Can inhA mutation predict ethionamide resistance?

SETTING: A tertiary care centre in Mumbai, India. OBJECTIVE: To estimate the extent of association between inhA mutant isoniazid (INH) resistant strains and ethionamide (ETH) resistance. DESIGN: A total of 140 clinical isolates processed for INH and ETH phenotypic drug susceptibility testing, and molecularly processed with the line-probe assay (LPA) Genotype (R) MTBDRplus, were considered. RESULTS: Among the 112 phenotypically determined INH-resistant strains, 69 (61.6%) strains were ETH-resistant. An inhA promoter mutation was identified in 24 (21.4%) INH-resistant isolates, 21 (87.5%) of which were ETH-resistant (P < 0.0001). CONCLUSION: An inhA promoter mutation could be considered as a marker for the determination of ETH resistance in India, where the use of LPA is being expanded.