Mannheimia haemolytica – Bioprocess improvement of leukotoxin production using a fed-batch process and a ceramic membrane based downstream strategy

Bovine respiratory disease (BRD) is the most important disease in the cattle industry with serious annual economic losses. Mannheimia haemolytica (M. haemolytica) is classified as the primary bacterial pathogen causing BRD and its leukotoxin (LKT) is the predominant virulence factor. Vaccines based on the culture supernatant of M. haemolytica (LKT as immunostimulating agent) offer the most promising measure to contain BRD outbreaks and are commercially available since the 1980s. However, insufficient LKT yields, predominantly reflecting a lack of knowledge about the optimal bioprocess conditions and medium requirements of M. haemolytica for LKT production. The primary objective of this work was to improve the LKT yield of the vaccine manufacturing process. In order to achieve an efficient LKT production process the effect of critical process parameters (pH, temperature, inoculum density, agitation speed, and aeration rate) were characterized and a pH and dissolved oxygen process control was applied. In addition to the physical process parameters, the optimization of the fermentation medium had a dramatic effect on LKT production. This work also addressed the application of ceramic membranes as a new downstream strategy, which was based on a two stage process with an initial biomass separation and subsequent LKT recovery. Finally, the downstream strategy was completed with the development of a novel LKT activity assay.