Natural products show diverse mechanisms of action against Clostridium difficile

A novel α-mangostin derivative synergistic to antibiotics against MRSA with unique mechanisms

Methicillin-resistant Staphylococcus aureus (MRSA) remains a leading cause of hospital-acquired infections, often linked to complicated treatments, increased mortality risk, and significant cost burdens. Several antibacterial agents have been developed to address MRSA resistance. In this study, potential agents to combat MRSA resistance were explored, with the antibacterial activity of synthesized α-mangostin (α-MG) derivatives being evaluated alongside investigations into their cellular mechanisms against MRSA2. α-MG-4, featuring an allyl group at C3 of the lead compound α-MG, restored the sensitivity of MRSA2 to penicillin, enrofloxacin, and gentamicin, while also demonstrating improved safety profiles. Although α-MG-4 alone was ineffective against MRSA2, it exhibited an optimal synergistic ratio in vitro when combined with these antibiotics. This significant synergistic antibacterial effect was further confirmed in vivo using a mouse skin abscess model. Additionally, the synergistic mechanisms revealed that α-MG-4 was associated with changes in membrane permeability and inhibition of the MepA and NorA genes, which encode the efflux pumps of MRSA2. α-MG-4 also inhibited PBP2a expression, potentially by occupying a crucial binding site in a dose-dependent manner.IMPORTANCEMethicillin-resistant Staphylococcus aureus (MRSA)'s resistance to multiple antibiotics poses significant health and safety concerns. A novel α-mangostin (α-MG) derivative, α-MG-4, was first identified as a xanthone-based PBP2a inhibitor that reverses MRSA2 resistance to penicillin. The synergistic antibacterial effects of α-MG-4 were linked to increased cell membrane permeability and the inhibition of genes involved in efflux pump function.

The Effects of Encapsulation on the In Vitro Anti-Clostridial Activity of Olive Mill Wastewater Polyphenolic Extracts: A Promising Strategy to Limit Microbial Growth in Food Systems

Despite the technologies applied to food production, microbial contamination and chemical deterioration are still matters of great concern. In order to limit these phenomena, new natural approaches should be applied. In this context, the present study aimed to assess the antioxidant and anti-Clostridial effects of two different polyphenolic extracts derived from olive mill vegetation water, one liquid (LE) and one encapsulated (EE). The extracts have been preliminary characterized using Liquid Chromatography Quadrupole Time-Of Flight spectrometry. The Oxygen Radical Absorbance Capacity method was used to determine the antioxidant capacity, registering a higher value for EE compared to that for LE (3256 ± 85 and 2446 ± 13 µgTE/g, respectively). The antibacterial activity against C. perfringens, C. botulinum and C. difficile was studied by the agar well diffusion method, MIC and MBC determination and a time-kill test. The results confirm that EE and LE are able to limit microbial growth, albeit with minor effects when the phenolic compounds are encapsulated. Further studies are needed to evaluate the possible application of these extracts in food systems.

Current and future interventions for improving poultry health and poultry food safety and security: A comprehensive review

Poultry is thriving across the globe. Chicken meat is the most preferred poultry worldwide, and its popularity is increasing. However, poultry also threatens human hygiene, especially as a fomite of infectious diseases caused by the major foodborne pathogens (Campylobacter, Salmonella, and Listeria). Preventing pathogenic bacterial biofilm is crucial in the chicken industry due to increasing food safety hazards caused by recurring contamination and the rapid degradation of meat, as well as the increased resistance of bacteria to cleaning and disinfection procedures commonly used in chicken processing plants. To address this, various innovative and promising strategies to combat bacterial resistance and biofilm are emerging to improve food safety and quality and extend shelf-life. In particular, natural compounds are attractive because of their potential antimicrobial activities. Natural compounds can also boost the immune system and improve poultry health and performance. In addition to phytochemicals, bacteriophages, nanoparticles, coatings, enzymes, and probiotics represent unique and environmentally friendly strategies in the poultry processing industry to prevent foodborne pathogens from reaching the consumer. Lactoferrin, bacteriocin, antimicrobial peptides, cell-free supernatants, and biosurfactants are also of considerable interest for their prospective application as natural antimicrobials for improving the safety of raw poultry meat. This review aims to describe the feasibility of these proposed strategies and provide an overview of recent published evidences to control microorganisms in the poultry industry, considering the human health, food safety, and economic aspects of poultry production.

