Automated Immunomagnetic Processing and Separation of Legionella Pneumophila with Manual Detection by Sandwich ELISA and PCR Amplification of the ompS Gene

The culture-independent and automated detection of bacteria in the environment is a scientific and technological challenge. For detection alone, a number of sensitive methods are known (e.g., PCR, enzyme-linked immunosorbent assay [ELISA], fluorescent in situ hybridization) but a major problem remaining is the enrichment and separation of the bacteria that usually occur at low concentrations. Here, we present an automated capturing and separation system, which can easily be combined with one of the sensitive detection techniques.

We have developed a method for enrichment and detection of Legionella pneumophila in liquid media. Concentrated microorganisms were either detected by PCR or by sandwich ELISA. The limit of detection with the immunological assay was about 750 bacteria. Using PCR, the equivalent of about 2000 genomes could be detected.

The assays were then transferred to a laboratory prototype for automated processing. It was possible to automatically enrich L. pneumophila by immunomagnetic separation (IMS), and again, the bacteria were detected by sandwich ELISA and PCR amplification of the ompS gene. As a novel aspect, ompS gene was used for the first time as a target for the detection of L. pneumophila on magnetic beads.

The aim of this work was to develop an automated procedure and a device for IMS of bacteria. With Legionella as a model organism, we could show that such a novel fully automated system can be an alternative to timeconsuming conventional cultivation methods for detecting bacteria or other microorganisms.