Comparison of the ATP-bioluminescence assay and the standard colony counting method for evaluation BCG products

The conventional method of evaluating the efficacy of BCG vaccine products is through colony count, which is very slow and cumbersome. A rapid test for estimating viable bacilli is necessary for vaccine quality control. ATP is a reliable marker for cell viability, and the amount of emitted light during bioluminescence reactions is directly proportional to the ATP content of the bacilli. In this study, the correlation between these two methods was evaluated.

CFU (colony-forming unit) value and bioluminescence signal (RLU) of BCG products were determined by microbiological conventional method and the special kit respectively. ATP content of the products were estimated based on ATP content and CFU value of standard NIBSC vaccine. Linear regression analysis were done by Graph Pad Prism 8.0 software to determine the extent of correlation between two methods. The coefficient K was determined to calculate the CFU value of BCG products.

Results:

 Linear relationship and significant correlation were obtained between two methods for BCG Bulk (r2= 0.9874) and Vaccine (r2= 0.9417) compared to Pastocys (r2= 0.7692). The coefficients K were determined for BCG and Bulk vaccine (0.447 and 0.26 respectively) and can be used to predict and estimate the CFU value of new bathes of products.

The study suggests that an optimized ATP bioluminescence assay is a rapid, sensitive, and reliable alternative method that can accelerate the quality control process for BCG vaccine