Cao Z, et al. - The correlation between pncA gene mutations and resistance to four first-line anti-tuberculosis drugs as well as treatment history in clinical isolates of Mycobacterium tuberculosis was examined. From 318 in-patients with smear-positive TB between October 2008 and September 2016 at a major hospital in Zunyi, Guizhou Province of China, researchers collected M. tuberculosis clinical isolates and tested them for drug susceptibility against four first-line anti-TB drugs. Using genomic DNA extracted from clinical isolates, PCR amplification and DNA sequencing of the pncA gene were performed. Among 318 clinical isolates, resistance to rifampicin, isoniazid, ethambutol, and streptomycin was evident in 129 (40.6%), 170 (53.5%), 66 (20.8%) and 109 (34.3%) isolates, respectively. Findings suggest an association of high prevalence of pncA mutations in clinical isolates of M. tuberculosis from Zunyi, Guizhou Province of China, with resistance to four first-line anti-TB drugs, multidrug-resistant tuberculosis, and previously treated tuberculosis cases.