title: A role for 16S rRNA dimethyltransferase (ksgA) in intrinsic clarithromycin resistance in Mycobacterium tuberculosis.
abstract: The emergence of extensively drug-resistant tuberculosis (XDR-TB) makes the control of tuberculosis (TB) difficult. As a result, there is an urgent need to develop new anti-TB drugs. Alternatively, drugs that have already been used in humans as anti-infectives and later found to have antitubercular activity might be useful as anti-TB drugs, particularly against drug-resistant TB. Clarithromycin (CLR), a 14-membered macrolide and protein synthesis inhibitor, has potent activity against most mycobacterial infections, except Mycobacterium tuberculosis. Mycobacterium tuberculosis is naturally resistant to CLR [minimum inhibitory concentration (MIC) of 8-16 μg/mL] owing to the presence of inducible erm methylase (ErmMT). With a view to gaining further insight into the mechanisms of innate CLR resistance in M. tuberculosis, CLR-susceptible M. tuberculosis H37Rv mutants were generated by transposon mutagenesis. One mutant, designated as Tn-196, was further investigated and it was found that ksgA (Rv1010) was inactivated by the transposon. The ksgA gene encodes a 16S rRNA adenine dimethyltransferase that methylates A1518 and A1519 (Escherichia coli numbering) of 16S rRNA and plays an important role in ribosome biogenesis. Complementation of the Tn-196 mutant with a wild-type ksgA gene restored the resistant phenotype (MIC of 8-16 μg/mL), corroborating the association of ksgA with intrinsic CLR resistance in M. tuberculosis.
authors.affiliation: Department of Biology, Faculty of Science, King Mongkut's Institute of Technology Ladkrabang, Bangkok 10520, Thailand.
authors.forename: Saranya
authors.initials: S
authors.lastname: Phunpruch
authors.forename: Saradee
authors.initials: S
authors.lastname: Warit
authors.forename: Rungaroon
authors.initials: R
authors.lastname: Suksamran
authors.forename: Pamaree
authors.initials: P
authors.lastname: Billamas
authors.forename: Sarinya
authors.initials: S
authors.lastname: Jaitrong
authors.forename: Prasit
authors.initials: P
authors.lastname: Palittapongarnpim
authors.forename: Therdsak
authors.initials: T
authors.lastname: Prammananan
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology*; D017291:Clarithromycin / Q000494:pharmacology*; D004251:DNA Transposable Elements; D024881:Drug Resistance, Bacterial; D055786:Gene Knockout Techniques; D005816:Genetic Complementation Test; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism*; D008826:Microbial Sensitivity Tests; D016254:Mutagenesis, Insertional; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics
chemical_list: D000995:Antitubercular Agents; D004251:DNA Transposable Elements; D008780:Methyltransferases; C047346:16S rRNA (adenine(1518)-N(6)-adenine(1519)-N(6))-dimethyltransferase; D017291:Clarithromycin