Industrial-scale optimization of fed-batch fermentation enhances biomass productivity of Pasteurella multocida B:2 for hemorrhagic septicemia vaccine.

Hemorrhagic septicemia (HS), caused by Pasteurella multocida serotype B:2, remains a major transboundary disease of cattle and buffalo, particularly in tropical regions. Efficient vaccine production requires high-density biomass generation under controlled and scalable fermentation conditions. This study designed as a sequential process-development and optimization study aimed to optimize industrial-scale cultivation of P. multocida B:2 using a 150-L bioreactor system with S1-S5 samples (n = 5) representing independent fermentation runs from analytical measurements through media selection, fed-batch supplementation, pH control, and thermal preconditioning strategies. Comparative batch cultivation demonstrated superior biomass production in tryptose phosphate broth (TPB) compared to casein sucrose yeast (CSY) medium (OD600 1.57 vs 0.76; p < 0.001). Implementation of fed-batch supplementation significantly enhanced cell density, with a glucose-yeast extract-heart infusion formulation yielding the highest biomass (OD600 3.96; 1.98 × 10⁹ cells/mL) within 8 h of fermentation. Optimal growth was achieved at a controlled pH range of 7.30-7.35, which reduced fermentation time by approximately 33% compared to pH 7.40-7.45. Additionally, pre-heating the culture medium to 40°C prior to inoculation significantly increased biomass yield (p < 0.001). Overall, process intensification through optimized fed-batch strategy and pH control resulted in a > 2.5-fold increase in biomass productivity compared to conventional batch cultivation. These findings provide a scalable and cost-effective fermentation framework for improved commercial production of HS vaccine antigen.