Loop-mediated Isothermal Amplification Test for Rapid Identification of Clinical Nocardia Isolates

Background: Nocardia is a Gram-positive and partially acid-fast bacterium. The species are widely distributed in the environment and cause severe human infections. Nocardiosis is not easily identifiable due to the lack of pathognomonic clinical signs. Objectives: The present study was designed to develop and evaluate a simple and quick method based on a loop-mediated isothermal amplification (LAMP) assay for detecting Nocardia spp isolated from bronchoalveolar lavage (BAL) samples. Methods: In this cross-sectional study, 357 BAL samples were collected from two teaching hospitals. The polymerase chain reaction (PCR) was performed using a set of species-specific primers for the 16S rRNA gene. Kinyoun acid-fast staining and culture were done on the Sabouraud dextrose plate. The optimal LAMP reaction condition was set at 65°C for 45 min, with the recognition limit as 1 pg DNA/tube and 100 CFU/reaction. In addition to calcein and manganous ions, agarose gel electrophoresis was used to visualize the amplified LAMP products. Results: Out of 357 BAL samples, 0 (0.0%), 4 (1.1%), 9 (2.5%), and 10 (2.8%) Nocardia strains were identified by direct staining of partial acid-fast, streak culture plate, PCR, and LAMP methods, respectively. Conclusions: We developed a new LAMP technique for the recognition of Nocardia, which is fast, very precise, simple, and low-cost. According to our knowledge, this is the first report of the LAMP method to detect Nocardia in clinical samples.