H. Liu

Mouse model of hematogenous implant-related Staphylococcus aureus biofilm infection reveals therapeutic targets

Significance Hematogenous implant-related infections are an important clinical problem because bacteria spread from the bloodstream to a previously well-functioning implant and result in infectious complications and failure of a medical device or prosthesis. To study these infections, we developed a preclinical animal model of a Staphylococcus aureus hematogenous implant infection with the capability to monitor noninvasively and longitudinally the dissemination of the bacteria from the blood to a surgically placed orthopedic implant. Using this model, α-toxin and clumping factor A were identified as key factors that contributed to the pathogenesis of these infections by promoting biofilm formation. Finally, neutralizing antibodies against these factors provided a targeted, nonantibiotic alternative approach to help prevent these difficult-to-treat and costly infections. Infection is a major complication of implantable medical devices, which provide a scaffold for biofilm formation, thereby reducing susceptibility to antibiotics and complicating treatment. Hematogenous implant-related infections following bacteremia are particularly problematic because they can occur at any time in a previously stable implant. Herein, we developed a model of hematogenous infection in which an orthopedic titanium implant was surgically placed in the legs of mice followed 3 wk later by an i.v. exposure to Staphylococcus aureus. This procedure resulted in a marked propensity for a hematogenous implant-related infection comprised of septic arthritis, osteomyelitis, and biofilm formation on the implants in the surgical legs compared with sham-operated surgical legs without implant placement and with contralateral nonoperated normal legs. Neutralizing human monoclonal antibodies against α-toxin (AT) and clumping factor A (ClfA), especially in combination, inhibited biofilm formation in vitro and the hematogenous implant-related infection in vivo. Our findings suggest that AT and ClfA are pathogenic factors that could be therapeutically targeted against S. aureus hematogenous implant-related infections.

Neutralizing α-toxin accelerates healing of Staphylococcus aureus-infected wounds in normal and diabetic mice

ABSTRACT Staphylococcus aureus wound infections delay healing and result in invasive complications such as osteomyelitis, especially in the setting of diabetic foot ulcers. In preclinical animal models of S. aureus skin infection, antibody neutralization of alpha-toxin (AT), an S. aureus-secreted pore-forming cytolytic toxin, reduces disease severity by inhibiting skin necrosis and restoring effective host immune responses. However, whether therapeutic neutralization of alpha-toxin is effective against S. aureus-infected wounds is unclear. Herein, the efficacy of prophylactic treatment with a human neutralizing anti-AT monoclonal antibody (MAb) was evaluated in an S. aureus skin wound infection model in nondiabetic and diabetic mice. In both nondiabetic and diabetic mice, anti-AT MAb treatment decreased wound size and bacterial burden and enhanced reepithelialization and wound resolution compared to control MAb treatment. Anti-AT MAb had distinctive effects on the host immune response, including decreased neutrophil and increased monocyte and macrophage infiltrates in nondiabetic mice and decreased neutrophil extracellular traps (NETs) in diabetic mice. Similar therapeutic efficacy was achieved with an active vaccine targeting AT. Taken together, neutralization of AT had a therapeutic effect against S. aureus-infected wounds in both nondiabetic and diabetic mice that was associated with differential effects on the host immune response.

Injury, dysbiosis, and filaggrin deficiency drive skin inflammation through keratinocyte IL-1α release

Background Atopic dermatitis (AD) is associated with epidermal barrier defects, dysbiosis, and skin injury caused by scratching. In particular, the barrier‐defective epidermis in patients with AD with loss‐of‐function filaggrin mutations has increased IL‐1&agr; and IL‐1&bgr; levels, but the mechanisms by which IL‐1&agr;, IL‐1&bgr;, or both are induced and whether they contribute to the aberrant skin inflammation in patients with AD is unknown. Objective We sought to determine the mechanisms through which skin injury, dysbiosis, and increased epidermal IL‐1&agr; and IL‐1&bgr; levels contribute to development of skin inflammation in a mouse model of injury‐induced skin inflammation in filaggrin‐deficient mice without the matted mutation (ft/ft mice). Methods Skin injury of wild‐type, ft/ft, and myeloid differentiation primary response gene–88–deficient ft/ft mice was performed, and ensuing skin inflammation was evaluated by using digital photography, histologic analysis, and flow cytometry. IL‐1&agr; and IL‐1&bgr; protein expression was measured by means of ELISA and visualized by using immunofluorescence and immunoelectron microscopy. Composition of the skin microbiome was determined by using 16S rDNA sequencing. Results Skin injury of ft/ft mice induced chronic skin inflammation involving dysbiosis‐driven intracellular IL‐1&agr; release from keratinocytes. IL‐1&agr; was necessary and sufficient for skin inflammation in vivo and secreted from keratinocytes by various stimuli in vitro. Topical antibiotics or cohousing of ft/ft mice with unaffected wild‐type mice to alter or intermix skin microbiota, respectively, resolved the skin inflammation and restored keratinocyte intracellular IL‐1&agr; localization. Conclusions Taken together, skin injury, dysbiosis, and filaggrin deficiency triggered keratinocyte intracellular IL‐1&agr; release that was sufficient to drive chronic skin inflammation, which has implications for AD pathogenesis and potential therapeutic targets. Graphical abstract Figure. No Caption available.