Biogenic phytochemicals (cassinopin and isoquercetin) capped copper nanoparticles (ISQ/CAS@CuNPs) inhibits MRSA biofilms

Purified glycosides, Isoquercetin and Cassinopin from Crotalaria candicans were selected for the synthesis of biogenic copper nanoparticles (CuNPs).The designed biogenic CuNPs was characterized and when evaluated against panel of gram negative and positive bacteria, the biogenic CuNPs were found to be more effective against methicillin resistant Staphylococcus aureus (MRSA). Antibacterial, anti-biofilm effects and time kill studies confirmed the ability of biogenic CuNPs to curtail MRSA. Scanning electron microscopy, Crystal violet staining and fluorescent live-dead imaging showed that treatment with sub lethal levels of glycoside capped CuNPs resulted in greater than 50% decline in biofilm formation by MRSA, which implies that anti-biofilm effect of biogenic CuNPs is not dependent on antibacterial effect. Alizarin red assay implied that prolonged treatment of biogenic CuNPs in presence of MRSA, releases Cu(II) ions and hence antibiofilm effect is primarily mediated by NP and is not due to released Cu(II) ion. The NPs caused altered membrane permeability and reduced surface hydrophobicity, thus accounting for its antibiofilm effect.

Sub lethal levels of platinum nanoparticle cures plasmid and in combination with carbapenem, curtails carbapenem resistant Escherichia coli

Drug resistance traits are rapidly disseminated across bacteria by horizontal gene transfer, especially through plasmids. Plasmid curing agents that are active both in vitro and in vivo will resensitize Multi Drug Resistant (MDR) bacteria to antimicrobial agents. Pectin capped platinum nanoparticles (PtNPs) at sub MIC (20 µM) concentration was effective, in causing loss of Extended Spectrum Beta Lactamase (ESBL) harboring plasmid as evidenced by, absence of plasmid in agarose gel and by a concomitant (16-64 fold) drop in MIC for cell wall inhibitors ceftriaxone and meropenem, in carbapenem resistant Escherichia coli (CREC). Interestingly, the plasmid cured strain exhibited small colony morphology and displayed slower growth both in vitro and in vivo. Complementation of cured strain with plasmid from the wild type strain restored resistance towards meropenem and ceftriaxone. Relative to wild type, plasmid cured strain displayed 50% reduction in biofilm formation. Plasmid curing also occurred in vivo in infected zebrafish with curing efficiency of 17% for nanoparticle + meropenem treatment. PtNPs + meropenem reduced bioburden of CREC in infected zebrafish by 2.4 log CFU. Mechanistic studies revealed that nanoparticle interacted with cell surface and perturbed inner membrane integrity. PtNPs did not induce ROS, yet it caused plasmid DNA cleavage, as evidenced by gyrase inhibition assay. Our study for the first time reveals that PtNPs as plasmid curing agent can resensitize MDR bacteria to selective antimicrobial agents in vivo.

Plant nutraceuticals (Quercetrin and Afzelin) capped silver nanoparticles exert potent antibiofilm effect against food borne pathogen Salmonella enterica serovar Typhi and curtail planktonic growth in zebrafish infection model

Purified plant nutraceuticals afzelin and quercetrin from an edible plant- Crotolaria tetragona was employed for the fabrication of silver nanoparticles (AgNPs) by a sunlight mediated process. From among a panel of strains tested, AgNPs displayed potent bacteriostatic and bactericidal effect against P. aeruginosa and S. Typhi. Time kill studies revealed green synthesized AgNPs displayed comparable bactericidal effect with chemically synthesized AgNPs against S. Typhi. Antibiofilm potential of AgNPs showed that they were highly effective at sub MIC concentrations in causing 50% biofilm inhibition against food borne pathogen S. Typhi implying that antibiofilm effect is independent of antibacterial effect, which was evidenced by fluorescent imaging and SEM imaging. Mechanistic studies revealed that reduced cell surface hydrophobicity, decreased surface adherence, loss of membrane potential contributed to antibiofilm potential of afzelin/quercetrin AgNPs. Green synthesized afzelin/quercetrin AgNPs were also relatively less toxic and more effective in curtailing bioburden of S. Typhi in infected zebrafish by > 3 log fold. Ability of sunlight reduced afzelin/quercetrin NPs to mitigate planktonic mode of growth in vitro and in vivo and curtail biofilm formation of S. Typhi in vitro demonstrates its potential to curtail food borne pathogen in planktonic and biofilm mode of growth.

N-lauryltyramine capped copper nanoparticles exhibit a selective colorimetric response towards hazardous mercury(ii) ions and display true anti-biofilm and efflux pump inhibitory effects in E. coli

Hg²⁺ ions selectively decolorize CuNPs through aggregation.