Severe Dermatitis Associated with Spontaneous Staphylococcus xylosus Infection in Rag^–/–Tpl2^–/– Mice

Staphylococcus xylosus is a commensal bacterium found on the skin and mucosal surfaces of SPF mice. S. xylosus is rarely pathogenic, most often causing skin lesions and dermatitis in immunocompromised mice, particularly those with impaired NADPH oxidase function. Here we report spontaneous infection with S. xylosus in Rag1^–/–Tpl2^–/– mice. Infection was characterized by the presence of alopecia, crusts, and scaly skin. S. xylosus was detected in the feces, skin, lymph nodes, and lungs of Rag1^–/–Tpl2^–/– mice and led to mortality or euthanasia due to humane endpoints. C57BL/6 mice were culture-positive for S. xylosus on the skin, and Rag1^–/– and Tpl2^–/– mice were culture-positive on the skin and occasionally in the feces. However, S. xylosus did not cause clinical symptoms in C57BL/6, Rag1^–/– , or Tpl2^–/– mice. Compared with those in Rag1^–/– mice, relative concentrations of circulating monocytes, but not neutrophils or lymphocytes, were increased in Rag1^–/–Tpl2^–/– mice, consistent with their increased incidence of clinical symptoms. Overall, this case study suggests a novel role for Tpl2 in T-cell–independent host resistance to the otherwise commensal organism S. xylosus.