Caprylic acid and glyceryl trinitrate combination for eradication of biofilm

Relocating Glyceryl Trinitrate as an Anti-Virulence Agent against Pseudomonas aeruginosa and Serratia marcescens: Insights from Molecular and In Vivo Investigations

The problem of antibiotic resistance is a global critical public health concern. In light of the threat of returning to the pre-antibiotic era, new alternative approaches are required such as quorum-sensing (QS) disruption and virulence inhibition, both of which apply no discernible selective pressure on bacteria, therefore mitigating the potential for the development of resistant strains. Bearing in mind the significant role of QS in orchestrating bacterial virulence, disrupting QS becomes essential for effectively diminishing bacterial virulence. This study aimed to assess the potential use of sub-inhibitory concentration (0.25 mg/mL) of glyceryl trinitrate (GTN) to inhibit virulence in Serratia marcescens and Pseudomonas aeruginosa. GTN could decrease the expression of virulence genes in both tested bacteria in a significant manner. Histopathological study revealed the ability of GTN to alleviate the congestion in hepatic and renal tissues of infected mice and to reduce bacterial and leukocyte infiltration. This study recommends the use of topical GTN to treat topical infection caused by P. aeruginosa and S. marcescens in combination with antibiotics.

Promising FDA-approved drugs with efflux pump inhibitory activities against clinical isolates of Staphylococcus aureus

Background and objectives

Staphylococcus aureus is an opportunistic pathogen that causes wide range of nosocomial and community-acquired infections which have spread worldwide leading to an urgent need for developing effective anti-staphylococcal agents. Efflux is an important resistance mechanism that bacteria used to fight the antimicrobial action. This study aimed to investigate the efflux mechanism in S. aureus and assess diclofenac, domperidone, glyceryl trinitrate and metformin as potential efflux pump inhibitors that can be used in combination with antibiotics for treating topical infections caused by S. aureus.

Materials and methods

Efflux was detected qualitatively by the ethidium bromide Cart-Wheel method followed by investigating the presence of efflux genes by polymerase chain reaction. Twenty-six isolates were selected for further investigation of efflux by Cart-Wheel method in absence and presence of tested compounds followed by quantitative efflux assay. Furthermore, antibiotics minimum inhibitory concentrations in absence and presence of tested compounds were determined. The effects of tested drugs on expression levels of efflux genes norA, fexA and tetK were determined by quantitative real time-polymerase chain reaction.

Results

Efflux was found in 65.3% of isolates, the prevalence of norA, tetK, fexA and msrA genes were 91.7%, 77.8%, 27.8% and 6.9%. Efflux assay revealed that tested drugs had potential efflux inhibitory activities, reduced the antibiotic’s MICs and significantly decreased the relative expression of efflux genes.

Conclusion

Diclofenac sodium, domperidone and glyceryl trinitrate showed higher efflux inhibitory activities than verapamil and metformin. To our knowledge, this is the first report that shows that diclofenac sodium, glyceryl trinitrate and domperidone have efflux pump inhibitory activities against S. aureus.

Synthesis, Cytotoxicity Evaluation, and Antifungal Activity of Novel Nitroglycerin Derivatives against Clinical Candida albicans Isolates

Background

Candida albicans remains the main cause of candidiasis in most clinical settings. Available drugs for candidiasis treatment have many side effects. In this work, novel nitroglycerin derivatives were synthesized and their cytotoxic and antifungal effects evaluated against fluconazole susceptible and resistant clinical C. albicans isolates.

Methods

This experimental study was performed in Tehran University of Medical Sciences and Baqiatallah University of Medical Sciences, Tehran, Iran between Feb to Dec 2019. The in vitro activities of two novel nitroglycerin derivatives (1b and 2b) against 25 clinical fluconazole-susceptible and resistant C. albicans isolates and four standard C. albicans strains were determined according to CLSI reference M27-A3 documents. The cytotoxicity of chemical compounds was investigated near the SNL76/7 cells by colorimetric assay. Real-time PCRs were performed to evaluate the alterations in the regulation of ERG11 and CDR1 genes under nitroglycerin derivatives-treated and untreated conditions.

Results

The derivatives 1b and 2b exhibited potent antifungal activity against C. albicans isolates; MICs and MFCs varied from 18 μg/ml to 72 μg/ml and 36 μg/ml to 144 μg/ml, respectively. The cell viability evaluation demonstrated that both chemical compounds are safe within 24h. The nitroglycerin derivatives were able to reduce the transcription level of CDR1 and ERG11 genes in all susceptible and resistant C. albicans isolates.

