Background: Mannheimia haemolytica
is the primary bacterial pathogen in causing bovine respiratory disease
with tremendous annual losses in the cattle industry. The leukotoxin from M. haemolytica
is the predominant
virulence factor. Several leukotoxin activity assays are available but not standardized regarding sample
preparation and cell line. Furthermore, these assays suffer from a high standard error, a prolonged time
consumption and often complex sample pretreatments, which is important from the bioprocess engineering
point of view.
Within this study, an activity assay based on the continuous cell line BL3.1 combined with a commercial
available adenosine triphosphate viability assay kit was established. The leukotoxin activity was found to be
strongly dependent on the sample preparation. Furthermore, the interfering effect of lipopolysaccharides in
the sample could be successfully suppressed by adding polymyxin B. We reached a maximum relative P95
value of 14%, which is more than seven times lower compared to current available assays as well as a time
reduction up to 88%.
Ultimately, the established leukotoxin activity assay is simple, fast and has a high reproducibility.
Critical parameters regarding the sample preparation were characterized and optimized making complex
sample purification superfluous.