RNA-Seq-based transcriptome analysis of methicillin-resistant Staphylococcus aureus biofilm inhibition by ursolic acid and resveratrol

Antibiofilm efficacies and mechanism of perillaldehyde against Shewanella putrefaciens

Shewanella putrefaciens is Gram-negative bacterium and important spoilage organism in aquatic products, negatively impacting the organoleptic properties of aquatic products. S. putrefaciens could form biofilm, which increases persistence and contamination in food system. Efficient antibiofilm strategies are urgently needed to reduce its presence in food environment. This study aimed to explore the impact of perillaldehyde on S. putrefaciens biofilm and the underlying mechanisms using transcriptomic analysis. Perillaldehyde remarkably reduced extracellular polymeric substance contents, inhibited metabolic activity of biofilm cells, disrupted bacterial motility, loose biofilm structure and decreased biofilm formation in food juice and on various surfaces (stainless steel, silicone, glass, razon clam and shrimp). Transcriptome analysis revealed that 553 differentially expressed genes were identified, among which 254 were down-regulated and 299 were up-regulated. The differentially expressed genes included ATP-binding cassette transporters, ribosome, two-component systems, resistance/nodulation/division efflux systems, quorum sensing, amino acid metabolism, biosynthesis and degradation pathways. The findings demonstrate antibiofilm properties of perillaldehyde against S. putrefaciens and indicate that perillaldehyde could be developed as an antibiofilm agent to mitigate existence and contamination of S. putrefaciens and to reduce associated food loss caused by this spoilage bacteria.

Resveratrol inhibits the formation of Staphylococcus aureus biofilms by reducing PIA, eDNA release, and ROS production

Introduction

Staphylococcus aureus is a zoonotic pathogen that is difficult to control. Resveratrol (RES) has been shown to have significant antibacterial effects. The present study aimed to investigate the inhibitory effect of RES on the formation of Staphylococcus aureus biofilms and their molecular mechanism.

Methods

First, the minimum inhibitory concentration and inhibitory action curve of RES against Staphylococcus aureus were obtained through testing. Second, we found that RES can inhibit biofilm formation by reducing the release of polysaccharide intercellular adhesion (PIA) and extracellular DNA (eDNA) from Staphylococcus aureus.

Results

RES treatment significantly reduced the production of reactive oxygen species (ROS) and nicotinamide adenine dinucleotide phosphate (NADPH) in Staphylococcus aureus, indicating that ROS and NADPH are closely related to biofilm formation.

Conclusion

This study demonstrates that RES inhibits the formation of Staphylococcus aureus biofilms by reducing PIA, eDNA release, and ROS production, and these results provide new ideas for the clinical application of RES in the treatment of Staphylococcus aureus infection.

Antibacterial and anti-virulence activity of eco-friendly resveratrol-loaded lipid nanocapsules against methicillin-resistant staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is challenging modern antimicrobial therapy due to its high antimicrobial resistance. Nutraceuticals have gained a lot of interest and their incorporation into nanoparticles further improves their efficacy. This study aimed to evaluate the antibacterial activity of linalool-based lipid nanocapsules loaded with resveratrol (LIN-LNC-RES) as a synergistic strategy against MRSA. LIN-LNC-RES were prepared by the phase inversion temperature method and characterized for their colloidal properties, in vitro release, and stability. The antibacterial and antibiofilm activity against S. aureus and different MRSA clinical isolates were investigated. Furthermore, scanning electron microscopy (SEM) imaging for visualization of biofilm formation and bacterial membrane integrity as well as mechanistic investigation using quantitative real-time polymerase chain reaction (qRT-PCR) analysis were performed. LIN-LNCs-RES demonstrated favorable properties with a size of 35.19 ± 0.72 nm, PDI of 0.09 ± 0.02 and a zeta potential of -2.53 ± 0.07 mV with RES 98% EE. They showed a controlled release of RES over 24 h and were stable at 4 °C for 3 months. Compared to free drug, LIN-LNC-RES showed a 4-fold decrease in MIC values and 10-fold decrease in half maximal biofilm inhibitory concentration value. Biofilm eradication assay showed superiority of LIN-LNC-RES over RES against all isolates with disrupted bacterial membranes as revealed by SEM. Mechanistically, qRT-PCR showed that LIN-LNC-RES significantly reduced RNAIII gene expression as well as the expression of SaeRS two component system, potentially affecting quorum sensing and virulence factors expression. RES-loaded LIN-based nanosystem offers a great potential for combating MRSA infections, neutralizing its virulence activity hence, overcoming antimicrobial resistance.

Regulatory roles of an sRNA derived from the 5´ UTR and sequence internal to lapA in Pseudomonas aeruginosa PAO1

Several key virulence factors of Pseudomonas aeruginosa are regulated by quorum-sensing systems, small noncoding RNAs (sRNAs), and environmental stress, leading to a high mortality rate. Our previous studies indicated that the alkaline phosphatase LapA regulated P. aeruginosa PAO1 biofilm formation in a chronic wound model established with ex vivo porcine skin explants. Notably, one particular sRNA located upstream of the lapA gene was highly expressed in the model. Therefore, the sRNA was further characterized via northern blotting and rapid amplification of cDNA ends. The results revealed that the sRNA we named LapS is 197 nucleotides in length and is derived from the 5´ UTR and sequence internal to the lapA gene. Next, LapS mutation, overexpression, and complementation strains were constructed from the PAO1 strain, and phenotypic experiments associated with lapA were performed and compared with those of the ΔlapA and wild-type strains. The results indicated that LapS is involved in regulating swarming motility, rhamnolipid and alkaline phosphatase production, las/rhl quorum-sensing systems, and biofilm formation by controlling the level of lapA mRNA under phosphate-depleted conditions. Therefore, this LapS-lapA signaling cascade is beneficial for balancing the virulence regulation of P. aeruginosa. Additionally, an in vitro study indicated that LapS directly and post-transcriptionally regulated at least one unlinked gene, putA, which encodes bifunctional proline dehydrogenase, a virulence factor of P. aeruginosa. Collectively, our findings reveal a previously unstudied regulatory sRNA and advance the understanding of the roles of sRNAs in the pathogenicity of P. aeruginosa.

IMPORTANCE

Pseudomonas aeruginosa is a common nosocomial pathogen that contains hundreds of virulence factors regulated by quorum-sensing systems and environmental stress. Small noncoding RNAs (sRNAs) involved in virulence regulation have been identified in P. aeruginosa. Recently, several potential sRNAs were identified in P. aeruginosa using transcriptome sequencing. However, some of these novel sRNAs have been functionally characterized. In this study, a previously uncharacterized sRNA, LapS, in P. aeruginosa PAO1 was identified as a novel sRNA. LapS is involved in regulating swarming motility, rhamnolipid production, and alkaline phosphatase production during phosphate-depleted stress by controlling the level of lapA mRNA. Furthermore, LapS deletion also reduced the mortality rate of Caenorhabditis elegans in a fast-kill assay. Additionally, LapS directly suppressed PutA, a virulence factor of P. aeruginosa. This study highlights the role of LapS in modulating P. aeruginosa virulence during phosphate-depleted stress.

Deciphering the inhibitory mechanisms of cinnamaldehyde on biofilm formation of Listeria monocytogenes and implement these strategies to control its transfer to beef surfaces

Natural essential oils have received widespread attention as promising microbial inhibitors, whereas a comprehensive understanding of their mechanisms underlying biofilm control and impact on biofilm cross-contamination on meat remains poorly understood. In this study, Listeria monocytogenes (Lm) biofilms were treated with sub-inhibitory concentrations of cinnamaldehyde (CA) and characterized over a 4-day period. Both 1/2 MIC (160 μg/mL) and 1/4 MIC (80 μg/mL) CA delayed the development of Lm biofilm on abiotic surfaces and reduced the maximum biofilm formation. The limited effect of 1/4 MIC CA on the flagellar-mediated motility of Lm during initial adhesion indicated that hindering bacterial motility was not the main reason for CA inhibition of biofilm formation. Transcriptomics results showed that CA was involved in inhibitory pathways dominated by energy metabolism and peptidoglycan synthesis during the initial adhesion period and the maturation period of the biofilm, respectively. This posed an obstacle to the polymers required for biofilm cell adhesion and the energy consumption required for their production. Down-regulation of genes associated with multiple signalling systems and virulence factors also suggested that CA further mitigated resistance and virulence in residual biofilm cells. In addition, quantification of biofilm cells transferred to beef surfaces confirmed that CA significantly reduces the biomass transferred and the risk of persistent biofilm contamination. This study provided the theoretical basis for the control of Lm biofilm and its cross-contamination in the food industry by natural essential oils.

