Quorum Sensing - A Stratagem for Conquering Multi-Drug Resistant Pathogens

Antibacterial Ingredients and Modes of the Methanol-Phase Extract from the Fruit of Amomum villosum Lour

Epidemics of infectious diseases threaten human health and society stability. Pharmacophagous plants are rich in bioactive compounds that constitute a safe drug library for antimicrobial agents. In this study, we have deciphered for the first time antibacterial ingredients and modes of the methanol-phase extract (MPE) from the fruit of Amomum villosum Lour. The results have revealed that the antibacterial rate of the MPE was 63.64%, targeting 22 species of common pathogenic bacteria. The MPE was further purified by high performance liquid chromatography (Prep-HPLC), and three different constituents (Fractions 1-3) were obtained. Of these, the Fraction 2 treatment significantly increased the cell membrane fluidity and permeability, reduced the cell surface hydrophobicity, and damaged the integrity of the cell structure, leading to the leakage of cellular macromolecules of Gram-positive and Gram-negative pathogens (p < 0.05). Eighty-nine compounds in Fraction 2 were identified by ultra HPLC-mass spectrometry (UHPLC-MS) analysis, among which 4-hydroxyphenylacetylglutamic acid accounted for the highest 30.89%, followed by lubiprostone (11.86%), miltirone (10.68%), and oleic acid (10.58%). Comparative transcriptomics analysis revealed significantly altered metabolic pathways in the representative pathogens treated by Fraction 2 (p < 0.05), indicating multiple antibacterial modes. Overall, this study first demonstrates the antibacterial activity of the MPE from the fruit of A. villosum Lour., and should be useful for its application in the medicinal and food preservative industries against common pathogens.

Research Note: The effects of a Lactobacillus helveticus ATCC 15009-derived postbiotic mitigating Salmonella Gallinarum colonization in commercial layer chicks

This study aimed to assess the effects of a Lactobacillus helveticus ATCC 15009-derived postbiotic in mitigating experimental Salmonella Gallinarum infection. For this purpose, a sample of Lactobacillus sp. was inoculated in 2 different media, each containing different postbiotics (sensitized and nonsensitized). Both inocula had their antagonistic effect over S. Gallinarum tested through the spot-on-the-lawn method. It revealed that the sensitized postbiotic had a higher action potential over Lactobacillus sp. than the nonsensitized one (P < 0.05). Then, 48 day of hatch chicks were divided into 4 groups: A = Lactobacillus sp. (109 CFU/mL) inoculum on the 18th day; B = Lactobacillus sp. (109 CFU/mL) inoculum on the 18th day and postbiotic inoculum on the 19th day; C = postbiotic inoculum on the 19th day; and D = sterile saline inoculum on 18th and 19th days. On the 21st day, all chicks were infected with S. Gallinarum (109 CFU/mL). On the 23rd day, the animals were euthanized by cervical dislocation, and the ceca and liver were aseptically removed. Bacterial count of S. Gallinarum with serial decimal dilution was performed with these organs. It revealed that the prophylactic treatment with the postbiotic that modulates the intestinal microbiota was as efficient as the probiotic administration in reducing S. Gallinarum in the cecum and liver of chicks (P < 0.05). These data point to a new range of alternatives for preventing S. Gallinarum, which might help the poultry industry produce safer food for human consumption.

Co-regulation of biofilm formation and antimicrobial resistance in Acinetobacter baumannii: from mechanisms to therapeutic strategies

In recent years, multidrug-resistant Acinetobacter baumannii has emerged globally as a major threat to the healthcare system. It is now listed by the World Health Organization as a priority one for the need of new therapeutic agents. A. baumannii has the capacity to develop robust biofilms on biotic and abiotic surfaces. Biofilm development allows these bacteria to resist various environmental stressors, including antibiotics and lack of nutrients or water, which in turn allows the persistence of A. baumannii in the hospital environment and further outbreaks. Investigation into therapeutic alternatives that will act on both biofilm formation and antimicrobial resistance (AMR) is sorely needed. The aim of the present review is to critically discuss the various mechanisms by which AMR and biofilm formation may be co-regulated in A. baumannii in an attempt to shed light on paths towards novel therapeutic opportunities. After discussing the clinical importance of A. baumannii, this critical review highlights biofilm-formation genes that may be associated with the co-regulation of AMR. Particularly worthy of consideration are genes regulating the quorum sensing system AbaI/AbaR, AbOmpA (OmpA protein), Bap (biofilm-associated protein), the two-component regulatory system BfmRS, the PER-1 β-lactamase, EpsA, and PTK. Finally, this review discusses ongoing experimental therapeutic strategies to fight A. baumannii infections, namely vaccine development, quorum sensing interference, nanoparticles, metal ions, natural products, antimicrobial peptides, and phage therapy. A better understanding of the mechanisms that co-regulate biofilm formation and AMR will help identify new therapeutic targets, as combined approaches may confer synergistic benefits for effective and safer treatments.

