Evidence for efflux pumps, other than PmrA, associated with fluoroquinolone resistance in Streptococcus pneumoniae

Area of Science:

• Microbiology
• Molecular Biology
• Antimicrobial Resistance

Background:

• Fluoroquinolone resistance in *Streptococcus pneumoniae* is often linked to the PmrA efflux pump.
• The precise mechanisms and potential involvement of other efflux systems in pneumococcal drug resistance remain incompletely understood.

Purpose of the Study:

• To investigate whether efflux systems other than PmrA contribute to fluoroquinolone resistance in *Streptococcus pneumoniae*.
• To characterize the role of PmrA in mediating resistance to levofloxacin and gemifloxacin.

Main Methods:

• Selection of mutants with efflux phenotypes using sub-inhibitory concentrations of levofloxacin or gemifloxacin.
• Transformation of efflux phenotypes into a susceptible *S. pneumoniae* strain (R6).
• Analysis of *pmrA* transcript levels using Northern blotting and assessment of efflux phenotype after *pmrA* inactivation.

Main Results:

• Transformants selected by fluoroquinolones did not exhibit increased *pmrA* transcripts.
• Inactivation of *pmrA* in these transformants did not eliminate the observed efflux phenotype.
• A separate set of mutants selected by ethidium bromide, but not norfloxacin, showed reduced ethidium bromide accumulation, suggesting alternative efflux mechanisms.

Conclusions:

• The PmrA efflux pump is not the sole determinant of fluoroquinolone resistance in *Streptococcus pneumoniae*.
• Additional efflux systems, independent of PmrA, can contribute significantly to drug resistance in pneumococci.
• These findings highlight the complexity of antimicrobial resistance mechanisms in clinically relevant bacteria.