various bioactives such as flavonoids, essential oils, carotenoids, limonoids, and synephrines, which protect from various ailments, including cancer and inflammatory, digestive, and cardiovascular diseases. The composition and content of nutrients and bioactives differ significantly among citrus varieties, fruit parts, and growth stages. To better understand the nutrient and bioactive profiles of citrus fruits and provide guidance for the utilization of high-value citrus resources, this review systematically summarizes the nutrients and bioactives in citrus fruit, including their contents, structural characteristics, and potential health benefits. We also explore the composition variation in different citrus varieties, fruits parts, and growth stages, as well as their health-promoting effects and applications.

Essential Oils Extracted from Organic Propolis Residues: An Exploratory Analysis of Their Antibacterial and Antioxidant Properties and Volatile Profile

The industrial processing of crude propolis generates residues. Essential oils (EOs) from propolis residues could be a potential source of natural bioactive compounds to replace antibiotics and synthetic antioxidants in pig production. In this study, we determined the antibacterial/antioxidant activity of EOs from crude organic propolis (EOP) and from propolis residues, moist residue (EOMR), and dried residue (EODR), and further elucidated their chemical composition. The EOs were extracted by hydrodistillation, and their volatile profile was tentatively identified by GC-MS. All EOs had an antibacterial effect on Escherichia coli and Lactobacillus plantarum as they caused disturbances on the growth kinetics of both bacteria. However, EODR had more selective antibacterial activity, as it caused a higher reduction in the maximal culture density (D) of E. coli (86.7%) than L. plantarum (46.9%). EODR exhibited mild antioxidant activity, whereas EOMR showed the highest antioxidant activity (ABTS = 0.90 μmol TE/mg, FRAP = 463.97 μmol Fe²⁺/mg) and phenolic content (58.41 mg GAE/g). Each EO had a different chemical composition, but α-pinene and β-pinene were the major compounds detected in the samples. Interestingly, specific minor compounds were detected in a higher relative amount in EOMR and EODR as compared to EOP. Therefore, these minor compounds are most likely responsible for the biological properties of EODR and EOMR. Collectively, our findings suggest that the EOs from propolis residues could be resourcefully used as natural antibacterial/antioxidant additives in pig production.

Chemical Composition and Antibacterial and Antioxidant Activity of a Citrus Essential Oil and Its Fractions

Essential oils (EOs) from Citrus are the main by-product of Citrus-processing industries. In addition to food/beverage and cosmetic applications, citrus EOs could also potentially be used as an alternative to antibiotics in food-producing animals. A commercial citrus EO—Brazilian Orange Terpenes (BOT)—was fractionated by vacuum fractional distillation to separate BOT into various fractions: F1, F2, F3, and F4. Next, the chemical composition and biological activities of BOT and its fractions were characterized. Results showed the three first fractions had a high relative amount of limonene (≥10.86), even higher than the whole BOT. Conversely, F4 presented a larger relative amount of BOT’s minor compounds (carvone, cis-carveol, trans-carveol, cis-p-Mentha-2,8-dien-1-ol, and trans-p-Mentha-2,8-dien-1-ol) and a very low relative amount of limonene (0.08–0.13). Antibacterial activity results showed F4 was the only fraction exhibiting this activity, which was selective and higher activity on a pathogenic bacterium (E. coli) than on a beneficial bacterium (Lactobacillus sp.). However, F4 activity was lower than BOT. Similarly, F4 displayed the highest antioxidant activity among fractions (equivalent to BOT). These results indicated that probably those minor compounds that detected in F4 would be more involved in conferring the biological activities for this fraction and consequently for the whole BOT, instead of the major compound, limonene, playing this role exclusively.

Huanglongbing and Foliar Spray Programs Affect the Chemical Profile of "Valencia" Orange Peel Oil

Florida orange trees have been affected by huanglongbing (HLB) for more than a decade. To alleviate disease-caused tree decline, maintain fruit productivity, and reduce disease transmission, enhanced foliar spray programs combining vector control and nutritional supplementation have been applied to healthy and diseased trees. The aim of this research was to discover if the various foliar sprays affect fruit peel oil chemical components. In this study, "Valencia" orange trees, with or without HLB (HLB±), were treated with the grower standard program (control, C) or one of four proprietary enhanced foliar spray programs (N1, N2, N3, and N4) over 16 months. Compared with HLB-, HLB+ samples had lower concentrations of typical peel oil components, including valencene, octanal, and decanal, and were abundant in oxidative/dehydrogenated terpenes, such as carvone and limonene oxide. However, limonene, the dominant component, was not affected by any treatment. Control and three out of four enhanced foliar spray programs, N2, N3, and N4, had very little influence on the chemical profiles of both HLB- and HLB+ samples, while N1 treatment greatly altered the chemical profile of HLB+ samples, resulting in peel oil similar to that of HLB- samples.

Natural Phenolic Compounds for the Control of Oxidation, Bacterial Spoilage, and Foodborne Pathogens in Meat

Alternative technologies for long-term preservation, quality assurance, and safety of meat are continuously pursued by the food industry to satisfy the demands of modern consumers for nutritious and healthy meat-based products. Naturally occurring phenolic compounds are considered promising substances by the meat industry for their antioxidant and antimicrobial properties, while consumers seem to embrace them for their claimed health benefits. Despite the numerous in vitro and in situ studies demonstrating their beneficial effects against meat oxidation, spoilage, and foodborne pathogens, wide application and commercialization has not been yet achieved. Major obstacles are still the scarcity of legislative framework, the large variety of meat-based products and targeted pathogens, the limited number of case-specific application protocols and the questionable universal efficiency of the applied ones. The objectives of the present review are i) to summarize the current knowledge about the applications of naturally occurring phenols in meat and meat-based products, emphasizing the mechanisms, determinants, and spectrum of their antioxidant and antimicrobial activity; ii) to present state-of-the-art technologies utilized for the application of phenolic compounds in meat systems; and iii) to discuss relevant regulation, limitations, perspectives, and future challenges for their mass industrial use.