Oral mucosal lipids are antibacterial against Porphyromonas gingivalis, induce ultrastructural damage, and alter bacterial lipid and protein compositions

Oral mucosal and salivary lipids exhibit potent antimicrobial activity for a variety of Gram-positive and Gram-negative bacteria; however, little is known about their spectrum of antimicrobial activity or mechanisms of action against oral bacteria. In this study, we examine the activity of two fatty acids and three sphingoid bases against Porphyromonas gingivalis, an important colonizer of the oral cavity implicated in periodontitis. Minimal inhibitory concentrations, minimal bactericidal concentrations, and kill kinetics revealed variable, but potent, activity of oral mucosal and salivary lipids against P. gingivalis, indicating that lipid structure may be an important determinant in lipid mechanisms of activity against bacteria, although specific components of bacterial membranes are also likely important. Electron micrographs showed ultrastructural damage induced by sapienic acid and phytosphingosine and confirmed disruption of the bacterial plasma membrane. This information, coupled with the association of treatment lipids with P. gingivalis lipids revealed via thin layer chromatography, suggests that the plasma membrane is a likely target of lipid antibacterial activity. Utilizing a combination of two-dimensional in-gel electrophoresis and Western blot followed by mass spectroscopy and N-terminus degradation sequencing we also show that treatment with sapienic acid induces upregulation of a set of proteins comprising a unique P. gingivalis stress response, including proteins important in fatty acid biosynthesis, metabolism and energy production, protein processing, cell adhesion and virulence. Prophylactic or therapeutic lipid treatments may be beneficial for intervention of infection by supplementing the natural immune function of endogenous lipids on mucosal surfaces. Researchers in the USA have identified five naturally occurring molecules that kill bacteria responsible for periodontal disease. The molecules are part of the diverse but sparsely documented countermeasures that the body uses to fight oral pathogens. Led by Philip Wertz and Carol Fischer of the University of Iowa, the researchers characterized the effects of naturally secreted lipids known as sphingoid bases and short-chain fatty acids, which are toxic to many bacteria, on Porphyromonas gingivalis, a key contributor to periodontitis. The two particularly potent molecules that they identified, phytosphingosine and sapienic acid, both killed this bacterium by inflicting severe damage to its outer membrane. Since these lipids are produced by the body and active at physiological concentrations, they may offer a safe and effective alternative to antibiotics for fighting P. gingivalis infection.