Biocide-induced Antimicrobial Peptide Resistance in Porphyromonas gingivalis

Abstract

Defensins belong to a class of small, cationic antimicrobial peptides (CAMPs) which have evolved as the primary defense against microbial flora such as Porphyromonas gingivalis, an oral bacteria and major contributor to periodontal disease. The focus of this research was to determine the potential for bacteria to develop resistance to defensins after exposure to sub-lethal levels of the biocide Triclosan and investigate the mechanism of that defensin resistance in P. gingivalis. In addition, we tested the bacteria for defensin resistance after exposure to sub-lethal doses of Polymyxin B, a peptide antibiotic with a similar function as defensins. Defensin resistance is an inducible gene function that may be activated by several factors, including sub-lethal levels of biocides and antibiotics. Triclosan (Irgasan™) is a biocide that has recently been formulated into numerous consumer products including toothpaste (Total™, Colgate). It is unknown whether the inclusion of Triclosan into such products has the potential to induced antimicrobial resistance to host immune system factors such as defensins. Since defensin resistance can be induced by a number of factors that cause bacterial stress we hypothesized that sub-lethal levels of Triclosan will induce resistance to defensins in P. gingivalis. Based on those experiments we concluded that exposure of P. gingivalis to sub-lethal levels of Triclosan induced a resistance to defensins but sub-lethal levels of Polymyxin B do not induce such resistance. When we examined the effect of Triclosan sub-MIC treatments on the expression of 21 genes associated with P. gingivalis virulence we found that rgp1, rgp2, recA, lon, groES, groEL, ftsH, dnaK, dnaJ were upregulated and dksA, dps, clpC, clpB were down-regulated compared to untreated bacteria. This pattern of changed expression may affect the pathogenisity of periodontal pathogens and suggests new lines of investigation into the role of antimicrobials in the treatment of periodontitis.