Development of a set of three real-time loop-mediated isothermal amplification (LAMP) assays for detection of Bacillus anthracis, the causative agent of anthrax.

Bacillus anthracis, the causative agent of anthrax is a Gram-positive, non-motile, spore forming bacterium. Its spores can persist in soil and water for years and can also be aerosolized. A rapid, sensitive and specific method to detect B. anthracis is important for clinical management and preventing spread of anthrax. Loop-mediated isothermal amplification (LAMP) assay is a rapid technique that amplifies target DNA in isothermal conditions with high sensitivity and specificity. In this study, a LAMP assay set targeting a chromosomal and two plasmid markers was developed. The individual assays of the LAMP set targeting pXO1 plasmid (lef), pXO2 plasmid (capB), and chromosome (BA5345) sequences could detect 10, 250, and 100 fg of genomic DNA and 10, 100, and 50 copies of the DNA targets harboured in recombinant plasmids, respectively. The lef and capB LAMP assays could detect ≥ 1 × 103 CFU per mL of bacteria in spiked human blood samples, while BA5345 LAMP assay could detect ≥ 1 × 104 CFU of bacteria per mL of spiked blood. The amplification was monitored in real-time by turbidimeter, and visual detection was also accomplished under normal and UV light after adding SYBR Green 1 dye on completion of the reaction. The assay set was found to be highly sensitive and did not cross-react with the closely related Bacillus spp. and other bacterial strains used in the study.