One step for Legionella pneumophila detection in environmental samples by DNA-gold nanoparticle probe

Aims: To develop and evaluate a DNA-gold nanoparticle (DNA-AuNP) probe assay to detect Legionella pneumophila, which causes Legionnaires' disease, compared with the gold standard culture method.

Methods and results: Gold nanoparticles (AuNPs) were conjugated with DNA probes to detect the mip gene of L. pneumophila. The DNA-AuNP probe assay was evaluated for its specificity, sensitivity and stability. The results showed that only L. pneumophila mixed with this probe resulted in a red solution that was easily detected by the naked eye, and the colour was stable when 10 mmol l^-1 MgSO₄ was added. The 100 Legionella isolates and 10 other bacteria led to 100% specificity. Compared with the culture method, our method showed a 100% negative predictive value, 100% sensitivity (kappa = 0·87), and a detection limit of 4·5 ng DNA μl^-1 with a 6-min response time for the 124 colonies suspected of being Legionella. The DNA-AuNP probe reagents were stable for more than 6 months.

Conclusions: The developed DNA-AuNP probe assay has good negative predictive value, sensitivity, rapidity and ease of use, which is helpful for ruling out negative samples.

Significance and impact of the study: The DNA-AuNP probe assay can detect the mip gene of L. pneumophila. Therefore, it may be an alternative method for screening colonies suspected of being L. pneumophila.