A two-step method for extraction of lipopolysaccharide from Shigella dysenteriae serotype 1 and Salmonella typhimurium: An improved method for enhanced yield and purity

Bacterial lipopolysaccharide (LPS) has been widely used as an antigen and adjuvant in immunological applications. Amongst the methods developed for extraction of LPS, hot phenol extraction (HPE) method is the gold standard. However, the HPE method provides poor yield of LPS (~ 4.5% by weight), is associated with relatively higher impurities of proteins and nucleic acids, and the acidic hot phenol can cause a degradative effect on LPS. In this work a two-step extraction (TSE) method was developed using a non-capsulated, [Shigella dysenteriae serotype-1] (Sd1) and capsulated [Salmonella typhimurium type B (StB)] species as model pathogens. The TSE method takes advantage of growth kinetics of bacteria wherein a two-step sequential approach for LPS extraction was employed. In step-1, culture supplemented with CaCl2 during early log phase of growth was induced to release LPS by the effect of EDTA at their late exponential phase of growth. In step-II, cells with left over LPS were subjected to modified HPE method that reduced both the degradative effect of acidic hot phenol and associated impurities. The LPS produced using TSE method enabled not only enhanced yield (~ 2.78 and ~ 2.91 fold higher for Sd1 and StB respectively) requiring nearly similar duration of extraction, but also was structurally and functionally comparable with LPS produced using HPE method and commercially procured LPS. Overall, the developed TSE method is relatively more efficient (enhanced yield), clean (healthy extraction with reduced impurities), safe (reduced handling of larger pathogenic culture) and cost-effective for LPS extraction with potential for scale up.