5.3.1 Propionibacterium acnes folliculitis

Invasive opportunistic infection of Propionibacterium acnes, a commensal in the hair follicle, has been described [72]. An aged afebrile Japanese male complained of a skin nodule on the chest. Biopsy revealed hair follicle-centered inflammation, and macrophages clustered around the hair follicle contained numerous granularlooking microbes. Microscopically, the possibility of yeast-form mycosis, rickettsiosis, and protozoan infection was suspected. Grocott positivity was faint. Immunostaining using B. cereus antiserum revealed positivity (see Figure 22), while antisera to BCG,T. pallidum, and E. coli did not. The patient's own serum diluted at 1:500 clearly demonstrated the pathogen not only in macrophages but also in commensal bacterial colonies in the hair follicle [23]. Finally, PAC3 antigen specific to P. acnes was positive (through the courtesy of Prof. Yoshinobu Eguchi, Department of Pathology, Tokyo Medical and Dental University, Tokyo) [73], and the diagnosis of P. acnes-induced folliculitis was thus confirmed (Figure 45).
