Anti-Quorum-Sensing Potential of Ethanolic Extracts of Aromatic Plants from the Flora of Cyprus

Plant-derived essential oil contributes to the reduction of multidrug resistance genes in the sludge composting process

Multidrug-resistant bacteria and multi-resistance genes in sludge have become a serious issue for public health. It is imperative to develop feasible and environmentally friendly methods of sludge composting to alleviate multidrug resistance genes. Plant-derived essential oil is an effective natural and eco-friendly antibacterial, which has great utilization in inhibiting pathogens in the agricultural industry. Nevertheless, the application of plant-derived essential oil to control pathogenic bacteria and antibiotic resistance in composting has not been reported. This study conducted a composting system by adding plant-derived essential oil i.e., oregano essential oil (OEO), to sludge composting. The findings indicated that multidrug resistance genes and priority pathogens (critical, high, and medium categories) were reduced by (17.0 ± 2.2)% and (26.5 ± 3.0)% in the addition of OEO (OH treatment) compared to control. Besides, the OH treatment changed the bacterial community and enhanced the gene sequences related to carbohydrate metabolism in compost microorganisms. Mantel test and variation partitioning analysis revealed that the target virulence factors (VFs), target mobile genetic elements (MGEs), and priority pathogens were the most important factors affecting multidrug resistance in composting. The OH treatment could significantly inhibit the target VFs, target MGEs, and priority pathogens, which were helpful for the suppression and elimination of multidrug resistance genes. These findings provide new insights into the regulation of multidrug resistance genes during sludge composting and a novel way to diminish the environmental risk of antibiotic resistance.

In vitro biofilm inhibition efficacy of Aerva lanata flower extract against Gram negative and Gram-positive biofilm forming bacteria and toxicity analysis using Artemia salina

A biofilm consists of Gram positive and Gram-negative bacteria enclosed in a matrix. Industrial biofouling is caused by biofilms, which can exhibit antimicrobial resistance during infections. Many biofilm studies find that nearly all biofilm communities consist of Gram positive and Gram-negative bacteria. It is therefore necessary to better understand the conserved themes in biofilm formation to develop therapeutics based on biofilm formation. Plant extracts can effectively combat pathogenic bacterial biofilms. This study evaluated the antibacterial and antibiofilm activity of Aerva lanata flower extract against Staphylococcus aureus and Pseudomonas aeruginosa. Methanol extract of dried A. lanata flower was tested against S. aureus and P. aeruginosa to determine the antibacterial activity (10, 25, 50, 75, 100 μg/mL) resulted in a maximum of 0.5-1 log reduction and 2 log reduction in comparison to the control or untreated bacterial cells respectively. A. lanata showed maximum biofilm inhibition up to 1.5-fold and 1-fold against P. aeruginosa and S. aureus. Light microscopic analysis of biofilm treated with A. lanata extract showed efficient distortion of the biofilm matrix. Further, the in vivo analysis of A. lanata in the Artemia salina brine shrimp model showed >50% survival and thus proving the efficacy of A. lanata extract in rescuing the brine shrimps against P. aeruginosa and S. aureus infection.

Evolving biofilm inhibition and eradication in clinical settings through plant-based antibiofilm agents

BACKGROUND

After almost 100 years since evidence of biofilm mode of growth and decades of intensive investigation about their formation, regulatory pathways and mechanisms of antimicrobial tolerance, nowadays there are still no therapeutic solutions to eradicate bacterial biofilms and their biomedical related issues.

PURPOSE

This review intends to provide a comprehensive summary of the recent and most relevant published studies on plant-based products, or their isolated compounds with antibiofilm activity mechanisms of action or identified molecular targets against bacterial biofilms. The objective is to offer a new perspective of most recent data for clinical researchers aiming to prevent or eliminate biofilm-associated infections caused by bacterial pathogens.

