Unique TTC Repeat Base Pair Loss Mutation In Cases of Pure Neural Leprosy: A Survival Strategy of Mycobacterium Leprae?

BACKGROUND: Genomic reduction helps obligate intracellular microbes to survive difficult host niches. Adaptation of Mycobacterium leprae in cases of pure neural leprosy (PNL) in the intracellular niche of peripheral nerves can be associated with some gene loss. Recently, a stable but variable number of tandem repefzats (TTC) have been reported in strains of M. leprae. FolP and rpoB genes are the two common mutation sites which deal with the susceptibility of the bacteria to drugs.

AIM: We attempted to find if genomic reduction of M. leprae in context of these TTC repeats or mutations in folP1 and rpoB can be the reason for the restriction of M. leprae in the nerves in PNL.

MATERIALS AND METHODS: DNA extracts taken from fine needle aspiration of affected nerves of 24 PNL cases were studied for tandem repeats with 21TTC primer in multiplex-PCR. Mutations were also studied by PCR Amplification of SRDR (Sulphone Resistance Determining Region) of the folP1 and multiple primer PCR amplification refractory mutation system (MARS) of the rpoB.

RESULTS: Of the 24 PNL, only 1 patient showed mutation in the rpoB gene and none in the folp1 gene. Studying the mutation in TTC region of the M. leprae gene we found that all the cases have a loss of a few bases in the sequence.

CONCLUSION: We can conclude that there is consistent loss in the bases in the TTC region in all cases of pure neural Hansen and we postulate that it may be an adaptive response of the bacteria to survive host niche resulting in its restriction to peripheral nerves.