Utilization of two improved enzyme immunoassays based on avidin-biotin interaction for the detection of Salmonella

Based on a strong interaction between avidin and biotin, two enzyme immunoassays have been modified and tested for the detection of Salmonella typhimurium in foodstuffs. In both assays, the antigen containing sample was first reacted with antibody to Salmonella which has precoated on a polystyrene microtiter plate. The bound antigen was then allowed to react with an appropriate amount of biotinylated antibody. In the first procedure, the presence of Salmonella was quantified by using peroxidase-labeled avidin. In the latter, avidin acted as a bridge between the biotinylated antibody and the biotinylated peroxidase. Samples containing 10³ and 10⁴ cells/ml of the Salmonella virulent strain, respectively, were detectable by these two methods. The results thus compared favorably with the detection limit of the standard ELISA (10⁵ cells/ml). The superiority of the modified ELISA's utilizing biotin/avidin interactions was also demonstrated for the detection of Salmonella in artificially contaminated food samples inoculated with only 2-5 Salmonella cells followed by two incubation steps. No significant interference of E. coli (up to 5×10⁶ cells/ml) was observed in the quantification of Salmonella cells.