Evaluation on molecular characterization of BCG Strains for vaccine quality control

Su-Lin Yang, Chan-dow Lee, Yafen Cheng, Pei-Yu Chen, Hui-Chuan Wu,Yu-Yin Fang, Hua-Jung Ku, Ching-Fang Chang, Ping-Fuai Wu

2011 Vol.27 NO.13

Correspondence Author: Su-Lin Yang


The risk of extra-pulmonary tuberculosis infection among infants and children under 2 years old was 2.88 times higher than children older than 2 years old in Taiwan. To prevent tuberculosis (TB) infection in infants and young children, 98% of neonates in Taiwan have received Bacillus Calmette-Guérin (BCG) vaccination at birth. Because the number of viable bacilli in BCG vaccine exerts a great influence on its efficacy, the vaccines manufactured by Taiwan Centers for Diseases Control (Taiwan CDC) were stored in batches for 1, 3, and 6 months at 4, 25, and 37 degrees Celsius for stability tests, which was evaluated by quantification of the viable organism. Under the worst case scenario, the vaccines stored at 37℃ for 6 months still retained 45% of their potency, which was above the standard set by World Health Organization (WHO), which requires that vaccines to retain 20% of their potency when stored at 37℃ for 28 days.
There are two different colony morphologies of mycobacteria isolated from BCG vaccines. Type I is a smooth form and Type II is a rough form. Using molecular biological methods to differentiate their genotypes, most mycobacteria colonies isolated from BCG vaccine strain are Type I. The proportion of Type I colony morphology of mycobacteria stored for 1, 3, and 6 months was 85%, 70% and > 60% respectively. Using PCR and DNA sequencing to detect RD 16 gene, the nucleotide number of Type I colony was 22 base pairs shorter than that of Type II colony. Using multiplex PCR to identify RD2, RD8, RD 14, and RD 16 genes, the only mutated gene of the BCG-vaccine strain in RD segments was RD 16. Among the vaccines stored at different temperatures, there was no significant difference in their genotypes. Therefore, the quality of BCG vaccines manufactured by Taiwan CDC fully met the WHO standards, and the molecular genotyping method could be helpful in quality control.