Enhanced antimicrobial activity of essential oil components immobilized on silica particles

Identification of Antimicrobial Peptides of Native and Heated Hydrolysates from Hen Egg White Lysozyme

Hen eggs are a source of bioactive compounds, of which the hen egg white lysozyme (HEWL) protein. HEWL has a demonstrated antibacterial activity. The aim of this study was to evaluate the antimicrobial activity of native and heated HEWL hydrolysates obtained through hydrolysis with pepsin and to identify their peptides using the reversed phase high performance liquid chromatography-electrospray ionization-tandem mass spectrometry (RP-HPLC-ESI-MS-MS) analysis. Native and heat-treated HEWL was hydrolyzed with pepsin at pH 1.2, and their antibacterial activity was tested against Escherichia coli and Staphylococcus carnosus. Two of the hydrolysates obtained presented high antibacterial activity against Gram-positive and Gram-negative bacteria. Native HEWL hydrolysate was a bactericide at 2.0 mg/mL against E. coli. Fifty-one peptide sequences were identified on the two hydrolysates. Peptides identified are cationic peptides. These peptides are rich in Lys and Arg cationic amino acids and have Trp in their sequences.

Hybrid-silica nanoparticles as a delivery system of the natural biocide carvacrol

Bacterial resistance to common antibiotics necessitates innovative solutions. The phenolic antimicrobial compound carvacrol, a major ingredient in the Essential Oils (EOs) of oregano and thyme, has the advantages of natural compounds such as Generally Recognized As Safe (GRAS) status, but needs an appropriate delivery system designed to overcome its drawbacks (such as low aqueous solubility, easy phenol oxidation, heat/light inactivation, distinct odor). An alkoxysilane incorporating the carvacrol moiety is synthesized and subsequently employed to fabricate hybrid silica nanoparticles (NPs) with carvacrol covalently bound to the silica matrix. The enzymatically hydrolyzable carbamate bond turns these NPs into a release-on-demand nanoscale system for the biocide carvacrol. Characterization of both silane linker and hybrid silica NPs, including quantification of the bioactive compound in the bulk and on the NP surface, is accomplished by spectroscopic methods, including X-ray Photoelectron Spectroscopy (XPS), and Thermo-Gravimetric Analysis (TGA), Dynamic Light Scattering (DLS), ζ-potential measurements, as well as electron microscopy. Preliminary biological testing with E. coli proves an antibacterial effect. The carbamoylation reaction employed to synthesize the hybrid silica precursor might be readily applied to other bioactive phenolic compounds.

The authors fabricated hybrid-silica NPs incorporating the natural antibiotic carvacrol from essential oils covalently with an enzymatically cleavable bond. They are a safe, on-demand antibacterial agent.

Antimicrobial Peptide-Polymer Conjugates with High Activity: Influence of Polymer Molecular Weight and Peptide Sequence on Antimicrobial Activity, Proteolysis, and Biocompatibility

We report the synthesis, characterization, activity, and biocompatibility of a novel series of antimicrobial peptide-polymer conjugates. Using parent peptide aurein 2.2, we designed a peptide array (∼100 peptides) with single and multiple W and R mutations and identified antimicrobial peptides (AMPs) with potent activity against Staphylococcus aureus (S. aureus). These novel AMPs were conjugated to hyperbranched polyglycerols (HPGs) of different molecular weights and number of peptides to improve their antimicrobial activity and toxicity. The cell and blood compatibility studies of these conjugates demonstrated better properties than those of the AMP alone. However, conjugates showed lower antimicrobial activity in comparison to that of peptides, as determined from minimal inhibition concentrations (MICs) against S. aureus, but considerably better than that of the available polymer-AMP conjugates in the literature. In addition to measuring MICs and characterizing the biocompatibility, circular dichroism spectroscopy was used to investigate the interaction of the novel conjugates with model bacterial biomembranes. Moreover, the novel conjugates were exposed to trypsin to evaluate their stability. It was found that the conjugates resist proteolysis in comparison with unprotected peptides. The peptide conjugates were active in serum and whole blood. Overall, the results show that combining a highly active AMP and low-molecular-weight HPG yields bioconjugates with excellent biocompatibility, MICs below 100 μg/mL, and proteolytic stability, which could potentially improve its utility for in vivo applications.