Catechin Hydrate Augments the Antibacterial Action of Selected Antibiotics against Staphylococcus aureus Clinical Strains

Understanding the synergistic sensitization of natural products and antibiotics: An effective strategy to combat MRSA

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most common multi-resistant organisms found in hospital-acquired infections and is associated with high morbidity and mortality. The development of new drugs and promising therapeutic strategies against MRSA is thus an urgent request. In recent years, some natural products have been demonstrated to show great potential in improving the efficacy of antibiotics to treat various drug-resistant bacteria, particularly MRSA. In this context, we aimed to analyze systematically from the prior arts that investigated the synergy between natural products and antibiotics against MRSA. These findings not only give us a better understanding on the mechanism of actions but also shed light on the bioactive molecular scaffolds identified from diverse natural products. In the present study, we concentratedly reviewed the studies that utilized natural products to enhance the potency of conventional antibiotics against MRSA in the last decade. The timely information reported herein may give meaningful insights into the molecular design of novel and potent antibacterial agents and/or effective therapeutics to combat MRSA for practical applications.

Phytotherapeutic potential against MRSA: mechanisms, synergy, and therapeutic prospects

BACKGROUND

Rising resistance to antimicrobials, particularly in the case of methicillin-resistant Staphylococcus aureus (MRSA), represents a formidable global health challenge. Consequently, it is imperative to develop new antimicrobial solutions. This study evaluated 68 Chinese medicinal plants renowned for their historical applications in treating infectious diseases.

METHODS

The antimicrobial efficacy of medicinal plants were evaluated by determining their minimum inhibitory concentration (MIC) against MRSA. Safety profiles were assessed on human colorectal adenocarcinoma (Caco-2) and hepatocellular carcinoma (HepG2) cells. Mechanistic insights were obtained through fluorescence and transmission electron microscopy (FM and TEM). Synergistic effects with vancomycin were investigated using the Fractional Inhibitory Concentration Index (FICI).

RESULTS

Rheum palmatum L., Arctium lappa L. and Paeonia suffructicosaas Andr. have emerged as potential candidates with potent anti-MRSA properties, with an impressive low MIC of 7.8 µg/mL, comparable to the 2 µg/mL MIC of vancomycin served as the antibiotic control. Crucially, these candidates demonstrated significant safety profiles when evaluated on Caco-2 and HepG2 cells. Even at 16 times the MIC, the cell viability ranged from 83.3% to 95.7%, highlighting their potential safety. FM and TEM revealed a diverse array of actions against MRSA, such as disrupting the cell wall and membrane, interference with nucleoids, and inducing morphological alterations resembling pseudo-multicellular structures in MRSA. Additionally, the synergy between vancomycin and these three plant extracts was evident against MRSA (FICI < 0.5). Notably, aqueous extract of R. palmatum at 1/4 MIC significantly reduced the vancomycin MIC from 2 µg/mL to 0.03 µg/mL, making a remarkable 67-fold decrease.

CONCLUSIONS

This study unveil new insights into the mechanistic actions and pleiotropic antibacterial effectiveness of these medicinal plants against resistant bacteria, providing robust evidence for their potential use as standalone or in conjunction with antibiotics, to effectively combat antimicrobial resistance, particularly against MRSA.

Bioactive Compounds from Plant Origin as Natural Antimicrobial Agents for the Treatment of Wound Infections

The rising prevalence of drug-resistant bacteria underscores the need to search for innovative and nature-based solutions. One of the approaches may be the use of plants that constitute a rich source of miscellaneous compounds with a wide range of biological properties. This review explores the antimicrobial activity of seven bioactives and their possible molecular mechanisms of action. Special attention was focused on the antibacterial properties of berberine, catechin, chelerythrine, cinnamaldehyde, ellagic acid, proanthocyanidin, and sanguinarine against Staphylococcus aureus, Enterococcus spp., Klebsiella pneumoniae, Acinetobacter baumannii, Escherichia coli, Serratia marcescens and Pseudomonas aeruginosa. The growing interest in novel therapeutic strategies based on new plant-derived formulations was confirmed by the growing number of articles. Natural products are one of the most promising and intensively examined agents to combat the consequences of the overuse and misuse of classical antibiotics.

