Mechanisms of Decreased Susceptibility to β-Defensins byTreponema denticola

Abstract

Treponema denticola, a periodontal pathogen, is relatively resistant to human beta-defensins, which are small cationic antimicrobial peptides produced by a number of cells, including the gingival epithelium. Using two independent methods, we previously demonstrated that T. denticola proteases are not responsible for decreased vulnerability to defensins. In this study, we confirmed that the major outer membrane protease, dentilisin, is not responsible for T. denticola insensitivity to defensins and examined several other possible mechanisms, including reduced binding to the bacterial surface and efflux pump activity. It has been suggested that some bacteria mask their surfaces with serum proteins. T. denticola grown in a serum-free medium did not exhibit increased susceptibility to human beta-defensin 2 and 3 (h␤D-2 and h␤D-3, respectively), suggesting that cloaking of the outer surface with host proteins is not involved in defensin resistance. Nonetheless, we demonstrated that T. denticola binds significantly less h␤D-2 and -3 than susceptible organisms bind, suggesting that the unusual outer membrane composition of T. denticola may discourage cationic peptide binding. Efflux pumps have been shown to mediate resistance to antibiotics and cationic peptides in other bacteria, and their role in T. denticola's relative resistance to ␤-defensins was investigated. Three inhibitors of bacterial ATP-binding cassette (ABC) efflux pumps had no effect on T. denticola's susceptibility to h␤D-2 or -3. In contrast, a proton motive force inhibitor, carbonyl cyanide 3-chlorophenylhydrazone, increased the susceptibility of T. denticola to killing by h␤D-3, demonstrating a potential role for efflux pumps (other than ABC pumps) in resistance to this peptide. Our data suggest that the combination of decreased defensin binding and efflux of any peptide which enters the cytoplasm may explain T. denticola's relative resistance to human beta-defensins.

Interspecies Interactions within Oral Microbial Communities

“…A number of oral bacteria, including S. mutans, have been shown to be susceptible to the histatins produced by salivary glands (160). However, some bacteria, including T. denticola, have demonstrated resistance to specific defensins (10). Since bacteria residing in biofilms are generally more resistant to antimicrobial agents than their planktonic counterparts, it is not yet clear if these endogenous antimicrobial agents play a significant role in modulating the properties of oral biofilms.…”

Virulence Factors of the Oral Spirochete Treponema denticola

“…Inhibition of components of the innate immune system is obviously of great advantage to a bacterium that has been shown to associate closely with epithelial cells in vivo. T. denticola can evade aspects of the innate immune defense by preventing efficient binding of antimicrobial peptides, such as β-defensins, that are produced by epithelial cells, and by inducing rapid efflux of some host defense peptides which enter the cytoplasm (Brissette and Lukehart, 2007). Recently, T. denticola has also been shown to suppress the production of β-defensin 3 by human gingival epithelial cells (Shin et al, 2010).…”

Skin bacteria after chlorhexidine exposure—is there a difference in response to human β-Defensin-3?

“…The role of an MDR efflux-related increase in 301 MIC and skin disinfection with CH is also discussed by DeMarco et al [33]. Efflux mechan-302 isms are also relevant for decreasing susceptibility, for example of Treponema denticola, to 303 hBD-3 [34], although current research findings suggest that MDR efflux pumps do not play 304 an important role in hBD-3-resistance [35]. 305…”

“…In a previous study, we 34 were able to show that chlorhexidine digluconate (CHG) in propan-1-ol slows down recoloni-35 zation of the skin for at least 72 h [13]. We therefore assumed that CHG persists on the skin 36 for at least 3 days after application when the skin is covered with an adhesive dressing after 37 evaporation of the alcohol.…”