Aptamers bind to Listeria surface proteins. A method of assaying a sample for the presence of Listeria monocytogenes includes exposing the sample to an aptamer that specifically binds one of the following proteins: Listeria monocytogenes internalin A protein, Listeria monocytogenes internalin E protein, and Listeria monocytogenes 0610 protein. The presence of Listeria monocytogenes in the sample is detected when the aptamer binds the protein present in the sample. A method of treating Listeria monocytogenes infection includes administering the aptamers to the mammal at a concentration sufficient to reduce Listeria monocytogenes infection.