Development of rapid gold nanoparticles based lateral flow assays for simultaneous detection of Shigella and Salmonella genera.

Salmonella and Shigella genera are common pathogens that contaminate foods and beverages. Lateral flow assays (LFA) are commonly used to detect these pathogens. However, most of the developed LFAs are for single detection. Simultaneous detection of pathogens is required to reduce cost and time. In this work, 40 nm gold nanoparticles (AuNPs) were synthesized using the seeding growth method as labeling agent. The AuNPs were characterized and conjugated with mouse anti-Gram negative endotoxin antibody. The nitrocellulose membrane HF135 was immobilized with anti-mouse IgG antibody as a control line and two separate test lines with either anti-Shigella or anti-Salmonella antibody, respectively. Color intensity of test lines was observed for positive samples. A milk sample was used as proof of concept to mimic actual contamination. The limit of detection of the LFA was 3.0 × 106 CFU/mL for multiplex detection of Shigella flexneri and Salmonella Typhi and for both single detections. The result was comparable with the enzyme-linked immunosorbent assay (ELISA) analysis. The produced LFA could differentiate between Shigella flexneri, Shigella boydii, Salmonella Enteritidis, and Salmonella Typhi. The developed LFA was able to identify Shigella flexneri and Salmonella Typhi with good sensitivity in milk samples, thus, beneficial to ensure the safety of food before entering the market.

Direct Resazurin Microplate Assay in Drug Susceptibility Testing of Smear-Positive Sputum Samples against Mycobacterium tuberculosis.

BACKGROUND: A new direct microplate-based colorimetric drug susceptibility test that omits the initial isolation of Mycobacterium tuberculosis from sputum specimens was evaluated. METHODS: A total of 51 M. tuberculosis acid fast bacilli (AFB) smear-positive sputum specimens were inoculated directly into drug-free and serial dilutions of drug-containing Middlebrook 7H9 broth media. With this direct resazurin micro plate assay (REMA) method, resazurin dye was used as a growth indicator in microplate wells. The minimum inhibitory concentrations (MIC) of isoniazid (INH) and rifampicin (RIF) were compared with those of the 'gold standard' absolute concentration method (ACM). The turnaround time (TAT) of the direct REMA and the ACM were also determined. RESULTS: At the selected cut-off points (INH: 0.0625 µg/mL; RIF: 0.125 µg/mL), good drug susceptibility test results were obtained for INH and RIF with an average sensitivity, specificity and accuracy of 90%, 100% and 97%, respectively, with a TAT of 15 days. The REMA method also correctly classified the resistant isolates with positive predictive values of 95% and negative predictive values of 98% for the two drugs. CONCLUSIONS: The direct REMA was reliable in routine diagnostic laboratories for the drug susceptibility testing of M. tuberculosis and the rapid detection of multi-drug-resistant tuberculosis.