An improved SELEX technique for selection of DNA aptamers binding to M-type 11 of Streptococcus pyogenes.Streptococcus pyogenes is a clinically important pathogen consisting of various serotypes determined by different M proteins expressed on the cell surface.  We describe here an in vitro technique that directly used live bacterial cells and the Systematic Evolution of Ligands by Exponential Enrichment (SELEX) strategy.  Those sequences that bound to the cells were separated, amplified using polymerase chain reaction (PCR), purified using gel electrophoresis, and served as the input DNA pool for the next round of SELEX selection.  Aptamer pools obtained from SELEX rounds 5-8 showed high affinity to the target S. pyogenes cells.  The improved bacterial cell-SELEX technique is successful in generating aptamers selective for S. pyogenes and some of its M-types. 
SELEX
Those sequences that bound to the cells were separated, amplified using polymerase chain reaction (PCR), purified using gel electrophoresis, and served as the input DNA pool for the next round of SELEX selection. 
polymerase chain reaction (PCR)
Those sequences that bound to the cells were separated, amplified using polymerase chain reaction (PCR), purified using gel electrophoresis, and served as the input DNA pool for the next round of SELEX selection.  A specially designed forward primer containing extended polyA20/5Sp9 facilitated gel electrophoresis purification of ssDNA after PCR amplification. 
gel electrophoresis
Aptamer pools from each round of selection were tested for their binding to the target and non-target cells using flow cytometry. 
flow cytometry