Identification of the leprosy agent Mycobacterium lepromatosis in Singapore.

Background: A new leprosy-causing species, namely Mycobacterium lepromatosis, was discovered recently to be the cause of diffuse lepromatous leprosy (DLL) in Mexico. It is unknown whether this organism exists beyond Mexico.

Methods: We sought to determine the identity of the mycobacteria in the skin tissue of two patients from Singapore who died of DLL. DNA was extracted from archived biopsy tissue, and conserved polymerase chain reaction primers were used to amplify and sequence two to three mycobacterial genes in each skin sample.

Results: Both M. lepromatosis and the well-known leprosy agent Mycobacterium leprae were identified in each DLL skin sample. The M. lepromatosis gene sequences from the Singapore cases matched 99.9% with the known Mexican M. lepromatosis strain, but they only matched the corresponding M. leprae sequences by 89.2%.

Conclusions: The new species M. lepromatosis exists beyond Mexico and is the cause of DLL in Singapore. It may cause dual infections along with M. leprae in endemic areas. Archived skin biopsy can be used to differentiate the leprosy agents.