Antibacterial and anti-staphylococcal enterotoxin activities of phenolic compounds

Bioactivity of Eugenol: A Potential Antibiotic Adjuvant with Minimal Ecotoxicological Impact

Combining commercial antibiotics with adjuvants to lower their minimum inhibitory concentration (MIC) is vital in combating antimicrobial resistance. Evaluating the ecotoxicity of such compounds is crucial due to environmental and health risks. Here, eugenol was assessed as an adjuvant for 7 commercial antibiotics against 14 pathogenic bacteria in vitro, also examining its acute ecotoxicity on various soil and water organisms (microbiota, Vibrio fischeri, Daphnia magna, Eisenia foetida, and Allium cepa). Using microdilution methods, checkerboard assays, and kinetic studies, the MICs for eugenol were determined together with the nature of its combinations with antibiotics against bacteria, some unexposed to eugenol previously. The lethal dose for the non-target organisms was also determined, as well as the Average Well Color Development and the Community-Level Physiological Profiling for soil and water microbiota. Our findings indicate that eugenol significantly reduces MICs by 75 to 98%, which means that it could be a potent adjuvant. Ecotoxicological assessments showed eugenol to be less harmful to water and soil microbiota compared to studied antibiotics. While Vibrio fischeri and Daphnia magna were susceptible, Allium cepa and Eisenia foetida were minimally affected. Given that only 0.1% of eugenol is excreted by humans without metabolism, its environmental risk when used with antibiotics appears minimal.

Antibacterial Activity Potential of Industrial Food Production Waste Extracts against Pathogenic Bacteria: Comparative Analysis and Characterization

The Food and Agricultural Organization estimates a 17% loss in the food production chain, making it imperative to adopt scientific and technological approaches to address this issue for sustainability. Industrial food production waste and its value-added applications, particularly in relation to a wide variety of pathogenic microorganisms and the health-related effects have not been thoroughly investigated. This study explores the potential of food production waste extracts-lemon peel (LP), hot trub (HT), and coffee silverskin (CSS) as sources of bioactive compounds. Extraction was conducted using hydro-methanolic extraction with yields in LP (482 mg/1 g) > HT (332 mg/1 g) > CSS (20 mg/1 g). The agar diffusion assay revealed the substantial antibacterial activity of all three extracts against Erwinia Amylovora, Escherichia coli, Bacillus subtilis, and Bacillus aquimaris. All extracts demonstrated activity against Gram-positive and Gram-negative bacteria, displaying minimum inhibitory concentrations effective against pathogenic bacteria like Listeria monocytogenes, Staphylococcus aureus, Vibrio parahaemolyticus, and Salmonella enterica. Total phenolic content (TPC in mg GAE/1g) was 100, 20, and 100 for CSS, HT, and LP, respectively. Antioxidant activity by ABTS indicated IC50 of 3.09, 13.09, and 2.61 for LP, HT, and CSS, respectively. Also, the antioxidant activity of the extracts was further confirmed by DPPH assay with the best activity in CSS (9.84 GAEg-1) and LP (9.77 mg of GAEg-1) rather than in HT (1.45 GAEg-1). No adverse cytotoxic effects on HaCaT cells were observed. Pancreatic amylase inhibition demonstrated antidiabetic potential, with LP showing the highest levels (92%). LC-MS characterization identified polyphenols as the main compounds in CSS, prenylated compounds in HT, and flavanols in LP. The findings imply the potential sustainable use of food production waste in industry.

The Potential of Wood Vinegar to Replace Antimicrobials Used in Animal Husbandry-A Review

The indiscriminate use of antimicrobials in animal husbandry can result in various types of environmental contamination. Part of the dose of these products is excreted, still active, in the animals' feces and urine. These excreta are widely used as organic fertilizers, which results in contamination with antimicrobial molecules. The impacts can occur in several compartments, such as soil, groundwater, and surface watercourses. Also, contamination by antimicrobials fed or administrated to pigs, chickens, and cattle can reach the meat, milk, and other animal products, which calls into question the sustainability of using these products as part of eco-friendly practices. Therefore, a search for alternative natural products is required to replace the conventional antimicrobials currently used in animal husbandry, aiming to mitigate environmental contamination. We thus carried out a review addressing this issue, highlighting wood vinegar (WV), also known as pyroligneous acid, as an alternative antimicrobial with good potential to replace conventional products. In this regard, many studies have demonstrated that WV is a promising product. WV is a nontoxic additive widely employed in the food industry to impart a smoked flavor to foods. Studies have shown that, depending on the WV concentration, good results can be achieved using it as an antimicrobial against pathogenic bacteria and fungi and a valuable growth promoter for poultry and pigs.

