Microwave-assisted rapid synthesis of silver nanoparticles using fucoidan: Characterization with assessment of biocompatibility and antimicrobial activity.

Silver nanoparticles (AgNPs) have gained attention due to their exceptional physicochemical properties and biological activities, owing to which they are extensively used in biomedical field. We synthesized AgNPs by rapid microwave-assisted method using fucoidan as a reducing agent. The synthesized fucoidan-AgNPs (F-AgNPs) were characterized for the structural and functional properties. The bactericidal effect and mode of action of F-AgNPs on the pathogenic bacteria and biofilm formation were investigated along with the cytotoxicity studies. The UV-Visible spectra of the F-AgNPs showed the surface resonance peak at 419 nm. The nanoparticles were spherical in shape with particle size of 59.5 ± 1.46 nm and polydispersity index (PDI) of 0.3 ± 0.01. Capping of fucoidan on AgNPs was confirmed by FTIR with characteristic peaks of sulfate group. Silver content of F-AgNPs was 87% with 13% contribution from the fucoidan moieties. The F-AgNPs showed antimicrobial activity against common pathogenic bacteria and was able to inhibit biofilm formation in Pseudomonas aeruginosa at 20 µg/mL concentration. The oxidative stress and intracellular protein leakage were observed due to the F-AgNP interaction with the cell bringing about bactericidal effect. The results highlight the synthesis and bioactivity of AgNPs doped with organic moieties for applications as antimicrobials.

A medicinal herb Cassia alata attenuates quorum sensing in Chromobacterium violaceum and Pseudomonas aeruginosa.

Quorum sensing (QS) has been shown to play a crucial role in the pathogenesis in many bacteria, and attenuation of QS is one of the targets of antimicrobial therapy with particular interest in combating drug resistance. This study reports the QS inhibitory activity of metabolites from Cassia alata L. (Ca. alata), an important medicinal herb widely used in the treatment of microbial infections. For investigating the QS inhibition (QSI), the potential of Ca. alata L., initially, metabolites of the leaves extracted using ethanol was tested against biosensor strain Chromobacterium violaceum CV026 and C. violaceum wild-type strains. Furthermore, a purified fraction rich in flavonoids (F-AF) was used for establishing QSI activity by studying the inhibition of violacein production in C. violaceum, and QS controlled virulence and biofilm formation in Pseudomonas aeruginosa PAO1. The study results showed 50% inhibition of violacein production in C. violaceum at 0·05 mg ml-1 concentration of F-AF. In P. aeruginosa PAO1, it inhibited the tested virulence factors and biofilm formation significantly. The F-AF contained major flavonoids namely, quercetin, quercetrin and kaempferol displaying QSI activity individually against the test organisms. SIGNIFICANCE AND IMPACT OF THE STUDY: Present study demonstrates the quorum sensing inhibitory activity of metabolites from Cassia alata, an important medicinal herb which is commonly used worldwide in the treatment of infections caused by microorganisms. An extract prepared from the leaves of the plant showed activity against quorum sensing in Chromobacterium violaceum and was also effective against attenuating the quorum sensing controlled virulence factors in Pseudomonas aeruginosa. Activity is attributed to the rich flavonoid composition of the plant. Results of the present investigation throw an insight into the possibility of developing drug formulations using the isolated compounds against infections caused by quorum sensing-mediated pathogenicity of bacteria.