Enhanced antimicrobial, anti-biofilm, and efflux pump inhibitory effects of ursolic acid-conjugated magnetic nanoparticles against clinical isolates of multidrug-resistant Pseudomonas aeruginosa

OBJECTIVES

In the present study, we investigate the effect of Fe3O4 nanoparticles conjugated with ursolic acid (Fe3O4NPs@UA) on inhibiting the growth, biofilm-forming ability and efflux pump activity in clinical isolates of Pseudomonas aeruginosa with multiple drug resistance.

METHODS

Iron oxide NPs conjugated with ursolic acid (Fe3O4NPs@UA) were synthesized. Physicochemical features of the NPs were studied by FT-IR, XRD, EDAX, and TEM. The antibacterial and antibiofilm effects of Fe3O4NPs@UA against P. aeruginosa isolates were determined by broth microdilution and microtiter plate methods, respectively. The efflux pump inhibitory effect of Fe3O4NPs@UA was determined using Cartwheel method and through determining the expression level of efflux pump genes, including mexA and oprD in selected P. aeruginosa isolates treated with sub-MIC concentration of Fe3O4NPs@UA by real-time PCR.

RESULTS

In investigating the antimicrobial effect of Fe3O4NPs@UA, the MIC of these nanoparticles varied between 0.19 and 0.78 mg/mL and in the study of the anti-biofilm effect of Fe3O4NPs@UA, it caused a 68-75 % decrease in biofilm formation compared to the control. Moreover, in the Cartwheel test, the anti-efflux effect of these nanoparticles was confirmed at 1/4-MIC concentrations, and the expression of mexA and oprD genes was reduced in bacteria treated with Fe3O4NPs@UA compared to the control.

CONCLUSION

According to the results, the use of Fe3O4NPs@UA can provide a basis for the development of new treatments against drug-resistant bacteria in P. aeruginosa. This substance can improve the concentration of antibiotics in bacterial cells and increase their effectiveness by inhibiting the efflux in P. aeruginosa isolates.

Anti-biofilm mechanisms of action of essential oils by targeting genes involved in quorum sensing, motility, adhesion, and virulence: A review

Biofilms are a critical factor for food safety, causing important economic losses. Among the novel strategies for controlling biofilms, essential oils (EOs) can represent an environmentally friendly approach, able to act both on early and mature stages of biofilm formation. This review reports the anti-biofilm mechanisms of action of EOs against five pathogenic bacterial species known for their biofilm-forming ability. These mechanisms include disturbing the expression of genes related to quorum sensing (QS), motility, adhesion, and virulence. Biofilms and QS are interconnected processes, and EOs interfere with the communication system (e.g. regulating the expression of agrBDCA, luxR, luxS, and pqsA genes), thus influencing biofilm formation. In addition, QS is an important mechanism that regulates gene expression related to bacterial survival, virulence, and pathogenicity. Similarly, EOs also influence the expression of many virulence genes. Moreover, EOs exert their effects modulating the genes associated with bacterial adhesion and motility, for example those involved in curli (csg), fimbriae (fim, lpf), and flagella (fla, fli, flh, and mot) production, as well as the ica genes responsible for synthetizing polysaccharide intercellular adhesin. This review provides a comprehensive framework on the topic for a better understanding of EOs biofilm mechanisms of action.

Natural compounds in the fight against Staphylococcus aureus biofilms: a review of antibiofilm strategies

Staphylococcus aureus is an important pathogen due to its ability to form strong biofilms and antibiotic resistance. Biofilms play an important role in bacterial survival against the host immune system and antibiotics. Natural compounds (NCs) have diverse bioactive properties with a low probability of resistance, making them promising candidates for biofilm control. NC such as curcumin, cinnamaldehyde, carvacrol, eugenol, thymol, citral, linalool, 1,8-cineole, pinene, cymene, terpineol, quercetin, and limonene have been widely utilized for the inhibition and destruction of S. aureus biofilms. NCs influence biofilm formation through several procedures. Some of the antibiofilm mechanisms of NCs are direct bactericidal effect, disrupting the quorum sensing system, preventing bacteria from aggregation and attachment to surfaces, reducing the microbial surface components recognizing adhesive matrix molecules (MSCRAMMs), interfering with sortase A enzyme, and altering the expression of biofilm-associated genes such as icaADBC, agr, and sarA. Furthermore, these compounds affect extracellular polymeric substances (EPS) and their components, such as polysaccharide intercellular adhesin (PIA) and eDNA. However, some disadvantages, such as low water solubility and bioavailability, limit their clinical usage. Therefore, scientists have considered using nanotechnology and drug platforms to improve NC's efficacy. Some NC, such as thymol and curcumin, can also enhance photodynamic therapy against S. aurous biofilm community. This article evaluates the anti-biofilm potential of NC, their mechanisms of action against S. aureus biofilms, and various aspects of their application.

Revealing sRNA expression profiles of NDM-5-producing CRKP and explore the role of sRNA207 in NDM-5-producing CRKP resistance

New Delhi metallo-beta-lactamase-5 (NDM-5)-producing carbapenem-resistant Klebsiella pneumoniae (CRKP) is characterized by high virulence, high morbidity, and mortality, and the detection rate in children has increased in recent years. Therefore, it is urgent to develop new therapeutic targets and strategies. Non-coding small RNA (sRNA)-mediated RNA-based therapies offer a new direction for the treatment of bacterial infections, especially resistant bacteria. This study first analyzed the transcriptional expression profiles of NDM-5-producing CRKP and Carbapenem-susceptible Klebsiella pneumoniae (CSKP) isolates from the clinic by RNA-seq. A total of 4,623 genes were obtained, of which 307 genes were differentially expressed in NDM-5-producing CRKP, and these differentially expressed genes are mainly related to metabolism. Then, by analyzing the length and secondary structure of genes that could not match the reference gene and non-redundant protein database, we obtained 268 sRNAs, of which 13 sRNAs were differentially expressed in NDM-5-producing CRKP. After the expression level of differentially expressed sRNA was verified by RT-PCR to be consistent with that of RNA-seq, we chose sRNA207 as our research target. By knockdown of sRNA207 and smf-1 (the predicted target mRNA of sRNA207) in the strain, we found that increased expression of sRNA207 promoted biofilm formation by stabilizing expression of smf-1, which in turn affected the resistance of NDM-5-producing CRKP to carbapenems. This provides a new approach to treat CRKP infection.

IMPORTANCE

sRNAs form a regulatory network that regulates bacterial virulence, drug resistance, and other functions by targeting mRNAs. However, sRNA expression profile and function of NDM-5-producing carbapenem-resistant Klebsiella pneumoniae (CRKP) are still unknown. In this study, we analyzed the sRNA expression profiles of NDM-5-producing CRKP obtained from clinical by referring to the methods of previous articles. A total of 268 candidates sRNAs were obtained, of which 248 were newly discovered. More importantly, 13 sRNAs were differentially expressed in NDM-5-producing CRKP compared with CSKP. We knocked down sRNA207 in NDM-5-producing CRKP to validate its effect on smf-1, biofilm, and resistance of strains. We also confirmed the role of smf-1 in biofilm formation and drug resistance of NDM-5-producing CRKP by constructing smf-1-knockdown strain. The results suggest that smf-1 is the target gene of sRNA207. Increased expression of sRNA207 in NDM-5-producing CRKP stabilizes smf-1 expression, which in turn affects the resistance of the strains through biofilm formation.

Recent advances in the use of resveratrol against Staphylococcus aureus infections (Review)

As a notorious bacterial pathogen, Staphylococcus aureus (S. aureus) can readily induce infections in the community and hospital, causing significant morbidity and mortality. With the extensive rise of multiple resistance, conventional antibiotic therapy has rapidly become ineffective for related infections. Resveratrol is a naturally occurring polyphenolic substance that has been demonstrated to have effective antimicrobial activity against S. aureus. Resveratrol at sub-inhibitory doses can suppress the expression of virulence factors, contributing to attenuated biofilm formation, interference with quorum sensing and the inhibition of the production of toxins. As a promising efflux pump inhibitor, resveratrol enhances antibiotic susceptibility to a certain extent. In conjunction with conventional antibiotics, resveratrol displays unique synergistic effects with norfloxacin and aminoglycoside on S. aureus, yet antagonizes the lethal effects of daptomycin, oxacillin, moxifloxacin and levofloxacin. Nevertheless, given the low oral bioavailability of resveratrol, advanced formulations need to be developed to delay the rapid metabolism conversion to low or inactive conjugates. The present review discusses the antibacterial properties of resveratrol against S. aureus, in an aim to provide in-depth insight for researchers to address the challenges of antimicrobial resistance.

