Bioprocessing of bacteriophages via rapid drying onto microcrystals

Abstract

We present an alternative bioprocess for bacteriophages involving room temperature coprecipitation of an aqueous mixture of phage (Siphoviridae) and a crystallizable carrier (glutamine or glycine) in excess of water miscible organic solvent (isopropanol or isobutanol). The resultant suspension of phage-coated microcrystals can be harvested by filtration and the residual solvent removed rapidly by air-drying at a relative humidity of 75%. Albumin or trehalose added at 5% w/w of the crystalline carrier provide for better stabilization of the phage during co-precipitation. Free-flowing dry powders generated from an aqueous solution of phage (∼13 log(10) pfu/mL) can be reconstituted in the same aqueous volume to a phage titer of almost 10 log(10) pfu/mL; high enough to permit subsequent formulation steps following bioprocessing. The phage-coated microcrystals remain partially stable at room temperature for at least one month, which compares favorably with phage immobilized into polyester microcarriers or lyophilized with excipient (1-5% polyethylene glycol 6000 or 0.1-0.5 M sucrose). We anticipate that this bioprocessing technique will have application to other phage families as required for the development of phage therapies.