New Insights into the Antimicrobial Potential of Polyalthia longifolia-Antibiofilm Activity and Synergistic Effect in Combination with Penicillin against Staphylococcus aureus

Widespread antibiotic resistance has led to the urgent need for the identification of new antimicrobials. Plants are considered a valuable potential resource for new effective antimicrobial compounds. Therefore, in the present study, we focused on the antimicrobial activity of Polyalthia longifolia plants harvested from Cameroon using the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and time-kill assays. The mechanism of action was investigated by employing fluorescence and scanning electron microscopy. The anti-Staphylococcus aureus activity was studied using biofilm inhibition and checkerboard assays. Our results revealed that the tested extracts possess important antimicrobial activities, notably against Gram positive bacteria (MICs as low as 0.039 mg/mL). P. longifolia leaf extracts exhibited a significant bactericidal effect, with a total kill effect recorded after only 2 h of exposure at concentrations equivalent to MBC (0.078 and 0.156 mg/mL). The extracts showed a synergistic antibacterial activity in combination with penicillin against a MRSA clinical isolate and significantly inhibited S. aureus biofilm formation. The mechanism of action is related to the impairment of cell membrane integrity and cell lysis. All these findings suggest that P. longifolia could be an important source of reliable compounds used to develop new antimicrobials.

Polyphenol and Tannin Nutraceuticals and Their Metabolites: How the Human Gut Microbiota Influences Their Properties

Nutraceuticals have been receiving increasing attention in the last few years due to their potential role as adjuvants against non-communicable chronic diseases (cardiovascular disease, diabetes, cancer, etc.). However, a limited number of studies have been performed to evaluate the bioavailability of such compounds, and it is generally reported that a substantial elevation of their plasma concentration can only be achieved when they are consumed at pharmacological levels. Even so, positive effects have been reported associated with an average dietary consumption of several nutraceutical classes, meaning that the primary compound might not be solely responsible for all the biological effects. The in vivo activities of such biomolecules might be carried out by metabolites derived from gut microbiota fermentative transformation. This review discusses the structure and properties of phenolic nutraceuticals (i.e., polyphenols and tannins) and the putative role of the human gut microbiota in influencing the beneficial effects of such compounds.

Effect of Hybrid Type and Harvesting Season on Phytochemistry and Antibacterial Activity of Extracted Metabolites from Salix Bark

Hundreds of different fast-growing Salix hybrids have been developed mainly for energy crops. In this paper, we studied water extracts from the bark of 15 willow hybrids and species as potential antimicrobial additives. Treatment of ground bark in water under mild conditions extracted 12-25% of the dry material. Preparative high-performance liquid chromatography is proven here as a fast and highly efficient tool in the small-scale recovery of raffinose from Salix bark crude extracts for structural elucidation. Less than half of the dissolved material was assigned by chromatographic (gas chromatography and liquid chromatography) and spectroscopic (mass spectrometry and nuclear magnetic resonance spectroscopy) techniques for low-molecular-weight compounds, including mono- and oligosaccharides (sucrose, raffinose, and stachyose) and aromatic phytochemicals (triandrin, catechin, salicin, and picein). The composition of the extracts varied greatly depending on the hybrid or species and the harvesting season. This information generated new scientific knowledge on the variation in the content and composition of the extracts between Salix hybrids and harvesting season depending on the desired molecule. The extracts showed high antibacterial activity on Staphylococcus aureus with a minimal inhibitory concentration (MIC) of 0.6-0.8 mg/mL; however, no inhibition was observed against Escherichia coli, Enterococcus faecalis, and Salmonella typhimurium. MIC of triandrin (i.e., 1.25 mg/mL) is reported for the first time. Although antibacterial triandrin and (+)-catechin were present in extracts, clear correlation between the antibacterial effect and the chemical composition was not established, which indicates that antibacterial activity of the extracts mainly originates from some not yet elucidated substances. Aquatic toxicity and mutagenicity assessments showed the safe usage of Salix water extracts as possible antibacterial additives.