METHODS

The search was performed considering original research articles published on PubMed, Web of Science and Scopus from 2015 to April 2023, using keywords such as "antibiofilm", "antivirulence", "phytochemicals" and "plant extracts".

RESULTS

Over 180 articles were considered for this review with a focus on the priority human pathogens listed by World Health Organization, including Pseudomonas aeruginosa, Staphylococcus aureus, Klebsiella pneumoniae and Escherichia coli. Inhibition and detachment or dismantling of biofilms formed by these pathogens were found using plant-based extract/products or derivative compounds. Although combination of plant-based products and antibiotics were recorded and discussed, this topic is currently poorly explored and only for a reduced number of bacterial species.

CONCLUSIONS

This review clearly demonstrates that plant-based products or derivative compounds may be a promising therapeutic strategy to eliminate bacterial biofilms and their associated infections. After thoroughly reviewing the vast amount of research carried out over years, it was concluded that plant-based products are mostly able to prevent biofilm formation through inhibition of quorum sensing signals, but also to disrupt mature biofilms developed by multidrug resistant bacteria targeting the biofilm extracellular polymeric substance. Flavonoids and phenolic compounds seemed the most effective against bacterial biofilms.

Evaluation of the Antibacterial and Antibiofilm Effects of Ethyl Acetate Root Extracts from Vernonia adoensis (Asteraceae) against Pseudomonas aeruginosa

There is an increase in mortality and morbidity in the health facilities due to nosocomial infections caused by multidrug-resistant nosocomial bacteria; hence, there is a need for new antibacterial agents. Vernonia adoensis has been found to possess medicinal value. Plant phytochemicals may have antimicrobial activity against some resistant pathogens. The antibacterial efficacy of root extracts against Staphylococcus aureus and Pseudomonas aeruginosa was investigated using the microbroth dilution method. All extracts from the roots had an inhibitory effect on the growth of both bacteria, with the most susceptible being P. aeruginosa. The most potent extract was the ethyl acetate extract which caused a percentage inhibition of 86% against P. aeruginosa. The toxicity of the extract was determined on sheep erythrocytes, and its effect on membrane integrity was determined by quantifying the amount of protein and nucleic acid leakage from the bacteria. The lowest concentration of extract used, which was 100 µg/ml, did not cause haemolysis of the erythrocytes, while at 1 mg/ml of the extract, 21% haemolysis was observed. The ethyl acetate extract caused membrane impairment of P. aeruginosa, leading to protein leakage. The effect of the extract on the biofilms of P. aeruginosa was determined in 96-microwell plates using crystal violet. In the concentration range of 0-100 µg/ml, the extract inhibited the formation of biofilms and decreased the attachment efficiency. The phytochemical constituents of the extract were determined using gas chromatography-mass spectrometry. Results of analysis showed the presence of 3-methylene-15-methoxy pentadecanol, 2-acetyl-6-(t-butyl)-4-methylphenol, 2-(2,2,3,3-tetrafluoropropanoyl) cyclohexane-1,4-dione, E,E,Z-1,3,12-nonadecatriene-5,14-diol, and stigmasta-5,22-dien-3-ol. Fractionation and purification will elucidate the potential antimicrobial compounds which are present in the roots of V. adoensis.

Virulence factors and quorum sensing as targets of new therapeutic options by plant-derived compounds against bacterial infections caused by human and animal pathogens

The emergence of antibiotic-resistant bacteria and hospital-acquired bacterial infection has become rampant due to antibiotic overuse. Virulence factors are secondary to bacterial growth and are important in their pathogenesis, and therefore, new antimicrobial therapies to inhibit bacterial virulence factors are becoming important strategies against antibiotic resistance. Here, we focus on anti-virulence factors that act through anti-quorum sensing and the subsequent clearance of bacteria by antimicrobial compounds, especially active herbal extracts. These quorum sensing systems are based on toxins, biofilms, and efflux pumps, and bioactive compounds isolated from medicinal plants can treat bacterial virulence pathologies. Ideally, bacterial virulence factors are secondary growth factors of bacteria. Hence, inhibition of bacterial virulence factors could reduce bacterial pathogenesis. Furthermore, anti-virulence factors from herbal compounds can be developed as novel treatments for bacterial infection. Therefore, this narrative review aims to discuss bacterial virulence factors acting through quorum sensing systems that are preserved as targets for treating bacterial infection by plant-derived compounds.