Conclusion

Considering the potential and efficacy of these compounds against clinical C. albicans isolates, the complementary in vivo and clinical trials should be investigated.

In vitro antagonistic inhibitory effects of palm seed crude oils and their main constituent, lauric acid, with oxacillin in Staphylococcus aureus

Infections caused by Staphylococcus aureus are a serious global threat, and with the emergence of antibiotic resistance, even more difficult to treat. One of the possible complications in antistaphylococcal therapy represents negative interactions of antibiotics with food. In this study, the in vitro interaction between oxacillin and crude palm seed oil from Astrocaryum vulgare, Cocos nucifera, and Elaeis guineensis against nine strains of S. aureus was determined using the checkerboard method. Lauric acid was identified as a major constituent of all tested oils by gas chromatography. The results showed strong concentration dependent antagonistic interactions between palm oils and oxacillin with values of fractional inhibitory concentrations indices ranging from 4.02 to 8.56 at concentrations equal or higher than 1024 µg/mL of the tested oils. Similarly, lauric acid in combination with oxacillin produced antagonistic action with fractional inhibitory concentration indices ranging from 4.01 to 4.28 at 1024 µg/mL. These findings suggest that interference between oxacillin and palm oils and their constituents can negatively affect the treatment of staphylococcal infections in humans and other animals.

A fast and effective alternative to a high-ethanol disinfectant: Low concentrations of fermented ethanol, caprylic acid, and citric acid synergistically eradicate biofilm-embedded methicillin-resistant Staphylococcus aureus

BACKGROUND

There is a growing need to develop a powerful bactericidal method with low ethanol concentrations due to the frequent ineffectiveness of traditional antibiotics against biofilms and the side effect of a high ethanol concentration.

OBJECTIVES

This study aims to develop a novel synergistic technique replacing a high-ethanol disinfectant.

METHODS

Low concentrations of fermented ethanol (FE, 10-20%) with naturally derived antimicrobials, citric acid (CTA, 0.5-1.0%) and caprylic acid (CAP, 0.05-0.15%), were examined against a methicillin-resistant S. aureus (MRSA) biofilm formed on silicone coupons (catheter materials).

RESULTS

CTA and CAP were identified as effective antimicrobials that exhibited a synergistic interaction with FE. Complete eradication of MRSA biofilms (>7 log reduction) was obtained within 5 min after treatment with 20% FE plus 1.0% CTA and 0.15% CAP at both 22 and 37 °C, while individual treatments with each material showed negligible bactericidal effects (<1 log reduction except 0.15% CAP treatment at 37 °C). No bacteria were recovered from the surface after the combined treatment (five enrichment tests). The developed compounds were able to disinfect surfaces with more than 5 log-reduction within only 1 min at 22 °C. Confocal microscopy images showed that the combination of all three materials resulted in remarkable membrane damage and cell detachment from the silicone surface.

DISCUSSON

Application of FE plus CTA and CAP, therefore, can be a valuable decontamination technique for medical devices or can work as a surface disinfectant, reducing the concerns regarding undesirable high ethanol concentrations in disinfectants.

Disparate Candida albicans Biofilm Formation in Clinical Lipid Emulsions Due to Capric Acid-Mediated Inhibition

Receipt of parenteral nutrition (PN) remains an independent risk factor for developing catheter-related bloodstream infections (CR-BSI) caused by fungi, including by the polymorphic fungus Candida albicans, which is notoriously adept at forming drug-resistant biofilm structures. Among a variety of macronutrients, PN solutions contain lipid emulsions to supply daily essential fats and are often delivered via central venous catheters (CVCs). Therefore, using an in vitro biofilm model system, we sought to determine whether various clinical lipid emulsions differentially impacted biofilm growth in C. albicans We observed that the lipid emulsions Intralipid and Omegaven both stimulated C. albicans biofilm formation during growth in minimal medium or a macronutrient PN solution. Conversely, Smoflipid inhibited C. albicans biofilm formation by approximately 50%. Follow-up studies revealed that while Smoflipid did not impair C. albicans growth, it did significantly inhibit hypha formation and hyphal elongation. Moreover, growth inhibition could be recapitulated in Intralipid when supplemented with capric acid-a fatty acid present in Smoflipid but absent in Intralipid. Capric acid was also found to dose dependently inhibit C. albicans biofilm formation in PN solutions. This is the first study to directly compare different clinical lipid emulsions for their capacity to affect C. albicans biofilm growth. Results derived from this study necessitate further research regarding different lipid emulsions and rates of fungus-associated CR-BSIs.

