Comparison Between Simple Batch and Fed-Batch Bioreactor Cultivation of Recombinant BCG.

Background/

Objectives

Tuberculosis continues to be a significant global health concern, causing 1.3 million deaths in 2022, particularly affecting children under 5 years old. The Bacillus Calmette-Guérin (BCG) vaccine, developed in 1921, remains the primary defense against tuberculosis but requires modernized production methods. The recombinant BCG-pertussis strain shows potential in providing dual protection against tuberculosis and whooping cough, especially for vulnerable newborns, and enhanced efficacy against bladder cancer. Implementing submerged cultivation techniques for rBCG-pertussis production can offer increased productivity and standardization.

Methods

This study explores a fed-batch cultivation strategy with pH-stat control to feed L-glutamic acid through the acid pump into 1 L bioreactor. Three pH values were evaluated for fed-batch and a simple batch without pH control was done for comparison. The viable cell concentration was compared before and after freeze-drying samples harvested during the cultures.

Results

L-glutamic acid was identified as the preferred substrate for rBCG-pertussis. While the fed-batch strategy did not enhance the maximum specific growth rate compared to simple batch cultivation, it did improve the specific growth rate after day 4 in the pH 7.4-controlled fed-batch cultures, thereby reducing the cultivation time. Fed-batch cultures controlled at three pH levels exhibited lower optical density than the simple batch, although the viable cell counts were similar. Notably, samples harvested after day 8 from the simple batch cultures showed a reduction in CFU/mL after freeze-drying, whereas all fed-batch samples exhibited high recovery of viable cell counts post lyophilization.

Conclusions

The additional glutamate supplied to the fed-batch cultures may have protected the cells during the lyophilization process.