Synergistic antibacterial effects of reuterin and catechin against Streptococcus mutans

The Antimicrobial Effects of Coffee and By-Products and Their Potential Applications in Healthcare and Agricultural Sectors: A State-of-Art Review

Coffee is one of the most consumed beverages around the world. Its production is dominated by the species Coffea arabica and Coffea canephora. However, the coffee elaboration process leads to generating a significant amount of waste, which arises in various stages of coffee bean processing and is rich in natural bioactive compounds such as phenolic compounds and alkaloids. Particularly, chlorogenic and caffeic acids have a high antimicrobial potential and have been demonstrated to be effective against bacteria and viruses of healthcare and food relevance, including multi-resistant pathogens. However, the production and accumulation of coffee waste have a negative environmental impact since they can contaminate the surrounding environment due to the presence of organic molecules such as caffeine and tannins. In this context, exploiting natural resources as a source of compounds with the antimicrobial potential of, for example, the bioactive compounds obtained from coffee, has been evaluated in previous works. This review aims to summarize the current knowledge on the antimicrobial properties of coffee and its by-products and their potential application in the healthcare sector and disease control in agricultural crops, with particular emphasis on improving sustainability and efficiency in agriculture through making use of waste, which carries high importance in today's society.

Reuterin Enhances the Efficacy of Peracetic Acid Against Multi-species Dairy Biofilm

Biofilms may contain pathogenic and spoilage bacteria and can become a recurring problem in the dairy sector, with a negative impact on product quality and consumer health. Peracetic acid (PAA) is one of the disinfectants most frequently used to control biofilm formation and persistence. Though effective, it cannot be used at high concentrations due to its corrosive effect on certain materials and because of toxicity concerns. The aim of this study was to test the possibility of PAA remaining bactericidal at lower concentrations by using it in conjunction with reuterin (3-hydroxypropionaldehyde). We evaluated the efficacy of PAA in pure form or as BioDestroy®, a PAA-based commercial disinfectant, on three-species biofilms formed by dairy-derived bacteria, namely Pseudomonas azotoformans PFlA1, Serratia liquefaciens Sl-LJJ01, and Bacillus licheniformis Bl-LJJ01. Minimum inhibitory concentrations of the three agents were determined for each bacterial species and the fractional inhibitory concentrations were then calculated using the checkerboard assay. The minimal biofilm eradication concentration (MBEC) of each antibacterial combination was then calculated against mixed-species biofilm. PAA, BioDestroy®, and reuterin showed antibiofilm activity against all bacteria within the mixed biofilm at respectively 760 ppm, 450 ppm, and 95.6 mM. The MBEC was lowered significantly to 456 ppm, 337.5 ppm, and 71.7 mM, when exposed to reuterin for 16 h followed by contact with disinfectant. Combining reuterin with chemical disinfection shows promise in controlling biofilm on food contact surfaces, especially for harsh or extended treatments. Furthermore, systems with reuterin encapsulation and nanotechnologies could be developed for sustainable antimicrobial efficacy without manufacturing disruptions.

Optimization of Flavonoid Extraction from Abelmoschus manihot Flowers Using Ultrasonic Techniques: Predictive Modeling through Response Surface Methodology and Deep Neural Network and Biological Activity Assessment

Understanding the optimal extraction methods for flavonoids from Abelmoschus manihot flowers (AMF) is crucial for unlocking their potential benefits. This study aimed to optimize the efficiency of flavonoid extraction from AMF. After comparing extraction methods, the ultrasonic cell crusher demonstrated superior performance over conventional techniques. Four key factors-solid-to-liquid ratio (1:10 to 1:50 g·mL-1), ethanol concentration (55% to 95%), ultrasonic time (10 to 50 min), and ultrasonic power (5% to 25% of 900 W)-were investigated and normalized using the entropy weight method. This led to a comprehensive evaluation (CE). Optimization of extraction conditions for the ultrasonic cell crusher was achieved through response surface methodology and a deep neural network model, resulting in optimal parameters: ethanol volume fraction of 66%, solid-to-liquid ratio of 1:21 g/mL, extraction efficiency of 9%, and extraction duration of 35 min, yielding a CE value of 23.14 (RSD < 1%). Additionally, the inhibitory effects of the optimized extracts against Streptococcus mutans (S. mutans) were assessed. The results revealed that AMF extract (AMFE) exhibits inhibitory effects on S. mutans, with concomitant inhibition of sucrase and lactate dehydrogenase (LDH). The MIC of AMFE against planktonic S. mutans is 3 mg/mL, with an MBC of 6 mg/mL. Within the concentration range of 1/8 MIC to 2 MIC of AMFE, the activities of sucrase and LDH decreased by 318.934 U/mg prot and 61.844 U/mg prot, respectively. The antioxidant activity of AMFE was assessed using the potassium ferricyanide reduction and phosphomolybdenum methods. Additionally, the effect of AMFE on DPPH, ABTS, and ·OH free radical scavenging abilities was determined. The concentrations at which AMFE exhibited over 90% scavenging rate for ABTS and DPPH free radicals were found to be 0.125 mg/mL and 2 mg/mL, respectively.