Suppression of virulence factors of uropathogenic Escherichia coli by Trans-resveratrol and design of nanoemulgel

BACKGROUND

Development of multidrug resistance in Uropathogenic Escherichia coli (UPEC) makes treatment of Urinary Tract Infections (UTIs) a major challenge. This study was conducted to investigate the effect of trans-resveratrol (t-RSV) at a subinhibitory concentration (sub-MIC-t-RSV) on phenotypic and genotypic expression of virulence factors of clinical isolates of UPEC and develop a nanoformulation of t-RSV. Fifty-five clinical UPEC strains were investigated for the presence of virulence factors by phenotypic methods and PCR detection of virulence genes. The effect of sub-MIC-t-RSV was studied on the phenotypic and genotypic expression of virulence factors. t-RSV-loaded nanoemulgel formulation was prepared and characterized.

RESULTS

Out of the 55 tested isolates, 50.9% were biofilm producers, 23.6% showed both mannose-sensitive and mannose-resistant hemagglutination, 21.8% were serum-resistant, 18.2% were hemolysin producers, while 36.4% showed cytotoxic effect on HEp-2 cells. A total of 25.5% of the isolates harbor one or more of hly-A, cnf-1 and papC genes, while 54.5% were positive for one or more of fimH, iss and BssS genes. A concentration of 100 µg/mL of t-RSV effectively downregulates the phenotypic and genotypic expression of the virulence factors in positive isolates. A stable t-RSV-nanaoemulgel with droplet size of 180.3 nm and Zetapotential of -46.9 mV was obtained.

CONCLUSION

The study proves the effective role of t-RSV as an antivirulence agent against clinical UPEC isolates in vitro and develops a stable t-RSV-nanoemulgel formulation to be assessed in vivo. The promising antibacterial and antivirulence properties of t-RSV place this natural compound to be a better alternative in the treatment of persistent UTIs.

Green-synthesized silver nanoparticles from Zataria multiflora as a promising strategy to target quorum sensing and biofilms in Pseudomonas aeruginosa

The global challenge to human health is significantly heightened by the resistance of harmful bacteria to antimicrobial treatments. Given the limited advancement in developing new antimicrobial medications, exploring innovative strategies is imperative to tackle the challenge of resistance to multiple drugs. Furthermore, there is a growing emphasis on the environmentally friendly synthesis of nanoparticles with potent medicinal attributes, specifically those targeting virulence, to combat the rise of multidrug resistance. Focusing on the inhibition of virulence factors and biofilms influenced by quorum sensing has become a promising and novel strategy in the development of anti-infective drugs. An aqueous extract of Zataria multiflora leaves was used to create green-synthesized silver nanoparticles, or AgNPs. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and UV-visible absorption spectroscopy were used to characterize the AgNPs. The impact of AgNPs on the virulence factors and biofilms of Pseudomonas aeruginosa PAO1, mediated by quorum sensing, was assessed at concentrations below the minimum inhibitory concentration (sub-MIC). Sub-MIC concentrations of Green-synthesized AgNPs inhibited various P. aeruginosa virulence factors, including bacterial motility (89 % inhibition), pyocyanin production (81.48 % inhibition), pyoverdin production (55.80 % inhibition), elastase activity (87.43 % inhibition), exoprotease activity (75.60 % inhibition), and rhamnolipid production (71.28 % inhibition). Additionally, these AgNPs demonstrated 80 % inhibition of P. aeruginosa biofilms. The in vitro efficacy of green-synthesized AgNPs against P. aeruginosa can be utilized for the creation of alternative therapeutic agents for managing bacterial infections, particularly for topical application in cases such as wound infections. Additionally, they can be used for surface coating to inhibit the attachment of bacteria to medical devices.

Antimicrobial efficiency and cytocompatibility of resveratrol and naringin as chemical decontaminants on SLA surface

Bacterial biofilms are the major etiology agent of peri-implant disease. Chemical decontamination is a promising treatment strategy against bacterial biofilms; however, its applications are limited by its low efficiency and poor biocompatibility. In contrast to three conventional cleaners (sterile saline, hydrogen peroxide, and chlorhexidine), this study used resveratrol and naringin solutions to remove mature Staphylococcus aureus and Porphyromonas gingivalis biofilm on sandblasted (with large grit and acid-etched (SLA) titanium surface. To determine changes in surface characteristics, the surface wettability and roughness were measured, and micromorphology was observed by scanning electron microscopy. With crystal violet (CV) and live/dead bacterial staining, residual plaque quantity and composition were measured. The biocompatibility was tested using pH and cytotoxicity, as well as by osteoblasts (MC3T3-E1) adhesion, proliferation, and differentiation, and fibroblasts (L-929) proliferation were also analyzed. It was found that resveratrol and naringin solutions were more effective in restoring surface characteristics and also showed that less plaque and viable bacteria were left. Naringin removed S. aureus biofilms better than chlorhexidine. Alkaline resveratrol and naringin solutions increased cell adhesion, proliferation, and osteogenic differentiation without any cytotoxicity. Resveratrol increased the expression of mRNA and protein associated with osteogenesis. In conclusion, resveratrol and naringin effectively restored SLA titanium surface characteristics and decontaminated the biofilm with good biocompatibility, suggesting their therapeutic potential as chemical decontaminants.

IMPORTANCE

Bacterial biofilms are considered the primary etiology of peri-implant disease. Physical cleaning is the most common way to remove bacterial biofilm, but it can cause grooving, melting, and deposition of chemicals that alter the surface of implants, which may hamper biocompatibility and re-osseointegration. Chemical decontamination is one of the most promising treatments but is limited by low efficiency and poor biocompatibility. Our study aims to develop safer, more effective chemical decontaminants for peri-implant disease prevention and treatment. We focus on resveratrol and naringin, two natural compounds, which have shown to be more effective in decontaminating biofilms on dental implant surfaces and exerting better biocompatibility. This research is groundbreaking as it is the first exploration of natural plant extracts' impact on mature bacterial biofilms on rough titanium surfaces. By advancing this knowledge, we seek to contribute to more effective and biocompatible strategies for combating peri-implant diseases, enhancing oral health, and prolonging implant lifespan.

Biological potential, chemical profiling, and molecular docking study of Morus alba L. extracts

Morus alba L. is a plant with a long history of dietary and medicinal uses. We hypothesized that M. alba possesses a significant biological potential. In that sense, we aimed to generate the chemical, antimicrobial, toxicological, and molecular profile of M. alba leaf and fruit extracts. Our results showed that extracts were rich in vitamin C, phenols, and flavonoids, with quercetin and pterostilbene concentrated in the leaf, while fisetin, hesperidin, resveratrol, and luteolin were detected in fruit. Extracts exhibited antimicrobial activity against all tested bacteria, including multidrug-resistant strains. The widest inhibition zones were in Staphylococcus aureus ATCC 33591. The values of the minimum inhibitory concentration ranged from 15.62 μg/ml in Enterococcus faecalis to 500 μg/ml in several bacteria. Minimum bactericidal concentration ranged from 31.25 μg/ml to 1000 μg/ml. Extracts impacted the biofilm formation in a concentration-dependent and species-specific manner. A significant difference in the frequency of nucleoplasmic bridges between the methanolic extract of fruit (0.5 μg/ml, 1 μg/ml, 2 μg/ml), as well as for the frequency of micronuclei between ethanolic extract of leaf (2 μg/ml) and the control group was observed. Molecular docking suggested that hesperidin possesses the highest binding affinity for multidrug efflux transporter AcrB and acyl-PBP2a from MRSA, as well as for the SARS-CoV-2 Mpro. This study, by complementing previous research in this field, gives new insights that could be of great value in obtaining a more comprehensive picture of the Morus alba L. bioactive potential, chemical composition, antimicrobial and toxicological features, as well as molecular profile.

