Evaluation of the dynal biotech Legionella immunomagnetic separation method versus conventional culture for the isolation of Legionella pneumophila serogroup 1 from water samples.

Environmental monitoring of water systems for Legionella is performed for routine microbiological surveillance and outbreak investigations. The recovery of Legionella from water samples using conventional culture on selective media can be improved by sample concentration and/or sample decontamination techniques, but there is a reduction in recovery associated with these processes. A new immunoseparation method has been developed to improve the recovery of Legionella by concentrating and selectively separating Legionella spp. directly from water samples using immunomagnetic separation (IMS). Immunomagnetic separation has been used successfully for detection of other pathogens including Salmonella spp. The authors conducted the study in two phases and evaluated the IMS process alone and in combination with concentration and/or acid pretreatment in detecting Legionella spp. and Legionella pneumophila serogroup 1 (sg 1). The IMS procedure was performed using the BeadRetriever apparatus (Dynal Biotech Ltd., Preston, United Kingdom) for automated IMS using Dynabeads anti-Legionella (Dynal Biotech Ltd.). With the 11 known potable water samples, there was concordance (100% sensitivity) of culture results between the two methods, regardless of concentration or pretreatment of samples. The unconcentrated, untreated samples showed the greatest agreement in CFU/ml. Compared to conventional culture for L. pneumophila sg 1 only, the IMS method demonstrated a specificity of 98.5% (65 were negative and 2 were false-positive).