Proteomic analysis reveals modulation of iron homeostasis and oxidative stress response in Pseudomonas aeruginosa PAO1 by curcumin inhibiting quorum sensing regulated virulence factors and biofilm production

Critical review on plant-derived quorum sensing signaling inhibitors in pseudomonas aeruginosa

Pseudomonas aeruginosa, a biofilm-forming organism with complex quorum mechanisms (Las, Rhl, PQS, and IQS), poses an imminent danger to the healthcare sector and renders current treatment options for chemotherapy ineffectual. The pathogen's diverse pathogenicity, antibiotic resistance, and biofilms make it difficult to eradicate it effectively. Quorum sensing, a complex system reliant on cell density, controls P. aeruginosa's pathogenesis. Quorum-sensing genes are key components of P. aeruginosa's pathogenic arsenal, and their expression determines how severe the spread of infection becomes. Over the past ten years, there has been a noticeable increase in the quest for and development of new antimicrobial medications. Quorum sensing may be an effective treatment for infections triggered by bacteria. Introducing quorum-sensing inhibitors as an anti-virulent strategy might be an intriguing therapeutic method that can be effectively employed along with current medications. Amongst the several speculated processes, a unique anti-virulence strategy using anti-quorum sensing and antibiofilm medications for targeting pseudomonal infestations seems to be at the forefront. Due to their noteworthy quorum quenching capabilities, biologically active phytochemicals have become more well-known in the realm of science in this context. Recent research showed how different phytochemical quorum quenching actions affect P. aeruginosa's QS-dependent pathogenicity. This review focuses on the most current data supporting the implementation of plant bio-actives to treat P.aeruginosa-associated diseases, as well as the benefits and future recommendationsof employing them in anti-virulence therapies as a supplementary drug development approach towards conventional antibiotic approaches.

Metal Nanoparticle-Based Biosensors for the Early Diagnosis of Infectious Diseases Caused by ESKAPE Pathogens in the Fight against the Antimicrobial-Resistance Crisis

The species included in the ESKAPE group (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and the genus Enterobacter) have a high capacity to develop antimicrobial resistance (AMR), a health problem that is already among the leading causes of death and could kill 10 million people a year by 2050. The generation of new potentially therapeutic molecules has been insufficient to combat the AMR "crisis", and the World Health Organization (WHO) has stated that it will seek to promote the development of rapid diagnostic strategies. The physicochemical properties of metallic nanoparticles (MNPs) have made it possible to design biosensors capable of identifying low concentrations of ESKAPE bacteria in the short term; other systems identify antimicrobial susceptibility, and some have been designed with dual activity in situ (bacterial detection and antimicrobial activity), which suggests that, in the near future, multifunctional biosensors could exist based on MNPs capable of quickly identifying bacterial pathogens in clinical niches might become commercially available. This review focuses on the use of MNP-based systems for the rapid and accurate identification of clinically important bacterial pathogens, exhibiting the necessity for exhaustive research to achieve these objectives. This review focuses on the use of metal nanoparticle-based systems for the rapid and accurate identification of clinically important bacterial pathogens.

Bibliometric analysis and visualization of quorum sensing research over the last two decade

Background

Quorum sensing (QS) research stands as a pivotal and multifaceted domain within microbiology, holding profound implications across various scientific disciplines. This bibliometric analysis seeks to offer an extensive overview of QS research, covering the period from 2004 to 2023. It aims to elucidate the hotspots, trends, and the evolving dynamics within this research domain.

Methods

We conducted an exhaustive review of the literature, employing meticulous data curation from the Science Citation Index Extension (SCI-E) within the Web of Science (WOS) database. Subsequently, our survey delves into evolving publication trends, the constellation of influential authors and institutions, key journals shaping the discourse, global collaborative networks, and thematic hotspots that define the QS research field.

Results

The findings demonstrate a consistent and growing interest in QS research throughout the years, encompassing a substantial dataset of 4,849 analyzed articles. Journals such as Frontiers in Microbiology have emerged as significant contributor to the QS literature, highlighting the increasing recognition of QS's importance across various research fields. Influential research in the realm of QS often centers on microbial communication, biofilm formation, and the development of QS inhibitors. Notably, leading countries engaged in QS research include the United States, China, and India. Moreover, the analysis identifies research focal points spanning diverse domains, including pharmacological properties, genetics and metabolic pathways, as well as physiological and signal transduction mechanisms, reaffirming the multidisciplinary character of QS research.

Conclusion

This bibliometric exploration provides a panoramic overview of the current state of QS research. The data portrays a consistent trend of expansion and advancement within this domain, signaling numerous prospects for forthcoming research and development. Scholars and stakeholders engaged in the QS field can harness these findings to navigate the evolving terrain with precision and speed, thereby enhancing our comprehension and utilization of QS in various scientific and clinical domains.

Inhibitory effect of natural compounds on quorum sensing system in Pseudomonas aeruginosa: a helpful promise for managing biofilm community

Pseudomonas aeruginosa biofilm is a community of bacteria that adhere to live or non-living surfaces and are encapsulated by an extracellular polymeric substance. Unlike individual planktonic cells, biofilms possess a notable inherent resistance to sanitizers and antibiotics. Overcoming this resistance is a substantial barrier in the medical and food industries. Hence, while antibiotics are ineffective in eradicating P. aeruginosa biofilm, scientists have explored alternate strategies, including the utilization of natural compounds as a novel treatment option. To this end, curcumin, carvacrol, thymol, eugenol, cinnamaldehyde, coumarin, catechin, terpinene-4-ol, linalool, pinene, linoleic acid, saponin, and geraniol are the major natural compounds extensively utilized for the management of the P. aeruginosa biofilm community. Noteworthy, the exact interaction of natural compounds and the biofilm of this bacterium is not elucidated yet; however, the interference with the quorum sensing system and the inhibition of autoinducer production in P. aeruginosa are the main possible mechanisms. Noteworthy, the use of different drug platforms can overcome some drawbacks of natural compounds, such as insolubility in water, limited oral bioavailability, fast metabolism, and degradation. Additionally, drug platforms can deliver different antibiofilm agents simultaneously, which enhances the antibiofilm potential of natural compounds. This article explores many facets of utilizing natural compounds to inhibit and eradicate P. aeruginosa biofilms. It also examines the techniques and protocols employed to enhance the effectiveness of these compounds.

Quenching and quorum sensing in bacterial bio-films

Quorum sensing (QS) is the ability of bacteria to monitor their population density and adjust gene expression accordingly. QS-regulated processes include host-microbe interactions, horizontal gene transfer, and multicellular behaviours (such as the growth and development of biofilm). The creation, transfer, and perception of bacterial chemicals known as autoinducers or QS signals are necessary for QS signalling (e.g. N-acylhomoserine lactones). Quorum quenching (QQ), another name for the disruption of QS signalling, comprises a wide range of events and mechanisms that are described and analysed in this study. In order to better comprehend the targets of the QQ phenomena that organisms have naturally developed and are currently being actively researched from practical perspectives, we first surveyed the diversity of QS-signals and QS-associated responses. Next, the mechanisms, molecular players, and targets related to QS interference are discussed, with a focus on natural QQ enzymes and compounds that function as QS inhibitors. To illustrate the processes and biological functions of QS inhibition in microbe-microbe and host-microbe interactions, a few QQ paradigms are described in detail. Finally, certain QQ techniques are offered as potential instruments in a variety of industries, including agriculture, medical, aquaculture, crop production, and anti-biofouling areas.

Pyrogallol impairs staphylococcal biofilm formation via induction of bacterial oxidative stress

AIMS

To examine the effect of the phenolic compound pyrogallol on staphylococcal biofilm formation.

METHODS AND RESULTS

In crystal violet biofilm assays, pyrogallol-reduced biofilm formation in Staphylococcus epidermidis ATCC 35984, Staph. epidermidis NRRL-B41021, Staphylococcus aureus USA300, and Staph. aureus Newman, without significantly impairing bacterial viability. Pyrogallol-mediated impairment of biofilm formation was likely due to induction of bacterial oxidative stress, as its effect was greater in catalase-deficient versus WT Staph. aureus, and biofilm production was rescued by exogenous catalase. The effect of pyrogallol on staphylococcal biofilm formation mirrored that of the known oxidant hydrogen peroxide, which also reduced biofilm formation in a dose-dependent manner.

