A study of the relatedness of Mycobacterium leprae isolates using restriction fragment length polymorphism analysis.

The inability to cultivate Mycobacterium leprae in vitro has severely hampered comprehensive phenotypic analysis of individual isolates, leaving unanswered the question of the relatedness of these isolates. Since the nucleotide sequence of a bacterial chromosome is its "genetic fingerprint", we have employed the use of restriction fragment length polymorphism (RFLP) analysis of chromosomal DNA of M. leprae isolates to assess the relatedness among these isolates. DNA of M. leprae was harvested from infected armadillo tissue originally inoculated with bacilli from lepromatous lesions of human patients from geographically distinct regions of the world. Restriction endonuclease (EcoRI, PstI, and PvuI) digests of chromosomal DNA were analysed using DNA probes encoding all or part of the 28-kDa, 65-kDa and 70-kDa proteins of M. leprae. Comparison of the resultant autoradiographs showed that the RFLP patterns were all identical indicating that these isolates contained no polymorphism with respect to the restriction endonuclease sites analysed. These results indicated that the M. leprae isolates tested in this study were indistinguishable at the genotypic level, suggesting the possibility of homogeneity among members of the species, M. leprae.