Proteomic Analysis of Horseweed (Conyza canadensis) Subjected to Caprylic Acid Stress

Caprylic acid (CAP) is anticipated to be a potential biocontrol herbicide in the control of weeds, however the molecular mechanism of how CAP affects weeds is poorly understood. Here, the physiological and biochemical (protein-level) changes in horseweed (Conyza canadensis L.) are studied under CAP treatment, with infrared gas analyzer and label-free quantitative proteomics methods. In total, 112 differentially-accumulated proteins (DAPs) (>1.5 fold change, p < 0.05) are present between treated horseweed and control samples, with 46 up-regulated and 66 down-regulated proteins. These DAPs are involved in 28 biochemical pathways, including photosynthesis pathways. In particular, six photosynthesis proteins show significant abundance changes in the CAP-treated horseweed. The qRT-PCR results confirm three of the six genes involved in photosynthesis. Moreover, by measuring photosynthesis characteristics, CAP was shown to decrease photosynthetic rate, stomatal conductance, intercellular CO₂ concentration, and the transpiration rate of horseweed. These results suggest that photosystem I is one of the main biological processes involved in the response of horseweed to CAP.

Glyceryl trinitrate blocks staphyloxanthin and biofilm formation in Staphylococcus aureus

Background

Staphylococcus aureus is an important nosocomial bacterium that is responsible for a number of infections that may be fatal. The treatment of such infections is limited by emergence of antibiotic resistance. Targeting virulence of Staphylococcus aureus may provide an alternative option to antibiotic that may bypass the emergence of resistant strains due to lack of stress on viability.

Objectives

Investigation of the ability of glyceryl trinitrate (GTN) to inhibit staphyloxanthin, biofilm and tolerance to oxidative stress.

Methods

The disk sensitivity method was used to detect the methicillin resistance of Staphylococcus aureus. The effect of sub-inhibitory concentration of GTN on biofilm formation, staphyloxanthin production and tolerance to oxidative stress was evaluated. Molecular docking study was used to investigate the ability of GTN to bind to dehydrosqualene synthase enzyme.

Results

GTN showed a significant inhibition of biofilm, staphyloxanthin and tolerance to oxidative stress. In the molecular docking study, it was found that GTN could bind to dehydrosqualene synthase enzyme by hydrogen bonding, electrostatic interaction and pi-cation interaction.

Conclusion

The present study revealed the ability of GTN to serve as a potential anti-virulence candidate for attenuation of S. aureus pathogenicity.

Differential requirements for processing and transport of short-chain versus long-chain O-acylcarnitines in Pseudomonas aeruginosa

The opportunistic pathogen Pseudomonas aeruginosa can metabolize carnitine and O-acylcarnitines, which are abundant in host muscle and other tissues. Acylcarnitines are metabolized to carnitine and a fatty acid. The liberated carnitine and its catabolic product, glycine betaine, can be used as osmoprotectants, to induce the secreted phospholipase C PlcH, and as sole carbon, nitrogen and energy sources. P. aeruginosa is incapable of de novo synthesis of carnitine and acylcarnitines, therefore they must be imported from an exogenous source. In this study, we present the first characterization of bacterial acylcarnitine transport. Short-chain acylcarnitines are imported by the ABC transporter CaiX-CbcWV. Medium- and long-chain acylcarnitines (MCACs and LCACs) are hydrolysed extracytoplasmically and the free carnitine is transported primarily through CaiX-CbcWV. These findings suggest that the periplasmic protein CaiX has a binding pocket that permits short acyl chains on its carnitine ligand and that there are one or more secreted hydrolases that cleave MCACs and LCACs. To identify the secreted hydrolase(s), we used a saturating genetic screen and transcriptomics followed by phenotypic analyses, but neither led to identification of a contributing hydrolase, supporting but not conclusively demonstrating redundancy for this activity.

Silencing the nosocomial pathogen Serratia marcescens by glyceryl trinitrate

BACKGROUND

Quorum sensing is a cell-to-cell communication system in bacteria that controls the production of virulence factors. Serratia marcescens is a causative agent of hospital-acquired infections that shows high resistance to antibiotics. This makes the treatment of these infections difficult. Quorum sensing regulates the production of virulence factors of S. marcescens such as prodigiosin, protease, swimming and swarming motilities and formation of biofilms. Inhibition of quorum sensing may be an alternative to antibiotic treatment to avoid emergence of resistance.

OBJECTIVES

Testing the ability of glyceryl trinitrate to inhibit quorum sensing and virulence factors of Serratia marcescens.