CONCLUSIONS

Pyrogallol reduces biofilm formation in S. aureus and Staph. epidermidis in a mechanism involving induction of bacterial oxidative stress.

Two novel phages PSPa and APPa inhibit planktonic, sessile and persister populations of Pseudomonas aeruginosa, and mitigate its virulence in Zebrafish model

The present study explores the avenue of phage therapy as an alternative antimicrobial therapeutic approach to counter multidrug-resistant (MDR) Pseudomonas aeruginosa infection. Our study investigated two novel virulent phages PSPa and APPa, specific to P. aeruginosa, in which in vitro evaluations were carried out to assess the therapeutic potential of phages. Both the identified phages exhibited host specificity by showing antagonistic activity of about 96.43% (27/28) and 92.85% (26/28) towards the 28 MDR clinical isolates of P. aeruginosa. The PSPa phage was found to have linear dsDNA with a sequence length of 66,368 bp and 92 ORFs, of which 32 were encoded for known functions of the phage life cycle and the remaining 60 were hypothetical functions. The APPa phage was found to have linear dsDNA with 59,591 bp of genome length and 79 ORFs, of which 15 were found to have known phage functions and the remaining 64 were found to be hypothetical proteins. Notably, the genome of both the phages lacks genes coding for tRNA, rRNA, and tmRNA. The phylogenetic analysis revealed that PSPa and APPa share > 95% sequence similarity with previously sequenced Pseudomonas viruses of their respective families. Further, the in vivo efficacy evaluation using the zebrafish model revealed that the treatment with PSPa and APPa has remarkably improved the survival rate of bacterial-infected zebrafish, reinforcing the anti-infective potential of the isolated phages PSPa and APPa against P. aeruginosa infection.

Quorum sensing interference by phenolic compounds - A matter of bacterial misunderstanding

Over the past decade, numerous publications have emerged in the literature focusing on the inhibition of quorum sensing (QS) by plant extracts and phenolic compounds. However, there is still a scarcity of studies that delve into the specific mechanisms by which these compounds inhibit QS. Thus, our question is whether phenolic compounds can inhibit QS in a specific or indirect manner and to elucidate the underlying mechanisms involved. This study is focused on the most studied QS system, namely, autoinducer type 1 (AI-1), represented by N-acyl-homoserine lactone (AHL) signals and the AHL-mediated QS responses. Here, we analyzed the recent literature in order to understand how phenolic compounds act at the cellular level, at sub-inhibitory concentrations, and evaluated by which QS inhibition mechanisms they may act. The biotechnological application of QS inhibitors holds promising prospects for the pharmaceutical and food industries, serving as adjunct therapies and in the prevention of biofilms on various surfaces.

Multimodal silver-chitosan-acylase nanoparticles inhibit bacterial growth and biofilm formation by Gram-negative Pseudomonas aeruginosa bacterium

Pseudomonas aeruginosa bacteria originate severe infections in hospitalized patients and those with chronic debilitating diseases leading to increased morbidity and mortality, longer hospitalization and huge financial burden to the healthcare system. The clinical relevance of P. aeruginosa infections is increased by the capability of this bacterium to grow in biofilms and develop multidrug resistant mechanisms that preclude conventional antibiotic treatments. Herein, we engineered novel multimodal nanocomposites that integrate in the same entity antimicrobial silver nanoparticles (NPs), the intrinsically antimicrobial, but biocompatible biopolymer chitosan, and the anti-infective quorum quenching enzyme acylase I. Acylase present in the NPs specifically degraded the signal molecules governing bacterial cell-to-cell communication and inhibited by ∼ 55 % P. aeruginosa biofilm formation, while the silver/chitosan template altered the integrity of bacterial membrane, leading to complete eradication of planktonic bacteria. The innovative combination of multiple bacteria targeting modalities resulted in 100-fold synergistic enhancement of the antimicrobial efficacy of the nanocomposite at lower and non-hazardous towards human skin cells concentrations, compared to the silver/chitosan NPs alone.

Curcumin and 10-undecenoic acid as natural quorum sensing inhibitors of LuxS/AI-2 of Bacillus subtilis and LasI/LasR of Pseudomonas aeruginosa

The quorum sensing (QS) system is related to cell-to-cell communication as a function of population density, which regulates several physiological functions including biofilm formation and virulence gene expression. QS inhibitors have emerged as a promising strategy to tackle virulence and biofilm development. Among a wide variety of phytochemicals, many of them have been described as QS inhibitors. Driven by their promising clues, this study aimed to identify active phytochemicals against LuxS/autoinducer-2 (AI-2) (as the universal QS system) from Bacillus subtilis and LasI/LasR (as a specific QS system) of Pseudomonas aeruginosa, through in silico analysis followed by in vitro validation. The optimized virtual screening protocols were applied to screen a phytochemical database containing 3479 drug-like compounds. The most promising phytochemicals were curcumin, pioglitazone hydrochloride, and 10-undecenoic acid. In vitro analysis corroborated the QS inhibitory activity of curcumin and 10-undecenoic acid, however, pioglitazone hydrochloride showed no relevant effect. Inhibitory effects on LuxS/AI-2 QS system triggered reduction of 33-77% by curcumin (at 1.25-5 µg/mL) and 36-64% by 10-undecenoic acid (at 12.5-50 µg/mL). Inhibition of LasI/LasR QS system was 21% by curcumin (at 200 µg/mL) and 10-54% by 10-undecenoic acid (at 15.625-250 µg/mL). In conclusion, in silico analysis allowed the identification of curcumin and, for the first time, 10-undecenoic acid (showing low cost, high availability, and low toxicity) as alternatives to counteract bacterial pathogenicity and virulence, avoiding the imposition of selective pressure usually related to classic industrial disinfection and antibiotics therapy.

Correlation between Perturbation of Redox Homeostasis and Antibiofilm Capacity of Phytochemicals at Non-Lethal Concentrations

Biofilms are the multicellular lifestyle of microorganisms and are present on potentially every type of biotic or abiotic surface. Detrimental biofilms are generally targeted with antimicrobial compounds. Phytochemicals at sub-lethal concentrations seem to be an exciting alternative strategy to control biofilms, as they are less likely to impose selective pressure leading to resistance. This overview gathers the literature on individual phytocompounds rather than on extracts of which the use is difficult to reproduce. To the best of our knowledge, this is the first review to target only individual phytochemicals below inhibitory concentrations against biofilm formation. We explored whether there is an overall mechanism that can explain the effects of individual phytochemicals at sub-lethal concentrations. Interestingly, in all experiments reported here in which oxidative stress was investigated, a modest increase in intracellular reactive oxygen species was reported in treated cells compared to untreated specimens. At sub-lethal concentrations, polyphenolic substances likely act as pro-oxidants by disturbing the healthy redox cycle and causing an accumulation of reactive oxygen species.

Antibacterial activity of curcumin and its essential nanoformulations against some clinically important bacterial pathogens: A comprehensive review

Multidrug-resistant bacterial infections can kill 700,000 individuals globally each year and is considered among the top 10 global health threats faced by humanity as the arsenal of antibiotics is becoming dry and alternate antibacterial molecule is in demand. Nanoparticles of curcumin exhibit appreciable broad-spectrum antibacterial activity using unique and novel mechanisms and thus the process deserves to be reviewed and further researched to clearly understand the mechanisms. Based on the antibiotic resistance, infection, and virulence potential, a list of clinically important bacteria was prepared after extensive literature survey and all recent reports on the antibacterial activity of curcumin and its nanoformulations as well as their mechanism of antibacterial action have been reviewed. Curcumin, nanocurcumin, and its nanocomposites with improved aqueous solubility and bioavailability are very potential, reliable, safe, and sustainable antibacterial molecule against clinically important bacterial species that uses multitarget mechanism such as inactivation of antioxidant enzyme, reactive oxygen species-mediated cellular damage, and inhibition of acyl-homoserine-lactone synthase necessary for quorum sensing and biofilm formation, thereby bypassing the mechanisms of bacterial antibiotic resistance. Nanoformulations of curcumin can thus be considered as a potential and sustainable antibacterial drug candidate to address the issue of antibiotic resistance.