Hazard of Staphylococcal Enterotoxins in Food and Promising Strategies for Natural Products against Virulence

Staphylococcal enterotoxins (SEs) secreted by Staphylococcus aureus frequently contaminate food and cause serious foodborne diseases but are ignored during food processing and even cold-chain storage. Notably, SEs are stable and resistant to harsh sterilization environments, which can induce more serious hazards to public health than the bacterium itself. Therefore, it is necessary to develop promising strategies to control SE contamination in food and improve food safety. Natural products not only have various pharmaceutical properties, such as antimicrobial and antitoxin activities, but they are also eco-friendly, safe, nutritive, and barely drug-resistant. Here, the hazards of SEs and the promising natural compounds with different inhibitory mechanisms are summarized and classified. The key points of future research and applications for natural products against bacterial toxin contamination in food are also prospected. Overall, this review may provide enlightening insights for screening effective natural compounds to prevent foodborne diseases caused by bacterial toxins.

Antimicrobial activity of Baccharis dracunculifolia DC and its synergistic interaction with nisin against food-related bacteria

The antimicrobial activities of Baccharis dracunculifolia DC essential oil (EO) and hydroalcoholic extract (HE) were evaluated. The EO showed broad antimicrobial activity and its synergistic combination with nisin was tested. Major components of EO were nerolidol, beta-pinene and D-limonene, while artepillin C, rutin and cafeic acid were major phenolics of HE. EO and HE were tested by agar diffusion assay against several strains of bacteria and yeasts, and mixed cultures of bacterial strains. The EO presented the largest spectrum of antimicrobial activity inhibiting all Gram-positive bacteria tested. Yeasts were not inhibited. The effect of EO against mixtures of sensitive and non-sensitive bacteria was tested on milk agar, being the inhibitory effect only observed on mixtures containing susceptible strains. The combination of EO and nisin at ½ MIC was evaluated on the growth curve of Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes and Salmonella Enteritidis during 24 h at 37 °C. The combination EO-nisin was effective and no viable counts of B. cereus, L. monocytogenes and S. Enteritidis was observed, while the individual antimicrobials caused no inhibition. The counts of S. aureus were about 4 log CFU/mL lower in comparison with EO or nisin alone. B. dracunculifolia DC may be a potential source of natural antimicrobials, and its synergistic effect with nisin would reduce the working concentration, minimizing the organoleptic effects associated with this plant antimicrobial.

In vitro anti-bacterial activity and network pharmacology analysis of Sanguisorba officinalis L. against Helicobacter pylori infection

Background

Helicobacter pylori (H. pylori) infection has become an international public health problem, and antibiotic-based triple or quadruple therapy is currently the mainstay of treatment. However, the effectiveness of these therapies decreases due to resistance to multiple commonly used antibiotics. Sanguisorba officinalis L. (S. officinalis), a traditional Chinese medicine clinically used for hemostasis and treatment of diarrhea, has various pharmacological activities. In this study, in vitro antimicrobial activity was used for the preliminary evaluation of S. officinalis against H. pylori. And a pharmacology analysis approach was also utilized to elucidate its underlying mechanisms against H. pylori infection.

Methods

Micro-broth dilution method, agar dilution method, checkerboard assay, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used for the assessment of anti-bacterial activity. Active ingredients screening, GO analysis, KEGG analysis, construction of PPI network, molecular docking, and RT-qPCR were used to elucidate the underlying pharmacological mechanisms of S. officinalis against H. pylori infection.

Results

The minimum inhibitory concentration (MIC) values of S. officinalis against multiple H. pylori strains including clinically isolated multi-drug resistant (MDR) strains were ranging from 160 to 320 µg/ml. These results showed that S. officinalis had additive interaction with four commonly used antibiotics and could exert antibacterial effect by changing the morphology of bacteria without developing drug resistance. Through network pharmacology analysis, 8 active ingredients in S. officinalis were screened out for subsequent studies. Among 222 putative targets of S. officinalis, 49 targets were identified as potential targets for treatment of H. pylori infection. And these 49 targets were significantly enriched in GO processes such as protein kinase B signaling, protein kinase activity, protein kinase binding, and KEGG pathways such as Pathways in cancer, MicroRNAs in cancer, and TNF signaling pathway. Protein-protein interaction analysis yielded 5 core targets (AKT1, VEGFA, EGFR, SRC, CCND1), which were validated by molecular docking and RT-qPCR.