In vitro gastrointestinal digestion and colonic fermentation of media-milled black rice particle-stabilized Pickering emulsion: Phenolic release, bioactivity and prebiotic potential

This is a pioneer study that investigated the digestive characteristics of Pickering emulsions stabilized by media-milled black rice particles during in vitro digestion and colonic fermentation. Free fatty acid release of the emulsions improved from 28.42 ± 3.13% to 33.68 ± 4.05% after media milling. The phenolics released from media-milled sample were close to those from unground sample. Media-milled sample exhibited higher DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging ability and α-glucosidase inhibition rate than unground sample. Media milling increased the generation of short-chain fatty acids (SCFAs) during colonic fermentation, especially acetic acid (23% improvement in media-milled sample over unground sample). It also inhibited the growth of harmful bacteria namely Escherichia Shigella and Streptococcus, and promoted the growth of beneficial bacteria including Bifidobacterium and Blautia. These findings revealed that media-milled black rice particle-stabilized Pickering emulsions possessed intrinsic bioactivity and prebiotic potentials in the gastrointestinal tract for the first time.

Antibacterial Effects of Ramulus mori Oligosaccharides against Streptococcus mutans

Ramulus mori has been widely used in traditional Chinese medicine because of its physiological activities, including antibacterial, anti-inflammatory, and antioxidant activities. Antimicrobial properties of Ramulus mori extract have been well described. However, no information is available regarding on Ramulus mori oligosaccharides (RMOS). The aim of this study was to investigate the effects of RMOS on the growth and virulence properties of the cariogenic bacterium Streptococcus mutans. The effects of RMOS on the biofilm structure and virulence gene expression of S. mutans were also evaluated, and the results were compared with the effects of commercial prebiotic galactooligosaccharides. RMOS were found to have an antibacterial effect against S. mutans, resulting in significant reductions in acid production, lactate dehydrogenase activity, adhesion, insoluble extracellular polysaccharide production, glucosyltransferase activity, and biofilm formation in a dose-dependent manner. Moreover, the biofilm structure was visibly damaged. A quantitative real-time PCR assay revealed downregulation of virulence gene-regulated acid production, polysaccharide production, adhesion, biofilm formation, and quorum sensing. These findings suggest that RMOS may be a promising natural product for the prevention of dental caries.

Tea Polyphenols Inhibit the Activity and Toxicity of Staphylococcus aureus by Destroying Cell Membranes and Accumulating Reactive Oxygen Species

Staphylococcus aureus can cause bacterial food intoxication and seriously affect human health. Tea polyphenols (TP) are a kind of natural, safe, and broad-spectrum bacteriostatic substances, with a wide range of bacteriostatic effects. In the study, we explored the possible bacteriostatic mode of TP. The minimum inhibitory concentration of TP against S. aureus was 64 μg/mL. Protein, DNA, and K+ leak experiments, fluorescence microscopy, and transmission electron microscopy suggested that TP disrupt cell membranes, leading to intracellular component loss. By studying the effect of TP on the toxicity of S. aureus, it was found that the expression levels of two toxin genes, coa and spa, were downregulated by 2.37 and 32.6, respectively. Furthermore, after treatment with TP, a large number of reactive oxygen species (ROS) were propagated and released, leading to oxidative stress in cells. We speculated that the bacteriostatic mechanism of TP may be through the destruction of the cell membrane and ROS-mediated oxidative stress. Meanwhile, the hemolysis activity proved the safety of TP. Our results suggested that TP may be a potential antimicrobial agent for food.