Protein targets in red complex pathogens for catechin

The development of antimicrobial drug resistance has encouraged scientists to develop alternate methods to combat infectious pathogens associated with dental diseases. Therefore, it is of interest to predict interactions for catechin (a plant derived compound) with protein targets in the red complex pathogens using computer aided network tools. However, in vitro and in vivo studies are warranted to confirm the antimicrobial effect of catechin (gallocatechin, epicatechin, epigallactocatechin (EGC) and gallolyl catechins) on the dental pathogens.

Enhancement of bioavailability and bioactivity of diet-derived flavonoids by application of nanotechnology: a review

Flavonoids, which are a class of polyphenols widely existing in food and medicine, have enormous pharmacological effects. The functional properties of flavonoids are mainly distributed to their anti-oxidative, anticancer, and anti-inflammatoryeffects, etc. However, flavonoids' low bioavailability limits their clinical application, which is closely related to their intestinal absorption and metabolism. In addition, because of the short residence time of oral bioactive molecules in the stomach, low permeability and low solubility in the gastrointestinal tract, flavonoids are easy to be decomposed by the external environment and gastrointestinal tract after digestion. To tackle these obstacles, technological approaches like microencapsulation have been developed and applied for the formulation of flavonoid-enriched food products. In the light of these scientific advances, the objective of this review is to establish the structural requirements of flavonoids for appreciable anticancer, anti-inflammatory, and antioxidant effects, and elucidate a comprehensive mechanism that can explain their activity. Furthermore, the novelty in application of nanotechnology for the safe delivery of flavonoids in food matrices is discussed. After a literature on the flavonoids and their health attributes, the encapsulation methods and the coating materials are presented.

Phytochemical profile, antimicrobial, and anti-quorum sensing properties of fruit stalks of Prunus avium L

The aim of this study is to investigate the phytochemical contents and antibacterial properties of 2-year Prunus avium L. standard cultivars [Cristalina (Cr), 0900 Ziraat (Zr)] and to elucidate the mechanism of action of the extracts on the quorum sensing (QS) system by using homology modelling and molecular docking. Phenolic contents of methanol extract of Cr and Zr stalks were detected by HPLC. As a result, catechin hydrate (6364·67-8127·93 µg g^-1 ) and chlorogenic acid (998·81-1273·4 µg g^-1 ) were found to be the highest in stalk extracts in the two varieties in 2017. All extracts had inhibitory effect on Gram-positive bacteria. Stalk extract of Zr showed higher inhibition rate (86%) on swarming motility. Stalk samples of Zr collected in 2017 and 2018 also reduced biofilm formation by 75 and 73%, respectively. The computational analysis revealed that one of the major component of the extracts, chlorogenic acid, was able to bind to the QS system receptors, LasR, RhlR, and PqsR. Therefore, the mechanism of decreasing the production of virulence factors by the extracts might be through inhibiting these receptors and thus interfering with the QS system.

Sensitivity of Staphylococcal Biofilm to Selected Compounds of Plant Origin

Staphylococcus epidermidis is a bacterium that belongs to the human microbiota. It is most plentiful on the skin, in the respiratory system, and in the human digestive tract. Moreover, it is the most frequently isolated microorganism belonging to the group of Coagulase Negative Staphylococci (CoNS). In recent years, it has been recognized as an important etiological factor of mainly nosocomial infections and infections related to the cardiovascular system. On the other hand, Staphylococcus aureus, responsible for in-hospital and out-of-hospital infections, is posing an increasing problem for clinicians due to its growing resistance to antibiotics. Biofilm produced by both of these staphylococcal species in the course of infection significantly impedes therapy. The ability to produce biofilm hinders the activity of chemotherapeutic agents-the only currently available antimicrobial therapy. This also causes the observed significant increase in bacterial resistance. For this reason, we are constantly looking for new substances that can neutralize microbial cells. In the present review, 58 substances of plant origin with antimicrobial activity against staphylococcal biofilm were replaced. Variable antimicrobial efficacy of the substances was demonstrated, depending on the age of the biofilm. An increase in the activity of the compounds occurred in proportion to increasing their concentration. Appropriate use of the potential of plant-derived compounds as an alternative to antibiotics may represent an important direction of change in the support of antimicrobial therapy.

