Actinomyces neuii in chronic hidradenitis suppurativa: a case series highlighting the value of extended culture.

Hidradenitis suppurativa (HS) is a chronic, relapsing inflammatory skin disease characterized by painful nodules, sinus tract formation and scarring. Lesional skin is frequently colonized by diverse aerobic and anaerobic bacteria, with anaerobes such as Prevotella spp., Campylobacter ureolyticus, Staphylococcus epidermidis and Actinomyces spp. commonly isolated. Actinomyces neuii, a Gram-positive, slow-growing anaerobe, has been previously described only occasionally in deep HS abscesses. We present three cases of treatment-resistant HS in which extended incubation of cultures yielded A. neuii. All patients were subsequently treated with long-term amoxicillin (3-6 months), resulting in marked clinical improvement. These findings suggest a potential pathogenic role for A. neuii in severe HS. Further research is required to establish its clinical relevance, evaluate optimal antibiotic regimens and monitor for resistance development.