In Vitro Analysis of Extracts of Plant Used in Mexican Traditional Medicine, Which Are Useful to Combat Clostridioides difficile Infection

Recently, a worrying acceleration of the emergence of antibiotic-resistant bacteria has been reported. The increase in antibiotic-associated diseases, such as Clostridioides difficile infection (CDI), has promoted research on new treatments that could be more effective and less aggressive for CDI patients. This study evaluates eight plants with antimicrobial activity commonly used in Mexican traditional medicine to evaluate their potential against C. difficile. We provide essential information about these plants’ activities and action mechanisms against C. difficile and their effect on different bacterial infection activities: motility, adherence, sporulation, and germination. The selected plants are rosemary, estafiate, rue, epazote, mint, toloache, ajenjo, and thyme. We used clinical isolates to test their activity against strains responsible for current outbreaks to provide more information about the clinical impact of these extracts. We found that thyme, ajenjo, and mint were the most effective against the isolates. We identified that the extracts affected protein synthesis. In addition, the extracts affect the strains’ motility, and some, such as thyme extract, affect adherence, whereas rue extract affects sporulation. These results led to the identification of new compounds beneficial to CDI treatment.

Antimicrobial Mechanisms of Enterocin CHQS Against Candida albicans

Candida albicans is the most common fungal pathogen in hospital-acquired infections, which is extremely harmful to health. The increasing fungal infections is requiring the rapid development of novel antifungal agents. In this study, the antimicrobial activity of CHQS, an enterocin isolated from Enterococcus faecalis TG2 against C. albicans was confirmed by the minimum inhibitory concentration, minimum fungicidal concentration, and time-kill curve. Aniline blue and calcofluor white staining methods showed that CHQS remarkably affected β-1,3-glucan and chitin cell wall components and made cell wall more vulnerable. The C. albicans cell wall rupture and intracellular vacuolation were observed by TEM and SEM. Moreover, CHQS induced the accumulation of intracellular reactive oxygen species and decreased mitochondrial membrane potential. These results suggested that CHQS might have a complex multi-target antimicrobial mechanism against C. albicans. In addition, the use of CHQS combined with amphotericin B showed synergistic antimicrobial effects against C. albicans. In conclusion, enterocin CHQS, a natural product with antimicrobial effect, might has a bright future for the development of new antifungal drugs.

Frontiers in antibiotic alternatives for Clostridioides difficile infection

Clostridioides difficile (C. difficile) is a gram-positive, anaerobic spore-forming bacterium and a major cause of antibiotic-associated diarrhea. Humans are naturally resistant to C. difficile infection (CDI) owing to the protection provided by healthy gut microbiota. When the gut microbiota is disturbed, C. difficile can colonize, produce toxins, and manifest clinical symptoms, ranging from asymptomatic diarrhea and colitis to death. Despite the steady-if not rising-prevalence of CDI, it will certainly become more problematic in a world of antibiotic overuse and the post-antibiotic era. C. difficile is naturally resistant to most of the currently used antibiotics as it uses multiple resistance mechanisms. Therefore, current CDI treatment regimens are extremely limited to only a few antibiotics, which include vancomycin, fidaxomicin, and metronidazole. Therefore, one of the main challenges experienced by the scientific community is the development of alternative approaches to control and treat CDI. In this Frontier article, we collectively summarize recent advances in alternative treatment approaches for CDI. Over the past few years, several studies have reported on natural product-derived compounds, drug repurposing, high-throughput library screening, phage therapy, and fecal microbiota transplantation. We also include an update on vaccine development, pre- and pro-biotics for CDI, and toxin antidote approaches. These measures tackle CDI at every stage of disease pathology via multiple mechanisms. We also discuss the gaps and concerns in these developments. The next epidemic of CDI is not a matter of if but a matter of when. Therefore, being well-equipped with a collection of alternative therapeutics is necessary and should be prioritized.

