New Synthetic Peptides Conjugated to Gold Nanoclusters: Antibiotic Activity Against Escherichia coli O157:H7 and Methicillin-Resistant Staphylococcus aureus (MRSA).

Gold nanoclusters protected with bovine serum albumin (AuNC) can be used in multiple biomedical applications through functionalization with two new and bioactive peptides. Both cationic peptides sequences of 17 amino acids in length and the cysteine residue at its C-terminus were designed and synthesized. Peptides were obtained by solid phase synthesis using the Fmoc strategy. Peptides may be coupled via disulfide bonds to AuNC with hydrodynamic size ~ 2 nm ± 0.3 determined by dynamic light scattering and it had a zeta potential value equal to - 42 mV. Peptides named NBC2253 and NBC2254 were attached to the AuNC using N-succinimidyl-3-(2-pyridyl-dithiol) propionate as crosslinker agent. AuNC@NBC2253 was more active against methicillin-resistant Staphylococcus aureus (MIC50 6.5 µM) and AuNC@NBC2254 exhibited higher antimicrobial activity than the free peptides on Escherichia coli O157:H7 (MIC50 3.5 µM). No hemolysis was detected for any of the peptides. It is evidenced that these antimicrobial peptides conjugated to AuNC serve as promising agents to combat some multi-resistant bacterial strains and that the specific binding of these antimicrobial peptides to gold nanoclusters improves the interaction of these nanostructured systems with the biological target.

A New Synthetic Peptide with In vitro Antibacterial Potential Against Escherichia coli O157:H7 and Methicillin-Resistant Staphylococcus aureus (MRSA).

In this work, we performed the rational design of a cationic antimicrobial peptide, GIBIMPY4, using the software DEPRAMPs developed at the GIBIM research group. GIBIMPY4 has a length of 17 amino acids, it is amphipathic, its structure is α-helix and it has a net charge of (+5). Solid-phase peptide synthesis was performed using the Fmoc strategy in acid medium. The primary structure was confirmed by MALDI-TOF mass spectrometry. The antimicrobial activity of the peptide was evaluated by broth microdilution method by measuring optical density in 96-well microplates. The minimal inhibitory concentration of GIBIMPY4 to kill 50 % of the bacterial cells (MIC50) was 6.20 ± 0.02 µM for MRSA and 4.55 ± 0.02 µM for E. coli O157:H7, while also reporting a bacteriostatic effect for the later. GIBIMPY4 activity was sensitive to salt concentration in E. coli but insignificant effect in its activity against MRSA. The peptide seems to be a broad-spectrum antimicrobial agent based on the results against Gram-positive and Gram-negative bacteria and was specific for bacterial cells E. coli O157:H7 with index of specificity equal to 9.01 in vitro assays.