Gallic acid exerts antibiofilm activity by inhibiting methicillin-resistant Staphylococcus aureus adhesion

Methicillin-resistant Staphylococcus aureus (MRSA) is a serious threat to patients with nosocomial infections, and infection is strongly associated with biofilm formation. Gallic acid (GA) is a natural bioactive compound found in traditional Chinese medicines that exerts potent antimicrobial activity. However, the anti-MRSA biofilm efficacy of GA remained to be determined. This study investigated the antimicrobial activities of GA against MRSA and the mechanisms involved. The results revealed the significant antibacterial and antibiofilm activities of GA. The minimal inhibitory concentration of GA against MRSA was 32 μg/mL and a growth curve assay confirmed the significant inhibitory effect of GA on planktonic MRSA. Crystal violet and XTT assays showed that 8 µg/mL GA effectively inhibited the formation of new biofilms and disrupted existing biofilms by reducing both biofilm biomass and metabolic activities. Alkaline phosphatase and β-galactosidase leakage assays and live/dead staining provided evidence that GA disrupted the integrity of bacterial cell walls and membranes within the biofilm. Scanning electron microscopy observations showed that GA significantly inhibited bacterial adhesion and aggregation, affecting the overall structure of the biofilm. Bacterial adhesion, polysaccharide intercellular adhesion (PIA) production and real-time quantitative PCR assay confirmed that GA inhibited bacterial adhesion, PIA synthesis, and the expression of icaAD and sarA. These results suggested that GA inhibited biofilm formation by inhibiting the expression of sarA, then downregulating the expression of icaA and icaD, thereby reducing the synthesis of PIA to attenuate the adhesion capacity of MRSA. GA is therefore a promising candidate for development as a pharmaceutical agent for the prevention and treatment of bacterial infections caused by MRSA.

1H-Pyrrole-2,5-dicarboxylic acid, a quorum sensing inhibitor from one endophytic fungus in Areca catechu L., acts as antibiotic accelerant against Pseudomonas aeruginosa

Pseudomonas aeruginosa has already been stipulated as a "critical" pathogen, emphasizing the urgent need for researching and developing novel antibacterial agents due to multidrug resistance. Bacterial biofilm formation facilitates cystic fibrosis development and restricts the antibacterial potential of many current antibiotics. The capacity of P. aeruginosa to form biofilms and resist antibiotics is closely correlated with quorum sensing (QS). Bacterial QS is being contemplated as a promising target for developing novel antibacterial agents. QS inhibitors are a promising strategy for treating chronic infections. This study reported that the active compound PT22 (1H-pyrrole-2,5-dicarboxylic acid) isolated from Perenniporia tephropora FF2, one endophytic fungus from Areca catechu L., presents QS inhibitory activity against P. aeruginosa. Combined with gentamycin or piperacillin, PT22 functions as a novel antibiotic accelerant against P. aeruginosa. PT22 (0.50 mg/mL, 0.75 mg/mL, and 1.00 mg/mL) reduces the production of QS-related virulence factors, such as pyocyanin and rhamnolipid, and inhibits biofilm formation of P. aeruginosa PAO1 instead of affecting its growth. The architectural disruption of the biofilms was confirmed by visualization through scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Real-time quantitative PCR (RT-qPCR) indicated that PT22 significantly attenuated the expression of QS-related genes followed by docking analysis of molecules against QS activator proteins. PT22 dramatically increased the survival rate of Galleria mellonella. PT22 combined with gentamycin or piperacillin presents significant inhibition of biofilm formation and eradication of mature biofilm compared to monotherapy, which was also confirmed by visualization through SEM and CLSM. After being treated with PT22 combined with gentamycin or piperacillin, the survival rates of G. mellonella were significantly increased compared to those of monotherapy. PT22 significantly enhanced the susceptibility of gentamycin and piperacillin against P. aeruginosa PAO1. Our results suggest that PT22 from P. tephropora FF2 as a potent QS inhibitor is a candidate antibiotic accelerant to combat the antibiotic resistance of P. aeruginosa.

Molecular mechanisms of DNase inhibition of early biofilm formation Pseudomonas aeruginosa or Staphylococcus aureus: A transcriptome analysis

In vitro studies show that DNase can inhibit Pseudomonas aeruginosa and Staphylococcus aureus biofilm formation. However, the underlying molecular mechanisms remain poorly understood. This study used an RNA-sequencing transcriptomic approach to investigate the mechanism by which DNase I inhibits early P. aeruginosa and S. aureus biofilm formation on a transcriptional level, respectively. A total of 1171 differentially expressed genes (DEGs) in P. aeruginosa and 1016 DEGs in S. aureus enriched in a variety of biological processes and pathways were identified, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses revealed that the DEGs were primarily involved in P. aeruginosa two-component system, biofilm formation, and flagellar assembly and in S. aureus biosynthesis of secondary metabolites, microbial metabolism in diverse environments, and biosynthesis of amino acids, respectively. The transcriptional data were validated using quantitative real-time polymerase chain reaction (RT-qPCR), and the expression profiles of 22 major genes remained consistent. These findings suggested that DNase I may inhibit early biofilm formation by downregulating the expression of P. aeruginosa genes associated with flagellar assembly and the type VI secretion system, and by downregulating S. aureus capsular polysaccharide and amino acids metabolism gene expression, respectively. This study offers insights into the mechanisms of DNase treatment-based inhibition of early P. aeruginosa and S. aureus biofilm formation.

Staphylococcus aureus biofilm: Formulation, regulatory, and emerging natural products-derived therapeutics

Staphylococcus aureus can readily form biofilm which enhances the drug-resistance, resulting in life-threatening infections involving different organs. Biofilm formation occurs due to a series of developmental events including bacterial adhesion, aggregation, biofilm maturation, and dispersion, which are controlled by multiple regulatory systems. Rapidly increasing research and development outcomes on natural products targeting S. aureus biofilm formation and/or regulation led to an emergent application of active phytochemicals and combinations. This review aimed at providing an in-depth understanding of biofilm formation and regulation mechanisms for S. aureus, outlining the most important antibiofilm strategies and potential targets of natural products, and summarizing the latest progress in combating S. aureus biofilm with plant-derived natural products. These findings provided further evidence for novel antibiofilm drugs research and clinical therapies.

Effect of baicalin on eradicating biofilms of bovine milk derived Acinetobacter lwoffii

BACKGROUND

Acinetobacter lwoffii (A.lwoffii) is a serious zoonotic pathogen that has been identified as a cause of infections such as meningitis, bacteremia and pneumonia. In recent years, the infection rate and detection rate of A.lwoffii is increasing, especially in the breeding industry. Due to the presence of biofilms, it is difficult to eradicate and has become a potential super drug-resistant bacteria. Therefore, eradication of preformed biofilm is an alternative therapeutic action to control A.lwoffii infection. The present study aimed to clarify that baicalin could eradicate A.lwoffii biofilm in dairy cows, and to explore the mechanism of baicalin eradicating A.lwoffii.

RESULTS

The results showed that compared to the control group, the 4 MIC of baicalin significantly eradicated the preformed biofilm, and the effect was stable at this concentration, the number of viable bacteria in the biofilm was decreased by 0.67 Log10CFU/mL. The total fluorescence intensity of biofilm bacteria decreased significantly, with a reduction rate of 67.0%. There were 833 differentially expressed genes (367 up-regulated and 466 down-regulated), whose functions mainly focused on oxidative phosphorylation, biofilm regulation system and trehalose synthesis. Molecular docking analysis predicted 11 groups of target proteins that were well combined with baicalin, and the content of trehalose decreased significantly after the biofilm of A.lwoffii was treated with baicalin.

CONCLUSIONS

The present study evaluated the antibiofilm potential of baicalin against A.lwoffii. Baicalin revealed strong antibiofilm potential against A.lwoffii. Baicalin induced biofilm eradication may be related to oxidative phosphorylation and TCSs. Moreover, the decrease of trehalose content may be related to biofilm eradication.

Plant-derived virulence arresting drugs as novel antimicrobial agents: Discovery, perspective, and challenges in clinical use

Antimicrobial resistance (AMR) emerges as a severe crisis to public health and requires global action. The occurrence of bacterial pathogens with multi-drug resistance appeals to exploring alternative therapeutic strategies. Antivirulence treatment has been a positive substitute in seeking to circumvent AMR, which aims to target virulence factors directly to combat bacterial infections. Accumulated evidence suggests that plant-derived natural products, which have been utilized to treat infectious diseases for centuries, can be abundant sources for screening potential virulence-arresting drugs (VADs) to develop advanced therapeutics for infectious diseases. This review sums up some virulence factors and their actions in various species of bacteria, as well as recent advances pertaining to plant-derived natural products as VAD candidates. Furthermore, we also discuss natural VAD-related clinical trials and patents, the perspective of VAD-based advanced therapeutics for infectious diseases and critical challenges hampering clinical use of VADs, and genomics-guided identification for VAD therapeutic. These newly discovered natural VADs will be encouraging and optimistic candidates that may sustainably combat AMR.