Proteomic profiling spotlights the molecular targets and the impact of the natural antivirulent umbelliferone on stress response, virulence factors, and the quorum sensing network of Pseudomonas aeruginosa

Pseudomonas aeruginosa easily adapts to newer environments and acquires several genome flexibilities to overcome the effect of antibiotics during therapeutics, especially in cystic fibrosis patients. During adaptation to the host system, the bacteria employ various tactics including virulence factor production and biofilm formation to escape from the host immune system and resist antibiotics. Hence, identifying alternative strategies to combat recalcitrant pathogens is imperative for the successful elimination of drug-resistant microbes. In this context, this study portrays the anti-virulence efficacy of umbelliferone (UMB) against P. aeruginosa. UMB (7-hydroxy coumarin) is pervasively found among the plant family of Umbelliferae and Asteraceae. The UMB impeded biofilm formation in the P. aeruginosa reference strain and clinical isolates on polystyrene and glass surfaces at the concentration of 125 µg/ml. Global proteomic analysis of UMB-treated cells revealed the downregulation of major virulence-associated proteins such as RhlR, LasA, AlgL, FliD, Tpx, HtpG, KatA, FusA1, Tsf, PhzM, PhzB2, CarB, DctP, MtnA, and MscL. A functional interaction study, gene ontology, and KEGG pathway analysis revealed that UMB could modulate the global regulators, enzymes, co-factors, and transcription factors related to quorum sensing (QS), stress tolerance, siderophore production, motility, and microcolony formation. In vitro biochemical assays further affirmed the anti-virulence efficacy of UMB by reducing pyocyanin, protease, elastase, and catalase production in various strains of P. aeruginosa. Besides the antibiofilm activity, UMB-treated cells exhibited enhanced antibiotic susceptibility to various antibiotics including amikacin, kanamycin, tobramycin, ciprofloxacin, and cefotaxime. Furthermore, in vitro cytotoxicity analysis revealed the biocompatibility of UMB, and the IC₅₀ value was determined to be 249.85 µg/ml on the HepG2 cell line. Altogether, the study substantiates the anti-virulence efficacy of UMB against P. aeruginosa, and the proteomic analysis reveals the differential expression of the regulators related to QS, stress response, and motility factors.

Two strategies of stubborn biofouling strains surviving from NaClO membrane cleaning: EPS shielding and/or quorum sensing

The declined performance of repeated chemically-enhanced-backwashing (CEB) seriously hampered the sustainable operation of membrane bioreactor (MBR) in long-term, and could be partially attributed to the strengthened anti-cleaning properties of residual stubborn microbes. Although plenty of research has been done towards either the model strains or the whole post-CEB microbial community, little was known about the resisting behavior of practical stubborn strains when confronting oxidative stresses induced by NaClO. Hence, this study isolated 21 strains from samples in a large-scale MBR plant with routine CEB treatment. To unravel how they survive and affect membrane fouling, their anti-oxidation ability, fouling potential and quorum sensing (QS) effect before and after NaClO stimuli were evaluated. The composition and molecular weight distribution of extracellular polymeric substance (EPS) were also investigated to understand their roles during the anti-CEB process. It was found that typical stubborn strains tended to secrete more EPS as protective shields, where polysaccharides (especially the ones >1 kDa) made major contribution. However, sometimes EPS could not well resist the stimuli, with consequent low survival rate and high intracellular ROS level. Under such circumstances, stubborn strains would rather choose to be sensitive with surged QS level and quick population regrowth to maintain vitality under the oxidative stresses. Both strategies aggravated biofouling and eventually enhanced the anti-cleaning properties of biofilm.

Rapid-killing efficacy substantiates the antiseptic property of the synergistic combination of carvacrol and nerol against nosocomial pathogens

Globally, new classes of synthetic and natural antibiotics and antivirulents have continuously been validated for their potential broad-spectrum antagonistic activity with the aim of identifying an effective active molecule to prevent the spread of infectious agents in both food industry and medical field. In view of this, present study is aimed at evaluating the rapid killing efficacy of bioactive molecules Carvacrol (C) and Nerol (N) through British Standard European Norm 1276: phase2/step1 (EN1276) protocol. Active molecules C and N showed broad-spectrum antimicrobial activity against the test strains Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Enterococcus hirae at concentration range of 78.125, 625, 156.25 and 312.5 μg/mL, respectively, for C, and 625 μg/mL for N. Whereas, combinatorial approach showed efficient activity with four times reduced concentration of C and N at 78.125 and 156.25 µg/mL, respectively, against test strains. Further, EN1276 results proved the rapid killing efficacy of test strains in 1 min of contact time with significant (> 5 log) growth reduction at 100X concentration of actives. SEM analysis and reduced concentration of protease, lipids and carbohydrate contents of treated group biofilm components ascertained preformed biofilm disruption potential of C + N on polystyrene and nail surfaces. C + N at synergistic concentration exhibited no adverse effect on HaCaT cells at 78.125 µg/mL (C) + 156.25 µg/mL (N). Taken together, based on the observed experimental results, present study evidence the antiseptic/disinfectant ability of C + N and suggest that the combination can preferentially be used in foam-based hand wash formulations.

Role of sodium salicylate in Staphylococcus aureus quorum sensing, virulence, biofilm formation and antimicrobial susceptibility

The widespread threat of antibiotic resistance requires new treatment options. Disrupting bacterial communication, quorum sensing (QS), has the potential to reduce pathogenesis by decreasing bacterial virulence. The aim of this study was to investigate the influence of sodium salicylate (NaSa) on Staphylococcus aureus QS, virulence production and biofilm formation. In S. aureus ATCC 25923 (agr III), with or without serum, NaSa (10 mM) downregulated the agr QS system and decreased the secretion levels of alpha-hemolysin, staphopain A and delta-hemolysin. Inhibition of agr expression caused a downregulation of delta-hemolysin, decreasing biofilm dispersal and increasing biofilm formation on polystyrene and titanium under static conditions. In contrast, NaSa did not increase biofilm biomass under flow but caused one log₁₀ reduction in biofilm viability on polystyrene pegs, resulting in biofilms being twice as susceptible to rifampicin. A concentration-dependent effect of NaSa was further observed, where high concentrations (10 mM) decreased agr expression, while low concentrations (≤0.1 mM) increased agr expression. In S. aureus 8325-4 (agr I), a high concentration of NaSa (10 mM) decreased hla expression, and a low concentration of NaSa (≤1 mM) increased rnaIII and hla expression. The activity of NaSa on biofilm formation was dependent on agr type and material surface. Eight clinical strains isolated from prosthetic joint infection (PJI) or wound infection belonging to each of the four agr types were evaluated. The four PJI S. aureus strains did not change their biofilm phenotype with NaSa on the clinically relevant titanium surface. Half of the wound strains (agr III and IV) did not change the biofilm phenotype in the 3D collagen wound model. In addition, compared to the control, ATCC 25923 biofilms formed with 10 mM NaSa in the collagen model were more susceptible to silver. It is concluded that NaSa can inhibit QS in S. aureus, decreasing the levels of toxin production with certain modulation of biofilm formation. The effect on biofilm formation was dependent on the strain and material surface. It is suggested that the observed NaSa inhibition of bacterial communication is a potential alternative or adjuvant to traditional antibiotics.

Combinatorial Therapeutic Strategy of Biogenics Derived from Lactobacillus fermentum PUM and Zingerone Against Pseudomonas aeruginosa PAO1-Induced Surgical Site Infection: an Experimental Study

Pseudomonas aeruginosa, a WHO-prioritized multidrug-resistant Gram-negative bacteria, is one of the frequently implicated pathogen in surgical site infection (SSI) due to its virulence phenotypes and biofilm-forming ability. In the present study, cell-free supernatant (CFS) and biogenics (organic acids and precipitated protein fraction) of indigenous potential probiotic, Lactobacillus fermentum PUM both alone and in combination with zingerone were found to inhibit pyocyanin, pyochelin, protease, elastase, the virulence factors, and motility of P. aeruginosa PAO1. Furthermore, scanning electron microscopy indicated that biofilm formation was attenuated maximally by CFS of L. fermentum combined with zingerone. In vivo study revealed reduced P. aeruginosa burden, suppuration at surgical site vis-a-vis reduced levels of oxidants, pro-inflammatory cytokines, ameliorated anti-oxidants, and healed infected surgical site compared with counter controls. In totality, combination of L. fermentum PUM-derived biogenics and zingerone could be employed to treat P. aeruginosa-induced SSI that needs to be correlated clinically.

