Performance Assessment of the BluePoint MycoID Plus Kit for Identification of Mycobacterium tuberculosis, Including Rifampin- and Isoniazid-resistant Isolates, and Nontuberculous Mycobacteria.

The performance of the BluePoint MycoID plus kit (Bio Concept Corporation, Taichung, Taiwan), which was designed to simultaneously detect Mycobacterium tuberculosis (MTB), rifampin- and isoniazid-resistant MTB, and nontuberculous mycobacteria (NTM) was first evaluated with 950 consecutive positive cultures in Mycobacterium Growth Indicator Tube (MGIT) system (BACTEC, MGIT 960 system, Becton-Dickinson, Sparks) from clinical respiratory specimens. The discrepant results between kit and culture-based identification were finally assessed by 16S rRNA gene sequencing and clinical diagnosis. The accuracy rate of this kit for identification of all Mycobacterium species was 96.3% (905/940). For MTB identification, the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the kit were 99.7%, 99.3%, 99.0% and 99.8%, respectively. For rifampicin-resistant MTB identification, the sensitivity, specificity, PPV, and NPV of the kit were 100.0%, 99.4%, 91.3%, and 100.0%, respectively, while the corresponding values of isoniazid-resistant MTB identification were 82.6%, 99.4%, 95.0%, and 97.6%, respectively. In identifying specific NTM species, the kit correctly identified 99.3% of M. abscessus (147/148) complex, 100% of M. fortuitum (32/32), M. gordonae (38/38), M. avium (39/39), M. intracellulare (90/90), M. kansasii (36/36), and M. avium complex species other than M. avium and M. intracellulare (94/94). In conclusions, the diagnostic value of the BluePoint MycoID plus kit was superior to culture method for recoveries and identification of NTM to species level. In addition, the diagnostic accuracy of BluePoint MycoID plus kit in MTB identification was similar to conventional culture method with high accuracy rate of rifampicin-resistant M. tuberculosis identification.

A newly developed immunoassay method based on optical measurement for Protein A detection.

We describe the development of an immunoassay using an antibody-silver nanoparticle (Ab-AgNP) conjugate as a catalyst for the silver enhancement reaction. The immuno-reaction signals that were magnified by silver metal precipitation were quantified using a commercial flatbed scanner. Protein A from Staphylococcus aureus (S. aureus), a common clinical pathogenic bacterium, was used in this research. The ease of infection of S. aureus necessitates the development of a fast detection method. The framework of the method described in this paper is based on the sandwich immunoassay and contains a 1st antibody (immunoglobulin G, IgG), an antigen (Protein A), and a 2nd antibody-colloidal silver conjugate (IgG-AgNPs). The silver enhancement reaction, a signal amplification method in which silver ions are reduced to metallic silver, is used to magnify the immuno-reaction signal. The change in signal, as visualized in grayscale, can be easily observed and analyzed by our optical scanning detection system. The relationship between antigen concentration and grayscale value is discussed. The detectable concentration limit for the antigen was found to be 1 ng/mL with 10 µg/mL of IgG and 300 µM of the IgG-AgNP conjugate. This immunoassay method provides the advantages of low cost, easy operation, and short detection time. Moreover, it has potential applications in clinical diagnoses.