Biocide-Induced Antimocrobial Peptide Resistance inPorphyromonas gingivalis

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Kujala, Nicholas G.
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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 bacterium associated with the overgrowth of periodontal disease. Defensin resistance has been attributed to an inducible microbial gene function that may be activated by several factors, including sub-lethal levels of biocides and antibiotics. Triclosan (Irgasan TM) is a biocide that has recently been formulated into numerous consumer products including toothpaste (TotaI™, 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. 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. gingiva lis . 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 to defensins. Based on those experiments we concluded that that exposure of P. gingivalis to sub-lethal levels (O.1µg/L) of Triclosan induced a resistance to defensins but a sub-lethal level (O.1µg/L) of Polymyxin B did not. When we examined the effect of sub-MIC Triclosan treatments on the expression of 20 genes associated with P. gingivalis virulence we found that rgp1, rgp2, recA, lon, groES, groEL, fisH, dnaK, dnaJ were upregulated and dksA, dps, clpC, clpB were down regulated compared to untreated bacteria. This pattern of changed expression may affect the virulence of the periodontal pathogen P. gingivalis. This may suggest new lines of investigation into the role of antimicrobials in the treatment of periodontitis, such as sequencing certain genes and further exploring their specific roles in antimicrobial resistance and finding new methods of preventing their tendencies to promote disease.
vi, 27 p.
Kalamazoo College
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