Chitosan-curcumin complexation to develop functionalized nanosystems with enhanced antimicrobial activity against hetero-resistant gastric pathogen

With the apparent stagnation in the antibiotic discovery and the propagation of multidrug resistance, Helicobacter pylori associated gastric infections are hard to eradicate. In pursuance of alternative medicines, in this study, covalent modification of chitosan (CS) polymer with curcumin (Cur) was accomplished. Proton Nuclear Magnetic Resonance and Fourier Transform Infrared spectroscopy elucidated the covalent interaction between Cur and CS with characteristic peak of imine functional group (C=N). Scanning Electron Microscopy provided visual proof for surface topology, while size and zeta potential values further affirmed the development of curcumin functionalized chitosan nanosystems (Cur-FCNS). The complexation efficiency of CS with Cur was found as 70 ± 3% at an optimal ratio of 5:1 for CS and Cur, respectively. Cur-FCNS developed with ionic gelation and ultrasonication method demonstrated synergistic anti-H. pylori activity in growth-kinetics and anti-biofilm assays, which was superior to free Cur and even chitosan nanosystems. Under simulated gastric conditions, Cur-FCNS revealed cumulative-release of only 16 ± 0.8% till 40 h, which indicated its improved stability to interact with H. pylori. In silico findings affirmed high binding affinity of Cur-FCNS with multiple bacterial virulence factors. Thus, our results affirmed the exceptional potential of Cur-FCNS as next-generation alternative-medicine to treat resistant H. pylori.

p38-MAPK recruits the proteolytic pathways in Caenorhabditis elegans during bacterial infection

In eukaryotic organisms, cell-signalling completely relies on Post Translational Modifications (PTMs) that can function as regulatory switches. Phosphorylation is a fundamental and frequently occurring PTM in almost all eukaryotes. Herein, we have studied the importance of protein phosphorylation using classical proteomic techniques in C. elegans upon bacterial infection. The differentially regulated proteins during bacterial infection were excised from SDS-PAGE (One-Dimensional) gel (TiO₂ column elutes) and subjected to MALDI-TOF-MS which ended up in identifying 220 proteins kinetically. KEGG pathway analysis of those proteins suggested that MAPK pathway was part of the innate immunity. Thus, we have characterized p38-MAPK (one of the crucial downstream MAPKs) using immunoblotting, subcellular fractionation, coimmunoprecipitation, LC-MS/MS, bioinformatics studies and qPCR. Meanwhile, KU25 strain (pmk-1 mutant) exhibited an earlier mortality during infection suggesting the crucial role of p38-MAPK during host-pathogen interaction. Interestingly, Reactome pathway analysis of p38 interactors (CoIP coupled to LC-MS/MS) revealed the involvement of various proteolytic pathway players (ubiquitination, SUMOylation and Neddylation) during bacterial infection. Further, the regulation of SUMOylation and Neddylation was identified and validated using immunoblotting and qPCR analyses, respectively. Concisely, our study indicated that bacterial infection triggers the MAPK cascade to elicit innate immunity which in turn recruits proteolytic pathways to counteract the invading pathogen.

Biomedical Applications and Bioavailability of Curcumin-An Updated Overview

Curcumin, a yellow-colored molecule derived from the rhizome of Curcuma longa, has been identified as the bioactive compound responsible for numerous pharmacological activities of turmeric, including anticancer, antimicrobial, anti-inflammatory, antioxidant, antidiabetic, etc. Nevertheless, the clinical application of curcumin is inadequate due to its low solubility, poor absorption, rapid metabolism and elimination. Advancements in recent research have shown several components and techniques to increase the bioavailability of curcumin. Combining with adjuvants, encapsulating in carriers and formulating in nanoforms, in combination with other bioactive agents, synthetic derivatives and structural analogs of curcumin, have shown increased efficiency and bioavailability, thereby augmenting the range of applications of curcumin. The scope for incorporating biotechnology and nanotechnology in amending the current drawbacks would help in expanding the biomedical applications and clinical efficacy of curcumin. Therefore, in this review, we provide a comprehensive overview of the plethora of therapeutic potentials of curcumin, their drawbacks in efficient clinical applications and the recent advancements in improving curcumin's bioavailability for effective use in various biomedical applications.

Proteomic analysis of Caenorhabditis elegans against Salmonella Typhi toxic proteins

Bacterial effector molecules are crucial infectious agents that can cause pathogenesis. In the present study, the pathogenesis of toxic Salmonella enterica serovar Typhi (S. Typhi) proteins on the model host Caenorhabditis elegans was investigated by exploring the host's regulatory proteins during infection through the quantitative proteomics approach. Extracted host proteins were analyzed using two-dimensional gel electrophoresis (2D-GE) and differentially regulated proteins were identified using MALDI TOF/TOF/MS analysis. Of the 150 regulated proteins identified, 95 were downregulated while 55 were upregulated. The interaction network of regulated proteins was predicted using the STRING tool. Most downregulated proteins were involved in muscle contraction, locomotion, energy hydrolysis, lipid synthesis, serine/threonine kinase activity, oxidoreductase activity, and protein unfolding. Upregulated proteins were involved in oxidative stress pathways. Hence, cellular stress generated by S. Typhi proteins in the model host was determined using lipid peroxidation as well as oxidant and antioxidant assays. In addition, candidate proteins identified via extract analysis were validated by western blotting, and the roles of several crucial molecules were analyzed in vivo using transgenic strains (myo-2 and col-19) and mutant (ogt-1) of C. elegans. To the best of our knowledge, this is the first study to report protein regulation in host C. elegans exposed to toxic S. Typhi proteins. It highlights the significance of p38 MAPK and JNK immune pathways.

New insights into the antibacterial and quorum sensing inhibition mechanism of Artemisia argyi leaf extracts towards Pseudomonas aeruginosa PAO1

This study aimed to investigate the anti-quorum sensing (QS) activity of Artemisia argyi leaf extracts (AALE) towards Pseudomonas aeruginosa PAO1 as well as the underlying molecular mechanisms. Using a biosensor Chromobacterium violaceum CV026, AALE were found to have anti-QS activity as AALE treatment significantly inhibited the violacein production of C. violaceum CV026 while produced little effect on the cell growth. Beyond that a higher dosage of AALE inhibited cell growth, sub-MIC of AALE significantly reduced the production of QS-regulated virulence factors (pyocyanin, elastase, and rhamnolipid), biofilm formation, and the swarming and swimming motility in P. aeruginosa PAO1 with a dosage-dependent manner. Quantitative real-time PCR (qRT-PCR) analysis did not detect the direct inhibitory effect of AALE on the expression of QS genes (lasI, lasR, rhlI, and rhlR). By iTRAQ-based quantitative proteomic analysis, 129 proteins were found to be differentially expressed upon AALE treatment, with 85 upregulated and 44 downregulated proteins, respectively. Functional enrichment analysis of the differential proteins revealed that AALE exerted anti-QS activity towards P. aeruginosa PAO1 by upregulating the expression of the global regulator CsrA, inducing oxidative stress, and perturbing protein homeostasis. Moreover, the inhibitory effect of AALE on the virulence of P. aeruginosa PAO1 was likely to be achieved by attenuating the expression of QS-regulated genes instead of QS genes. Collectively, the results of this study provide a basis for the future use of AALE as a preservative in controlling food spoilage caused by P. aeruginosa.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02663-5.

