Identification of Mycobacterium marinum in sea-urchin granulomas

Background Sea-urchin granuloma is a chronic granulomatous reaction arising after injury with sea-urchin spines. Classified as an allergic foreign-body type of granuloma, it is believed to be a delayed-type reaction to an as yet unidentified antigen. In a clinicopathological study, 50 biopsy specimens from 35 patients diagnosed as having sea-urchin granuloma caused by Paracentrotus lividus, we found different inflammatory patterns that in some cases suggested a mycobacterial infection. Objectives To investigate and identify mycobacterial DNA in formalin-fixed and paraffin-embedded skin biopsy specimens diagnosed as sea-urchin granulomas. Methods A search combining polymerase chain reaction amplification using Mycobacterium genus-specific primers, and subsequent restriction enzyme analysis enabling identification to the species level, was performed in 41 samples. Results Amplification of a 924-bp DNA fragment encoding mycobacterial 16S rRNA gene was positive in eight biopsy specimens from seven patients (21%). M. marinum-specific restriction patterns were identified in three samples. Conclusions Although further controlled studies are necessary, from these data it would appear that myobacteria may play a pathogenic role in some cases of sea-urchin granuloma.