Molecular characteristics of ofloxacin mono-resistant Mycobacterium tuberculosis isolates from new and previously treated tuberculosis patients.

BACKGROUND: Ofloxacin (OFX) resistant Mycobacterium tuberculosis (MTB) isolates have been increasingly observed and are a major concern in recent years. This study investigated the genetic mutations associated with OFX resistance among clinical OFX mono-resistant MTB isolates from new and previously treated tuberculosis patients.

METHODS: A total of 50 unrelated OFX mono-resistant MTB isolates were analyzed. For all isolates, the quinolone resistance determining regions of gyrA and gyrB were PCR amplified and sequenced.

RESULTS: Single mutations in the quinolone resistance determining regions of gyrA (positions D94A, G, N, and Y; A90V; and S91P) and gyrB (positions T539A and E540D) were observed in 62% (31/50) and 4% (2/50) of all OFX mono-resistant isolates, respectively. No differences were detected between the proportions of isolates with mutations in gyrA/gyrB from new and previously treated tuberculosis patients (P=.820).

CONCLUSIONS: Although mutations in gyrB were rare, they were as important as mutations in gyrA in predicting OFX resistance in MTB in Tianjin, China.