Exploring calcium channel blocker as a candidate drug for Pseudomonas aeruginosa through network pharmacology and experimental validation

Calcium channel blocker (CCB) is known to possess antibacterial effects. We aimed to apply network pharmacology (docking and protein-protein interaction [PPI] analyses) to predict the potential targets and mechanisms of CCB against Pseudomonas aeruginosa (PA) as well as to verify the effect of these drugs. The chemical structures of three CCBs were obtained through the Drug Bank platform. The potential channel proteins, efflux pump proteins and ion channel proteins of CCB against bacteria were derived from the literature. These proteins were collected through the PDB and Uniprot platform. The binding mode of the docking complexes was simulated by the CB-Dock platform and Discovery Studio 2019 Client software. The PPI network was constructed by the String platform and Cytoscape 3.8.2 platform. GO was explained by the PANTHER platform. The pathway diagram was drawn with the Pathway Builder Tool 2.0 software. The inhibitory effect of CCB on PA was verified through antibacterial experiments. Finally, 76 proteins were obtained: the iron channel protein of PA demonstrated a good docking relationship with all three CCBs, and the optimum binding energy was approximately -9.0 kcal/mol. GO analysis (biological process [BP], cellular component [CC], and molecular function [MF]) of protein genes showed a good docking relationship (optimum binding energy <-8.0 kcal/mol). The MF annotation results indicated that the target of CCB may be present on the PA membrane protein. The ion channel protein PPI enrichment p-value was 6.65e-08, and PfeA showed the strongest correlation. The experimental results suggested that CCB could inhibit the growth of PA. CCB might be an effective and interesting antimicrobial treatment strategy as CCB can potentially inhibit the growth of PA.

Employing of Curcumin-Silver Nanoparticle-Incorporated Sodium Alginate-Co-Acacia Gum Film Hydrogels for Wound Dressing

Skin wound healing is time-consuming and frequently accompanied by bacterial infections and the development of scars. The rise of antibiotic-resistant bacterial strains has sparked a growing interest in naturally occurring bioactive substances, like curcumin, that possess wound-healing capabilities. Silver is a natural antimicrobial agent, and finds extensive use in specialized wound dressings. Silver nanoparticles (AgNPs) were synthesized using an eco-friendly approach, employing curcumin. The prepared nanoparticles have been characterized using TEM, DLS, and zeta potential. The prepared AgNPs were loaded on sodium alginate-co-gum arabic hydrogel. Two hydrogel samples (with and without AgNPs) have been applied for wound healing. The developed silver nanoparticles that were created exhibited effective action against both types of bacteria, namely Gram-negative and Gram-positive. Alg-co-AG-AgNPs demonstrated faster wound healing rates compared to using the control hydrogel sample. The novel dressings of curcumin-silver nanoparticle-incorporated sodium alginate-co-gum arabic hydrogels (Alg-co-AG-AgNPs) exhibited exceptional biocompatibility and have the potential to serve as a wound dressing that possesses antibacterial properties and reduces scarring.

Modulation of Pseudomonas aeruginosa quorum sensing by ajoene through direct competition with small RNAs for binding at the proximal site of Hfq - a structure-based perspective

Bacteria can communicate to each other via quorum sensing, a cell density-dependent gene regulation system that stimulates the expression of virulence factors in the neighboring cells. Although the interaction of the natural product ajoene with the Hfq protein has been associated with the disruption of the quorum sensing system in Pseudomonas aeruginosa, there is no information concerning the corresponding ligand-target interaction process. Herein we observed a strong correlation (p < 0.00001) between the estimated affinities for the binding of 23 ajoene analogues at the proximal site of the Hfq protein of P. aeruginosa and their corresponding IC₅₀ values, which reflect the reduction in the transcription of a virulence factor after quorum sensing inhibition. In this concern, our analyses reinforces previous propositions suggesting that ajoene could target the Hfq protein and affects its interaction with RNAs. Based on docking simulations, we tried to elucidate the binding mode of ajoene into the proximal Hfq site and the also to established the minimum set of groups that would be necessary for a good interaction at this site, which includes a single hydrogen bond acceptor feature surrounded by groups that interact via π-sulfur (i.e., disulfide sulfurs) and/or π-alkyl/π-π stacking interactions (e.g., vinyl or small aryl/heteroaryl/heterocyclic groups). Because of the widespread role of Hfq as a matchmaker between messenger and small regulatory RNAs in Gram-negatives, we believe the discussion here provided for P. aeruginosa could be extrapolated for Gram-negatives in general, while the interaction of ajoene over the Hfq protein of Gram-positives would still remain more controversial.

