Efflux-mediated fluoroquinolone resistance in Staphylococcus aureus

Abstract

Transport processes are used by all organisms to obtain essential nutrients and to expel wastes and other potentially harmful substances from cells. Such processes are important means by which resistance to selected antimicrobial agents in bacteria is achieved. The recently described Staphylococcus aureus norA gene encodes a membrane-associated protein that mediates active efflux of fluoroquinolones from cells. SA-1199B is a fluoroquinolone-resistant strain of S. aureus from which we cloned an allele of norA (norA1199). Similar to that of norA, the protein product of norA1199 preferentially mediates efflux of hydrophilic fluoroquinolones in both S. aureus and an Escherichia coli host, a process driven by the proton motive force. Determination of the nucleotide sequence of norA1199 revealed an encoded 388-amino-acid hydrophobic polypeptide 95% homologous with the norA-encoded protein. Significant homology with other proteins involved in transport processes also exists, but especially with tetracycline efflux proteins and with the Bacillus subtilis Bmr protein that mediates active efflux of structurally unrelated compounds, including fluoroquinolones. In S. aureus, the norA1199-encoded protein also appears to function as a multidrug efflux transporter. Southern hybridization studies indicated that norA1199 (or an allele of it) is a naturally occurring S. aureus gene and that related sequences are present in the S. epidermidis genome. The nucleotide sequence of the wild-type allele of norA1199, cloned from the fluoroquinolone-susceptible parent strain of SA-1199B, did not differ from that of norA1199 throughout the coding region. Northern (RNA) and Southern hybridization studies showed that increased transcription, and not gene amplification, of norA1199 is the basis for fluoroquinolone resistance in SA-1199B.

Fluoroquinolone resistant mechanisms in methicillin-resistant Staphylococcus aureus clinical isolates in Cairo, Egypt

“…This gene encodes a multidrug efflux protein (NorA) capable of transporting fluoroquinolones outside the bacteria. Studies have shown that a mutant of S.aureus with a knockout in the norA gene -coding for the MDR pump -has a substantially increased sensitivity to a large number of antimicrobials, including therapeutically significant compounds [36][37][38]. As inihibitors of the NorA efflux pump, reserpine, omeprazole, and lansprazole can improve fluoroquinolone activity against strains expressing different levels of NorA [16].…”

Frequency and Genetic Characterization of Multidrug-Resistant Mutants of Staphylococcus aureus after Selection with Individual Antiseptics and Fluoroquinolones.

“…13) However, the norA mutations in the TP178 (T→C) and SA-1199B (T→A) mutants differ from the flqB mutation. 4,5) Further studies are necessary to elucidate the mechanism of increased norA expression in the TP178 and SA1199B mutants.…”

Susceptibilities to antiseptic agents and distribution of antiseptic-resistance genes qacA/B and smr of methicillin-resistant Staphylococcus aureus isolated in Asia during 1998 and 1999

“…Decreased susceptibility to cationic antiseptic agents, i.e. an increase in MIC, has been attributed mainly to the excretion of drugs into the extracellular space by proton motive forcedependent multidrug-transport systems (Grinius et al, 1992;Kaatz et al, 1993;. In S. aureus, qacA (Rouch et al, 1990), qacB (Paulsen et al, 1996), smr (Grinius et al, 1992) and norA (Neyfakh et al, 1993), which encode multidrug-transporter proteins, have been identified as antiseptic-resistance genes which confer resistance to cationic antiseptic agents including dyes such as acriflavine, acrinol and ethidium bromide, quaternary ammonium compounds (QACs) such as benzethonium chloride and benzalkonium chloride, and biguanides such as chlorhexidine digluconate (Littlejohn et al, 1992;.…”