A size exclusion chromatography- and ultrafiltration-based two-step process for purifying phage for therapeutic applications

• Two-step process for bacteriophage purification. • Combination of size exclusion chromatography and ultrafiltration with backflow recovery. • High phage titer and recovery. • Excellent removal of endotoxins and protein impurities. The rise in the number of antibiotic-resistant bacteria has created the need for alternative therapeutic approaches, including bacteriophage therapy. Bacteriophages are viruses that infect and lyse bacteria and therefore offer a highly targeted and adaptable solution to combat multidrug-resistant pathogens. However, the scalable purification of bacteriophages, while achieving high yield of product and efficient removal of impurities such as endotoxins, remains a significant barrier to their therapeutic adoption. This study presents a two-step purification process combining size-exclusion chromatography (SEC) and ultrafiltration as an efficient and scalable method for bacteriophage purification. T7 was used as the model bacteriophage. Preparative SEC using a cuboid device served as the first step for removing endotoxin and other impurities from bacterial culture filtrate. The SEC-purified phage sample was then processed using a carrier phase ultrafiltration and backflow recovery technique to further purify and enrich the bacteriophage. Phage titer, endotoxin level, and protein concentration were quantified at each stage to evaluate purification performance. The endotoxin level was substantially reduced, decreasing from 1.44 EU/mL in the initial culture filtrate to 0.49 EU/mL in the final purified phage sample, the FDA's acceptable limit for products that directly or indirectly contact the cardiovascular and lymphatic systems being 0.50 EU/mL. The phage titer was enhanced from 5.33×10⁹ PFU/mL (in the cell culture filtrate) to 9.33×10⁹ PFU/mL in the final product. The overall protein removal achieved was 95.8 % while the overall endotoxin removal was 92.5 %. These findings suggest that the proposed two-step purification process could be developed further and adopted for scalable production of high-purity bacteriophage preparations suitable for therapeutic applications.