Transcriptome Analysis revealed the Synergism of Novel Rhodethrin inhibition on Biofilm architecture, Antibiotic Resistance and Quorum sensing inEnterococcus faecalis

Enterococcus sp. emerged as an opportunistic nosocomial pathogen with the highest antibiotic resistance and mortality rate. Biofilm is problematic primarily since it is regulated by the global bacterial cell to cell communication mediated by the quorum sensing system. sing system. Thus, potential natural antagonists in a novel drug formulation against biofilm-forming Enterococcus faecalis is critical. We used RNA-Seq to evaluate the effects of the novel molecule rhodethrin with chloramphenicol induced on Enterococcus faecalis and DEGs were identified. In transcriptome sequence analysis, a total of 448 with control Vs rhodethrin, 1591 were in control Vs chloramphenicol, 379 genes were DEGs from control Vs synergies, in rhodethrin with chloramphenicol, 379 genes were differentially expressed, whereas 264 genes were significantly downregulated, indicating that 69.69% ofE. faecaliswas altered. The transcriptional sequence data further expression analysis qRT-PCR, and the results shed that the expression profiles of five significant biofilm formation responsible genes such as, Ace, AtpB, lepA, bopD, and typA, 3 genes involved in quorum sensing are sylA, fsrC and camE, and 4 genes involved in resistance were among including liaX, typA, EfrA, and lepA, were significantly suppressed expressions of the biofilm, quorum sensing, and resistance that are supported by transcriptome analysis.

Recent Approaches for Downplaying Antibiotic Resistance: Molecular Mechanisms

Antimicrobial resistance (AMR) is a ubiquitous public health menace. AMR emergence causes complications in treating infections contributing to an upsurge in the mortality rate. The epidemic of AMR in sync with a high utilization rate of antimicrobial drugs signifies an alarming situation for the fleet recovery of both animals and humans. The emergence of resistant species calls for new treatments and therapeutics. Current records propose that health drug dependency, veterinary medicine, agricultural application, and vaccination reluctance are the primary etymology of AMR gene emergence and spread. Recently, several encouraging avenues have been presented to contest resistance, such as antivirulent therapy, passive immunization, antimicrobial peptides, vaccines, phage therapy, and botanical and liposomal nanoparticles. Most of these therapies are used as cutting-edge methodologies to downplay antibacterial drugs to subdue the resistance pressure, which is a featured motive of discussion in this review article. AMR can fade away through the potential use of current cutting-edge therapeutics, advancement in antimicrobial susceptibility testing, new diagnostic testing, prompt clinical response, and probing of new pharmacodynamic properties of antimicrobials. It also needs to promote future research on contemporary methods to maintain host homeostasis after infections caused by AMR. Referable to the microbial ability to break resistance, there is a great ultimatum for using not only appropriate and advanced antimicrobial drugs but also other neoteric diverse cutting-edge therapeutics.

Bringing Antimicrobial Strategies to a New Level: The Quorum Sensing System as a Target to Control Streptococcus suis

Streptococcus suis (S. suis) is an important zoonotic pathogen. It mainly uses quorum sensing (QS) to adapt to complex and changeable environments. QS is a universal cell-to-cell communication system that has been widely studied for its physiological functions, including the regulation of bacterial adhesion, virulence, and biofilm formation. Quorum sensing inhibitors (QSIs) are highly effective at interfering with the QS system and bacteria have trouble developing resistance to them. We review the current research status of the S. suis LuxS/AI-2 QS system and QSIs. Studies showed that by inhibiting the formation of AI-2, targeting the LuxS protein, inhibiting the expression of luxs gene can control the LuxS/AI-2 QS system of S. suis. Other potential QSIs targets are summarized, which may be preventing and treating S. suis infections, including AI-2 production, transmission, LuxS protein, blockage of AI-2 binding to receptors, AI-2-mediated QS. Since antibiotics are becoming increasingly ineffective due to the emergence of resistant bacteria, including S. suis, it is thus critical to find new antibacterial drugs with different mechanisms of action. QSIs provide hope for the development of such drugs.

Multidrug-Resistant Biofilms (MDR): Main Mechanisms of Tolerance and Resistance in the Food Supply Chain

Biofilms are mono- or multispecies microbial communities enclosed in an extracellular matrix (EPS). They have high potential for dissemination and are difficult to remove. In addition, biofilms formed by multidrug-resistant strains (MDRs) are even more aggravated if we consider antimicrobial resistance (AMR) as an important public health issue. Quorum sensing (QS) and horizontal gene transfer (HGT) are mechanisms that significantly contribute to the recalcitrance (resistance and tolerance) of biofilms, making them more robust and resistant to conventional sanitation methods. These mechanisms coordinate different strategies involved in AMR, such as activation of a quiescent state of the cells, moderate increase in the expression of the efflux pump, decrease in the membrane potential, antimicrobial inactivation, and modification of the antimicrobial target and the architecture of the EPS matrix itself. There are few studies investigating the impact of the use of inhibitors on the mechanisms of recalcitrance and its impact on the microbiome. Therefore, more studies to elucidate the effect and applications of these methods in the food production chain and the possible combination with antimicrobials to establish new strategies to control MDR biofilms are needed.

