A novel resistance mutation in eccC5of the ESX-5 secretion system confers ofloxacin resistance in Mycobacterium tuberculosis

Brandon Eilertson, Fernanda Maruri, Amondrea Blackman, Yan Guo, Miguel Herrera, Yuri Van Der Heijden, Yu Shyr, Timothy R. Sterling

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)


Background: Fluoroquinolone resistance in Mycobacterium tuberculosis is often conferred by DNA gyrase mutations. However, a substantial proportion of fluoroquinolone-resistant M. tuberculosis isolates do not have such mutations. Methods: Ofloxacin-resistant and lineage-matched ofloxacin-susceptible M. tuberculosis isolates underwent WGS. Novel candidate resistance mutations were confirmed by Sanger sequencing and conferral of resistance was assessed via site-directed mutagenesis and allelic exchange. Ofloxacin MIC was determined by resazurin microtitre assay (REMA) and the effects on MICs of efflux pump inhibitors (CCCP, reserpine and verapamil) were determined. Results: Of 26 ofloxacin-resistant isolates, 8 (31%) did not have resistance-conferring DNA gyrase mutations. The V762G mutation in Rv1783 (eccC5, encoding a protein in the ESX-5 membrane complex secretion system) was present on WGS in 8/26 (31%) resistant isolates and 0/11 susceptible isolates (P=0.005). The mutation was identified in five isolates without DNA gyrase mutations and three isolates with such mutations; it was identified in both European-American and East Asian M. tuberculosis lineages. The ofloxacin MIC increased from 1 to 32 mg/L after introduction of the V762G mutation into M. tuberculosis H37Rv. In this strain with the V762G mutation, ofloxacin MIC did not change in the presence of efflux pump inhibitors. Conclusions: A novel V762G mutation in Rv1783 conferred ofloxacin resistance in M. tuberculosis by a mechanism other than drug efflux. This occurred in a substantial proportion of resistant isolates, particularly those without DNA gyrase mutations.

Original languageEnglish
Pages (from-to)2419-2427
Number of pages9
JournalJournal of Antimicrobial Chemotherapy
Issue number9
Publication statusPublished - 2016 Sep 1

All Science Journal Classification (ASJC) codes

  • Pharmacology
  • Microbiology (medical)
  • Infectious Diseases
  • Pharmacology (medical)

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