Antibacterial green tea catechins from a molecular perspective: mechanisms of action and structure-activity relationships

This review summarizes the mechanisms of antibacterial action of green tea catechins, discussing the structure-activity relationship (SAR) studies for each mechanism. The antibacterial activity of green tea catechins results from a variety of mechanisms that can be broadly classified into the following groups: (1) inhibition of virulence factors (toxins and extracellular matrix); (2) cell wall and cell membrane disruption; (3) inhibition of intracellular enzymes; (4) oxidative stress; (5) DNA damage; and (6) iron chelation. These mechanisms operate simultaneously with relative importance differing among bacterial strains. In all SAR studies, the highest antibacterial activity is observed for galloylated compounds (EGCG, ECG, and theaflavin digallate). This observation, combined with numerous experimental and theoretical evidence, suggests that catechins share a common binding mode, characterized by the formation of hydrogen bonds and hydrophobic interactions with their target.

Antibiotic Potentiation of Natural Products: A Promising Target to Fight Pathogenic Bacteria

Pathogenic microorganisms should be considered as the number one foe of human, as witnessed by recent outbreaks of coronavirus disease (COVID-19) and with bacteria no longer sensitive to existing antibiotics. The resistance of pathogenic bacteria and deaths attributable to bacterial infections is increasing exponentially. Bacteria used different mechanisms to counterattack to existing antibiotics, namely (i) enzymatic inhibition, (ii) penicillin-binding protein modification, (iii) porin mutations, (iv) efflux pumps and (v) molecular modifications of antibiotic targets. Developing new antibiotics would be time-consuming to address such a situation, thus one of the promising approaches is by potentiating existing antibiotics. Plants used synergism to naturally defend and protect themselves from microbes. Using the same strategy, several studies have shown that the combinations of natural products and antibiotics could effectively prolong the lifespan of existing antibiotics and minimize the impact and emergence of antibiotic resistance. Combining essential oils constituents, namely uvaol, ferruginol, farnesol and carvacrol, with antibiotics, have proved to be efficient efflux pump inhibitors. Plant-derived compounds such as gallic acid and tannic acid are effective potentiators of various antibiotics, including novobiocin, chlorobiocin, coumermycin, fusidic acid, and rifampicin, resulting in a 4-fold increase in the potencies of these antibiotics. Several lines of research, as discussed in this review, have demonstrated the effectiveness of natural products in potentiating existing antibiotics. For this reason, the search for more efficient combinations should be an ongoing process with the aim to extend the life of the ones that we have and may preserve the life for the ones that are yet to come.

Exploring the powerful phytoarsenal of white grape marc against bacteria and parasites causing significant diseases

Natural extracts containing high polyphenolic concentration possess antibacterial, anti-parasitic and fungicidal activities. The present research characterises two extracts based on white grape marc, a winemaking by-product, describing their physicochemical features and antimicrobial capacities. The main components of these extracts are phenolic acids, flavan-3-ols and their gallates and flavonols and their glycosides. As a result of this complex composition, the extracts showed pronounced bioactivities with potential uses in agricultural, pharmaceutical and cosmetic industries. Polyphenol compounds were extracted by using hydro-organic solvent mixtures from the by-product of Albariño white wines (Galicia, NW Spain) production. The in vitro antimicrobial activity of these extracts was evaluated on Gram-positive and Gram-negative bacteria and Apicomplexan and Oomycota parasites. Microbial species investigated are causing agents of several human and animal diseases, such as foodborne illnesses (Bacillus cereus, Escherichia coli, Salmonella enterica, and Toxoplasma gondii), skin infections and/or mastitis (Staphylococcus aureus and Streptococcus uberis), malaria (Plasmodium falciparum) and plant infections as "chestnut ink" or "root rot" (Phytophthora cinnamomi). Both extracts showed activity against all the tested species, being nontoxic for the host. So, they could be used for the development of biocides to control a wide range of pathogenic agents and contribute to the enhancement of winemaking industry by-products.

