Use of DNA aptamer for sandwich type detection of Listeria monocytogenes

A single stranded (ss) DNA aptamer, specific to members of Listeria genus, was used to develop a two-site binding sandwich assay for capture and detection of L. monocytogenes. Antibody-immobilized immunomagnetic beads were used to capture L. monocytogenes, followed by their exposure to the aptamer detector. Detection was achieved by amplification of cell-bound aptamers by qPCR. The lower limit of detection for the combined assay was 2.5 CFU L. monocytogenes in 500 mu l buffer. This is juxtaposed to a detection limit of 2.4 log(10) CFU in 500 mu l buffer for immunomagnetic separation coupled with qPCR detection of L monocytogenes targeting the lily gene. When applied to turkey deli meat, subjected to 24 h of non-selective enrichment, the two-site binding sandwich assay showed positive results at initial inoculum levels of 1-2 log(10) CFU per 25 g sample. Because of its lower limit of detection, the assay reported here could be useful for detection of L monocytogenes in foods and environmental samples.