Specific capture and detection of S taphylococcus aureus with high‐affinity modified aptamers to cell surface components

Slow off‐rate modified aptamer ( SOMA mer) reagents were generated to several S taphylococcus aureus cell surface‐associated proteins via SELEX with multiple modified DNA libraries using purified recombinant or native proteins. High‐affinity binding agents with sub‐nanomolar K d 's were obtained for staphylococcal protein A ( S p A ), clumping factors ( C lf A , C lf B ), fibronectin‐binding proteins ( F nb A , F nb B ) and iron‐regulated surface determinants (Isd). Further screening revealed several SOMA mers that specifically bound to S taph. aureus cells from all strains that were tested, but not to other staphylococci or other bacteria. Sp A and C lf A SOMA mers proved useful for the selective capture and enrichment of Staph. aureus cells, as shown by culture and PCR , leading to improved limits of detection and efficient removal of PCR inhibitors. Detection of S taph. aureus cells was enhanced by several orders of magnitude when the bacterial cell surface was coated with SOMA mers followed by q PCR of the SOMA mers. Furthermore, fluorescence‐labelled S p A SOMA mers demonstrated their utility as direct detection agents in flow cytometry. Significance and Impact of the Study Monitoring for microbial contamination of food, water, nonsterile products or the environment is typically based on culture, PCR or antibodies. Aptamers that bind with high specificity and affinity to well‐conserved cell surface epitopes represent a promising novel type of reagents to detect bacterial cells without the need for culture or cell lysis, including for the capture and enrichment of bacteria present at low cell densities and for the direct detection via q PCR or fluorescent staining.