Isolation and concentration of Salmonellae with an immunoaffinity column

A method for rapidly and selectively isolating Salmonellae from buffer solutions and concentrating the bacteria by a factor of approximately 500 was developed. Anti-Salmonellae antibody was covalently linked to 40 microm polyacrylamide beads to prepare a solid phase with affinity for the bacteria. The beads were packed into 1-mm diameter glass tubes to form a column 20 microl in volume. Buffer containing Salmonellae at concentrations ranging from 10(2) to 10(6)/ml was pumped through the column to trap and concentrate the bacteria. At a flow rate of 50 microl/min, more than 95% of the bacteria introduced to the column were captured, while at 800 microl/min capture dropped to 32%. Specificity was high, with no detectable capture of Escherichia coli at a concentration of 10(5)/ml. Capture of more than 90% of Salmonellae in a 5-ml sample was achieved in 40 min by re-circulating the sample through the column at a flow rate of 500 microl/.