Screening for Community-Acquired Strains of MRSA Susceptible to Extracts of Tyrol Knapweed, Centaurea nigrescens.

Abstract

The rates of infection by community-acquired multi-drug resistant Staphylococcus aureus (CA-MRSA) have risen dramatically over the past decade and a half in the United States.  CA-MRSA is responsible for rapidly progressive diseases, including necrotizing pneumonia, severe sepsis, and necrotizing fasciitis.  Consequently, novel antibacterial strategies are needed to combat the rising antibiotic resistance seen in CA-MRSA strains.  The USA300 CA-MRSA strain has been mutagenized using the Bursa aurealis transposon to create the Nebraska Transposon Mutant Library (NTML). We have screened the 1920 non-essential, defined transposon insertions in the NTML for strains that are either susceptible or resistant to methanol extracts of Centaurea nigrescens leaves and flowers. Of the insertion strains screened, ~2% show marked increased susceptibility to methanol extracts of C. nigrescens.  Insertions in two different drug efflux transporters, EmrB/QacA and epi-G ABC-like transporter, have been identified. The EmrB/QacA drug resistance transporter subfamily is a multi-drug efflux pump responsible for the export of toxic molecules from bacteria and yeast. The epi-G ABC transporters are involved in lantibiotic (peptide antibiotics containing thioether bridges) export. These results confirm the effectiveness of the screen as a means for identifying drug-resistance genes affected by the C. nigrescens methanolic extract and suggest a role for drug efflux proteins in the resistance of S. aureus CA-MRSA to antibacterial plant metabolytes.