A novel llama single domain antibody (pSJF2H-ToxA5.1) neutralizing Clostridium difficile toxin A (TcdA) was expressed in recombinant Escherichia coli TG1. The effects of several parameters on the expression of ToxA5.1 were studied in Erlenmeyer flasks and bioreactors. Amongst the parameters studied, yeast extract and temperature proved to have the most effects on the expression of ToxA5.1 both in flasks and in bioreactors. Inducer concentration and induction timing must also be taken in consideration to enhance ToxA5.1 yields. In flasks, under conditions tested, a yield of 182 mg/g DCW was achieved. In bioreactors, E. coli TG1-ToxA5.1 was grown to a final biomass concentration of 12.26 g DCW/L in defined media using a dual-point pH-stat fed-batch control strategy. Expression of ToxA5.1 required an increase in the fermentation temperature from 28 ºC to 37 ºC, supplementation of yeast extract of 54 g/L in the feed solution and the addition of 1 mM inducer molecule, isopropyl β-D-1-thiogalactopyranoside  (IPTG). Under these conditions, ToxA5.1 was expressed to 127 mg ToxA5.1/L in bioreactors.