Marine Peptide-N6NH2 and Its Derivative-GUON6NH2 Have Potent Antimicrobial Activity Against Intracellular Edwardsiella tarda in vitro and in vivo

Abstract

Edwardsiella tarda is a facultative intracellular pathogen in humans and animals. There is no effective way except vaccine candidates to eradicate intracellular E. tarda. In this study, four derivatives of marine peptide-N6NH2 were designed by an introduction of unnatural residues or substitution of natural ones, and their intracellular activities against E. tarda were evaluated in macrophages and in mice, respectively. The minimum inhibitory concentration (MIC) value of N6NH2 and GUON6NH2 against E. tarda was 8 μg/mL. GUON6NH2 showed higher stability to trypsin, lower toxicity (<1%) and longer post-antibiotic effect (PAE) than N6NH2 and other derivatives. Antibacterial mechanism results showed that GUON6NH2 could bind to LPS and destroyed outer/inner cell membranes of E. tarda, superior to N6NH2 and norfloxacin. Both N6NH2 and GUON6NH2 were internalized into macrophages mainly via lipid rafts, micropinocytosis, and microtubule polymerization, respectively, and distributed in the cytoplasm. The intracellular inhibition rate of GUON6NH2 against E. tarda was 97.05–100%, higher than that in case of N6NH2 (96.82–100%). In the E. tarda-induced peritonitis mouse model, after treatment with of 1 μmol/kg N6NH2 and GUON6NH2, intracellular bacterial numbers were reduced by 1.54- and 1.97-Log10 CFU, respectively, higher than norfloxacin (0.35-Log10 CFU). These results suggest that GUON6NH2 may be an excellent candidate for novel antimicrobial agents to treat infectious diseases caused by intracellular E. tarda.

In Vitro Pharmacodynamics and Bactericidal Mechanism of Fungal Defensin-Derived Peptides NZX and P2 against Streptococcus agalactiae

“…After treatment with peptides, the bacteria were washed twice with PBS and stained with propidium iodide (PI). Finally, a flow cytometer (FACS Calibur, BD, USA) was applied to determine the fluorescence [ 34 ].…”

Strategies for the eradication of intracellular bacterial pathogens

“…168 Moreover, synergistic antibacterial effects can be achieved by conjugating AMPs with other compounds, including CPPs or antibiotics. [169][170][171][172] Wang and coworkers constructed two CPP-AMP conjugates (B6N2 and T11N2) and found that these conjugates mainly locate in endosomes of RAW264.7 macrophage cells. Moreover, these conjugates exhibited enhanced activity against intracellular S. typhimurium as compared to AMP alone or non-conjugated mixtures.…”

Antimicrobial peptides´ immune modulation role in intracellular bacterial infection

“…In addition, esculentin-1a-derived peptides can penetrate the plasma membrane of bronchial cells and promote the rapid clearance of intracellular Pseudomonas aeruginosa since there is a ~ 40% and 60% decrease in the number of intracellular bacteria one hour after exposure ( 83 ).. Likewise, peptides like N6NH2 and their derivative, GUON6NH2, can be internalized in infected macrophages and exert their antibacterial activity against Edwardsiella tarda , thus helping reduce intracellular bacterial numbers ( 84 ). Another peptide that was able to enter murine and human macrophages in vivo is mature bovine neutrophil β-defensin 4.…”