Isolation and characterization of DNA aptamers against Escherichia coli using a bacterial cell-systematic evolution of ligands by exponential enrichment approach.

Aptamers are powerful capturing probes against various targets such as proteins, small organic compounds, metal ions, and even cells. In this study, we isolated and characterized single-stranded DNA (ssDNA) aptamers against Escherichia coli. A total of 28 ssDNAs were isolated after 10 rounds of selection using a bacterial cell-SELEX (systematic evolution of ligands by exponential enrichment) process. Other bacterial species (Klebsiella pneumoniae, Citrobacter freundii, Enterobacter aerogenes, and Staphylococcus epidermidis) were used for counter selection to enhance the selectivity of ssDNA aptamers against E. coli. Finally, four ssDNA aptamers showed high affinity and selectivity to E. coli, The dissociation constants (K(d)) of these four ssDNA aptamers to E. coli were estimated to range from 12.4 to 25.2 nM. These aptamers did not bind to other bacterial species, including four counter cells, but they showed affinity to different E. coli strains. The binding of these four aptamers to E. coli was observed directly by fluorescence microscopy.