Resveratrol and Resveratrol-Loaded Galactosylated Liposomes: Anti-Adherence and Cell Wall Damage Effects on Staphylococcus aureus and MRSA

Antibiotic resistance due to bacterial biofilm formation is a major global health concern that makes the search for new therapeutic approaches an urgent need. In this context,, trans-resveratrol (RSV), a polyphenolic natural substance, seems to be a good candidate for preventing and eradicating biofilm-associated infections but its mechanism of action is poorly understood. In addition, RSV suffers from low bioavailability and chemical instability in the biological media that make its encapsulation in delivery systems necessary. In this work, the anti-biofilm activity of free RSV was investigated on Staphylococcus aureus and, to highlight the possible mechanism of action, we studied the anti-adherence activity and also the cell wall damage on a MRSA strain. Free RSV activity was compared to that of RSV loaded in liposomes, specifically neutral liposomes (L = DOPC/Cholesterol) and cationic liposomes (LG = DOPC/Chol/GLT1) characterized by a galactosylated amphiphile (GLT1) that promotes the interaction with bacteria. The results indicate that RSV loaded in LG has anti-adherence and anti-biofilm activity higher than free RSV. On the other side, free RSV has a higher bacterial-growth-inhibiting effect than encapsulated RSV and it can damage cell walls by creating pores; however, this effect can not prevent bacteria from growing again. This RSV ability may underlie its bacteriostatic activity.

Alkaline phosphatase LapA regulates quorum sensing-mediated virulence and biofilm formation in Pseudomonas aeruginosa PAO1 under phosphate depletion stress

IMPORTANCE

Our previous study demonstrated that the expression of lapA was induced under phosphate depletion conditions, but its roles in virulence and biofilm formation by Pseudomonas aeruginosa remain largely unknown. This study presents a systematic investigation of the roles of lapA in virulence induction and biofilm formation by constructing a lapA-deficient strain with P. aeruginosa PAO1. The results showed that deletion of the lapA gene evidently reduced elastase activity, swimming motility, C4-HSL, and 3-oxo-C12-HSL production, and increased rhamnolipid production under phosphate depletion stress. Moreover, lapA gene deletion inhibited PAO1 biofilm formation in porcine skin explants by reducing the expression levels of las and rhl quorum sensing systems and extracellular polymeric substance synthesis. Finally, lapA gene deletion also reduced the virulence of PAO1 in Caenorhabditis elegans in fast-kill and slow-kill infection assays. This study provides insights into the roles of lapA in modulating P. aeruginosa virulence and biofilm formation under phosphate depletion stress.

Antibacterial and antibiofilm activity of Abroma augusta stabilized silver (Ag) nanoparticles against drug-resistant clinical pathogens

Infectious diseases remain among the most pressing concerns for human health. This issue has grown even more complex with the emergence of multidrug-resistant (MDR) bacteria. To address bacterial infections, nanoparticles have emerged as a promising avenue, offering the potential to target bacteria at multiple levels and effectively eliminate them. In this study, silver nanoparticles (AA-AgNPs) were synthesized using the leaf extract of a medicinal plant, Abroma augusta. The synthesis method is straightforward, safe, cost-effective, and environment friendly, utilizing the leaf extract of this Ayurvedic herb. The UV-vis absorbance peak at 424 nm indicated the formation of AA-AgNPs, with the involvement of numerous functional groups in the synthesis and stabilization of the particles. AA-AgNPs exhibited robust antibacterial and antibiofilm activities against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE). The MIC values of AA-AgNPs ranged from 8 to 32 μg/mL. Electron microscopic examination of the interaction of AA-AgNPs with the test bacterial pathogens showed a deleterious impact on bacterial morphology, resulting from membrane rupture and leakage of intracellular components. AA-AgNPs also demonstrated a dose-dependent effect in curtailing biofilm formation below inhibitory doses. Overall, this study highlights the potential of AA-AgNPs in the successful inhibition of both the growth and biofilms of MRSA and VRE bacteria. Following studies on toxicity and dose optimization, such AgNPs could be developed into effective medical remedies against infections.

Synthesis and Antibacterial Activity of Polyalthic Acid Analogs

Polyalthic acid (PA) is a diterpene found in copaiba oil. As a continuation of our work with PA, we synthesized PA analogs and investigated their antibacterial effects on preformed biofilms of Staphylococcus epidermidis and determined the minimal inhibitory concentration (MIC) of the best analogs against planktonic bacterial cells. There was no difference in activity between the amides 2a and 2b and their corresponding amines 3a and 3b regarding their ability to eradicate biofilm. PA analogs 2a and 3a were able to significantly eradicate the preformed biofilm of S. epidermidis and were active against all the Gram-positive bacteria tested (Enterococcus faecalis, Enterococcus faecium, S. epidermidis, Staphylococcus aureus), with different MIC depending on the microorganism. Therefore, PA analogs 2a and 3a are of interest for further in vitro and in vivo testing to develop formulations for antibiotic drugs against Gram-positive bacteria.

What’s old is new again: Insights into diabetic foot microbiome

Diabetes is a chronic disease that is considered one of the most stubborn global health problems that continues to defy the efforts of scientists and physicians. The prevalence of diabetes in the global population continues to grow to alarming levels year after year, causing an increase in the incidence of diabetes complications and health care costs all over the world. One major complication of diabetes is the high susceptibility to infections especially in the lower limbs due to the immunocompromised state of diabetic patients, which is considered a definitive factor in all cases. Diabetic foot infections continue to be one of the most common infections in diabetic patients that are associated with a high risk of serious complications such as bone infection, limb amputations, and life-threatening systemic infections. In this review, we discussed the circumstances associated with the high risk of infection in diabetic patients as well as some of the most commonly isolated pathogens from diabetic foot infections and the related virulence behavior. In addition, we shed light on the different treatment strategies that aim at eradicating the infection.

Antimicrobial, Antibiofilm Activities and Synergic Effect of Triterpene 3β,6β,16β-trihydroxyilup-20(29)-ene Isolated from Combretum leprosum Leaves Against Staphylococcus Strains

Antimicrobial resistance is a natural phenomenon and is becoming a huge global public health problem, since some microorganisms not respond to the treatment of several classes of antibiotics. The objective of the present study was to evaluate the antibacterial, antibiofilm, and synergistic effect of triterpene 3β,6β,16β-trihydroxyilup-20(29)-ene (CLF1) against Staphylococcus aureus and Staphylococcus epidermidis strains. Bacterial susceptibility to CLF1 was evaluated by minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) assay. In addition, the effect combined with antibiotics (ampicillin and tetracycline) was verified by the checkerboard method. The biofilms susceptibility was assessed by enumeration of colony-forming units (CFUs) and quantification of total biomass by crystal violet staining. The compound showed bacteriostatic and bactericidal activity against all Staphylococcal strains tested. The synergistic effect with ampicillin was observed only for S. epidermidis strains. Moreover, CLF1 significantly inhibited the biofilm formation and disrupted preformed biofilm of the all strains. Scanning electron microscopy (SEM) images showed changes in the cell morphology and structure of S. aureus ATCC 700698 biofilms (a methicillin-resistant S. aureus strain). Molecular docking simulations showed that CLF1 has a more favorable interaction energy than the antibiotic ampicillin on penicillin-binding protein (PBP) 2a of MRSA, coupled in different regions of the protein. Based on the results obtained, CLF1 proved to be a promising antimicrobial compound against Staphylococcus biofilms.