Conclusions

Overall, this study confirmed the in vitro inhibitory activity of S. officinalis against H. pylori and explored the possible pharmacological mechanisms, laying the foundation for further research and clinical application.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13020-021-00442-1.

Sub-Inhibitory Concentrations of Ciprofloxacin Alone and Combinations with Plant-Derived Compounds against P. aeruginosa Biofilms and Their Effects on the Metabolomic Profile of P. aeruginosa Biofilms

INTRODUCTION

Alternative anti-biofilm agents are needed to combat Pseudomonas aeruginosa infections. The mechanisms behind these new agents also need to be revealed at a molecular level.

MATERIALS AND METHODS

The anti-biofilm effects of 10 plant-derived compounds on P. aeruginosa biofilms were investigated using minimum biofilm eradication concentration (MBEC) and virulence assays. The effects of ciprofloxacin and compound combinations on P. aeruginosa in mono and triple biofilms were compared. A metabolomic approach and qRT-PCR were applied to the biofilms treated with ciprofloxacin in combination with baicalein, esculin hydrate, curcumin, and cinnamaldehyde at sub-minimal biofilm inhibitory concentration (MBIC) concentrations to highlight the specific metabolic shifts between the biofilms and to determine the quorum sensing gene expressions, respectively.

RESULTS

The combinations of ciprofloxacin with curcumin, baicalein, esculetin, and cinnamaldehyde showed more reduced MBICs than ciprofloxacin alone. The quorum sensing genes were downregulated in the presence of curcumin and cinnamaldehyde, while upregulated in the presence of baicalein and esculin hydrate rather than for ciprofloxacin alone. The combinations exhibited different killing effects on P. aeruginosa in mono and triple biofilms without affecting its virulence. The findings of the decreased metabolite levels related to pyrimidine and lipopolysaccharide synthesis and to down-regulated alginate and lasI expressions strongly indicate the role of multifactorial mechanisms for curcumin-mediated P. aeruginosa growth inhibition.

CONCLUSIONS

The use of curcumin, baicalein, esculetin, and cinnamaldehyde with ciprofloxacin will help fight against P. aeruginosa biofilms. To the best of our knowledge, this is the first study of its kind to define the effect of plant-based compounds as possible anti-biofilm agents with low MBICs for the treatment of P. aeruginosa biofilms through metabolomic pathways.

Synergistic effects of Cinnamomum cassia L. essential oil in combination with polymyxin B against carbapenemase-producing Klebsiella pneumoniae and Serratia marcescens

Multidrug resistance prompts the search for new sources of antibiotics with new targets at bacteria cell. To investigate the antibacterial activity of Cinnamomum cassia L. essential oil (CCeo) alone and in combination with antibiotics against carbapenemase-producing Klebsiella pneumoniae and Serratia marcescens. The antimicrobial susceptibility of the strains was determined by Vitek^® 2 and confirmed by MALDI-TOF/TOF. The antibacterial activity of CCeo and its synergism with antibiotics was determined using agar disk diffusion, broth microdilution, time-kill, and checkboard methods. The integrity of the bacterial cell membrane in S. marcescens was monitored by protein leakage assay. CCeo exhibited inhibitory effects with MIC = 281.25 μg.mL^-1. The association between CCeo and polymyxin B showed a decrease in terms of viable cell counts on survival curves over time after a 4 hour-treatment with a FIC index value of 0.006. Protein leakage was observed with increasing concentrations for CCeo and CCeo + polymyxin B treatments. CCeo showed antibacterial activity against the studied strains. When associated with polymyxin B, a synergistic effect was able to inhibit bacterial growth rapidly and consistently, making it a potential candidate for the development of an alternative treatment and drug delivery system for carbapenemase-producing strains.

Plant Phenolics and Phenolic-Enriched Extracts as Antimicrobial Agents against Food-Contaminating Microorganisms

Phenolic compounds and extracts with bioactive properties can be obtained from many kinds of plant materials. These natural substances have gained attention in the food research as possible growth inhibitors of foodborne pathogenic and spoilage bacteria. Many phenolic-enriched plant extracts and individual phenolics have promising anti-quorum sensing potential as well and can suppress the biofilm formation and toxin production of food-related pathogens. Various studies have shown that plant phenolics can substitute or support the activity of synthetic food preservatives and disinfectants, which, by the way, can provoke serious concerns in consumers. In this review, we will provide a brief insight into the bioactive properties, i.e., the antimicrobial, anti-quorum sensing, anti-biofilm and anti-enterotoxin activities, of plant phenolic extracts and compounds, with special attention to pathogen microorganisms that have food relation. Carbohydrase aided applications to improve the antimicrobial properties of phenolic extracts are also discussed.