Attenuation of quorum sensing mediated virulence factors production and biofilm formation in Pseudomonas aeruginosa PAO1 by Colletotrichum gloeosporioides HM3

Signal dependent microbial communication in Pseudomonas aeruginosa PAO1 is a typical phenomenon mediated by acyl homo-serine lactone molecules that helps in developing biofilm and enhance antibiotic resistance. Microbial sources provide insight to the hidden treasure of secondary metabolites, and these structurally diversified chemical motifs can be used as antimicrobial and anti-infective agents. In the present study, endophytic fungus, Colletotrichum gloeosporioides HM3 isolated from Carica papaya leaves was explored for anti-infective potential against P. aeruginosa PAO1. The crude extract of C. gloeosporioides HM3 displayed bacteriostatic effect on P. aeruginosa PAO1 growth at 750 μg/ml concentration. A significant decline was observed in the production of quorum sensing regulated virulence factors, i.e. 56.32%, 62.54%, and 66.67% of pyocyanin, chitinase, and elastase enzyme, respectively. A drastic reduction in pathogenic determinant behaviour after treatment with crude extract of C. gloeosporioides HM3 i.e. EPS, rhamnolipid, and HCN production was noted. Light microscopy and CLSM analysis revealed that fungal extract treatment has reduced bacterial ability to form dense biofilm architecture. In silico analysis demonstrated the binding efficiency of bioactive compound, 4-(2,3-dimethoxybenzylidene)-3-methyl-1-(4-nitrophenyl)-2-pyrazolin-5-one, which is equipotent to the natural ligand and displayed a docking score of -5.436 kcal/mol with QS transcriptional regulator (LasR). Whereas the compound Acetamide, n-[tetrahydro-3-(phenylmethyl) thieno [3,4-d]thiazol-2 (3 h)-ylidene]-, s,s-dioxide exhibits a docking score of -4.088 kcal/mol (LasR) and -1.868 kcal/mol (RhlR) with cognate receptor proteins. Henceforth, the research report suggests C. gloeosporioides HM3 derived metabolites could be considered as a potential inhibitors of QS regulated virulence factors and biofilm production in P. aeruginosa PAO1.

Antibiofilm and Antivirulence Properties of Indoles Against Serratia marcescens

Indole and its derivatives have been shown to interfere with the quorum sensing (QS) systems of a wide range of bacterial pathogens. While indole has been previously shown to inhibit QS in Serratia marcescens, the effects of various indole derivatives on QS, biofilm formation, and virulence of S. marcescens remain unexplored. Hence, in the present study, we investigated the effects of 51 indole derivatives on S. marcescens biofilm formation, QS, and virulence factor production. The results obtained revealed that several indole derivatives (3-indoleacetonitrile, 5-fluoroindole, 6-fluoroindole, 7-fluoroindole, 7-methylindole, 7-nitroindole, 5-iodoindole, 5-fluoro-2-methylindole, 2-methylindole-3-carboxaldehyde, and 5-methylindole) dose-dependently interfered with quorum sensing (QS) and suppressed prodigiosin production, biofilm formation, swimming motility, and swarming motility. Further assays showed 6-fluoroindole and 7-methylindole suppressed fimbria-mediated yeast agglutination, extracellular polymeric substance production, and secretions of virulence factors (e.g., proteases and lipases). QS assays on Chromobacterium violaceum CV026 confirmed that indole derivatives interfered with QS. The current results demonstrate the antibiofilm and antivirulence properties of indole derivatives and their potentials in applications targeting S. marcescens virulence.

Proteomic and Systematic Functional Profiling Unveils Citral Targeting Antibiotic Resistance, Antioxidant Defense, and Biofilm-Associated Two-Component Systems of Acinetobacter baumannii To Encumber Biofilm and Virulence Traits

Acinetobacter baumannii is a nosocomial-infection-causing bacterium and also possesses multidrug resistance to a wide range of conventional antibiotics. The biofilm-forming ability of A. baumannii plays a major role in its resistance and persistence. There is an alarming need for novel treatment strategies to control A. baumannii biofilm-associated issues. The present study demonstrated the strong antibiofilm and antivirulence efficacy of citral against A. baumannii. In addition, proteomic analysis revealed the multitarget potential of citral against A. baumannii. Furthermore, citral treatment enhances the susceptibility of A. baumannii to the host innate immune system and reactive oxygen species (ROS). Cytotoxicity analysis revealed the nonfatal effect of citral on human PBMCs. Therefore, citral could be the safest therapeutic compound and can be taken for further clinical evaluation for the treatment of biofilm-associated infections by A. baumannii.

Acinetobacter baumannii has been reported as a multidrug-resistant bacterium due to biofilms and antimicrobial resistance mechanisms. Hence, novel therapeutic strategies are necessary to overcome A. baumannii infections. This study revealed that citral at 200 μg/ml attenuated A. baumannii biofilms by up to 90% without affecting viability. Furthermore, microscopic analyses and in vitro assays confirmed the antibiofilm efficacy of citral. The global effect of citral on A. baumannii was evaluated by proteomic, transcriptional, and in silico approaches. Two-dimensional (2D) gel electrophoresis and matrix-assisted laser desorption ionization–time of flight/time of flight (MALDI-TOF/TOF) analyses were used to assess the effect of citral on the A. baumannii cellular proteome. Quantitative real-time PCR (qPCR) analysis was done to validate the proteomic data and identify the differentially expressed A. baumannii genes. Protein-protein interactions, gene enrichment, and comparative gene network analyses were performed to explore the interactions and functional attributes of differentially expressed proteins of A. baumannii. Global omics-based analyses revealed that citral targeted various mechanisms such as biofilm formation, antibiotic resistance, antioxidant defense, iron acquisition, and type II and type IV secretion systems. The results of antioxidant analyses and antibiotic sensitivity, blood survival, lipase, and hemolysis assays validated the proteomic results. Cytotoxicity analysis showed a nontoxic effect of citral on peripheral blood mononuclear cells (PBMCs). Overall, the current study unveiled that citral has multitarget efficacy to inhibit the biofilm formation and virulence of A. baumannii.

IMPORTANCEAcinetobacter baumannii is a nosocomial-infection-causing bacterium and also possesses multidrug resistance to a wide range of conventional antibiotics. The biofilm-forming ability of A. baumannii plays a major role in its resistance and persistence. There is an alarming need for novel treatment strategies to control A. baumannii biofilm-associated issues. The present study demonstrated the strong antibiofilm and antivirulence efficacy of citral against A. baumannii. In addition, proteomic analysis revealed the multitarget potential of citral against A. baumannii. Furthermore, citral treatment enhances the susceptibility of A. baumannii to the host innate immune system and reactive oxygen species (ROS). Cytotoxicity analysis revealed the nonfatal effect of citral on human PBMCs. Therefore, citral could be the safest therapeutic compound and can be taken for further clinical evaluation for the treatment of biofilm-associated infections by A. baumannii.

Regulatory Mechanisms and Promising Applications of Quorum Sensing-Inhibiting Agents in Control of Bacterial Biofilm Formation

A biofilm is an assemblage of microbial cells attached to a surface and encapsulated in an extracellular polymeric substance (EPS) matrix. The formation of a biofilm is one of the important mechanisms of bacterial resistance, which not only leads to hard-to-control bacterial infections in humans and animals but also enables bacteria to be a major problem in various fields, such as food processing, wastewater treatment and metalworking. Quorum sensing (QS) is a bacterial cell-to-cell communication process that depends on the bacterial population density and is mediated by small diffusible signaling molecules called autoinducers (AIs). Bacteria use QS to regulate diverse arrays of functions, including virulence and biofilm formation. Therefore, the interference with QS by using QS inhibiting agents, including QS inhibitors (QSIs) and quorum quenching (QQ) enzymes, to reduce or even completely repress the biofilm formation of pathogenic bacteria appears to be a promising approach to control bacterial infections. In this review, we summarize the mechanisms of QS-regulating biofilm formation and QS-inhibiting agents that control bacterial biofilm formation, strategies for the discovery of new QS inhibiting agents, and the current applications of QS-inhibiting agents in several fields to provide insight into the development of effective drugs to control pathogenic bacteria.