Antibacterial plant compounds, extracts and essential oils: An updated review on their effects and putative mechanisms of action

BACKGROUND

Antibiotic-resistant bacteria pose a global health threat. Traditional antibiotics can lose their effectiveness, and the development of novel effective antimicrobials has become a priority in recent years. In this area, plants represent an invaluable source of antimicrobial compounds with vast therapeutic potential.

PURPOSE

To review the full possible spectrum of plant antimicrobial agents (plant compounds, extracts and essential oils) discovered from 2016 to 2021 and their potential to decrease bacterial resistance. Their activities against bacteria, with special emphasis on multidrug resistant bacteria, mechanisms of action, possible combinations with traditional antibiotics, roles in current medicine and future perspectives are discussed.

METHODS

Studies focusing on the antimicrobial activity of compounds of plant origin and their mechanism of action against bacteria were identified and summarized, including contributions from January 2016 until January 2021. Articles were extracted from the Medline database using PubMed search engine with relevant keywords and operators.

RESULTS

The search yielded 11,689 articles from 149 countries, of which 101 articles were included in this review. Reports from 41 phytochemicals belonging to 20 families were included. Reports from plant extracts and essential oils from 39 plant species belonging to 17 families were also included. Polyphenols and terpenes were the most active phytochemicals studied, either alone or as a part of plant extracts or essential oils. Plasma membrane disruption was the most common mechanism of antimicrobial action. Number and position of phenolic hydroxyl groups, double bonds, delocalized electrons and conjugation with sugars in the case of flavonoids seemed to be crucial for antimicrobial capacity. Combinations of phytochemicals with beta-lactam antibiotics were the most studied, and the inhibition of efflux pumps was the most common synergistic mechanism.

CONCLUSION

In recent years, terpenes, flavones, flavonols and some alkaloids and phenylpropanoids, either isolated or as a part of extracts, have shown promising antimicrobial activity, being membrane disruption their most common mechanism. However, their utilization as appropriate antimicrobials need to be boosted by means of new omics technologies and network pharmacology to find the most effective combinations among them or in combination with antibiotics.

Investigation on the Antibacterial Activity of Electronic Cigarette Liquids (ECLs): A Proof of Concept Study

BACKGROUND

The key ingredients of e-cigarettes liquid are commonly propane-1,2-diol (also called propylene glycol) and propane-1,2,3-triol (vegetal glycerol) and their antimicrobial effects are already established. The nicotine and flavors which are often present in e-liquids can interfere with the growth of some microorganisms.

OBJECTIVE

The effect of combining these elements in e-liquids is unknown. The aim of the study was to investigate the possible effects of these liquids on bacterial growth in the presence or absence of nicotine and flavors.

METHODS

Susceptibilities of pathogenic strains (Klebsiella pneumoniae, Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii, Escherichia coli, Enterococcus faecalis and Sarcina lutea) were studied by means of a multidisciplinary approach. Cell viability and antioxidant assays were also evaluated.

RESULTS

All e-liquids investigated showed antibacterial activity against at least one pathogenic strain. Higher activity was correlated to the presence of flavors and nicotine.

DISCUSSION

In most cases, the value of minimal bactericidal concentration is equal to the value of minimal inhibitory concentration showing that these substances have a bactericidal effect. This effect was observed in concentrations up to 6.25% v/v. Antioxidant activity was also correlated to the presence of flavors. Over time, the viability assay in human epithelial lung A549 cells showed a dose-dependent inhibition of cell growth.

CONCLUSION

Our results have shown that flavors considerably enhance the antibacterial activity of propane-1,2-diol and propane-1,2,3-triol. This study provides important evidence that should be taken into consideration in further investigative approaches, to clarify the different sensitivity of the various bacterial species to e-liquids, including the respiratory microbiota, to highlight the possible role of flavors and nicotine.

