Abstract
The development of new antimicrobial peptides has become an attractive alternative to conventional antibiotics due to the increasing rates of microbial drug resistance. Ib-M corresponds to a family of cationic synthetic peptides, 20 amino acids in length, that have shown inhibitory effect against the non-pathogenic strain Escherichia coli K-12. This work evaluated the antimicrobial potential of Ib-M peptides against the pathogenic E. coli O157: H7 using a reference strain and a clinical isolate. The Ib-M peptides showed antibacterial activity against both strains of E. coli O157: H7; the minimum inhibitory concentration of Ib-M peptides ranged from 1.6 to 12.5 μM and the minimum bactericidal concentration ranged from 3.7 to 22.9 μM, being Ib-M1 and Ib-M2 the peptides that presented the highest inhibitory effect. Time-kill kinetics assay showed a reduction of the bacterial population by more than 95% after 4 hours of exposure to 1xMIC of Ib-M1. Low cytotoxicity was observed in VERO cells with 50% cytotoxic concentration in the range from 197.5 to more than 400 μM. All peptides showed a random structure in hydrophilic environments, except Ib-M1, and all of them transitioned to an α-helical structure when the hydrophobicity of the medium was increased. In conclusion, these findings support the in vitro antimicrobial effect of Ib-M peptides against the pathogenic bacteria E. coli O157: H7 and prove to be promising molecules for the development of new therapeutic alternatives.
Highlights
MethodsThe Ib-M peptides (Ib-M1, Ib-M2, Ib-M4, Ib-M5, and Ib-M6) were used in this study
Pathogenic bacteria with antimicrobial resistance has become a global public health threat leading to the research and development of new antibiotics [1]
All Ib-M peptides showed an α-helical structure in sodium dodecyl sulfate (SDS); these results suggest the peptides acquired their secondary structure in the presence of the cell membrane of E. coli (Fig 1)
Summary
The Ib-M peptides (Ib-M1, Ib-M2, Ib-M4, Ib-M5, and Ib-M6) were used in this study. They have a cationic charge of +6 and 20 amino acids in their structure. General characteristics of peptides have already been described by Florez-Castillo [7]. Ib-M peptides were manufactured by Biomatik and stock solutions were prepared in Tris-HCl buffer (10 mM pH 7.4) and stored at -80 ̊C until used. Streptomycin (STP) and gentamicin (GNT) from SIGMA-ALDRICH were used as reference antibiotics. Stock solutions were prepared in Muller Hinton Broth (MHB) before each experiment
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