Antipathogenic Potential of a Polyherbal Wound-Care Formulation (Herboheal) against Certain Wound-Infective Gram-Negative Bacteria

Sub-lethal concentration of a colloidal nanosilver formulation (Silversol®) triggers dysregulation of iron homeostasis and nitrogen metabolism in multidrug resistant Pseudomonas aeruginosa

BACKGROUND

Pseudomonas aeruginosa is a notorious pathogen. Its multidrug resistant strains are listed among priority pathogens against whom discovery of novel antibacterial agents and, elucidation of new anti-pathogenicity mechanisms are urgently warranted. This study describes multiple antibacterial effects of a colloidal nano-silver formulation- Silversol® against a multi-drug resistant strain of P. aeruginosa.

RESULTS

Minimum inhibitory concentration (MIC) of Silversol® against P. aeruginosa was found to be 1.5 ppm; and at sub-MIC of 1 ppm, it was able to alter quorum-sensing regulated pigmentation (pyocanin 82%↓; pyoverdine 48%↑), exopolysaccharide synthesis (76%↑) and biofilm formation, susceptibility to antibiotics (streptomycin and augmentin), protein synthesis and export (65%↑), nitrogen metabolism (37%↑ nitrite accumulation), and siderophore production in this pathogen. Network analysis of the differentially expressed genes in the transcriptome of the silversol-treated bacterium identified ten genes as the potential molecular targets: norB, norD, nirS, nirF, nirM, nirQ, nosZ, nosY, narK1, and norE (all associated with nitrogen metabolism or denitrification). Three of them (norB, narK1, and norE) were also validated through RT-PCR.

CONCLUSIONS

Generation of nitrosative stress and disturbance of iron homeostasis were found to be the major mechanisms associated with anti-Pseudomonas activity of Silversol®.

Identification of anti-pathogenic activity among in silico predicted small-molecule inhibitors of Pseudomonas aeruginosa LasR or nitric oxide reductase (NOR)

Introduction

Antibiotic-resistant Pseudomonas aeruginosa strains cause considerable morbidity and mortality globally. Identification of novel targets in this notorious pathogen is urgently warranted to facilitate discovery of new anti-pathogenic agents against it. This study attempted to identify small-molecule inhibitors of two important proteins LasR and nitric oxide reductase (NOR) in P. aeruginosa. 'Las' system can be said to be the 'master' regulator of quorum sensing in P. aeruginosa, whose receptor protein is LasR. Similarly, NOR is crucial to detoxification of reactive nitrogen species.

Methods

In silico identification of potential LasR or NOR inhibitors was attempted through a virtual screening platform AtomNet® to obtain a final subset of <100 top scoring compounds. These compounds were evaluated for their in vivo anti-pathogenic activity by challenging the model host Caenorhabditis elegans with P. aeruginosa in the presence or absence of test compounds. Survival of the worm population in 24-well assay plates was monitored over a period of 5 days microscopically.

Results

Of the 96 predicted LasR inhibitors, 11 exhibited anti-Pseudomonas activity (23%-96% inhibition of bacterial virulence as per third-day end-point) at 25-50 µg/mL. Of the 85 predicted NOR inhibitors, 8 exhibited anti-Pseudomonas activity (40%-85% inhibition of bacterial virulence as per second-day end-point) at 25-50 µg/mL.

Conclusion

Further investigation on molecular mode of action of compounds found active in this study is warranted. Virtual screening can be said to be a useful tool in narrowing down the list of compounds requiring actual wet-lab screening, saving considerable time and efforts for drug discovery.

In Silico and In Vitro Screening of Antipathogenic Properties of Melianthus comosus (Vahl) against Pseudomonas aeruginosa

Bacterial quorum sensing (QS) system regulates pathogenesis, virulence, and biofilm formation, and together they contribute to nosocomial infections. Opportunistic pathogens, such as Pseudomonas aeruginosa, rely on QS for regulating virulence factors. Therefore, blocking the QS system may aid management of various infectious diseases caused by human pathogens. Plant secondary metabolites can thwart bacterial colonization and virulence. As such, this study was undertaken to evaluate three extracts from the medicinal plant, Melianthus comosus, from which phytochemical compounds were identified with potential to inhibit QS-dependent virulence factors in P. aeruginosa. Chemical profiling of the three extracts identified 1,2-benzene dicarboxylic acid, diethyl ester, neophytadiene and hexadecanoic acid as the common compounds. Validation of antibacterial activity confirmed the same MIC values of 0.78 mg/mL for aqueous, methanol and dichloromethane extracts while selected guanosine showed MIC 0.031 mg/mL. Molecular docking analysis showed anti-quorum sensing (AQS) potential of guanosine binding to CviR’ and 2UV0 proteins with varying docking scores of −5.969 and −8.376 kcal/mol, respectively. Guanosine inhibited biofilm cell attachment and biofilm development at 78.88% and 34.85%, respectively. Significant swimming and swarming motility restriction of P. aeruginosa were observed at the highest concentration of plant extracts and guanosine. Overall, guanosine revealed the best swarming motility restrictions. M. comosus extracts and guanosine have shown clear antibacterial effects and subsequent reduction of QS-dependent virulence activities against P.aeruginosa. Therefore, they could be ideal candidates in the search for antipathogenic drugs to combat P.aeruginosa infections.

