Abstract
During infection, Staphylococcus aureus is exposed to exogenous menaquinone which is essential for the human blood clotting cascade. The effect of exogenous menaquinone on S. aureus phenotypic expression is not known. To test whether menaquinone affects expression of virulence-associated phenotypes, methicillin-sensitive (MSSA) and -resistant (MRSA) S. aureus strains (n = 8) were grown in the presence of menaquinone (0.001 - 12 μg/ml). Capsule production, biofilm formation (plastic and fibronectin-coated microtiter plates) and carotenoid levels were determined spectrophotometrically after growth in Mueller Hinton broth (MH; 24-hr, 37°C). All experiments were, at minimum, done in triplicate and repeated twice. Menaquinone at physiologic levels (0.01 μg/ml MH) significantly increased (p 0.05) biofilm formation on plastic in a manner that was bacterial population size dependent. In addition, menaquinone (0.05 - 4 μg/ml) significantly increased (p 0.05) biofilm formation on fibronectin-coated surfaces for four MSSA strains and one MRSA strain by two to six-fold as compared to medium controls. However, menaquinone had no effect on capsule production or cell-associated carotenoid levels. Menaquinone’s effect on biofilm formation on fibronectin-coated surfaces appears to be regulated by sarA. These findings are the first to demonstrate that a vitamin at concentrations reported in humans affects S. aureus virulence-associated phenotypes.
Highlights
Bacterial adaptations to environmental changes are, in part, dependent on inter-cell and inter-kingdom communication [1] [2]
Menaquinone (0.01 - 0.09 μg/ml) caused a significant (p < 0.05) concentration specific increase in the level of S. aureus biofilm formation on plastic, which was dependent upon bacterial density (Figure 1(a))
Biofilm formation on plastic was significantly increased at the lowest bacterial density tested (104 CFU/ml)
Summary
Bacterial adaptations to environmental changes are, in part, dependent on inter-cell and inter-kingdom communication [1] [2]. E.g. insulin and dehydroepiandrosterone and neurotransmitters, e.g. norepinephrine have been reported to function as interkingdom communication signals [1] [3]-[7]. How to cite this paper: Kirby, D.T., et al (2014) Menaquinone (Vitamin K2) Enhancement of Staphylococcus aureus Biofilm Formation. S. aureus is an important community-acquired and nosocomial pathogen that produces endogenous (vitamin K2) for respiration [12]-[16]. The potential effects of exogenous menaquinone on S. aureus is an important question since in vivo staphylococci are exposed to menaquinone, an essential factor for hemostasis in humans [14] [17] [18]
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