In Vitro Antibiofilm Activity of Resveratrol against Aeromonas hydrophila

Aeromonas hydrophila is a Gram-negative bacterium that widely exists in various aquatic environments and causes septicemia in fish and humans. Resveratrol, a natural polyterpenoid product, has potential chemo-preventive and antibacterial properties. In this study, we investigated the effect of resveratrol on A. hydrophila biofilm formation and motility. The results demonstrated that resveratrol, at sub-MIC levels, can significantly inhibit the biofilm formation of A. hydrophila, and the biofilm was decreased with increasing concentrations. The motility assay showed that resveratrol could diminish the swimming and swarming motility of A. hydrophila. Transcriptome analyses (RNA-seq) showed that A. hydrophila treated with 50 and 100 μg/mL resveratrol, respectively, presented 230 and 308 differentially expressed genes (DEGs), including 90 or 130 upregulated genes and 130 or 178 downregulated genes. Among them, genes related to flagellar, type IV pilus and chemotaxis were significantly repressed. In addition, mRNA of virulence factors OmpA, extracellular proteases, lipases and T6SS were dramatically suppressed. Further analysis revealed that the major DEGs involved in flagellar assembly and bacterial chemotaxis pathways could be regulated by cyclic-di-guanosine monophosphate (c-di-GMP)- and LysR-Type transcriptional regulator (LTTR)-dependent quorum sensing (QS) systems. Overall, our results indicate that resveratrol can inhibit A. hydrophila biofilm formation by disturbing motility and QS systems, and can be used as a promising candidate drug against motile Aeromonad septicemia.

Deciphering the antibiofilm potential of 2-Phenylethyl methyl ether (PEME), a bioactive compound of Kewda essential oil against Staphylococcus aureus

Opportunistic pathogenic bacteria and their pathogenicity linked with biofilm infections become a severe issue as they resist the actions of multiple antimicrobial drugs. Naturally derived drugs having antibiofilm properties are more effective than chemically synthesized drugs. The plant derived essential oils are a rich source of phytoconstituents with widespread pharmacological values. In the present investigation, a major phytoconstituent, 2-Phenyl Ethyl Methyl Ether (PEME) of Kewda essential oil extracted from the flowers of Pandanus odorifer was explored for its prospective antimicrobial and anti-biofilm properties against ESKAPE pathogenic bacterial strain, Staphylococcus aureus and MTCC 740. The minimum inhibitory concentration (MIC) of PEME was found to be 50 mM against the tested bacterial strains. A gradual decrease in biofilm production was observed when PEME was treated with the sub-MIC concentration. The reduction in biofilm formation was noticeable from qualitative assay i.e., Congo Red Agar Assay (CRA) and further quantified by crystal violet staining assay. The decline in exopolysaccharides production was quantified, with the highest inhibition against MTCC 740 with a decrease of 71.76 ± 4.56% compared to untreated control. From the microscopic analysis (light and microscopic fluorescence method), PEME exhibited inhibitory effect on biofilm formation on the polystyrene surface. The In silico studies stated that PEME could invariably bind to biofilm associated target proteins. Further, transcriptomic data analysis suggested the role of PEME in the down-regulation of specific genes, agrA, sarA, norA and mepR, which are critically associated with bacterial virulence, biofilm dynamics and drug resistance patterns in S. aureus. Further, qRT-PCR analysis validated the role of PEME on biofilm inhibition by relative downregulation of agrA, sarA, norA and mepR genes. Further, advanced in silico methodologies could be employed in future investigations to validate its candidature as promising anti-biofilm agent.

Biofilm Lifestyle in Recurrent Urinary Tract Infections

Urinary tract infections (UTIs) represent one of the most common infections that are frequently encountered in health care facilities. One of the main mechanisms used by bacteria that allows them to survive hostile environments is biofilm formation. Biofilms are closed bacterial communities that offer protection and safe hiding, allowing bacteria to evade host defenses and hide from the reach of antibiotics. Inside biofilm communities, bacteria show an increased rate of horizontal gene transfer and exchange of resistance and virulence genes. Additionally, bacterial communication within the biofilm allows them to orchestrate the expression of virulence genes, which further cements the infestation and increases the invasiveness of the infection. These facts stress the necessity of continuously updating our information and understanding of the etiology, pathogenesis, and eradication methods of this growing public health concern. This review seeks to understand the role of biofilm formation in recurrent urinary tact infections by outlining the mechanisms underlying biofilm formation in different uropathogens, in addition to shedding light on some biofilm eradication strategies.

Phosphorylcholine-Based Contact Lenses for Sustained Release of Resveratrol: Design, Antioxidant and Antimicrobial Performances, and In Vivo Behavior

Design of advanced contact lenses (CLs) demands materials that are safe and comfortable for the wearers and that preserve the normal eye microbiota, avoiding chronic inflammation and biofilm development. This work aimed to combine the natural antibiofouling phosphorylcholine and the antioxidant and prebiotic resveratrol as integral components of CLs that may have the additional performance of preventing oxidative-stress related eye diseases. Different from previous uses of 2-methacryloyloxyethyl phosphorylcholine (MPC) as coating, we explored the feasibility of adding MPC at high proportions as a comonomer of 2-hydroxyethyl methacrylate (HEMA)-based hydrogels while still allowing for the loading of the hydrophobic resveratrol. Homogeneous distribution of MPC along the hydrogel depth (confirmed by Raman spectroscopy) notably increased solvent uptake and the proportion of free water while it decreased Young's modulus. Relevantly, MPC did not hinder the uptake of resveratrol by CLs (>10 mg/g), which indeed showed network/water partition coefficients of >100. Protocols for CLs sterilization and loading of resveratrol under aseptic conditions were implemented, and the effects of tear proteins on resveratrol release rate were investigated. CLs sustained resveratrol release for more than 24 h in vitro, and sorption of albumin onto the hydrogel, although attenuated by MPC, slowed down the release. The combination of MPC and resveratrol reduced P. aeruginosa and S. aureus growth as tested in a novel hydrogel disk-agar interface biofilm growth setup. The developed CLs showed excellent anti-inflammatory properties and biocompatibility in in ovo and rabbit tests and provided higher and more prolonged levels of resveratrol in tear fluid, which favored resveratrol biodistribution in anterior and posterior eye segments compared to eye drops. Correlations between the release profiles of resveratrol in vitro and in vivo were assessed. Relevantly, the CLs preserved the antioxidant properties of resveratrol during the entire 8 h of wearing. In sum, CLs prepared with high proportion in MPC may help address safety and comfort requirements while having drug releasing capabilities.

Recent advances on the regulation of bacterial biofilm formation by herbal medicines

Biofilm formation is a fundamental part of life cycles of bacteria which affects various aspects of bacterial-host interactions including the development of drug resistance and chronic infections. In clinical settings, biofilm-related infections are becoming increasingly difficult to treat due to tolerance to antibiotics. Bacterial biofilm formation is regulated by different external and internal factors, among which quorum sensing (QS) signals and nucleotide-based second messengers play important roles. In recent years, different kinds of anti-biofilm agents have been discovered, among which are the Chinese herbal medicines (CHMs). CHMs or traditional Chinese medicines have long been utilized to combat various diseases around the world and many of them have the ability to inhibit, impair or decrease bacterial biofilm formation either through regulation of bacterial QS system or nucleotide-based second messengers. In this review, we describe the research progresses of different chemical classes of CHMs on the regulation of bacterial biofilm formation. Though the molecular mechanisms on the regulation of bacterial biofilm formation by CHMs have not been fully understood and there are still a lot of work that need to be performed, these studies contribute to the development of effective biofilm inhibitors and will provide a novel treatment strategy to control biofilm-related infections.

Does Secondary Plant Metabolite Ursolic Acid Exhibit Antibacterial Activity against Uropathogenic Escherichia coli Living in Single- and Multispecies Biofilms?

Multispecies bacterial biofilms are the often cause of chronic recurrent urinary tract infections within the human population. Eradicating such a complex bacterial consortium with standard pharmacotherapy is often unsuccessful. Therefore, plant-derived compounds are currently being researched as an alternative strategy to antibiotic therapy for preventing bacterial biofilm formation and facilitating its eradication. Therefore, our research aimed to determine the effect of secondary plant metabolite ursolic acid (UA) on the growth and survival, the quantity of exopolysaccharides formed, metabolic activity, and morphology of uropathogenic Gram-negative rods living in single- and mixed-species biofilms at various stages of their development. Spectrophotometric methods were used for biofilm mass formation and metabolic activity determination. The survival of bacteria was established using the serial dilution assay. The decrease in survival and inhibition of biofilm creation, both single- and multispecies, as well as changes in the morphology of bacterial cells were noticed. As UA exhibited better activity against young biofilms, the use of UA-containing formulations, especially during the initial steps of urinary tract infection, seems to be reasonable. However, the future direction should be a thorough understanding of the mechanisms of UA activity as a bioactive substance.