Targeting the Holy Triangle of Quorum Sensing, Biofilm Formation, and Antibiotic Resistance in Pathogenic Bacteria

Chronic and recurrent bacterial infections are frequently associated with the formation of biofilms on biotic or abiotic materials that are composed of mono- or multi-species cultures of bacteria/fungi embedded in an extracellular matrix produced by the microorganisms. Biofilm formation is, among others, regulated by quorum sensing (QS) which is an interbacterial communication system usually composed of two-component systems (TCSs) of secreted autoinducer compounds that activate signal transduction pathways through interaction with their respective receptors. Embedded in the biofilms, the bacteria are protected from environmental stress stimuli, and they often show reduced responses to antibiotics, making it difficult to eradicate the bacterial infection. Besides reduced penetration of antibiotics through the intricate structure of the biofilms, the sessile biofilm-embedded bacteria show reduced metabolic activity making them intrinsically less sensitive to antibiotics. Moreover, they frequently express elevated levels of efflux pumps that extrude antibiotics, thereby reducing their intracellular levels. Some efflux pumps are involved in the secretion of QS compounds and biofilm-related materials, besides being important for removing toxic substances from the bacteria. Some efflux pump inhibitors (EPIs) have been shown to both prevent biofilm formation and sensitize the bacteria to antibiotics, suggesting a relationship between these processes. Additionally, QS inhibitors or quenchers may affect antibiotic susceptibility. Thus, targeting elements that regulate QS and biofilm formation might be a promising approach to combat antibiotic-resistant biofilm-related bacterial infections.

Nanoarchitectonics of Electrically Activable Phosphonium Self-Assembled Monolayers to Efficiently Kill and Tackle Bacterial Infections on Demand

Prosthetic implants are widely used in dentistry and orthopedics and, as a result, infections can occur which cause their removal. Therefore, it is essential to propose methods of eradicating the bacteria that remain on the prosthesis during treatment. For this purpose, it is necessary to develop surfaces whose antibacterial activity can be controlled. Herein, we designed innovative and smart phosphonium self-assembled monolayer (SAM) interfaces that can be electrically activated on demand for controlling bacterial contaminations on solid surfaces. Upon electroactivation with a low potential (0.2 V for 60 min., conditions determined through a DOE), a successful stamping out of Gram-positive and Gram-negative bacterial strains was obtained with SAM-modified titanium surfaces, effectively killing 95% of Staphylococcus aureus and 90% Klebsiellapneumoniae. More importantly, no toxicity towards eukaryotic cells was observed which further enhances the biocompatible character of these novel surfaces for further implementation.

Effects of wound dressing based on the combination of silver@curcumin nanoparticles and electrospun chitosan nanofibers on wound healing

Healing of various skin wounds is a lengthy process and often combined with bacterial infection and scar formation. Biomimetic electrospun nanofibrous wound dressing loaded with materials that possess properties of dual antibacterial and tissue repair would be developed to address this problem. In this study, a composite chitosan electrospun nanofibrous material containing Cur@β-CD/AgNPs nanoparticles composed of silver and curcumin possessed synergic effects on antibacterial activity and wound healing. The developed functionalized silver nanoparticles showed effective activity against both Gram-negative and Gram-positive bacteria. In vivo, Cur@β-CD/AgNPs chitosan dressing displayed enhanced wound closure rates compared to commercial AquacelAg. Moreover, Cur@β-CD/AgNPs chitosan dressing contributed to the most uniform collagen distribution by Masson’s trichrome staining. In brief, Cur@β-CD/AgNPs chitosan nanofibers work as a potential wound dressing with antibacterial and antiscarring properties.

Development and Research Progress of Anti-Drug Resistant Bacteria Drugs

Bacterial resistance has become increasingly serious because of the widespread use and abuse of antibiotics. In particular, the emergence of multidrug-resistant bacteria has posed a serious threat to human public health and attracted the attention of the World Health Organization (WHO) and the governments of various countries. Therefore, the establishment of measures against bacterial resistance and the discovery of new antibacterial drugs are increasingly urgent to better contain the emergence of bacterial resistance and provide a reference for the development of new antibacterial drugs. In this review, we discuss some antibiotic drugs that have been approved for clinical use and a partial summary of the meaningful research results of anti-drug resistant bacterial drugs in different fields, including the antibiotic drugs approved by the FDA from 2015 to 2020, the potential drugs against drug-resistant bacteria, the new molecules synthesized by chemical modification, combination therapy, drug repurposing, immunotherapy and other therapies.