Evaluation of polymerase chain reaction-based detection of Mycobacterium leprae for the diagnosis of leprosy

Because Mycobacterium leprae cannot be cultivated in vitro, laboratory diagnosis of leprosy is generally made by microscopic and histopathological examination. The objective of the present study was to evaluate the sensitivity and utility of polymerase chain reaction (PCR) to detect M. leprae in comparison with other conventional methods for diagnosis such as split skin smears, histopathology and serodiagnosis. PCR amplification of the M. leprae-specific 16S ribosomal RNA was compared to other methods. Samples included 37 multibacillary (MB) patients with a positive bacteriological index (BI), 32 newly diagnosed paucibacillary (PB) patients whose BI were negative and 30 plaque psoriasis patients not residing in leprosy endemic areas as controls. The sensitivity of PCR was 30 fg of M. leprae DNA, which is equivalent to the DNA from 8.3 bacilli. The detection rate in MB and PB were 100% and 50%, respectively; the specificity was 100%. Semiquantitative evaluation of PCR correlated well with BI, but not with the morphological index (MI) nor with the serum antibody against phenolic glycolipid-1 (PGL-1). PCR detection of M. leprae targeting 16S ribosomal RNA was specific and more sensitive than conventional methods, and can contribute to early and accurate diagnosis of leprosy.