Effects of metformin on Streptococcus suis LuxS/AI-2 quorum sensing system and biofilm formation

Streptococcus suis (S. suis) regulates biofilm formation through LuxS/AI-2 quorum sensing system, increasing drug resistance and exacerbating infection. The anti-hyperglycaemic agent metformin has anti-bacterial and anti-biofilm activities. This study aimed to investigate the anti-biofilm and anti-quorum sensing activity of metformin in S. suis. We first determined the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of metformin on S. suis. The results indicated that metformin showed no obvious inhibitory or bactericidal effect. Crystal violet staining showed that metformin significantly inhibited the formation of S. suis biofilm at sub-MIC concentration, which was also confirmed by scanning electron microscopy. Then, we quantified the AI-2 signal molecules in S. suis, and the results showed that metformin had a significant inhibitory effect on the production of AI-2 signal in S. suis. Inhibition of enzyme activity and molecular docking experiments showed that metformin has a significant binding activity to LuxS protein. In addition, qRT-PCR results showed that metformin significantly down-regulated the expression of AI-2 synthesis-related genes luxS and pfs, and adhesion-related genes luxS, pfs, gapdh, sly, fbps, and ef. Western blotting also showed that metformin significantly reduced the expression of LuxS protein. Our study suggests that metformin seems to be a suitable candidate for the inhibition of S. suis LuxS/AI-2 QS system and prevention of biofilm formation, which provided a new idea for the prevention and control of S. suis.

Effects of chlorogenic acid on antimicrobial, antivirulence, and anti-quorum sensing of carbapenem-resistant Klebsiella pneumoniae

The rise in infections caused by the hypervirulent carbapenem-resistant Klebsiella pneumoniae (hv-CRKP) is an emergent threat to public health. We assessed the effects of chlorogenic acid (CA), a natural phenolic compound, on antibacterial, antivirulence, and anti-quorum sensing (QS) of hv-CRKP. Five hv-CRKP were selected for antimicrobial susceptibility test and confirmed to carry virulence genes and carbapenem-resistant genes by polymerase chain reaction (PCR). Subsequently, a series of time-kill assay, determinations of protease activity and capsule content, biofilm-related experiment, scanning electron microscopy (SEM) and transmission electron microscope (TEM) observation, G. mellonella infection model, quantitative real-time PCR (qRT-PCR) of QS-related genes and biofilm formation genes, as well as AI-2 binding test were conduct to verify the effect of CA on hv-CRKP. Five CRKP strains showed varying degrees of resistance to antibacterial agents. All strains carried the bla _KPC-2 gene, primarily carrying rmpA2, iucA, and peg-344. CA showed no effect on CRKP growth at the 1/2 minimum inhibitory concentration (MIC), 1/4 MIC, and 1/8 MIC, CA could reduce the production of extracellular protease and capsular polysaccharides, and improve the survival rate of larvae in Galleria mellonella (G. mellonella) infection model. By means of crystal violet staining and scanning electron microscopy experiments, we observed that CA can inhibit the formation of CRKP biofilm. On the quantitative real-time PCR analysis, the expression of the luxS, mrkA and wbbm genes in most CRKP strains appeared downregulated because of the CA treatment. Besides, CA significantly inhibited the effect of AI-2 activity of BB170. Our study suggests that CA can be an effective antimicrobial, antivirulent compound that can target QS in hv-CRKP infections, thus providing a new therapeutic direction for treating bacterial infections.