Influence of apitoxin and melittin from Apis mellifera bee on Staphylococcus aureus strains

The antibacterial activities of apitoxin, a venom produced by Apis mellifera bee, and melittin, an antimicrobial peptide from apitoxin, were tested against planktonic and biofilm states of Staphylococcus aureus methicillin-resistant (MRSA), including clinical, and enterotoxin-producing isolates. Also, the synergism of apitoxin and melittin in combination with oxacillin were evaluated as well. The induced morphological changes on S. aureus cells of both products were detected by transmission electronic microscopy (TEM). The minimum inhibitory concentration (MIC) values were 7.2 μg/mL, and 6.7 μg/mL, for apitoxin and melittin, respectively. The minimum bactericidal concentration (MBC) values were 28.7 μg/mL, and 26 μg/mL for apitoxin and melittin, respectively. The time-kill curve assays of apitoxin or melittin with oxacillin exhibited bactericidal synergism against MRSA isolates. TEM images showed cell distortion, cell disintegration with leakage of cytoplasmic content and loss of cytoplasm content. However, apitoxin and melittin did not interfere with staphylococcal enterotoxin production or release. Thus, apitoxin and melittin are potential agents against MRSA that can serve as possible models for new antibacterial drugs.

Design and Evaluation of pH-Dependent Nanosystems Based on Cellulose Acetate Phthalate, Nanoparticles Loaded with Chlorhexidine for Periodontal Treatment

This work aimed to develop and evaluate pH-dependent systems based on nanospheres (NSphs) and nanocapsules (NCs) loaded with chlorhexidine (CHX) base as a novel formulation for the treatment of periodontal disease. Cellulose acetate phthalate (CAP) was employed as a pH-dependent polymeric material. The NSphs and NCs were prepared using the emulsion-diffusion technique and then characterized according to encapsulation efficiency (EE), size, zeta-potential, morphology, thermal properties, release profiles and a preliminary clinical panel test. The formulations showed 77% and 61% EE and 57% and 84% process efficiency (PE), respectively. Both systems were spherical with an average size of 250–300 nm. Differential scanning calorimetry (DSC) studies showed that the drug has the potential to be dispersed molecularly in the NSph matrix or dissolved in the oily center of the NCs. The CHX release test revealed that the release of NSphs-CHX follows Fickian diffusion involving diffusion-erosion processes. The NCs showed a slower release than the NSphs, following non-Fickian diffusion, which is indicative of anomalous transport. These nanosystems may, therefore, be employed as novel formulations for treating periodontal disease, due to (1) their coverage of a large surface area, (2) the controlled release of active substances at different pH, and (3) potential gingival tissue infiltration.

Rubus ulmifolius Schott as a Novel Source of Food Colorant: Extraction Optimization of Coloring Pigments and Incorporation in a Bakery Product

(1) Background: Color has been considered to be the flashiest attribute of foodstuffs and researchers have shown a great interest in the extraction of pigmented compounds from vegetal products, with the purpose to provide alternative counterparts to the food industry; (2) Methods: This study aimed to explore Rubus ulmifolius Schott fruits as a potential source of anthocyanins, optimizing the extraction method, evaluating the bioactivity and incorporating the rich extract into a bakery food product; (3) Results: After the extraction optimization, results showed R. ulmifolius fruits to be a great source of anthocyanins, obtaining an amount of 33.58 mg AT/g E, with an extraction yield of 62.08%. The rich anthocyanin extract showed antitumor and antimicrobial potential in some tumor cell lines and strains, respectively, as well as the absence of toxicity; (4) Conclusions: The extract when incorporated in a bakery product showed a good coloring capacity, maintaining the nutritional value, revealing its use to be a great approach for replacing artificial colorants.

Rubus ulmifolius Schott fruits: A detailed study of its nutritional, chemical and bioactive properties