Iron metabolism in Pseudomonas aeruginosa biofilm and the involved iron-targeted anti-biofilm strategies

Pseudomonas aeruginosa is a gram-negative bacterium that exists in various ecosystems, causing severe infections in patients with AIDS or cystic fibrosis. P. aeruginosa can form biofilm on a variety of surfaces, whereby the bacteria produce defensive substances and enhance antibiotic-resistance, making themselves more adaptable to hostile environments. P. aeruginosa resistance represents one of the main causes of infection-related morbidity and mortality at a global level. Iron is required for the growth of P. aeruginosa biofilm. This review summarises how the iron metabolism contributes to develop biofilm, and more importantly, it may provide some references for the clinic to achieve novel anti-biofilm therapeutics by targeting iron activities.

sarA-Dependent Antibiofilm Activity of Thymol Enhances the Antibacterial Efficacy of Rifampicin Against Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a serious human pathogen which has been listed as a high-priority multi-drug resistance pathogen by the World Health Organization (WHO). Persistent MRSA infections are often associated with biofilm formation and resistance to conventional antimicrobial therapy. Inhibiting the surface adherence and the virulence of the bacterium is the current alternative approach without affecting growth to reduce the possibility of resistance development. Although numerous antibiofilm agents have been identified, their mode of action remains unclear. Combining two drugs with different modes of action will improve the efficiency of the treatment strategy against MRSA. The present study was aimed to decipher the molecular mechanism underlying the antibiofilm activity of thymol against MRSA and assess the ability of thymol to improve the antibacterial activity of rifampicin. Thymol significantly inhibited 88% of MRSA biofilm formation at 100 μg/ml and reduced the surface adherence of MRSA on glass, stainless steel, and titanium surface coated with human plasma as evidenced by microscopic analyses. qPCR analysis of global virulence regulatory genes and biofilm assay with S. aureus wild type, ΔsarA, and Δagr strains revealed the sarA-mediated antibiofilm activity of thymol and inhibition of sarA-controlled virulence factors. Congo red assay and erythrocyte lysis assay further confirmed the reduction in polysaccharide intracellular adhesin and hemolysin. Importantly, thymol enhanced the antibacterial and the biofilm eradication efficiency of rifampicin against MRSA and also reduced the formation of persisters. Thus, the present study reveals the sarA-dependent antibiofilm efficacy of MRSA and suggests thymol as the promising combinatorial candidate in potentiating the antibacterial activity of rifampicin against persistent MRSA infections.

Palmitic Acid Inhibits the Virulence Factors of Candida tropicalis: Biofilms, Cell Surface Hydrophobicity, Ergosterol Biosynthesis, and Enzymatic Activity

Biofilm is the fortitude of Candida species infections which eventually causes candidiasis in human. C. tropicalis is one of the predominant Candida species commonly found in systemic infections, next to C. albicans. In Candida species, biofilm maturity initiates irreversible surface attachment of cells and barricades the penetration of conventional antifungals. Hence, the current study investigated the antifungal and antivirulence potency of palmitic acid (PA) against C. tropicalis mature biofilm and its associated virulence factors. In vitro results revealed an effective inhibition of biofilm in PA-treated C. tropicalis, compared to C. albicans and C. glabrata. Also, PA reduced C. tropicalis mature biofilm at various time points. Further, PA treatment triggered apoptosis in C. tropicalis through ROS mediated mitochondrial dysfunction as demonstrated by confocal microscopic observation of PI, DAPI and DCFDA staining. PA regulated other virulence factors such as cell surface hydrophobicity, ergosterol biosynthesis, protease and lipase after 48 h of treatment. Downregulation of ERG11 (Lanosterol 14-alpha demethylase) was contributed to the reduction of ergosterol in PA-treated C. tropicalis. However, enhanced hyphal growth was observed in PA-treated C. tropicalis through upregulation HWP1 (Hyphal wall protein) and EFG1 (Enhanced filamentous growth). This study highlighted the antibiofilm and antivirulence potency of PA against C. tropicalis. Hence, PA could be applied synergistically with other antifungal agents to increase the efficacy for regulating NCAC infections.

Proteomic profiling unveils citral modulating expression of IsaA, CodY and SaeS to inhibit biofilm and virulence in methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the dangerous human pathogens and it is categorized as a high priority multi-drug resistant bacterium by WHO. Biofilm forming ability of MRSA is responsible for persistent infections and also difficult to eradicate using antibiotic therapy as biofilm is much more resistant to antibiotics. Thus, targeting biofilm and virulence has become an alternative approach to attenuate the pathogenicity of bacterium without affecting the growth. Hence, the present study was aimed at evaluation of antibiofilm potential of citral against MRSA and to decode the possible mode of action. Citral inhibited biofilm formation by MRSA without affecting growth at 100 μg/mL. Microscopic analyses evidenced that citral greatly hampered the surface adherence of MRSA. Effect of citral on cellular proteome of MRSA was studied using two-dimensional gel electrophoresis (2DGE) and differentially regulated proteins were identified using nano LC-MS/MS and MALDI-TOF/TOF analysis. Gene ontology and STRING analysis revealed that citral differentially regulated the proteins involved in pleotropic transcriptional repression (CodY), cell wall homeostasis (IsaA), regulation of exotoxin secretion (SaeS), cell adhesion, hemolysis, capsular polysaccharide biosynthesis and pathogenesis. Gene expression analysis and in vitro assays further validated the alteration in synthesis of slime, hemolysin, lipase, staphyloxanthin and oxidant susceptibility. Thus, the present study unveiled the multiple protein targeted antibiofilm potential of citral and portrays citral as a promising therapeutic agent to combat biofilm mediated MRSA infections with less possibility of resistance development.

Lactonase Specificity Is Key to Quorum Quenching in Pseudomonas aeruginosa

The human opportunistic pathogen Pseudomonas aeruginosa orchestrates the expression of many genes in a cell density-dependent manner by using quorum sensing (QS). Two acyl-homoserine lactones (AHLs) are involved in QS circuits and contribute to the regulation of virulence factors production, biofilm formation, and antimicrobial sensitivity. Disrupting QS, a strategy referred to as quorum quenching (QQ) can be achieved using exogenous AHL-degrading lactonases. However, the importance of enzyme specificity on quenching efficacy has been poorly investigated. Here, we used two lactonases both targeting the signal molecules N-(3-oxododecanoyl)-L-homoserine lactone (3-oxo-C₁₂ HSL) and butyryl-homoserine lactone (C₄ HSL) albeit with different efficacies on C₄ HSL. Interestingly, both lactonases similarly decreased AHL concentrations and comparably impacted the expression of AHL-based QS genes. However, strong variations were observed in Pseudomonas Quinolone Signal (PQS) regulation depending on the lactonase used. Both lactonases were also found to decrease virulence factors production and biofilm formation in vitro, albeit with different efficiencies. Unexpectedly, only the lactonase with lower efficacy on C₄ HSL was able to inhibit P. aeruginosa pathogenicity in vivo in an amoeba infection model. Similarly, proteomic analysis revealed large variations in protein levels involved in antibiotic resistance, biofilm formation, virulence and diverse cellular mechanisms depending on the chosen lactonase. This global analysis provides evidences that QQ enzyme specificity has a significant impact on the modulation of QS-associated behavior in P. aeruginosa PA14.

Enhancing curcumin's solubility and antibiofilm activity via silica surface modification

Bacterial biofilms are microbial communities in which bacterial cells in sessile state are mechanically and chemically protected against foreign agents, thus enhancing antibiotic resistance. The delivery of active compounds to the inside of biofilms is often hindered due to the existence of the biofilm extracellular polymeric substances (EPS) and to the poor solubility of drugs and antibiotics. A possible strategy to overcome the EPS barrier is the incorporation of antimicrobial agents into a nanocarrier, able to penetrate the matrix and deliver the active substance to the cells. Here, we report the synthesis of antimicrobial curcumin-conjugated silica nanoparticles (curc-NPs) as a possibility for dealing with these issues. Curcumin is a known antimicrobial agent and to overcome its low solubility in water it was grafted onto the surface of silica nanoparticles, the latter functioning as nanocarrier for curcumin into the biofilm. Curc-NPs were able to impede the formation of model P. putida biofilms up to 50% and disrupt mature biofilms up to 54% at 2.5 mg mL^-1. Cell viability of sessile cells in both cases was also considerably affected, which is not observed for curcumin delivered as a free compound at the same concentration. Furthermore, proteomics of extracted EPS matrix of biofilms grown in the presence of free curcumin and curc-NPs revealed differences in the expression of key proteins related to cell detoxification and energy production. Therefore, curc-NPs are presented here as an alternative for curcumin delivery that can be exploited not only to other bacterial strains but also to further biological applications.

