This
study describes the selection of single-stranded DNA (ssDNA)
aptamers against Salmonella enterica serovar Typhimurium
using a modified whole cell systematic evolution of ligands by exponential
enrichment (whole cell SELEX). For evolving specific aptamers, ten
rounds of selection to live Salmonella cells, alternating
with negative selection against a cocktail of related pathogens, were
performed. The resulting highly enriched oligonucleotide pools were
sequenced and clustered into eight groups based on primary sequence
homology and predicted secondary structure similarity. Fifteen sequences
from different groups were selected for further characterization.
The binding affinity and specificity of aptamers were determined by
fluorescence binding assays. Aptamers (SAL 28, SAL 11, and SAL 26)
with dissociation constants of 195 ± 46, 184 ± 43, and 123
± 23 nM were used to develop a nanogold-based colorimetric detection
method and a sedimentation assay. The former showed a better sensitivity
limit of 102 CFU/mL using aptamer SAL 26. This approach
should enable further refinement of diagnostic methods for the detection
of Salmonella enterica serovar Typhimurium and of
other microbial pathogens.