Genomic alterations involved in fluoroquinolone resistance development in Staphylococcus aureus

Area of Science:

• Microbiology
• Genetics
• Pharmacology

Background:

• Fluoroquinolones (FQ) are critical antibiotics, but their efficacy is threatened by rapidly emerging resistance.
• Staphylococcus aureus (S. aureus) can develop multidrug resistance (MDR), posing a significant clinical challenge.

Purpose of the Study:

• To investigate the genomic and molecular mechanisms driving the emergence of MDR S. aureus strains following exposure to fluoroquinolones.
• To identify specific mutations and gene expression changes associated with FQ resistance in S. aureus.

Main Methods:

• Serial sub-minimum inhibitory concentration (sub-MIC) exposure of S. aureus ATCC 29213 to ciprofloxacin, ofloxacin, or levofloxacin.
• Whole genome sequencing (WGS) and target sequencing to identify genomic alterations.
• RT-qPCR to quantify the expression levels of genes involved in FQ resistance, efflux pumps, and alternative sigma factors.

Main Results:

• Significant and irreversible increases in minimum inhibitory concentrations (MICs) for FQs were observed in exposed S. aureus strains.
• WGS revealed multiple mutations in FQ-exposed strains, including alterations in GrlA (R570H), SACOL0573, and rimI.
• Overexpression of genes related to efflux pumps (norA, norB, norC, mgrA) and alternative sigma factors (sigB, sigS) was detected in FQ-resistant strains.

Conclusions:

• The emergence of MDR S. aureus under FQ pressure is strongly linked to mutations within FQ target sequences.
• Upregulation of efflux pump systems and their regulators plays a crucial role in the development of fluoroquinolone resistance in S. aureus.