The immunofluorescent detection of Entamoeba histolytica in pus using avidin-biotin system

Immunoprecipitation studies with biotinylated Entamoeba histolytica antigens

The biotinylation of protein antigens for use in immunoprecipitation studies with parasite antigens is described. This technique was standardized to produce maximal labelling without compromising either the viability of the parasite or the antigenicity of labelled proteins. Live axenic Entamoeba histolytica trophozoites were optimally labelled by incubation of 10(7) parasites in 1 ml phosphate-buffered saline for 20 min at 37 degrees C with a final concentration of 10 mM N-hydroxy succinimido-biotin (NHS-B). Examination of antigens recognized by immunoglobulin from convalescent amoebic liver abscess patients and precipitated by protein A-Sepharose showed a general increase in immune response to amoebic antigens with time following treatment. Mass ratio mol. wts of immunoprecipitated antigens concur with those presented by other authors using alternate technology, in addition to recognizing antigens previously not identified by human sera. We therefore recommend biotinylation as a viable alternative to radiolabelling techniques for the study of parasite antigens and the humoral immune responses raised against them.

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 was 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 10(3) and 10(4) 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 (10(5) 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 x 10(6) cells/ml) was observed in the quantification of Salmonella cells.