Application of real-time PCR to recognize atypical mycobacteria in archival skin biopsies: high prevalence of Mycobacterium haemophilum.

Atypical mycobacterial skin infections are difficult to diagnose owing to their aspecific histopathologic presentations and to the presence of few bacteria. Therefore, these infections are often not recognized. Molecular detection of mycobacterial DNA has proven to be useful in clinical samples. The aim of this study was to investigate the incidence of mycobacterial involvement in skin biopsies showing granulomatous inflammation, using real-time polymerase chain reaction (PCR). Real-time PCR specific for the genus Mycobacterium and the species Mycobacterium avium and Mycobacterium haemophilum was performed on formalin-fixed/paraffin-embedded biopsies from patients with granulomatous inflammation of the skin, from the period 1984 to 2004. A control group was assembled from patients with proven basal cell carcinoma. Amplicons of all positive reactions were sequenced to confirm or identify the mycobacterial species. Of 30 patients, 13 (43%) were found to be positive for mycobacterial infection, of whom only 5 patients had been previously diagnosed with a mycobacterial disease. M. haemophilum was identified as the most common species (n=7). The other identified species were Mycobacterium malmoense, Mycobacterium gordonae, and Mycobacterium marinum. The results show that real-time PCR is useful in detecting mycobacterial infections in undiagnosed formalin-fixed/paraffin-embedded skin samples and that the application of molecular approaches would improve the diagnoses of mycobacterial skin infections.