[Guideline for the treatment of Hansen's disease in Japan (Second edition)]

Impact of amino acid substitutions in B subunit of DNA gyrase in Mycobacterium leprae on fluoroquinolone resistance

BACKGROUND

Ofloxacin is a fluoroquinolone (FQ) used for the treatment of leprosy. FQs are known to interact with both A and B subunits of DNA gyrase and inhibit supercoiling activity of this enzyme. Mutations conferring FQ resistance have been reported to be found only in the gene encoding A subunit of this enzyme (gyrA) of M. leprae, although there are many reports on the FQ resistance-associated mutation in gyrB in other bacteria, including M. tuberculosis, a bacterial species in the same genus as M. leprae.

METHODOLOGY/PRINCIPAL FINDINGS

To reveal the possible contribution of mutations in gyrB to FQ resistance in M. leprae, we examined the inhibitory activity of FQs against recombinant DNA gyrases with amino acid substitutions at position 464, 502 and 504, equivalent to position 461, 499 and 501 in M. tuberculosis, which are reported to contribute to reduced sensitivity to FQ. The FQ-inhibited supercoiling assay and FQ-induced cleavage assay demonstrated the important roles of these amino acid substitutions in reduced sensitivity to FQ with marked influence by amino acid substitution, especially at position 502. Additionally, effectiveness of sitafloxacin, a FQ, to mutant DNA gyrases was revealed by low inhibitory concentration of this FQ.

SIGNIFICANCE

Data obtained in this study suggested the possible emergence of FQ-resistant M. leprae with mutations in gyrB and the necessity of analyzing both gyrA and gyrB for an FQ susceptibility test. In addition, potential use of sitafloxacin for the treatment of problematic cases of leprosy by FQ resistant M. leprae was suggested.

Amino acid substitutions at position 95 in GyrA can add fluoroquinolone resistance to Mycobacterium leprae

Amino acid substitutions at position 89 or 91 in GyrA of fluoroquinolone-resistant Mycobacterium leprae clinical isolates have been reported. In contrast, those at position 94 in M. tuberculosis, equivalent to position 95 in M. leprae, have been identified most frequently. To verify the possible contribution of amino acid substitutions at position 95 in M. leprae to fluoroquinolone resistance, we conducted an in vitro assay using wild-type and mutant recombinant DNA gyrases. Fluoroquinolone-mediated supercoiling activity inhibition assay and DNA cleavage assay revealed the potent contribution of an amino acid substitution of Asp to Gly or Asn at position 95 to fluoroquinolone resistance. These results suggested the possible future emergence of quinolone-resistant M. leprae isolates with these amino acid substitutions and the usefulness of detecting these mutations for the rapid identification of fluoroquinolone resistance in leprosy.

Clinical analysis of multibacillary leprosy patients after 1-year fixed World Health Organization recommended multidrug therapy at Yangon General Hospital, Myanmar

This study included 200 randomly selected multibacillary leprosy cases who had completed 1 year of fixed World Health Organization recommended multidrug therapy (WHO-MDT) without prior dapsone (DDS) monotherapy. The time interval after release from treatment varied from a few months to 8 years. All cases were clinically reviewed in 2006 by comparison with their old clinical records. Reactions, particularly reversal reactions, occurred frequently among patients who had completed MDT within the last 3 years. It was difficult to distinguish relapse cases and late reversal reactions in skin smear-negative multibacillary cases. Based on bacteriological and histological analyses, one patient was confirmed to have relapsed 1 year after release from treatment. The overall relapse rate was 0.5%. No drug resistance mutations were detected by polymerase chain reaction or dot blot hybridization. The present study indicates that it is important to follow up patients for several years after completion of MDT in order to detect possible lepra reactions and relapses.