Transcript Profiling of Nitroxoline-Treated Biofilms Shows Rapid Up-regulation of Iron Acquisition Gene Clusters

Bacterial biofilms are surface-attached communities of slow- or non-replicating cells embedded within a protective matrix of biomolecules. Unlike free-floating planktonic bacteria, biofilms are innately tolerant to conventional antibiotics and are prevalent in recurring and chronic infections. Nitroxoline, a broad-spectrum biofilm-eradicating agent, was used to probe biofilm viability. Transcript profiling (RNA-seq) showed that 452 of 2594 genes (17.4%) in methicillin-resistant Staphylococcus aureus (MRSA) biofilms were differentially expressed after a 2 h treatment of nitroxoline. WoPPER analysis and time-course validation (RT-qPCR) revealed that gene clusters involved in iron acquisition (sbn, isd, MW2101, MW0695, fhu, and feo) were rapidly up-regulated following nitroxoline treatment, which is indicative of iron starvation in MRSA biofilms. In addition, genes related to oligopeptide transporters and riboflavin biosynthesis were found to be up-regulated, while genes related to carotenoid biosynthesis and nitrate assimilation were down-regulated. RT-qPCR experiments revealed that iron uptake transcripts were also up-regulated in established Staphylococcus epidermidis and Acinetobacter baumannii biofilms following nitroxoline treatment. Overall, we show RNA-seq to be an ideal platform to define cellular pathways critical for biofilm survival, in addition to demonstrating the need these bacterial communities have for iron.

Actinomycin D: a novel Pseudomonas aeruginosa quorum sensing inhibitor from the endophyte Streptomyces cyaneochromogenes RC1

The infections caused by Pseudomonas aeruginosa are difficult to treat due to its multidrug resistance. A promising strategy for controlling P. aeruginosa infection is targeting the quorum sensing (QS) system. Actinomycin D isolated from the metabolite of endophyte Streptomyces cyaneochromogenes RC1 exhibited good anti-QS activity against P. aeruginosa PAO1. Actinomycin D (50, 100, and 200 μg/mL) significantly inhibited the motility as well as reduced the production of multiple virulence factors including pyocyanin, protease, rhamnolipid, and siderophores. The images of confocal laser scanning microscopy and scanning electron microscopy revealed that the treatment of actinomycin D resulted in a looser and flatter biofilm structure. Real-time quantitative PCR analysis showed that the expression of QS-related genes lasI, rhlI, rhlR, pqsR, pslA, and pilA were downregulated dramatically. The production of QS signaling molecules N-(3-oxododecanoyl)-L-homoserine lactone and N-butanoyl-L-homoserine lactone were also decreased by actinomycin D. These findings suggest that actinomycin D, a potent in vitro anti-virulence agent, is a promising candidate to treat P. aeruginosa infection by interfering with the QS systems.

Antibacterial activity of Chinese propolis and its synergy with β-lactams against methicillin-resistant Staphylococcus aureus

Propolis has exhibited effective antibacterial activities in preventing the growth of multiple pathogenic bacteria. However, the antibacterial activity of Chinese propolis against methicillin-resistant Staphylococcus aureus (MRSA) is almost unknown. The present study aimed to explore the antibacterial activity and action mechanism of Chinese propolis ethanol extract (CPEE) against MRSA. Thirteen compounds of CPEE were identified using HPLC-DAD/Q-TOF-MS, and none of them showed better anti-MRSA activity than CPEE. The diameter of inhibition zone (DIZ) of CPEE was 20.1 mm. The minimal inhibitory concentration (MIC) of CPEE was 32 mg/L, while the minimal bactericidal concentration (MBC) against MRSA was 64 mg/L. Moreover, CPEE showed significant synergistic effects with β-lactam antibiotics (ampicillin and oxacillin). Nucleic acid and protein leakage assays showed that CPEE can stimulate the release of intracellular macromolecules by damaging the cell membrane integrity of MRSA. Live/dead-staining and SDS-PAGE assays further confirmed that CPEE could inhibit bacterial activities by disrupting the membrane. The reduction in PBP2a expression and β-lactamase activity, as shown by western blot and β-lactamase detection assays, suggested that CPEE was able to reverse the drug resistance of MRSA. These results demonstrated the anti-MRSA activity of CPEE was mainly due to changing the cell membrane and reversing resistance, which indicates that CPEE could be an attractive candidate for use in future food and medical applications.

Terpenes Combinations Inhibit Biofilm Formation in Staphyloccocus aureus by Interfering with Initial Adhesion

The biofilm is a conglomerate of cells surrounded by an extracellular matrix, which contributes to the persistence of infections. The difficulty in removing the biofilm drives the research for new therapeutic options. In this work, the effect of terpenes (−)-trans-Caryophyllene, (S)-cis-Verbenol, (S)-(−)-Limonene, (R)-(+)-Limonene, and Linalool was evaluated, individually and in combinations on bacterial growth, by assay with resazurin; the formation of biofilm, by assay with violet crystal; and the expression of associated genes, by real-time PCR, in two clinical isolates of Staphyloccocus aureus, ST30-t019 and ST5-t311, responsible for more than 90% of pediatric infections by this pathogen in Paraguay. All combinations of terpenes can inhibit biofilm formation in more than 50% without affecting bacterial growth. The most effective combination was (−)-trans-Caryophyllene and Linalool at a 500 μg/mL concentration for each, with an inhibition percentage of 88%. This combination decreased the expression levels of the sdrD, spa, agr, and hld genes associated with the initial cell adhesion stage and quorum sensing. At the same time, it increased the expression levels of the cap5B and cap5C genes related to the production of capsular polysaccharides. The combinations of compounds tested are promising alternatives to inhibit biofilm formation in S. aureus.

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.

Commensal Bacillus subtilis from cow milk inhibits Staphylococcus aureus biofilm formation and mastitis in mice

The colonization and virulence production of Staphylococcus aureus (S. aureus), a known pathogen that induces mastitis, depend on its quorum-sensing (QS) system and biofilm formation. It has been reported that Bacillus can inhibit the QS system of S. aureus, thereby reducing S. aureus colonization in the intestine. However, whether Bacillus affects S. aureus biofilm formation and consequent colonization during mastitis is still unknown. In this study, the differences in the colonization of S. aureus and Bacillus were first analyzed by isolating and culturing bacteria from milk samples. It was found that the colonization of Bacillus and S. aureus in cow mammary glands was negatively correlated. Secondly, we found that although Bacillus did not affect S. aureus growth, it inhibited the biofilm formation of S. aureus by interfering its QS signaling. The most significant anti-biofilm effect was found in Bacillus subtilis H28 (B. subtilis H28). Finally, we found that B. subtilis H28 treatment alleviated S. aureus-induced mastitis in a mice model. Our results rerealed that bovine milk derived commensal Bacillus inhibited S. aureus colonization and alleviated S. aureus-induced mastitis by influencing biofilm formation, suggesting a potential targeted strategy to limit the colonization of S. aureus in vivo.

Resveratrol Oligomers, Plant-Produced Natural Products With Anti-virulence and Plant Immune-Priming Roles

Antibiotic resistance has become increasingly prevalent in the environment. Many alternative strategies have been proposed for the treatment and prevention of diverse diseases in agriculture. Among them, the modulation of bacterial virulence to bypass antibiotic resistance or boost plant innate immunity can be considered a promising drug target. Plant-produced natural products offer a broad spectrum of stereochemistry and a wide range of pharmacophores, providing a great diversity of biological activities. Here, we present a perspective on the putative role of plant-produced resveratrol oligomers as anti-virulence and plant-immune priming agents for efficient disease management. Resveratrol oligomers can decrease (1) bacterial motility directly and (2) indirectly by attenuating the bacterial type III secretion system (TT3S). They induce enhanced local immune responses mediated by two-layered plant innate immunity, demonstrating (3) a putative plant immune priming role.

Comparative Transcriptome Analysis Reveals Differentially Expressed Genes Related to Antimicrobial Properties of Lysostaphin in Staphylococcus aureus

Comparative transcriptome analysis and de novo short-read assembly of S. aureus Newman strains revealed significant transcriptional changes in response to the exposure to triple-acting staphylolytic peptidoglycan hydrolase (PGH) 1801. Most altered transcriptions were associated with the membrane, cell wall, and related genes, including amidase, peptidase, holin, and phospholipase D/transphosphatidylase. The differential expression of genes obtained from RNA-seq was confirmed by reverse transcription quantitative PCR. Moreover, some of these gene expression changes were consistent with the observed structural perturbations at the DNA and RNA levels. These structural changes in the genes encoding membrane/cell surface proteins and altered gene expressions are the candidates for resistance to these novel antimicrobials. The findings in this study could provide insight into the design of new antimicrobial agents.