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.

The Relationship between Fruit Size and Phenolic and Enzymatic Composition of Avocado Byproducts (Persea americana Mill.): The Importance for Biorefinery Applications

Avocado byproducts are a rich source of health-promoting biomolecules. The purpose of this work is to study three groups of statistically different avocado fruit sizes (Persea americana Mill.) (small (S), medium (M), and large (L)), and their relationship with total phenolic and flavonoid contents (TPC and TFC, respectively), DPPH (2,2-diphenyl-1-picrylhydrazyl) scavenging capacity and individual phenolics, and the activities of phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), and polyphenol oxidase (PPO) in avocado peel extract (APE). The results indicated that TPC, TFC, and antioxidant and enzymatic activities were higher in the APE of the S group (p < 0.05). The flavonoids (flavanols and flavonols) and phenolic acids were also significatively concentrated in S group’s APE. Overall, the phenolic content was significantly lower in the L group. Positive correlations (p < 0.0001 and p < 0.05) were observed between TPC, TPF, DPPH, and enzymatic activity, and negative correlations resulted for avocado weight and volume. The outstanding phenolic content and enzymatic activity of avocado peels from low-cost avocado byproducts are ideal for biorefinery applications, thereby increasing the bioeconomy of the avocado industry.

Catechin isolated from cashew nut shell exhibits antibacterial activity against clinical isolates of MRSA through ROS-mediated oxidative stress

Staphylococcus aureus causes severe infections and among all methicillin-resistant S. aureus (MRSA) remains a great challenge in spite of decade research of antibacterial compounds. Even though some synthetic antibiotics have been developed, they are not effective against MRSA, and hence, there is a search for natural, alternative and plant-based antibacterial compound. In this connection, catechin isolated from cashew nut shell was investigated for its antibacterial potential against MRSA. Catechin exhibited zone of inhibition (ZOI) and minimum inhibitory concentration (MIC) in a range of 15.1-19.5 mm and 78.1-156.2 μg/ml, respectively, against ATCC and clinical isolates of MRSA. Among all clinical isolates, clinical isolate-3 exhibited highest sensitivity to catechin. Catechin has arrested the growth of MRSA strains and also caused toxicity by membrane disruption which was illustrated by AO/EB fluorescence staining. Increased nucleic acid leakage (1.58-28.6-fold) and protein leakage (1.40-23.50-fold) was noticed in MRSA due to catechin treatment when compared to methicillin. Bacteria treated with catechin at its MIC showed 1.52-, 1.87- and 1.74-fold increase of ROS production in methicillin susceptible S. aureus (MSSA), MRSA and clinical isolate-3 strains, respectively, as compared to control. Superoxide dismutase (5.31-9.63 U/mg protein) and catalase (1573-3930 U/mg protein) were significantly decreased as compared to control in catechin-treated S. aureus. Thus, catechin exhibited antibacterial activity through oxidative stress by increased production of ROS and decreased antioxidant enzymes. Altogether results suggest that catechin is a promising lead compound with antibacterial potential against MRSA. KEY POINTS: • Catechin was isolated and identified as active compound in cashew nut shell. • Catechin exhibited antimicrobial activity against clinical isolates of MRSA. • Bacterial cell wall damage was caused by catechin in MRSA strains. • Catechin increased the oxidative stress in MRSA by intracellular ROS production.

Role of symbiosis in the discovery of novel antibiotics

Antibiotic resistance has been an ongoing challenge that has emerged almost immediately after the initial discovery of antibiotics and requires the development of innovative new antibiotics and antibiotic combinations that can effectively mitigate the development of resistance. More than 35,000 people die each year from antibiotic resistant infections in just the United States. This signifies the importance of identifying other alternatives to antibiotics for which resistance has developed. Virtually, all currently used antibiotics can trace their genesis to soil derived bacteria and fungi. The bacteria and fungi involved in symbiosis is an area that still remains widely unexplored for the discovery and development of new antibiotics. This brief review focuses on the challenges and opportunities in the application of symbiotic microbes and also provides an interesting platform that links natural product chemistry with evolutionary biology and ecology.

