Reverse transcription-PCR detection of Mycobacterium leprae in clinical specimens

A reverse transcription (RT)-PCR assay targeting the 16S rRNA of Mycobacterium leprae was developed to detect the organism in clinical specimens. A 171-bp fragment was amplified when M. leprae RNA was used as a template but not when a panel of RNAs from 28 potentially cross-reacting mycobacterial species, seven genera related to Mycobacterium, and three organisms normally found among skin or nose flora were tested. As few as 10 organisms isolated from infected tissue could be detected, confirming the sensitivity of the assay. When the test was applied to clinical specimens, M. leprae was detected in 82% of skin biopsy specimens obtained from untreated leprosy patients, while skin biopsy specimens from healthy volunteers and patients with other dermatological disorders were negative. The sensitivity of the RT-PCR was higher than that of slit skin smear staining for acid-fast bacilli or acid-fast staining of fixed biopsy specimens since 53% of acid-fast bacillus-negative biopsy specimens were RT-PCR positive. Because 16S rRNA is rapidly degraded upon cell death, the assay may detect only viable organisms and may prove to be useful in assessing the efficacy of chemotherapy.