Comparative evaluation of duopath Legionella lateral flow assay against the conventional culture method using Legionella pneumophila and Legionella anisa strains

Abstract

Duopath Legionella is a new immunochromatographic assay for the identification of Legionella pneumophila and Legionella spp. As excellent specificity has been previously reported for this kit, we attempted an evaluation of its sensitivity using L. pneumophila serogroup 1 and Legionella anisa strains. Bacterial suspensions of L. pneumophila at concentrations of 1.2 × 108 cfu/ml and 1.2 × 107 cfu/ml were detected, but those below 1.2 × 106 cfu/ml were not recognized by the Duopath kit. After centrifugation and the sediment resuspension, a 2.8 × 106 cfu/ml concentration of bacterial suspension showed a positive result, but negative results were obtained below 2.8 × 106 cfu/ml. Also, bacterial suspension with concentrations of 3.2 × 109 cfu/ml and 1.4 × 109 cfu/ml after centrifugation of L. anisa were detected, but those below 3.2 × 108 cfu/ml and 1.4 × 108 cfu/ml after centrifugation were not recognized by the Duopath kit. Meanwhile, this kit was less sensitive to the L. pneumophila serogroup 1 suspension, and was more sensitive to the L. pneumophila serogroup 2 and L. anisa than the Binax NOW immunochromatographic kit. It was realized that the sensitivity of this kit is too low for determining the presence of Legionella in water samples. Although this kit may have excellent specificity, it has low sensitivity.