Global proteomic analysis deciphers the mechanism of action of plant derived oleic acid against Candida albicans virulence and biofilm formation

Candida albicans is a commensal fungus in humans, mostly found on the mucosal surfaces of the mouth, gut, vagina and skin. Incidence of ever increasing invasive candidiasis in immunocompromised patients, alarming occurrence of antifungal resistance and insufficient diagnostic methods demand more focused research into C. albicans pathogenicity. Consequently, in the present study, oleic acid from Murraya koenigii was shown to have the efficacy to inhibit biofilm formation and virulence of Candida spp. Results of in vitro virulence assays and gene expression analysis, impelled to study the protein targets which are involved in the molecular pathways of C. albicans pathogenicity. Proteomic studies of differentially expressed proteins reveals that oleic acid induces oxidative stress responses and mainly targets the proteins involved in glucose metabolism, ergosterol biosynthesis, lipase production, iron homeostasis and amino acid biosynthesis. The current study emphasizes anti-virulent potential of oleic acid which can be used as a therapeutic agent to treat Candida infections.

Novel thiazolinyl-picolinamide based palladium(II) complex-impregnated urinary catheters quench the virulence and disintegrate the biofilms of uropathogens

Pseudomonas aeruginosa and Serratia marcescens are prominent members belonging to the group of ESKAPE pathogens responsible for Urinary Tract Infections (UTI) and nosocomial infections. Both the pathogens regulate several virulence factors, including biofilm formation through quorum sensing (QS), an intercellular communication mechanism. The present study describes the anti-biofilm and QS quenching effect of thiazolinyl-picolinamide based palladium(II) complexes against P. aeruginosa and S. marcescens. Palladium(II) complexes showed quorum sensing inhibitory potential in inhibiting swarming motility behaviour, pyocyanin production and other QS mediated virulence factors in both P. aeruginosa and S. marcescens. In addition, the establishment of biofilms was prevented on palladium (II) coated catheters. Overall, the present study demonstrates that thiazolinyl-picolinamide based palladium (II) complexes will be a promising strategy to combat device-mediated UTI infections.

Plant-Derived Inhibitors of AHL-Mediated Quorum Sensing in Bacteria: Modes of Action

Numerous gram-negative phytopathogenic and zoopathogenic bacteria utilise acylated homoserine lactone (AHL) in communication systems, referred to as quorum sensing (QS), for induction of virulence factors and biofilm development. This phenomenon positions AHL-mediated QS as an attractive target for anti-infective therapy. This review focused on the most significant groups of plant-derived QS inhibitors and well-studied individual compounds for which in silico, in vitro and in vivo studies provide substantial knowledge about their modes of anti-QS activity. The current data about sulfur-containing compounds, monoterpenes and monoterpenoids, phenylpropanoids, benzoic acid derivatives, diarylheptanoids, coumarins, flavonoids and tannins were summarized; their plant sources, anti-QS effects and bioactivity mechanisms have also been summarized and discussed. Three variants of plant-derived molecules anti-QS strategies are proposed: (i) specific, via binding with LuxI-type AHL synthases and/or LuxR-type AHL receptor proteins, which have been shown for terpenes (carvacrol and l-carvone), phenylpropanoids (cinnamaldehyde and eugenol), flavonoid quercetin and ellagitannins; (ii) non-specific, by affecting the QS-related intracellular regulatory pathways by lowering regulatory small RNA expression (sulphur-containing compounds ajoene and iberin) or c-di-GMP metabolism reduction (coumarin); and (iii) indirect, via alteration of metabolic pathways involved in QS-dependent processes (vanillic acid and curcumin).

Extracted chitosan disrupts quorum sensing mediated virulence factors in Urinary tract infection causing pathogens

Quorum sensing (QS) plays an important role during the aetiology of urinary tract infection (UTI), as several virulence factors are under the regulation of QS. Pseudomonas aeruginosa and Serratia marcescens, the primary causative agents of UTI, employ acyl homoserine lactone (AHL) as signal molecules to coordinate various virulence factors. In this present study, chitosan extracted from the marine crab Portunus sanguinolentus was screened for its ability to inhibit the QS-signaling molecules of P. aeruginosa (PA01) and few clinical isolates of P. aeruginosa and S. marcescens. The extracted chitosan on comparison with a commercial chitosan showed significant inhibition of several QS-dependent virulence factors in P. aeruginosa and S. marscenes. Furthermore, qPCR analysis was carried out to confirm the down-regulation of fimA, fimC and flhD genes involved in adhesion and pathogenesis of S. marcescens and lasI and rhlI genes that governs the P. aeruginosa quorum sensing system. Moreover, the chitosan when coated on a catheter was also able to disrupt the mature biofilms which was revealed by scanning electron microscopy. Collectively, the present study showcases the QS inhibitory property of extracted chitosan from crab shells which is being discarded as a recalcitrant biowaste.

Validation of the anti-infective potential of a polyherbal 'Panchvalkal' preparation, and elucidation of the molecular basis underlining its efficacy against Pseudomonas aeruginosa

BACKGROUND

A Panchvalkal formulation (Pentaphyte P-5®) mentioned in ancient texts of Indian traditional medicine was investigated for its anti-infective potential against Pseudomonas aeruginosa.

METHODS

Effect of the test formulation on bacterial growth and pigment production was evaluated by broth dilution assay. In vivo efficacy was evaluated using Caenorhabditis elegans as the model host. Whole transcriptome approach was taken to study the effect of test formulation on bacterial gene expression.

RESULTS

This formulation in vitro was found to be capable of affecting quorum sensing (QS)-regulated traits (pyocyanin, pyoverdine, biofilm) of Pseudomonas aeruginosa. In combination with antibiotics, it enhanced susceptibility of the test bacterium to antibiotics like cephalexin and tetracycline. Effect of Panchvalkal formulation (PF) on QS-regulated traits of P. aeruginosa was not reversed even after repeated exposure of the bacterium to PF. In vivo efficacy of PF was demonstrated employing Caenorhabditis elegans as the model host, wherein PF-treated bacteria were able to kill lesser worms than their extract-unexposed counterparts. Whole transcriptome study revealed that approximately 14% of the P. aeruginosa genome was expressed differently under the influence of PF.

CONCLUSIONS

Major mechanisms through which Panchvalkal seems to exert its anti-virulence effect are generation of nitrosative and oxidative stress, and disturbing iron and molybdenum homeostasis, besides interfering with QS machinery. This study is a good demonstration of the therapeutic utility of the 'polyherbalism' concept, so common in ayurved. It also demonstrates utility of the modern 'omics' tools for validating the traditional medicine i.e. ayuromics.

Proteomic analysis of iron-regulated membrane proteins identify FhuE receptor as a target to inhibit siderophore-mediated iron acquisition in Acinetobacter baumannii

Survival of the Acinetobacter baumannii inside host requires different micronutrients such as iron, but their bioavailability is limited because of nutritional immunity created by host. A. baumannii has to develop mechanisms to acquire nutrient iron during infection. The present study is an attempt to identify membrane proteins involved in iron sequestration mechanism of A. baumannii using two-dimensional electrophoresis and LC-MS/MS analysis. The identified iron-regulated membrane protein (IRMP) of A. baumannii was used for its interaction studies with different siderophores, and designing of the inhibitor against A. baumannii targeting this IRMP. Membrane proteomic results identified over-expression of four membrane proteins (Fhu-E receptor, ferric-acinetobactin receptor, ferrienterochelin receptor, and ferric siderophore receptor) under iron-limited condition. A. baumannii produces siderophores that have good interaction with the FhuE receptor. Result also showed that FhuE receptor has interaction with siderophores produced by other bacteria. Interaction of FhuE receptor and siderophores helps in iron sequestration and survival of Acinetobacter under nutritional immunity imposed by the host. Hence it becomes essential to find a potential inhibitor for the FhuE receptor that can inhibit the survival of A. baumannii in the host. In-silico screening, and molecular mechanics studies identified ZINC03794794 and ZINC01530652 as a likely lead to design inhibitor against the FhuE receptor of A. baumannii. The designed inhibitor is experimentally validated for its antibacterial activity on the A. baumannii. Therefore, designed inhibitor interferes with the iron acquisition mechanism of Acinetobacter hence may prove useful for preventing infection caused by A. baumannii by limiting nutrient availability.

