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Evidence that phosphate specific transporter is amplified in a fluoroquinolone resistant Mycobacterium smegmatis
K Bhatt1, S K Banerjee, P K Chakraborti
1Institute of Microbial Technology, Chandigarh, India.
Abstract:
We reported in an earlier study that active efflux of drug has a predominant role in conferring resistance in a laboratory-generated ciprofloxacin-resistant mutant of Mycobacterium smegmatis. This mutant exhibited mRNA level overexpression, as well as chromosomal amplification, of the gene pstB, encoding the putative ATPase subunit of phosphate specific transport (Pst) system. We demonstrate here that this mutant shows enhanced phosphate uptake and that inactivation of pstB in the parental strain results in loss of high affinity phosphate uptake and hypersensitivity to fluoroquinolones. These findings suggest a novel role of the Pst system in active efflux, in addition to its involvement in phosphate transport.
Insights
The phosphate transport (Pst) system in Mycobacterium smegmatis plays a novel role in active drug efflux, contributing to fluoroquinolone resistance. Inactivating pstB impairs phosphate uptake and increases fluoroquinolone sensitivity.
Area of Science:
- Microbiology
- Molecular Biology
- Drug Resistance Mechanisms
Background:
- Active drug efflux is a primary mechanism of fluoroquinolone resistance in Mycobacterium smegmatis.
- A previously studied resistant mutant showed overexpression and gene amplification of pstB, encoding a component of the phosphate transport system.
- The precise function of the Pst system in drug resistance was not fully understood.
Purpose of the Study:
- To investigate the role of the pstB gene and the phosphate transport (Pst) system in conferring ciprofloxacin resistance in Mycobacterium smegmatis.
- To determine if the Pst system is involved in active drug efflux beyond its known role in phosphate transport.
Main Methods:
- Comparative analysis of phosphate uptake in wild-type and pstB-mutant strains of Mycobacterium smegmatis.
- Gene inactivation of pstB in the parental Mycobacterium smegmatis strain.
- Assessment of fluoroquinolone susceptibility in strains with altered Pst system function.
Main Results:
- The ciprofloxacin-resistant mutant exhibited enhanced phosphate uptake.
- Inactivation of pstB in the parental strain led to a loss of high-affinity phosphate uptake.
- Disruption of pstB resulted in hypersensitivity to fluoroquinolones, indicating a link between the Pst system and drug resistance.
Conclusions:
- The phosphate transport (Pst) system has a novel, dual role in Mycobacterium smegmatis, participating in both phosphate uptake and active drug efflux.
- The pstB gene is crucial for both high-affinity phosphate transport and the intrinsic fluoroquinolone resistance of Mycobacterium smegmatis.
- Targeting the Pst system could be a potential strategy to overcome fluoroquinolone resistance in mycobacterial infections.