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Susceptibility of oral bacteria to an antimicrobial decapeptide

S. P. Concannon¹, T. D. Crowe¹, J. J. Abercrombie¹, C. M. Molina¹, P. Hou¹, D. K. Sukumaran², P. A. Raj³ and K. -P. Leung¹

¹Microbiology Branch, US Army Dental Research Detachment, Walter Reed Army Institute of Research, Great Lakes, IL 60088, USA ²Department of Chemistry, State University of New York at Buffalo, Buffalo, NY 14260, USA ³School of Dentistry, Marquette University, Milwaukee, WI 53233, USA

Correspondence K.-P. Leung kai.leung{at}amedd.army.mil

Received April 14, 2003
Accepted August 24, 2003

Naturally occurring antimicrobial peptides have emerged as alternative classes of antimicrobials. In general, these antimicrobial peptides exhibit selectivity for prokaryotes and minimize the problems of engendering microbial resistance. As an alternative method to search for more effective broad-spectrum peptide antimicrobials, investigators have developed peptide libraries by using synthetic combinatorial technology. A novel decapeptide, KKVVFKVKFK (KSL), has been identified that shows a broad range of antibacterial activity. The purpose of this study was to test the efficacy of this antimicrobial peptide in killing selected strains of oral pathogens and resident saliva bacteria collected from human subjects. Cytotoxic activity of KSL against mammalian cells and the structural features of this decapeptide were also investigated, the latter by using two-dimensional NMR in aqueous and DMSO solutions. MICs of KSL for the majority of oral bacteria tested in vitro ranged from 3 to 100 µg ml^-1. Minimal bactericidal concentrations of KSL were, in general, within one to two dilutions of the MICs. KSL exhibited an ED₉₉ (the dose at which 99 % killing was observed after 15 min at 37 °C) of 6.25 µg ml^-1 against selected strains of Lactobacillus salivarius, Streptococcus mutans, Streptococcus gordonii and Actinobacillus actinomycetemcomitans. In addition, KSL damaged bacterial cell membranes and caused 1.05 log units reduction of viability counts of saliva bacteria. In vitro toxicity studies showed that KSL, at concentrations up to 1 mg ml^-1, did not induce cell death or compromise the membrane integrity of human gingival fibroblasts. NMR studies suggest that KSL adopts an -helical structure in DMSO solution, which mimics the polar aprotic membrane environment, whereas it remains unstructured in aqueous medium. This study shows that KSL may be a useful antimicrobial agent for inhibiting the growth of oral bacteria that are associated with caries development and early plaque formation.

Abbreviations: CD, circular dichroism; DMF, N,N-dimethylforamide; DQF-COSY, double quantum-filtered correlated spectroscopy; Fmoc, 9-fluorenylmethoxycarbonyl; HGF, human gingival fibroblasts; LDH, lactate dehydrogenase; MALDI-TOF, matrix-assisted laser desorption/ionization–time of flight; MBC, minimal bactericidal concentration; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; NOE, nuclear Overhauser effect; NOESY, nuclear Overhauser effect spectroscopy; RMSD, root mean square deviation; TOCSY, total correlated spectroscopy.

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				K.-P. Leung, T.D. Crowe, J.J. Abercrombie, C.M. Molina, C.J. Bradshaw, C.L. Jensen, Q. Luo, and G.A. Thompson Control of Oral Biofilm Formation by an Antimicrobial Decapeptide J. Dent. Res., December 1, 2005; 84(12): 1172 - 1177. [Abstract] [Full Text] [PDF]