Exploring Novel Gene Mutations Associated with Fluoroquinolone Resistance in Mycobacterium tuberculosis: Gene Sequencing Results from 275 Clinical Isolates in Chongqing, China

Purpose: This study aimed to investigate whether mutations in the rv2005c, PPE59 , and recC genes are associated with fluoroquinolone (FQ) resistance in Mycobacterium tuberculosis (Mtb), particularly in strains lacking mutations in the known resistance genes gyrA and gyrB . Methods: A total of 275 clinical isolates, consisting of 217 pre-extensively drug-resistant strains and 58 fluoroquinolone-sensitive strains, were included in this study. Gene sequencing was performed on all isolates, and functional assessments through both overexpression and knockout experiments of the gene were conducted to evaluate its effect on fluoroquinolone susceptibility. Results: Results: Among 275 isolates, no mutations were detected in PPE59 or recC . In the 217 pre-XDR isolates, gyrA mutations were found in 214 (98.6%), predominantly at codons 94, 90, and 91. Only two isolates harbored synonymous mutations in rv2005c (P235P), both with concurrent gyrA D94G mutations. Overexpression or knockout of rv2005c in Mtb did not alter FQ susceptibility. Notably, two FQ-resistant isolates lacked mutations in any of the five genes sequenced, suggesting the presence of unknown resistance mechanisms. Conclusion: Our results showed that mutations of the rv2005c, PPE59 and recC genes may not contribute to FQ resistance in clinical isolates of Mtb in Chongqing, China. Furthermore, our study results also showcased the complexity of mechanisms of FQ resistance in clinical Mtb isolates. Keywords: Mycobacterium tuberculosis , fluoroquinolone resistance, drug susceptibility, gene mutations, mechanism