Phytochemical Profile and Biological Activities of Tendrils and Leaves Extracts from a Variety of Vitis vinifera L

Winery industry by-products have a great reuse potential in the pharmaceutical and cosmetic fields due to their bioactive compounds. This study investigates the phytochemical profile and the bioactivity of Vitis vinifera variety Fetească neagră tendrils extract (TE) and leaves extract (LE), intended to be used in oral hygiene products recommended in periodontal disease. The evaluation of the phenolic content was performed by colorimetric analysis. Liquid chromatography coupled with mass spectrometry was used to determine the chemical profile of the two extracts obtained from V. vinifera. Moreover, the antioxidant activity of the extracts was determined by spectrophotometric methods, as well as on human gingival fibroblasts (HGF) cell line. The cytocompatibility and cytoprotective effect against nicotine-induced cytotoxicity were tested, as well as the anti-inflammatory and antimicrobial effects. The TE showed higher total polyphenolic content, rich in rutin, compared to the leaves extract that displayed important amounts of isoquercitrin. The antioxidant effect was confirmed by both non-cellular and cellular tests. The cytocompatibility of the extracts was confirmed at a wide range of concentrations. The cytoprotective effect was demonstrated in HGF exposed to cytotoxic doses of nicotine; 300 µg/mL of both tested extracts decreased nicotine toxicity by approximately 20%. When challenged with E. coli polysaccharides, in HGF cells co-exposed to TE and LE, a reduction in the release of proinflammatory cytokines (IL-8, IL-6 and IL-1β) was observed. The extracts were both able to reduce the levels of reactive oxygen species and inflammatory cytokines, and had notable antimicrobial effects on pathogenic bacteria associated with periodontitis.

Phenolic Compounds Diminish Antibiotic Resistance of Staphylococcus Aureus Clinical Strains

There is a growing body of evidence that flavonoids show antibacterial activity against both Gram-positive and Gram-negative bacteria. The mechanisms of action of phenolic compounds on bacterial cell have been partially attributed to damage to the bacterial membrane, inhibition of virulence factors such as enzymes and toxins, and suppression of bacterial biofilm formation. What is more, some natural polyphenols, aside from direct antibacterial activity, exert a synergistic effect when combined with common chemotherapeutics. Many studies have proved that in synergy with antibiotics plant flavonoids pose a promising alternative for therapeutic strategies against drug resistant bacteria. In this review most recent reports on antimicrobial action of polyphenols on Staphylococcus aureus strains are described, highlighting where proven, the mechanisms of action and the structure–activity relationships. Since many reports in this field are, to some extent, conflicting, a unified in vitro and in vivo susceptibility testing algorithms should be introduced to ensure the selection of effective antibacterial polyphenolic compounds with low cytotoxicity and minimal side effects.

Properties of novel surfactin-derived biosurfactants obtained through solid-phase synthesis

Eight molecules, four peptides (SPs) and four lipopeptides (LPs) derived by rational design from surfactin, a well-known secreted biosurfactant from Bacillus subtilis, were produced employing Fmoc-based solid-phase synthesis. These new peptides were tested to evaluate their potential biosurfactant and biological activities, aiming at possible applications in industrial, biological, pharmaceutical, and medical use. Five molecules (SP1, SP2, SP4, LP5, and LP8) presented potential for medical uses, mainly due to their drug delivery properties as suggested by their synergistic activity with the antibiotic vancomycin against Staphylococcus aureus. All synthetic peptides showed low toxicity against Vero cell cultures, in assays of hemolysis, and in different cytotoxicity assays. In addition, we found that three peptides (SP1, LP6, and LP7) had potential technological and industrial use because of their emulsifying capacity, low toxicity, and ability to physically stabilize solutions. These novel molecules retained some properties of the parental molecule (surfactin, which was originally obtained through nonribosomal synthesis in Bacillus subtilis) but have the advantage of being linear peptides, which can be produced at large scales through the use of conventional heterologous protein expression protocols.

