Efflux-mediated fluoroquinolone resistance in Staphylococcus aureus

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Transport processes are vital for cellular nutrient uptake and waste removal in all organisms.
• Antimicrobial resistance in bacteria is often mediated by efflux pumps that expel drugs.
• The Staphylococcus aureus norA gene encodes a protein involved in fluoroquinolone efflux.

Purpose of the Study:

• To investigate the role of the norA gene in fluoroquinolone resistance in Staphylococcus aureus.
• To characterize the function and homology of the norA1199 allele.
• To determine the mechanism of increased norA expression in resistant strains.

Main Methods:

• Cloning and sequencing of the norA1199 allele from a resistant S. aureus strain.
• Expression of the cloned gene in both S. aureus and Escherichia coli.
• Nucleotide sequence determination and homology analysis.
• Southern and Northern hybridization studies.

Main Results:

• The norA1199 allele encodes a protein homologous to NorA, mediating hydrophilic fluoroquinolone efflux driven by proton motive force.
• The norA1199-encoded protein shares homology with other efflux proteins, including the Bacillus subtilis Bmr protein.
• norA1199 is a naturally occurring gene in S. aureus, with related sequences in S. epidermidis.
• Fluoroquinolone resistance in the studied strain resulted from increased norA1199 transcription, not gene amplification.

Conclusions:

• The norA gene product is a key mediator of fluoroquinolone efflux in S. aureus.
• Increased transcription of norA is the primary mechanism for fluoroquinolone resistance in the SA-1199B strain.
• The norA gene and its products represent potential targets for antimicrobial drug development.