Bactericidal activity of the human skin fatty acid cis-6-hexadecanoic acid on Staphylococcus aureus.

Human skin fatty acids are a potent aspect of our innate defenses, giving surface protection against potentially invasive organisms. They provide an important parameter in determining the ecology of the skin microflora, and alterations can lead to increased colonization by pathogens such as Staphylococcus aureus. Harnessing skin fatty acids may also give a new avenue of exploration in the generation of control measures against drug-resistant organisms. Despite their importance, the mechanism(s) whereby skin fatty acids kill bacteria has remained largely elusive. Here, we describe an analysis of the bactericidal effects of the major human skin fatty acid cis-6-hexadecenoic acid (C6H) on the human commensal and pathogen S. aureus. Several C6H concentration-dependent mechanisms were found. At high concentrations, C6H swiftly kills cells associated with a general loss of membrane integrity. However, C6H still kills at lower concentrations, acting through disruption of the proton motive force, an increase in membrane fluidity, and its effects on electron transfer. The design of analogues with altered bactericidal effects has begun to determine the structural constraints on activity and paves the way for the rational design of new antistaphylococcal agents.

Cellular-FLIP, Raji isoform (c-FLIP R) modulates cell death induction upon T-cell activation and infection.

Dysregulation of apoptosis caused by an imbalance of pro- and anti-apoptotic protein expression can lead to cancer, neurodegenerative, and autoimmune diseases. Cellular-FLIP (c-FLIP) proteins inhibit apoptosis directly at the death-inducing signaling complex of death receptors, such as CD95, and have been linked to apoptosis regulation during immune responses. While the isoforms c-FLIPL and c-FLIPS are well characterized, the function of c-FLIPR remains poorly understood. Here, we demonstrate the induction of endogenous murine c-FLIPR in activated lymphocytes for the first time. To analyze c-FLIPR function in vivo, we generated transgenic mice expressing murine c-FLIPR specifically in hematopoietic cells. As expected, lymphocytes from c-FLIPR transgenic mice were protected against CD95-induced apoptosis in vitro. In the steady state, transgenic mice had normal cell numbers and unaltered frequencies of B cells and T-cell subsets in lymphoid organs. However, when challenged with Listeria monocytogenes, c-FLIPR transgenic mice showed less liver necrosis and better bacterial clearance compared with infected wild-type mice. We conclude that c-FLIPR expression in hematopoietic cells supports an efficient immune response against bacterial infections.

Dendritic cells are central coordinators of the host immune response to Staphylococcus aureus bloodstream infection.

Dendritic cells (DCs) play an important role in integration of the immune responses induced by pathogens. The purpose of this study was to determine the importance of DCs in host defense against Staphylococcus aureus bacteremia. Using a murine infection model, we demonstrated that DCs are rapidly recruited into infected tissue after intravenous inoculation with S. aureus. The recruited DCs were fully functional and in a more advanced stage of maturation than those isolated from uninfected mice. Depletion of DCs in CD11c-DTR transgenic mice resulted in substantial worsening of infection, as indicated by increased bacterial loads in kidneys and lungs, accelerated mortality, and more severe pathology. Furthermore, DC depletion completely abolished IL-12 production in response to infection. The beneficial effect afforded by DCs during S. aureus infection was not mediated by their contribution to direct bacterial killing, nor by increased neutrophil recruitment. Instead, neutrophil influx (along with expression of CXC chemokines) was significantly enhanced in infected tissue after depletion of DCs. We also found that the bactericidal capacity of the recruited neutrophils was significantly impaired in DC-depleted mice. More importantly, the detrimental effect of DC depletion was practically reversed by treatment with exogenous recombinant mouse IL-12. Our results demonstrated that DCs, probably through their production of IL-12, play an important role in coordinating the inflammatory response during S. aureus infection.

The iron-regulated surface proteins IsdA, IsdB, and IsdH are not required for heme iron utilization in Staphylococcus aureus.

The iron-regulated surface determinant proteins (Isd) of Staphylococcus aureus are expressed during iron limitation and have been proposed to be involved in the scavenging of iron from heme. In this study, the genes encoding the surface proteins IsdA, IsdB, and IsdH were inactivated in order to determine their combined role. The triple mutant was found to have no defect in growth under any conditions of iron limitation tested. Also using a mouse septic arthritis model of S. aureus systemic disease, no significant difference in bacterial load was observed for the triple mutant, compared with its otherwise isogenic parent.