Antimicrobial Potential of Caffeic Acid against Staphylococcus aureus Clinical Strains

Phenolic compounds constitute one of the most promising and ubiquitous groups with many biological activities. Synergistic interactions between natural phenolic compounds and antibiotics could offer a desired alternative approach to the therapies against multidrug-resistant bacteria. The objective of the presented study was to assess the antibacterial potential of caffeic acid (CA) alone and in antibiotic-phytochemical combination against Staphylococcus aureus reference and clinical strains isolated from infected wounds. The caffeic acid tested in the presented study showed diverse effects on S. aureus strains with the minimum inhibitory concentration (MIC) varied from 256 μg/mL to 1024 μg/mL. The supplementation of Mueller-Hinton agar (MHA) with 1/4 MIC of CA resulted in augmented antibacterial effect of erythromycin, clindamycin, and cefoxitin and to the lesser extent of vancomycin. The observed antimicrobial action of CA seemed to be rather strain than antibiotic dependent. Our data support the notion that CA alone exerts antibacterial activity against S. aureus clinical strains and has capacity to potentiate antimicrobial effect in combination with antibiotics. The synergy between CA and antibiotics demonstrates its potential as a novel antibacterial tool which could improve the treatment of intractable infections caused by multidrug-resistant strains.

Effects of Blue-Light-Induced Free Radical Formation from Catechin Hydrate on the Inactivation of Acinetobacter baumannii, Including a Carbapenem-Resistant Strain

Catechin is a flavan-3-ol, a derivative of flavans, with four phenolic hydroxyl groups, which exhibits a wide range of physiological properties. Chromatographic analyses were employed to examine the effects of blue light irradiation on the changes of catechin hydrate in an alkaline condition. In particular, the detection of a superoxide anion radical (O₂•⁻), a reactive oxygen species (ROS), and the inactivation of Acinetobacter baumannii (A. baumannii)—including a carbapenem-resistant A. baumannii (CRAB)—was investigated during the photoreaction of catechin hydrate. Following basification with blue light irradiation, the transparent solution of catechin hydrate turned yellowish, and a chromogenic catechin dimer was separated and identified as a proanthocyanidin. Adding ascorbic acid during the photolytic treatment of catechin hydrate decreased the dimer formation, suggesting that ascorbic acid can suppress the photosensitive oxidation of catechin. When catechin hydrate was irradiated by blue light in an alkaline solution, O₂•⁻ was produced via photosensitized oxidation, enhancing the inactivation of A. baumannii and CRAB. The present findings on the photon-induced oxidation of catechin hydrate provides a safe practice for the inactivation of environmental microorganisms.

Chemical Composition, Antibacterial Activity, and Synergistic Effects with Conventional Antibiotics and Nitric Oxide Production Inhibitory Activity of Essential Oil from Geophila repens (L.) I.M. Johnst

Geophila repens (L.) I.M. Johnst, a perennial herb, belongs to the Rubiaceae family. In this study, we identified the chemical composition of the Geophila repens essential oil (GR-EO) for the first time. Totally, seventy-seven compounds were identified according to GC and GC-MS, which represent 98.0% of the oil. And the major components of GR-EO were β-caryophyllene (23.3%), β-elemene (8.0%), farnesyl butanoate (7.4%), myrcene (3.5%), and trans-nerolidol (3.3%). Then we evaluated the antibacterial activities of GR-EO and the synergistic effects of GR-EO in combination with commercial antibiotics using the microdilution and Checkerboard method. The results demonstrated that GR-EO possessed an excellent broad spectrum antibacterial activity, especially against Pseudomonas aeruginosa and Bacillus subtilis. It also showed that the combined application of GR-EO with antibiotics led to synergistic effects in most cases. And the most prominent synergistic effect was noticed when GR-EO was in combination with Streptomycin and tested against Escherichia coli (fractional inhibitory concentration indices (FICI) of 0.13). Additionally, the results of a Griess assay revealed that GR-EO exhibited a potent inhibitory effect on NO production in lipopolysaccharide (LPS)-activated RAW 264.7 (murine macrophage) cells. In conclusion, the combination of GR-EO and the commercial antibiotics has significant potential for the development of new antimicrobial treatment and reduction of drug resistance.