Sensitive and Rapid Detection of the New Delhi Metallo-Beta-Lactamase Gene by Loop-Mediated Isothermal Amplification

New Delhi metallo-β-lactamase 1 (NDM-1), which is associated with resistance to carbapenem, was first reported in 2008. A sensitive and rapid molecular assay to detect the plasmid blaNDM-1 in clinical isolates is needed to control its spread. We describe a loop-mediated isothermal amplification (LAMP) assay for the rapid detection of blaNDM-1 from pure culture and sputum, urine, and fecal samples. Eight sets of primers were designed to recognize six or eight distinct sequences on target blaNDM-1, and one set was selected as the most appropriate set of primers for its rapid detection. The specificity and sensitivity of the primers in the LAMP reactions for blaNDM-1 detection were determined. The sensitivity of the LAMP assay for blaNDM-1 detection in sputum, urine, and fecal samples was also tested. Two methods, namely, monitoring of turbidity and addition of calcein to the reaction tube, were used to determine negative and positive results. The results showed that target DNA was amplified and visualized by the two detection methods within 70 min at an isothermal temperature of 65°C. The sensitivity of LAMP, with a detection limit of 10.70 pg/μl DNA, was 100-fold greater than that of PCR. Thirteen infection bacterial strains without blaNDM-1 were selected for testing of specificity, and the results of the amplification were negative, which showed that the primers had good levels of specificity. The LAMP method reported here is demonstrated to be a potentially valuable means for the detection of blaNDM-1 and rapid clinical diagnosis, being fast, simple, and low in cost.