Performance of Sequencing in Predicting Ofloxacin Resistance in Mycobacterium tuberculosis from Positive Bactec MGIT 960 Cultures.

Ofloxacin (OFX) resistant Mycobacterium tuberculosis (MTB) isolates have been increasingly observed worldwide, complicating tuberculosis control. This study investigated the performance of sequencing which could predict OFX resistance in MTB isolates from positive Bactec MGIT 960 cultures. A total of 214 Bactec MGIT 960 positive cultures were identified by p-nitrobenzoic-acid and thiophene-2-carboxylic hydrazide. Drug susceptibility testing was performed using the proportion method and sequencing. The sequence results were compared with the results of the proportion method to analyze the consistency between the results. We identified a total of 204 MTB and 10 nontuberculous mycobacteria (NTM) isolates. Among the MTB isolates, 98% (200/204) carried gyrA and gyrB genes, whereas 20% (2/10) of the NTM isolates had gyrA and gyrB genes. Of the 202 MTB isolates, 7.4% (15/202) and 92.6% (187/202) were OFX-resistant and susceptible isolates, respectively. Among the OFX resistant isolates, 80% (12/15) had mutations in gyrA (n=9), gyrB (n=1), or both gyrA and gyrB (n=2). Among the OFX-susceptible isolates, 2.7% (5/187) had mutations in gyrA (n=2) or gyrB (n=3). Compared with the proportion method, the sensitivity and specificity of sequencing were 78.6% and 99.5%, respectively. Sequencing had good performance for detecting OFX resistance and could be used for predicting OFX susceptibility.