Anti-Planktonic and Anti-Biofilm Properties of Pentacyclic Triterpenes-Asiatic Acid and Ursolic Acid as Promising Antibacterial Future Pharmaceuticals

Due to the ever-increasing number of multidrug-resistant bacteria, research concerning plant-derived compounds with antimicrobial mechanisms of action has been conducted. Pentacyclic triterpenes, which have a broad spectrum of medicinal properties, are one of such groups. Asiatic acid (AA) and ursolic acid (UA), which belong to this group, exhibit diverse biological activities that include antioxidant, anti-inflammatory, diuretic, and immunostimulatory. Some of these articles usually contain only a short section describing the antibacterial effects of AA or UA. Therefore, our review article aims to provide the reader with a broader understanding of the activity of these acids against pathogenic bacteria. The bacteria in the human body can live in the planktonic form and create a biofilm structure. Therefore, we found it valuable to present the action of AA and UA on both planktonic and biofilm cultures. The article also presents mechanisms of the biological activity of these substances against microorganisms.

The cold adaption profiles of Pseudoalteromonas shioyasakiensis D1497 from Yap trench to cope with cold

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P. shioyasakiensis D1497converted more substrate into biomass at low temperature.

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P. shioyasakiensis D1497 prefered to use codons with A/T in the third position.

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The energy metabolism related genes were down regulated in cold environment.

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P. shioyasakiensis D1497 presented an energy saving metabolism strategy to cope with cold.

Genome sequencing of Pseudoalteromonas shioyasakiensis D1497, a psychrophile from the Yap trench, revealed that it contained a circle chromosome of 3,631,285 bp with 40.94% GC content and prefered to use codons with A/T in the third position. Additionally, the relative synonymous codon usage (RSCU) values indicated the codons with A and T in the third position were always the most used. Cultivation of P. shioyasakiensis D1497 presented lower substrate consumption rate, higher ATP pool and higher conversion rate of biomass per unit substrate consumed at low temperature (15 °C) than that of the room temperature (25 °C) culture. Comparative transcriptomic analysis revealed that the mRNA abundance of energy metabolism related genes was decreased in 15 °C culture compared with that of 25 °C culture. In addition to its codon usage biases profile, P. shioyasakiensis D1497 presented an energy saving metabolism strategy to cope with cold, converting more carbon source into biomass in cold environment.

Efficacy of Ursolic Acid-Enriched Water-Soluble and Not Cytotoxic Nanoparticles against Enterococci

Ursolic acid (UA), a pentacyclic triterpenoid acid found in many medicinal plants and aromas, is known for its antibacterial effects against multi-drug-resistant (MDR) Gram-positive bacteria, which seriously threaten human health. Unfortunately, UA water-insolubility, low bioavailability, and systemic toxicity limit the possibilities of its application in vivo. Consequently, the beneficial activities of UA observed in vitro lose their potential clinical relevance unless water-soluble, not cytotoxic UA formulations are developed. With a nano-technologic approach, we have recently prepared water-soluble UA-loaded dendrimer nanoparticles (UA-G4K NPs) non-cytotoxic on HeLa cells, with promising physicochemical properties for their clinical applications. In this work, with the aim of developing a new antibacterial agent based on UA, UA-G4K has been tested on different strains of the Enterococcus genus, including marine isolates, toward which UA-G4K has shown minimum inhibitory concentrations (MICs) very low (0.5-4.3 µM), regardless of their resistance to antibiotics. Time-kill experiments, in addition to confirming the previously reported bactericidal activity of UA against E. faecium, also established it for UA-G4K. Furthermore, cytotoxicity experiments on human keratinocytes revealed that nanomanipulation of UA significantly reduced the cytotoxicity of UA, providing UA-G4K NPs with very high LD50 (96.4 µM) and selectivity indices, which were in the range 22.4-192.8, depending on the enterococcal strain tested. Due to its physicochemical and biological properties, UA-G4K could be seriously evaluated as a novel oral-administrable therapeutic option for tackling difficult-to-treat enterococcal infections.

Exploring Phenolic Compounds as Quorum Sensing Inhibitors in Foodborne Bacteria

The emergence of multidrug-resistant bacteria stimulates the search for new substitutes to traditional antimicrobial agents, especially molecules with antivirulence properties, such as those that interfere with quorum sensing (QS). This study aimed to evaluate the potential of phenolic compounds for QS inhibition in a QS biosensor strain (Chromobacterium violaceum) and three foodborne bacterial species (Aeromonas hydrophila, Salmonella enterica serovar Montevideo, and Serratia marcescens). Initially, an in silico molecular docking study was performed to select the compounds with the greatest potential for QS inhibition, using structural variants of the CviR QS regulator of C. violaceum as target. Curcumin, capsaicin, resveratrol, gallic acid, and phloridizin presented good affinity to at least four CviR structural variants. These phenolic compounds were tested for antimicrobial activity, inhibition of biofilm formation, and anti-QS activity. The antimicrobial activity when combined with kanamycin was also assessed. Curcumin, capsaicin, and resveratrol inhibited up to 50% of violacein production by C. violaceum. Biofilm formation was inhibited by resveratrol up to 80% in A. hydrophila, by capsaicin and curcumin up to 40% in S. Montevideo and by resveratrol and capsaicin up to 60% in S. marcescens. Curcumin completely inhibited swarming motility in S. marcescens. Additionally, curcumin and resveratrol increased the sensitivity of the tested bacteria to kanamycin. These results indicate that curcumin and resveratrol at concentrations as low as 6μM are potential quorum sensing inhibitors besides having antimicrobial properties at higher concentrations, encouraging applications in the food and pharmaceutical industries.

Target-based screening for natural products against Staphylococcus aureus biofilms

As a notorious food-borne pathogen, Staphylococcus aureus can readily cause diseases in humans via contaminated food. Biofilm formation on various surfaces can increase the capacity of viable S. aureus cells for self-protection due to the stubborn structure of the biofilm matrix. Increased disease risk and economic losses caused by biofilm contamination in the food industry necessitate the urgent development of effective strategies for the inhibition and removal of S. aureus biofilms. Natural products have been extensively used as important sources of "eco-friendly" antibiofilm agents to avoid the side effects of conventional strategies on human health and the environment. This review discusses biofilm formation of S. aureus in food industries and focuses on providing an overview of potential promising target-oriented natural products and their mechanisms of S. aureus biofilm inhibition or removal. Hoping to provide valuable information of attractive research targets or potential undeveloped targets to screen potent natural anti-biofilm agents in food industries.

Antimicrobial Properties of Palladium and Platinum Nanoparticles: A New Tool for Combating Food-Borne Pathogens

Although some metallic nanoparticles (NPs) are commonly used in the food processing plants as nanomaterials for food packaging, or as coatings on the food handling equipment, little is known about antimicrobial properties of palladium (PdNPs) and platinum (PtNPs) nanoparticles and their potential use in the food industry. In this study, common food-borne pathogens Salmonella enterica Infantis, Escherichia coli, Listeria monocytogenes and Staphylococcus aureus were tested. Both NPs reduced viable cells with the log₁₀ CFU reduction of 0.3–2.4 (PdNPs) and 0.8–2.0 (PtNPs), average inhibitory rates of 55.2–99% for PdNPs and of 83.8–99% for PtNPs. However, both NPs seemed to be less effective for biofilm formation and its reduction. The most effective concentrations were evaluated to be 22.25–44.5 mg/L for PdNPs and 50.5–101 mg/L for PtNPs. Furthermore, the interactions of tested NPs with bacterial cell were visualized by transmission electron microscopy (TEM). TEM visualization confirmed that NPs entered bacteria and caused direct damage of the cell walls, which resulted in bacterial disruption. The in vitro cytotoxicity of individual NPs was determined in primary human renal tubular epithelial cells (HRTECs), human keratinocytes (HaCat), human dermal fibroblasts (HDFs), human epithelial kidney cells (HEK 293), and primary human coronary artery endothelial cells (HCAECs). Due to their antimicrobial properties on bacterial cells and no acute cytotoxicity, both types of NPs could potentially fight food-borne pathogens.