Gram-negative folliculitis frequently complicates long-term antibiotic therapy for acne. Follicular lesions caused by Staphylococcus aureus are also common, particularly in patients who chronically carry the organism. The patient in this case developed gram-negative folliculitis with Citrobacter diversus (koseri), an organism that has not previously been reported to be pathogenic in this condition. He also experienced repeated episodes of Citrobacter and staphylococcal folliculitis in an alternating fashion because treatment directed against one organism caused a secondary infection by the other.
Mark A. Chastain. A Cycle: Recurrent Gram-negative Folliculitis With Citrobacter diversus (koseri) Following Eradication of Recurrent Staphylococcal Pyoderma. Arch Dermatol. 2000;136(6):803. doi: