Activity of Synthetic Antimicrobial Peptide GH12 against Oral Streptococci

Abstract

Controlling the growth of cariogenic microorganisms such as oral streptococci is an adjunct therapy for caries-active individuals to prevent and treat caries. Here we investigated the antimicrobial activity of the synthetic amphipathic α- helical antimicrobial peptide GH12 (GLLWHLLHHLLH-NH₂) against oral streptococci in vitro. Circular dichroism studies showed that GH12 takes on an α-helical conformation in the presence of membrane-mimicking solvents, and reversed-phase high-performance liquid chromatography studies showed that GH12 remains stable in saliva. The peptide showed bactericidal activity against oral streptococci, with minimum inhibitory concentrations ranging from 6.7 to 32.0 μg/ml. GH12 concentrations 4-fold higher than the minimum bactericidal concentration completely killed oral streptococci within 20 min. Treating oral streptococci with GH12 caused noticeable changes in bacterial viability and morphology based on confocal laser scanning microscopy and scanning electron microscopy. Effects of GH12 on biofilm formation and on viability of mature biofilm were quantified by crystal violet staining and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. GH12 effectively inhibited biofilm formation and metabolic activity in biofilms of oral streptococci, especially S. mutans, S. sobrinus and S. salivarius. These results suggest that GH12 shows rapid and strong antimicrobial activity against oral streptococci in vitro, opening the door to preclinical and clinical studies to explore its potential for caries prevention and treatment.

Ecological Approaches to Dental Caries Prevention: Paradigm Shift or Shibboleth?

“…More recently, a hydroxyapatite-binding AMP was designed, based on the fusion of specific hydroxyapatite-binding heptapeptide (HBP7) with KSL-W, and this bioconjugate was shown to have improved oral retention and antibacterial efficacy [Huang et al, 2016b]. Other AMPs that have shown in vitro antimicrobial activity against cariogenic bacteria and inhibited oral biofilm formation include a synthetic peptide called L-K6 (derived from the naturally occurring peptide temporin-1CEb), a short synthetic amphiphilic peptide known as 1018, and an amphipathic α-helical peptide containing only 12 amino acids named GH12 [Shang et al, 2014;Wang et al, 2015;Tu et al, 2016].…”

Antimicrobial peptide GH12 suppresses cariogenic virulence factors of Streptococcus mutans

“…In combat against cariogenic bacteria, our group de novo designed and synthesized a series of cationic, amphipathic α-helical AMPs and selected the most promising one, GH12, a 12-amino acids peptide with optimal structure and potency. Previous studies [20,21] showed that GH12 at the concentration of 8 mg/L, the minimal inhibitory concentration (MIC) and minimal bactericidal inhibitory concentration (MBC) of GH12 against S. mutans , was potent against growth of planktonic bacteria and had a rapid mechanism of action, killing 90% of bacteria in less than 5 min of exposure. Moreover, GH12 effectively inhibited S. mutan s biofilm formation and metabolism, as well as significantly reduced the biomass of 1-day old S. mutans biofilm.…”

“…Cytomembrane observation showed that GH12 had a mechanism of killing S. mutans through formation lysis and pores on the cell membrane and envelope. Meanwhile, GH12 had showed little toxic effect on the viability of human gingival fibroblasts [21], and kept stable in human saliva [20]. …”

A Membrane-Targeted Peptide Inhibiting PtxA of Phosphotransferase System Blocks <b><i>Streptococcus mutans</i></b>

“…Samples were fixed overnight in 2.5% glutaraldehyde solution, dehydrated in graded ethanol solutions, and finally vacuum dried. After being sputter-coated with gold, the samples were observed using a field emission scanning electron microscope (Merlin, Zeiss, Oberkochen, Germany) [Tu et al, 2016].…”

“…Previous studies have shown that native AMPs isolated from bacteria, fungi, animals, and plants, can have significant bactericidal effects; however, they are expensive to produce and possess potential toxicity [Diamond and Ryan, 2011;Kosciuczuk et al, 2012;Tati et al, 2014]. As a result, modified AMPs have been developed with a lower production cost, a lower host toxicity, and a range of linear or cyclic forms, as well as other forms [Wu and Hancock, 1999;Da et al, 2013;Shang et al, 2014;Tu et al, 2016]. It has also been reported that combinations of a traditional antibiotic and AMPs can be effective as antimicrobial agents against oral pathogens [Lobos et al, 2009].…”