Whooping cough vaccines: production of virulent B. pertussis

key words: acellular, fed batch, metabolism, pertussis toxin

The production of acellular pertussis in comparison with whole cell pertussis
vaccines demands 5 to 25 times the amount of B. pertussis' virulence factors such
as pertussis toxin (PT), to produce the same number of vaccine doses. An
increase in the volumetric productivity by employing fed-batch rather than the
currently used batch cultivations of B. pertussis could reduce the cost price of
acellular pertussis vaccines. This study defined the conditions that enable fed
batch cultivations at high specific PT production. A solution containing lactate and
glutamate was fed to the cultures at various rates. The feed rate and whether or
not the fed substrates were completely consumed, significantly influenced cellular
metabolism. If lactate was detectable in the culture broth while glutamate was not,
poly-hydroxy-butyrate (PHB) was formed. Any PHB present was metabolized
when glutamate became detectable again in the culture liquid. At higher lactate
and glutamate concentrations, free fatty acids were produced. Though toxic, free
fatty acids were not the reason cultures stopped growing. By choosing appropriate
conditions, a cell density of 6.5 g.L-1 dry weight was reached, i.e. a 7-fold increase
compared to batch culture. The metabolic mechanisms behind the formation of
PHB and fatty acids are discussed, as well as how to further increase the cell
density. The PT production stopped at 12 mg.L-1, well before growth stopped,
indicating that regulatory mechanisms of PT production may be involved.