There is a growing interest in wild edible species that represent a source of several health-promoting compounds, providing a potential strategy to diversify and enrich the daily diet. The aim of the present work was to characterize the nutritional and chemical composition of Rubus ulmifolius Schott fruits. Furthermore, their antimicrobial activity, non-anthocyanin and anthocyanin phenolic profile were also determined. According to the obtained results, R. ulmifolius fruits exhibited a high concentration in carbohydrates and a low fat content, in comparison with the other nutrients and non-nutrients detected in this sample. The colour parameters demonstrated differences in a* and b* parameters after lyophilisation process. Glucose and fructose were the most abundant free sugars detected and quinic acid showed the highest content compared to the other five organic acids identified. The fatty acids profile revealed 25 compounds, being mostly represented by polyunsaturated fatty acids and evidencing linolenic and α-linolenic acid as the most abundant. All tocopherol isoforms were detected, revealing γ-tocopherol with highest amount. Cyanidin-3-O-glucoside, ellagic acid pentoside, ellagic acid glucuronide and sanguiin H-10 were the main phenolic compounds present, which could be related to the antimicrobial activity (MIC values ranging between 5 and 20 mg/mL) revealed by R. ulmifolius fruits. These results showed that this fruit is a good source of nutrients as also non-nutrient compounds, with human health benefits.

The impact of Cymbopogon martinii essential oil on Cutibacterium (formerly Propionibacterium) acnes strains and its interaction with keratinocytes

OBJECTIVES

The human skin microbiota is mainly composed of bacteria belonging to the genera Staphylococcus, Cutibacterium, Micrococcus and Corynebacterium, but on the skin of the face and back, ca. 50% of the total microbiota is represented by the bacterium Cutibacterium acnes. The aim of this research was to evaluate the impact of C. martini EO and its major compound, geraniol, on C. acnes.

METHODS

The minimum inhibitory concentration against C. acnes strains, phenotypic changes and responses of the proteome was determined. In addition, was assessed the effect of compounds in RNA-binding assay, on C. acnes-exposed keratinocytes and on the C. acnes type distribution on shoulder skin.

KEY FINDINGS

The range of the MIC was 0.7 to 1.6 mg/ml for the three main C. acnes types. There were no cytotoxic effects of compounds in the absence or presence of C. acnes; after 7 days of exposure to C. martini EO, we could not detect a major shift of the C. acnes types on shoulder skin that was found to be dominated by C. acnes strains of types II and IA2.

CONCLUSIONS

Our work gives novel insight into the skin microbiota-interacting properties of C. martini EO.

Eugenol derivatives: synthesis, characterization, and evaluation of antibacterial and antioxidant activities

Eugenol is the major component of clove essential oil and has demonstrated relevant biological potential with well-known antimicrobial and antioxidant action. Therefore, this work carried out the synthesis, purification, characterization, and evaluation of the antioxidant and antibacterial potential of 19 eugenol derivatives. The derivatives were produced by esterification reactions in the hydroxyl group (−OH) of eugenol with different carboxylic acids and also by addition reactions in the double bond of the allyl group. The derivatives had a promising antibacterial potential, including a lower minimum inhibitory concentration of 500 μg/mL than eugenol (1000 μg/mL). In addition, the derivatives were active against bacterial strains (Escherichia coli, Staphylococcus aureus) that eugenol itself showed no activity, thus increasing the spectrum of antibacterial action. As for the antioxidant activity, it was observed that the derivatives that involved esterification reactions in the hydroxyl group (−OH) of the eugenol molecule’s phenol resulted in a significant reduction of the antioxidant action (IC₅₀ > 100 μg/mL) when compared with the eugenol precursor molecule (IC₅₀ = 4.38 μg/mL). On the other hand, the structural changes located in the double bond affected much more smoothly the capacity of capturing radicals than the starting molecule, also being obtained derivatives with proximal antioxidant capacity (IC₅₀ = 19.30 μg/mL) to commercial standards such as Trolox (IC₅₀ = 16.00 μg/mL).

Inhibitory effects of food additives derived from polyphenols on staphylococcal enterotoxin A production and biofilm formation by Staphylococcus aureus

In this study, we examined the inhibitory effects of 14 food additives derived from polyphenol samples on staphylococcal enterotoxin A (SEA) production and biofilm formation by Staphylococcus aureus. Tannic acid AL (TA), Purephenon 50 W (PP) and Polyphenon 70A (POP) at 0.25 mg/mL and Gravinol®-N (GN), Blackcurrant polyphenol AC10 (BP), and Resveratrol-P5 (RT) at 1.0 mg/mL significantly decreased SEA production by S. aureus C-29 (p < 0.05). TA, GN, BP, and RT significantly inhibited the expression of the sea gene in S. aureus C-29 (p < 0.05), while suppression attempts by PP and POP proved unsuccessful. After result analysis, it can be derived that TA, GN, BP, and RT inhibit the production of SEA. Of the six samples, each one significantly inhibited biofilm formation (p < 0.05). Food additives derived from polyphenols have viability to be used as a means to inhibit the enterotoxin production and control the biofilm formation of foodborne pathogens.