METHODS

The inhibiting activities of sub-inhibitory concentration of glyceryl trinitrate against the quorum-sensing regulated violacein pigment in Chromobacterium violaceum CV026 was performed to evaluate the anti-quorum sensing effect of glyceryl trinitrate. The anti-virulence activity was assessed against prodigiosin, protease, biofilm formation in addition to swimming and swarming motilities.

RESULTS

Glyceryl trinitrate at at a concentration of 0.25 mg/ml produced significant inhibitory effects against violacein (67.01%), prodigiosin (82.67%), protease, swimming (36.72%) and swarming (79.31%) motilities and biofilm formation (87.83%).

CONCLUSION

Glyceryl trinitrate is a quorum sensing and virulence inhibitor that may be useful in treatment of nosocomial infections caused by Serratia marcescens.

Glyceryl trinitrate is a novel inhibitor of quorum sensing in Pseudomonas aeruginosa

BACKGROUND

Targeting quorum sensing is an alternative approach to antibiotics.Targeting quorum sensing-regulated virulence will disarm the pathogen without exerting pressure on its growth. As a result, emergence of resistance is avoided and the immune system can easily eradicate bacteria.

OBJECTIVES

Investigation of the possible inhibition of quorum sensing-regulated virulence of Pseudomonas aeruginosa by glyceryltrinitrate.

METHODS

The quorum sensing inhibiting activity of glyceryl trinitrate was assessed by inhibition of violacein production in Chromobacterium violaceum ATCC 12472. Its ability to inhibit pyocyanin, protease, biofilm and tolerance to oxidative stress was evaluated. Docking study was performed to study the interference of glyceryl trinitrate with the binding of autoinducers with LasR and rhlR receptors.

RESULTS

Glyceryl trinitrate exerted a significant biofilm inhibiting and eradicating activities. It decreased the production of quorum-sensing dependent violacein production. It significantly inhibited the production of pyocyanin and protease and diminished the tolerance against oxidative stress. Molecular docking study showed that glyceryl trinitrate interferes with the binding of autoinducers to their receptors. It could bind to Las Rand rhlr receptors with binding energy of -93.47 and -77.23, respectively.

CONCLUSION

Glyceryl trinitrate can be an antivirulence agent in the treatment of Pseudomonas aeruginosa topical infections such as burn infections.

Eradication of Staphylococcus aureus Catheter-Related Biofilm Infections Using ML:8 and Citrox

Staphylococci are a leading cause of catheter-related infections (CRIs) due to biofilm formation. CRIs are typically managed by either device removal or systemic antibiotics, often in combination with catheter lock solutions (CLSs). CLSs provide high concentrations of the antimicrobial agent at the site of infection. However, the most effective CLSs against staphylococcal biofilm-associated infections have yet to be determined. The purpose of this study was to evaluate the efficacy and suitability of two newly described antimicrobial agents, ML:8 and Citrox, as CLSs against Staphylococcus aureus biofilms. ML:8 (1% [vol/vol]) and Citrox (1% [vol/vol]), containing caprylic acid and flavonoids, respectively, were used to treat S. aureus biofilms grown in vitro using newly described static and flow biofilm assays. Both agents reduced biofilm viability >97% after 24 h of treatment. Using a rat model of CRI, ML:8 was shown to inactivate early-stage S. aureus biofilms in vivo, while Citrox inactivated established, mature in vivo biofilms. Cytotoxicity and hemolytic activity of ML:8 and Citrox were equivalent to those of other commercially available CLSs. Neither ML:8 nor Citrox induced a cytokine response in human whole blood, and exposure of S. aureus to either agent for 90 days was not associated with any increase in resistance. Taken together, these data reveal the therapeutic potential of these agents for the treatment of S. aureus catheter-related biofilm infections.

Methods for eradication of the biofilms formed by opportunistic pathogens using novel techniques – A review

The inconvenient environmental conditions force microorganisms to colonize either abiotic surfaces or animal and plant tissues and, therefore, form more resistant structures – biofilms. The phenomenon of microbial adherence, opportunistic pathogens in particular, is of a great concern. Colonization of medical devices and biofilm formation on their surface, may lead to severe infections mainly in humans with impaired immune system. Although, current research consider various methods for prevention of microbial biofilms formation, still, once a biofilm is formed, its elimination is almost impossible. This study focuses on the overview of novel methods applied for eradication of mature opportunistic pathogens' biofilms. Among various techniques the following: cold plasma, electric field, ultrasounds, ozonated water treatment, phagotherapy, matrix targeting enzymes, bacteriocins, synthetic chemicals and natural origin compounds used for biofilm matrix disruption were briefly described.