Loss of outer membrane integrity in Gram-negative bacteria by silver nanoparticles loaded with Camellia sinensis leaf phytochemicals: plausible mechanism of bacterial cell disintegration

Abstract

New generation antimicrobial and smart drugs are the needs of the present era in fighting microbial infection and various chronic diseases. Nowadays nanoparticles (NPs) are widely applied in biomedical fields by virtue of their surface modification, which enhances both target selectivity and function. This study is a continuation of our earlier study that demonstrated antimicrobial property of NPs against both Gram-positive and Gramnegative organisms (Goswami et al, 2015). Silver NPs were synthesized using tea leaves (Camellia sinensis) decoction and were characterized using UV-vis spectrophotometry, transmission electron microscopy (TEM) and Fouriertransformed infrared spectroscopy (FTIR). The silver NPs were stable at various environmental conditions. The stability of the particles may be due to various phytochemicals of tea that were bound to the surface of reduced silver ions as a capping agent. The antimicrobial activity of NP was investigated against three Gram-negative pathogenic bacteria (Shigella dysentriae, Salmonella infestis and Vibrio parahaemolyticus). The outer membrane of Gram-negative bacteria is a lipopolysaccharide (LPS) in nature and provides protection from various stress conditions and antibiotics. But a silver NP destroys its membrane integrity and thus helps in cell killing. Spectral changes confirmed NP interaction with hydrophobic moiety of LPS. Minimum inhibitory concentrations for S. dysentriae, S. infestis and V. parahaemolyticus were 3.75, 5.25 and 5.25 μg ml −1 , respectively. Inhibition of biofilm formation was significant with the three bacterial strains. Cytoplasmic leakage from each bacterial strain was also demonstrated on account of NP treatment. The particles demonstrated good biocompatibility. No damage of human buccal mucosal cells was recorded even at concentration of 10 mg ml −1. Thus, silver NPs would be potential oral therapeutic molecules against Gram-negative bacteria.

Antimicrobial photodynamic activity of toluidine blue encapsulated in mesoporous silica nanoparticles againstPseudomonas aeruginosaandStaphylococcus aureus

“…Further studies revealed that cytoplasmic leakage and lipid peroxidation are the possible mechanisms of action of aPDT on the test bacterial species. It can also be concluded that the major target of ROS was the cell membrane that resulted in protein leakage and lipid peroxidation, as previously suggested by other authors (Misba et al 2016;Singh et al 2016;Misba et al 2017).…”

“…CTAB (N,cetyl-N,N,N-trimethylammonium bromide) was used as a positive control in order to release the complete protein content inside the cells. The assay was performed similar to the protocol described by Singh et al (2016). Test cultures were treated with MSN, TB, and TB MSN at the same concentrations used for antimicrobial photodynamic inactivation.…”

Potential of grape byproducts as functional ingredients in baked goods and pasta

“…Some studies revealed that extracts from Cabernet Sauvignon grape pomace exhibited higher antimicrobial activities compared to Syrah and Merlot pomaces, as a result of the total phenolics contents differences (Oliveira et al, 2013;Sanhueza et al, 2014). Antimicrobial activity against S. aureus and Listeria monocytogenes of different grape pomace varieties extracts was also reported by Xu et al (2016), whereas for Salmonella typhimurium and E. coli growth no effects were obtained, probably due to the cell structure of Gram-negative bacteria, which have two-layer cell membrane and high outer membrane hydrophilicity, leading to great resistance on grape pomace extracts (Singh, Mallick, Banerjee, & Kumar, 2016;Xu et al, 2016). On contrary, other study reported growth inhibition of grape pomace on both Gramnegative and Gram-positive bacteria, depending on the extract concentration, better results being obtained at higher extract concentrations (Faisal, Mosammad, & Heri, 2015).…”

Effect of antimicrobial nanocomposites on Vibrio cholerae lifestyles: Pellicle biofilm, planktonic and surface-attached biofilm

“…Due to the mechanism of action of NPs against other Gram-negative bacteria, specifically targeting the membrane integrity [37], we evaluated changes in OMPs expression under the different NPs treatments (Figs 6 and 7). OMPs fractionation allowed us to identify the most abundant pore-forming proteins (porins) in V. cholerae: OmpT and OmpU, and the OMPs: OmpC, OmpA and OmpW.…”