The Bactericidal Activity and Spore Inhibition Effect of Manuka Honey against Clostridioides Difficile

Clostridioides difficile colitis overgrowth occurs when the normal gut microbiome becomes disrupted, often due to antibiotics. Effective treatment remains elusive, due partly to the persistence of its spores in the gut. Natural substances like manuka honey offer an alternative antimicrobial mechanism of action to conventional antibiotics. We investigated the antibiotic activity of manuka honey against 20 C. difficile isolates. The minimum inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBC) of manuka honeys of methylglyoxal (MGO) grades 30⁺, 100⁺, 250⁺, and 400⁺ were determined based on broth microdilution. Sporicidal activity was assessed in a range of honey concentrations by enumerating total viable cell and spore counts at 0–96 h after organism inoculation. The MICs of C. difficile ranged from 4% to >30% (w/v). MIC₅₀ for the four MGO grades were similar at 10–14%. MBC results for the majority of isolates were distributed bimodally at MBC/MIC ratios ≤4 or MBC >30%. Growth kinetics in honey showed total viable cell counts remaining >10⁵ colony-forming units (CFU)/mL at all time points, whereas spore counts remained within 1-log of baseline (10² CFU/mL) in honey but steadily increased in the drug-free control to >10⁵ CFU/mL by 96 h. Manuka honey demonstrated variable inhibitory and bactericidal activity against C. difficile. MGO grade had no noticeable impact on overall MIC distributions or bactericidal activity. Although manuka honey could inhibit spore proliferation, it did not eradicate spores completely.

Antioxidant, Anti-Inflammatory, and Microbial-Modulating Activities of Essential Oils: Implications in Colonic Pathophysiology

Essential oils (EOs) are a complex mixture of hydrophobic and volatile compounds synthesized from aromatic plants, most of them commonly used in the human diet. In recent years, many studies have analyzed their antimicrobial, antioxidant, anti-inflammatory, immunomodulatory and anticancer properties in vitro and on experimentally induced animal models of colitis and colorectal cancer. However, there are still few clinical studies aimed to understand their role in the modulation of the intestinal pathophysiology. Many EOs and some of their molecules have demonstrated their efficacy in inhibiting bacterial, fungi and virus replication and in modulating the inflammatory and oxidative processes that take place in experimental colitis. In addition to this, their antitumor activity against colorectal cancer models makes them extremely interesting compounds for the modulation of the pathophysiology of the large bowel. The characterization of these EOs is made difficult by their complexity and by the different compositions present in the same oil having different geographical origins. This review tries to shift the focus from the EOs to their individual compounds, to expand their possible applications in modulating colon pathophysiology.

The effect of berberine chloride and/or its combination with vancomycin on the growth, biofilm formation, and motility of Clostridioides difficile

This study aims to investigate the antimicrobial and antibiofilm activity of berberine chloride (BBR) and vancomycin (VAN) as well as synergistic combinations of BBR with VAN against Clostridioides difficile strains. The effect of different concentrations of BBR on strain motility was also assessed. Twelve C. difficile strains (two reference C. difficile 630, ATCC 9689, and one control M120, and 9 clinical C. difficile strains belonging to the PCR-ribotype (RT027)) were collected and investigated for their susceptibility to BBR and VAN in planktonic and biofilm forms. Both the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of BBR for the C. difficile strains were found to vary over a broad range (256–1.024 mg/L and 256–16.384 mg/L, respectively). The MIC and MBC of VAN also varied greatly, ranging from 0.25 to 4.0 mg/L for MIC and 0.25 to 64.0 mg/L for MBC. The synergistic effect of the sub-MIC (1/2 MIC) BBR with VAN reduced of MICs of VAN against the planktonic forms of ten C. difficile strains. The sub-MIC of BBR enhanced the biofilm formation of one strain and was found to be statistically significant. In addition, the sub-MIC of BBR with VAN surprisingly enhanced the biofilm formation of one C. difficile strain. The effect of inhibition of motility in the presence of BBR was statistically significant for 3 clinical strains (p < 0.05). Altogether, BBR exhibited strong antimicrobial activity against C. difficile, and the analysis of the combination of BBR with VAN showed a synergistic effect.