Identifying the Molecular Targets of an Anti-pathogenic Hydroalcoholic Extract of Punica granatum Peel Against Multidrug-resistant Serratia marcescens

BACKGROUND

Antibiotic-resistant members of the family Enterobacteriaceae are among the serious threats to human health globally. This study reports the anti-pathogenic activity of Punica granatum peel extract (PGPE) against a multi-drug resistant, beta-lactamase producing member of this family i.e. Serratia marcescens.

OBJECTIVE

This study aimed at assessing the anti-pathogenic activity of PGPE against the gramnegative bacterial pathogen S. marcescens and identifying the molecular targets of this extract in the test bacterium.

METHODS

Effect of PGPE on S. marcescens growth and quorum sensing (QS)-regulated pigment production was assessed through broth dilution assay. In vivo anti-infective and prophylactic activity of PGPE was assessed employing the nematode worm Caenorhabditis elegans as a model host. Differential gene expression in PGPE-exposed S. marcescens was studied through a whole transcriptome approach.

RESULTS

PGPE was able to modulate QS-regulated pigment production in S. marcescens without exerting any heavy growth-inhibitory effect at concentrations as low as ≥2.5 μg/mL. It could attenuate the virulence of the test bacterium towards the worm host by 22-42% (p≤0.01) at even lower concentrations (≥0.5 μg/mL). PGPE also exerted a post-extract effect on S. marcescens. This extract was found to offer prophylactic benefit too, to the host worm, as PGPE-pre-fed worms scored better (34-51%; p≤0.001) survival in face of subsequent bacterial attack. Differential gene expression analysis revealed that PGPE affected the expression of a total of 66 genes in S. marcescens by ≥1.5 fold.

CONCLUSION

The anti-virulence effect of PGPE against S. marcescens is multifaceted, affecting stress-response machinery, efflux activity, iron homeostasis, and cellular energetics of this bacterium notably. Among the major molecular targets identified in this study are LPS export transporter permease (LptF), t-RNA pseudouridine synthase (TruB), etc.

Anti-pathogenic potential of a classical ayurvedic Triphala formulation

A classical ayurvedic polyherbal formulation namely Triphala was assessed for its anti-pathogenic potential against five different pathogenic bacteria. Virulence of four of them towards the model host Caenorhabditis elegans was attenuated (by 18-45%) owing to pre-treatment with Triphala Formulation (TF) (≤20 µg/ml). TF could also exert significant therapeutic effect on worms already infected with Chromobacterium violaceum (MTCC 2656), Serratia marcescens (MTCC 97) or Staphylococcus aureus (MTCC 737). Prophylactic use of TF allowed worms to score 14-41% better survival in face of subsequent pathogen challenge. Repeated exposure to this formulation induced resistance in S. marcescens, but not in P. aeruginosa. It also exerted a post-extract effect (PEE) on three of the test pathogens. TF was able to modulate production of quorum sensing (QS)-regulated pigments in three of the multidrug-resistant gram-negative test bacteria. Haemolytic activity of S. aureus was heavily inhibited under the influence of this formulation. P. aeruginosa's lysozyme-susceptibility was found to increase by ~25-43% upon TF-pretreatment. These results validate therapeutic potential of one of the most widely used polyherbal ayurvedic formulations called Triphala.

Anti-pathogenic potential of a classical ayurvedic Triphala formulation

A classical ayurvedic polyherbal formulation namely Triphala was assessed for its anti-pathogenic potential against five different pathogenic bacteria. Virulence of four of them towards the model host Caenorhabditis elegans was attenuated (by 18-45%) owing to pre-treatment with Triphala Formulation (TF) (≤20 µg/ml). TF could also exert significant therapeutic effect on worms already infected with Chromobacterium violaceum (MTCC 2656), Serratia marcescens (MTCC 97) or Staphylococcus aureus (MTCC 737). Prophylactic use of TF allowed worms to score 14-41% better survival in face of subsequent pathogen challenge. Repeated exposure to this formulation induced resistance in S. marcescens, but not in P. aeruginosa. It also exerted a post-extract effect (PEE) on three of the test pathogens. TF was able to modulate production of quorum sensing (QS)-regulated pigments in three of the multidrug-resistant gram-negative test bacteria. Haemolytic activity of S. aureus was heavily inhibited under the influence of this formulation. P. aeruginosa's lysozyme-susceptibility was found to increase by ~25-43% upon TF-pretreatment. These results validate therapeutic potential of one of the most widely used polyherbal ayurvedic formulations called Triphala.