Division of Microbiology, Department of Pathobiology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
BCG Vaccine Production Plant, Pasteur Institute of Iran, Karaj, Iran.
PLoS One. 2023 Jan 23;18(1):e0280294. doi: 10.1371/journal.pone.0280294. eCollection 2023.
Since the introduction of the Bacillus Calmette-Guérin (BCG) vaccine, the genomes of vaccine strains have undergone variations due to repeated passages in different laboratories and vaccine production facilities. Genetic variations have been considered as one of the effective factors in the BCG variable protective efficacy. Consecutive subcultures have been shown to play an essential role in causing genetic variations in several microorganisms, including Mycobacterium bovis BCG. Therefore, the world health organization (WHO) recommendation to limit the passages of master seed lot in the BCG vaccine production should be considered. Besides, the role of other external variables such as quality of the raw ingredients of the culture media, the type of the culture medium and the cultivation methods in the vaccine production has been poorly studied. Here, the effect of passages and culture medium on genetic variations in a BCG seed lot was investigated during a year. The findings of this study revealed a total of 19 variants compared to seed lot while the passages were more than the number recommended by WHO. The first culture of seed lot in the Sauton broth and Middlebrook 7H9 media, and the last subculture in Sauton broth had the least and the most variants, respectively. The observation of the higher number of variants in the last cultures on Sauton broth and Middlebrook 7H9 in comparison to the first and the middle cultures may indicate the effect of passages on the genetic variations in BCG. Additionally, more variants in BCG grown in the Sauton broth do not necessarily represent the greater ability of this medium to cause genetic mutations. For a better conclusion, it is required to examine the medium components as independent variables.
自卡介苗（BCG）疫苗问世以来，由于在不同实验室和疫苗生产设施中的反复传代，疫苗株的基因组发生了变异。遗传变异被认为是 BCG 保护效力可变的有效因素之一。连续传代会导致包括牛分枝杆菌 BCG 在内的几种微生物发生遗传变异。因此，应该考虑世界卫生组织（WHO）关于限制 BCG 疫苗生产中主种子批传代次数的建议。此外，其他外部变量（如培养基的原料质量、培养基类型和培养方法）在疫苗生产中的作用尚未得到充分研究。在此，研究了传代和培养基对一年中 BCG 种子批遗传变异的影响。与种子批相比，研究共发现了 19 种变异，而传代次数超过了 WHO 推荐的数量。在 Sauton 肉汤和 Middlebrook 7H9 培养基中首次培养种子批，以及最后在 Sauton 肉汤中进行的最后一次传代，变体数量最少和最多。与第一和中间培养物相比，Sauton 肉汤和 Middlebrook 7H9 中的最后培养物中观察到更多变体，这可能表明传代对 BCG 遗传变异的影响。此外，在 Sauton 肉汤中生长的 BCG 中出现更多变体并不一定代表该培养基更有能力引起基因突变。为了得出更好的结论，需要将培养基成分作为自变量进行检查。
