A Turbidimetric Method for Assay of Vi Antigen

Isolation of Vi Antigen and a Simple Method for Its Measurement

“…The quality and quantity of this antigen have caused much concern in the control of typhoid vaccines. As compared with other quantitative methods (3,9,20), EID, as described here, has the advantage of being sensitive, specific, and relatively simple. EID has been used successfully by other investigators for measuring immunoglobulins and other proteins (12,13).…”

“…Landy (9) claimed to have measured the relative amounts of Vi antigen in various enteric organisms by an active immunization mouse protection test. Webster et al (20) used a turbidimetric method which depends on the tendency of acidic mucopolysaccharides to flocculate with albumin at low pH. Sensitivity of this procedure ranges from 125 to 500 Aig of antigen per ml, but the reaction is not specific for the Vi antigen.…”

“…Selected Vi-negative colonies of Citrobacter strain Acetone-killed and -dried cells Suspend cells in 10 volumes (w/v) of 0.85% NaCl containing 0.1% sodium azide. Shake at 35 C for 30 min; centrifuge(20,200 x g) for 30 min.…”

Purification and immunochemical properties of Escherichia coli B polysaccharide cross-reacting with Salmonella typhi Vi antigen: preliminary evidence for cross-reaction of the polysaccharide with Escherichia coli K1 antigen

“…Nucleic acids were determined by measuring absorption at 260 nm assuming an extinction coefficient of 20 for a solution of 1.0 mg of DNA per ml in a 1-cm cuvette. Acidic polysaccharides in eluates from columns were determined by the method of Webster et al (40). The standard curve was prepared for Vi antigen solutions.…”

Immunochemical properties of Vi antigen from Salmonella typhi Ty2: presence of two antigenic determinants

“…Determinations of O-acyl content were performed by the method of Snyder and Stephens (10). Acidic polysaccharides in eluates from columns were determined by the method of Webster et al (13).…”