Formulation of water-soluble Buddleja globosa Hope extracts and characterization of their antimicrobial properties against Pseudomonas aeruginosa

Buddleja globosa Hope (BG) extracts are traditionally used to treat skin and gastric ulcers due to their healing properties. Non-aqueous solvents such as ethanol and DMSO are usually used to extract naturally occurring compounds. However, the cytotoxicity of these solvents and the low water solubility of the extracted compounds can hinder their biomedical applications. To overcome the limited solubility of the BG extracts, we aimed to enhance the solubility by processing a standardized hydroalcoholic extract (BG-126) through spray drying (SD), with and without two solubility enhancers. Spray-dried BG (BG-SD) extracts and spray-dried BG extracts plus polyvinylpyrrolidone (BG-SD PVP) and Soluplus® (BG-SD SP) were developed starting from BG-126 (containing 53% ethanol). These four formulations were characterized by total phenolic content, water solubility at 25°C and 37°C, and antimicrobial properties against Pseudomonas aeruginosa. All the SD formulations presented a solubility that allowed them to reach maximum concentrations of 1,024 μg/ml catechin for BG-SD and 2,048 μg/ml catechin for BG-SD PVP and BG-SD SP for antimicrobial testing. BG-SD showed the highest antimicrobial potency with a minimum inhibitory concentration (MIC) of 512 μg/ml catechin, followed by BG-126 with a MIC of 1,024 μg/ml catechin and SP. BG-126 was also shown to inhibit biofilm formation, as well as the excipients PVP and SP. The spray-dried BG (BG-SD) extract represents a promising natural active component with enhanced antimicrobial properties against P. aeruginosa for further research and the development of novel phytopharmaceuticals.

The antimicrobial and antibiofilm effects of three herbal extracts on Streptococcus mutans compared with Chlorhexidine 0.2% (in vitro study)

There is a special focus on using natural materials and herbal plants to prevent dental caries. Previous studies showed that some herbal plants have antimicrobial effects on oral pathogens. Thus we investigated the antimicrobial effects of three herbal extracts (Carum copticum, Phlomis bruguieri, and Marrubium parviflorum) on the growth of Streptococcus mutans, as the most important bacteria causing dental caries. First, plant methanolic extracts were prepared. Then, to evaluate the antimicrobial activity of the three herbal extracts, the agar well diffusion method and MIC were performed. The biofilm formation was carried out using a broth dilution method with 2% glucose-supplemented BHIS in sterile 96-well microplates. Serial dilutions (50, 25, 12.5, 6.25, 3.12 mg/ml) of extracts were prepared. Next, a 0.5 McFarland Suspension of S. mutans was added to wells. The inhibitory effect on biofilm formation was measured by the ELISA reader apparatus. The assay was repeated three times, and the average was calculated as 3. The results were compared with those of Chlorhexidine 0.2%. Carum copticum showed a better effect in the agar well diffusion method than others. MIC of the extracts of Carum coptimum, Phlomis bruguieri, and Marrubium parviflorum were 3.12, 6.25, and 12.5 mg/ml, respectively. Overall, the highest activity belonged to Carum copticum extract. For the anti-biofilm effect, the OD values of Carum copticum and Marrubium parviflorum were significantly different from that of Phlomis bruguieri. Although all of the methanolic herbal extracts can inhibit S. mutans growth and remove the biofilm, the effect of Carum copticum was better than Phlomis bruguieri and Marrubium parviflorum. Further studies are recommended to indicate how these extracts perform against the bacteria.

Synergistic antibacterial activity and mechanism of action of nisin/carvacrol combination against Staphylococcus aureus and their application in the infecting pasteurized milk

Synergistic antibacterial effect is a promising way to overcome the challenge of microbial contamination in food. In this study, we detected the synergistic interactions of nisin and carvacrol. The MIC of nisin and carvacrol against S. aureus were 60 and 125 μg/mL, respectively. The FICI and FBCI were 0.28125 and 0.09375, which suggested that the nisin/carvacrol combination presented synergistic antibacterial effect against S. aureus. The antibacterial activity of nisin/carvacrol combination was much higher than their individuals and the dose of antibacterials was obviously reduced. The combination could completely kill S. aureus within 8 h, accelerate the destruction of cell membrane, and inhibit formation of biofilm. Under the intervention of nisin, more CAR could enter cell to hunt intracellular targets, leading to an increase in intracellular antibacterial level. Besides, in the storage of pasteurized milk, the combinational treatment successfully inhibited microbial reproduction at 25 °C and 4 °C. Thus, the combination of nisin and carvacrol was a potential synergistic strategy for food preservation.