Scale-up of transgenic tobacco cells that express intimin of enterohemorrhagic Escherichia coli O157:H7 for use as a transitional platform for an oral cattle vaccine

Intimin is the primary adhesin protein of enterohemorrhagic Escherichia coli O157:H7, a pathogen carried by cattle and transmitted to humans via contaminated food and water. This work describes the rapid production of 1.3 kg dry weight of transgenic tobacco cells expressing the C-terminal 261 amino acids of intimin (Int261) for subsequent oral vaccine testing to reduce cattle colonization by E. coli O157:H7. Both a stirred-tank bioreactor (60 L) and a less capital-intensive oxygenated carboy culture were shown feasible for generating this scale of transgenic plant tissue culture biomass. Antibiotic selection pressure was not required during scale-up to maintain Int261 expression over the 13-wk culture period. Extended medium autoclave times of up to 90 min used for bioreactor sterilization had only minimal impact on nutrient uptake, culture growth, and intimin expression. Plant tissue was transformed, produced in vitro, and available for feeding studies in a fraction of the time required to develop and grow transgenic plants.