Development and validation of a loop-mediated isothermal amplification (LAMP) assay for rapid detection of Glaesserella (Haemophilus) parasuis
<i>Glaesserella parasuis</i> is a fastidious pathogen that colonizes the respiratory tract of pigs and can lead to considerable economic losses in pig production. Therefore, a rapid detection assay for the pathogen, preferably applicable in the field, is important. In the current study, we developed a new and improved detection method using loop-mediated isothermal amplification (LAMP). This assay, which targets the <i>infB</i> gene, was tested on a collection of 60 field isolates of <i>G. parasuis</i> comprising 14 different serovars. In addition, 63 isolates from seven different closely related species of the family Pasteurellaceae, including <i>A. indolicus</i>, <i>A. porcinus</i>, and <i>A. minor</i>, and a species frequently found in the respiratory tract of pigs were used for exclusivity experiments. This assay showed an analytical specificity of 100% (both inclusivity and exclusivity) and an analytical sensitivity of 10 fg/µL. In further steps, 36 clinical samples were tested with the LAMP assay. An agreement of 77.1 (95% CI: 59.9, 89.6) and 91.4% (95% CI: 75.9, 98.2) to the culture-based and PCR results was achieved. The mean limit of detection for the spiked bronchoalveolar lavage fluid was 2.58 × 10<sup>2</sup> CFU/mL. A colorimetric assay with visual detection by the naked eye was tested to provide an alternative method in the field and showed the same sensitivity as the fluorescence-based LAMP assay. Overall, the optimized LAMP assay represents a fast and reliable method and is suitable for detecting <i>G. parasuis</i> in the laboratory environment or in the field.