Current anti-biofilm strategies and potential of antioxidants in biofilm control

INTRODUCTION

Biofilm formation is a strategy for microorganisms to adapt and survive in hostile environments. Microorganisms that are able to produce biofilms are currently recognized as a threat to human health. Areas covered: Many strategies have been employed to eradicate biofilms, but several drawbacks from these methods had subsequently raised concerns on the need for alternative approaches to effectively prevent biofilm formation. One of the main mechanisms that drives a microorganism to transit from a planktonic to a biofilm-sessile state, is oxidative stress. Chemical agents that could target oxidative stress regulators, for instance antioxidants, could therefore be used to treat biofilm-associated infections. Expert commentary: The focus of this review is to summarize the function and limitation of the current anti-biofilm strategies and will propose the use of antioxidants as an alternative method to treat, prevent and eradicate biofilms. Studies have shown that water-soluble and lipid-soluble antioxidants can reduce and prevent biofilm formation, by influencing the expression of genes associated with oxidative stress. Further in vivo work should be conducted to ensure the efficacy of these antioxidants in a biological environment. Nevertheless, antioxidants are promising anti-biofilm agents, and thus is a potential solution for biofilm-associated infections in the future.

Environmental proteomic studies: closer step to understand bacterial biofilms

Advancement in proteome analytical techniques and the development of protein databases have been helping to understand the physiology and subtle molecular mechanisms behind biofilm formation in bacteria. This review is to highlight how the evolving proteomic approaches have revealed fundamental molecular processes underlying the formation and regulation of bacterial biofilms. Based on the survey of research reports available on differential expression of proteins in biofilms of bacterial from wide range of environments, four important cellular processes viz. metabolism, motility, transport and stress response that contribute to formation of bacterial biofilms are discussed. This review might answer how proteins related to these cellular processes contribute significantly in stabilizing biofilms of different bacteria in diverse environmental conditions.

O-GlcNAcylation confers protection against Staphylococcus aureus infection in Caenorhabditis elegans through ubiquitination

Glycosylation is one of the most prevalent post-translational modifications in biological systems. In Caenorhabditis elegans, O-GlcNAcylation has been shown to be actively involved in the regulation of dauer formation and detoxification of toxins secreted by invading pathogens. On this backdrop, the present study is focused on understanding the role of O-GlcNAcylation in C. elegans during Staphylococcus aureus infection using a gel based proteomic approach. Results of time course killing assays with wild-type and mutants of glycosylation and comparison of results revealed an increase in the survival of the C. elegans oga-1 mutant when compared to wild-type N2 and the ogt-1 mutant. Increased survival of C. elegans N2 upon S. aureus infection in the presence of O-(2-acetamido-2-deoxy-d-glucopyranosylidenamino) N-phenylcarbamate (PUGNAc-an OGA inhibitor) further confirmed the involvement of O-GlcNAcylation in protecting C. elegans from infection. The two-dimensional gel-based proteomic analysis of the control and S. aureus infected C. elegans oga-1 mutant followed by mass spectrometric identification of differentially expressed proteins has been carried out. The results revealed that key proteins involved in ubiquitination such as Cullin-1 (CUL-1), Cullin-3 (CUL-3), BTB and MATH domain-containing protein 15 (BATH-15), ubiquitin-conjugating enzyme E2 variant 3 (UEV-3) and probable ubiquitin-conjugating enzyme E2 7 (UBC-7) are upregulated. Real-time PCR analysis further confirms the upregulation of genes encoding the above-mentioned proteins which are involved in the ubiquitin-mediated pathways in C. elegans. In addition, treatment of C. elegans wild-type N2 and the oga-1 mutant with PUGNAc + suramin and suramin (an ubiquitination inhibitor), respectively has resulted in increased sensitivity to S. aureus infection. Hence, it is presumed that upregulation of proteins involved in the ubiquitination pathway could be the key regulatory mechanism responsible for the enhanced survival of the oga-1 mutant during S. aureus infection.

Inhibitory effect of α-mangostin on Acinetobacter baumannii biofilms - an in vitro study

The present study was designed to investigate the anti-biofilm potential of alpha-mangostin (α-MG) against Acinetobacter baumannii (AB). The biofilm inhibitory concentration (BIC) of α-MG against AB was found to be 2 μg ml^-1. α-MG (0.5, 1 and 2 μg ml^-1) exhibited non-bactericidal concentration-dependent anti-biofilm activities against AB. However, α-MG failed to disintegrate the mature biofilms of AB even at a 10-fold increased concentration from its BIC. Results from qRT-PCR and in vitro bioassays further demonstrated that α-MG downregulated the expression of bfmR, pgaA, pgaC, csuA/B, ompA, bap, katE, and sodB genes, which correspondingly affects biofilm formation and its associated virulence traits. The present study suggests that α-MG exerts its anti-biofilm property by interrupting initial biofilm formation and the cell-to-cell signaling mechanism of AB. Additional studies are required to understand the mode of action responsible for the anti-biofilm property.

Biofilm inhibition and pathogenicity attenuation in bacteria by Proteus mirabilis

Biofilms play an important role in the antibiotic resistance of encased bacteria, and biofilm formation is regulated by quorum sensing (QS). Inhibiting the QS system may, therefore, degrade the integrity of a biofilm and expose the bacterial pathogens within it to the deleterious effects of molecules such as antibiotics. Moreover, the use of QS inhibitors (QSIs) may provide a novel approach for treating bacterial infections of aquacultures. In the present study, the bacterium Proteus mirabilis was identified as a potential producer of QSIs. Varying concentrations (0.1-1.1%) of filtrates prepared from the culture of P. mirabilis inhibited biofilm formation by the pathogens Pseudomonas aeruginosa, Vibrio harveyi and Staphylococcus aureus by as much as 58.9%, 41.5% and 41.9%, respectively. These filtrates as well as the crude aqueous extracts prepared from them increased the sensitivities of pathogens to the inhibitory effects of kanamycin. The filtrates also showed pathogenicity attenuation potential in P. aeruginosa by decreasing the production of virulence factors. Moreover, the filtrates did not influence the planktonic growth of these pathogens. The results indicate that P. mirabilis may act as a non-specific (or broad-spectrum) inhibitor of biofilm formation that will help control infectious diseases that adversely affect the aquaculture industry.

Mechanisms and Targeted Therapies for Pseudomonas aeruginosa Lung Infection

Pseudomonas aeruginosa is a complex gram-negative facultative anaerobe replete with a variety of arsenals to activate, modify, and destroy host defense mechanisms. The microbe is a common cause of nosocomial infections and an antibiotic-resistant priority pathogen. In the lung, P. aeruginosa disrupts upper and lower airway homeostasis by damaging the epithelium and evading innate and adaptive immune responses. The biology of these interactions is essential to understand P. aeruginosa pathogenesis. P. aeruginosa interacts directly with host cells via flagella, pili, lipoproteins, lipopolysaccharides, and the type III secretion system localized in the outer membrane. P. aeruginosa quorum-sensing molecules regulate the release of soluble factors that enhance the spread of infection. These characteristics of P. aeruginosa differentially affect lung epithelial, innate, and adaptive immune cells involved in the production of mediators and the recruitment of additional immune cell subsets. Pathogen interactions with individual host cells and in the context of host acute lung infection are discussed to reveal pathways that may be targeted therapeutically.

Vanillic acid from Actinidia deliciosa impedes virulence in Serratia marcescens by affecting S-layer, flagellin and fatty acid biosynthesis proteins

Serratia marcescens is one of the important nosocomial pathogens which rely on quorum sensing (QS) to regulate the production of biofilm and several virulence factors. Hence, blocking of QS has become a promising approach to quench the virulence of S. marcescens. For the first time, QS inhibitory (QSI) and antibiofilm potential of Actinidia deliciosa have been explored against S. marcescens clinical isolate (CI). A. deliciosa pulp extract significantly inhibited the virulence and biofilm production without any deleterious effect on the growth. Vanillic acid was identified as an active lead responsible for the QSI activity. Addition of vanillic acid to the growth medium significantly affected the QS regulated production of biofilm and virulence factors in a concentration dependent mode in S. marcescens CI, ATCC 14756 and MG1. Furthermore vanillic acid increased the survival of Caenorhabditis elegans upon S. marcescens infection. Proteomic analysis and mass spectrometric identification of differentially expressed proteins revealed the ability of vanillic acid to modulate the expression of proteins involved in S-layers, histidine, flagellin and fatty acid production. QSI potential of the vanillic acid observed in the current study paves the way for exploring it as a potential therapeutic candidate to treat S. marcescens infections.