Diagnosis of cutaneous nocardiosis with Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS)

Nocardiosis is a rare but potentially life-threatening infectious disease caused by several species of the genus Nocardia (N.), which are aerobic, filamentous, gram-positive bacilli. A definitive diagnosis depends on the isolation and identification of Nocardia species. But identification from clinical specimens may involve performing invasive techniques on the patient and lengthy process (take up to 1 or 3 weeks) owing to slow growth, and require a professional microbiologist. Currently the genus Nocardia is best identified using 16S rRNA and 18S rRNA gene sequence analysis. Recently matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has launched a new era in the routine microbiology laboratory. This method has proved its efficacy for the identification and diagnosis of microorganism. MALDI-TOF MS has potential for use as a rapid (within 1 hour) and dependable method for the identification of Nocardia species with reproducibility and cost effectiveness. We report a 76-year-old woman who suffered from ulcer with papules on her right wrist and forearm. A biopsy of the skin showed granulomatous inflammation with central suppuration. A bacterial isolate from the skin was identified to be N. brasiliensis on comparative 16S rRNA gene sequencing and MALDI-TOF MS. To the best of our knowledge, this is the first case of nocardiosis in Korea caused by N. brasiliensis identified on MALDI-TOF MS.