Activity of an Antimicrobial Peptide Mimetic against Planktonic and Biofilm Cultures of Oral Pathogens

Abstract

Antimicrobial peptides (AMPs) are naturally occurring, broad-spectrum antimicrobial agents that have recently been examined for their utility as therapeutic antibiotics. Unfortunately, they are expensive to produce and are often sensitive to protease digestion. To address this problem, we have examined the activity of a peptide mimetic whose design was based on the structure of magainin, exhibiting its amphiphilic structure. We demonstrate that this compound, meta-phenylene ethynylene (mPE), exhibits antimicrobial activity at nanomolar concentrations against a variety of bacterial and Candida species found in oral infections. Since Streptococcus mutans, an etiological agent of dental caries, colonizes the tooth surface and forms a biofilm, we quantified the activity of this compound against S. mutans growing under conditions that favor biofilm formation. Our results indicate that mPE can prevent the formation of a biofilm at nanomolar concentrations. Incubation with 5 nM mPE prevents further growth of the biofilm, and 100 nM mPE reduces viable bacteria in the biofilm by 3 logs. Structure-function analyses suggest that mPE inhibits the bioactivity of lipopolysaccharide and binds DNA at equimolar ratios, suggesting that it may act both as a membrane-active molecule, similar to magainin, and as an intracellular antibiotic, similar to other AMPs. We conclude that mPE and similar molecules display great potential for development as therapeutic antimicrobials.

New trends in peptide-based anti-biofilm strategies: a review of recent achievements and bioinformatic approaches

“…AMPs have been recognized as promising candidates for replacing classical antibiotics (Figure 1) due to their multiple mechanisms of action and low specificity in terms of molecular targets, which reduces the chance of acquired resistance (Zasloff 2002;Beckloff et al 2007). Moreover, compared with conventional antimicrobials, which are generally active only against bacteria or fungi, AMPs exert activity against a broad spectrum of microorganisms, such as both Gram-negative and Gram-positive bacteria, including drug-resistant strains, parasites, enveloped viruses and even some cancer cells (Sang and Blecha 2008;Splith and Neundorf 2011;Wimley and Hristova 2011).…”

“…Moreover, compared with conventional antimicrobials, which are generally active only against bacteria or fungi, AMPs exert activity against a broad spectrum of microorganisms, such as both Gram-negative and Gram-positive bacteria, including drug-resistant strains, parasites, enveloped viruses and even some cancer cells (Sang and Blecha 2008;Splith and Neundorf 2011;Wimley and Hristova 2011). AMPs are also cell specific and are able to distinguish host from non-host cells based on their charge (Beckloff et al 2007). Besides their antimicrobial action, AMPs can also influence processes which support antimicrobial action, like cytokine release, chemotaxis, antigen presentation, angiogenesis and wound healing (Lai and Gallo 2009).…”

“…For example, it is thought that the synthetic AMP meta-phenylene ethynylene (mPE), based on magainin and active at nanomolar concentrations against biofilms of Streptococcus mutans, acts both as a membrane-active molecule, inhibiting lipopolysaccharides (LPSs), similar to magainin, and as an intracellular antibiotic by binding to DNA at equimolar ratios (Beckloff et al 2007). Another example is pleurocidin, which is thought to inhibit nucleic acid and protein synthesis without damaging the cytoplasmic membrane of Escherichia coli at low concentrations (Patrzykat et al 2002), but it is able to cause membrane leakage and pore-like channels at higher concentrations (Mason et al 2006).…”

“…AMPs are difficult and expensive to obtain in large quantities (Beckloff et al 2007), mainly due to the complex processes needed for their extraction, isolation and purification. While large amounts of AMPs may be applied to a localized external site (as topical agents), the use of AMPs for internal infections raises some problems: (1) their antimicrobial power is reduced in the presence of biological fluids, (2) inadequate safety margins and rapid renal clearance, (3) the non-specific effect of AMPs may compromise the eradication of a specific infectious agent, and (4) some AMPs display toxicity to the host cells and may induce unwanted pro-inflammatory responses (Baltzer and Brown 2011;Batoni et al 2011).…”

Non-conventional therapeutics for oral infections

“…103 For example, mimetics based upon the defensin structure have demonstrated a high therapeutic index in pre-clinical studies. 104 With regards to the oral cavity, the development of novel antimicrobials should allow control of pathogens without loss of beneficial commensals. 105 Approaches that stimulate or restore the normal expression patterns of AMPs, rather than being used as exogenous therapeutic agents, may be particularly useful in the prevention of periodontal disease.…”