Non-PmrA-mediated multidrug resistance in Streptococcus pneumoniae

The PmrA multidrug transporter protein gene was inactivated in Streptococcus pneumoniae strains CP1000 (wild-type) and EBR (mutant with enhanced active multidrug efflux). While the resistance to fluoroquinolones and ethidium bromide shown by EBR was reduced to the wild-type level, neither the susceptibility to reserpine in the presence of ethidium bromide and selected fluoroquinolones, nor the ability to produce ethidium bromide-resistant mutants was eliminated in the CP1000 pmrA mutant, indicating the presence of an additional multidrug export protein(s).