Bovine serum albumin labeled with alkaline phosphatase and antibody have been employed as a model to determine if the use of Protein A bearing Staphylococcus aureus Cowan I strain (SACl) bacteria could be extended to enzyme immunoassay (EIA). SACl do not activate " per se" the enzyme substrate and bind aspecifically minimum amount of enzyme labeled antigen. Experimental conditions are described for the use of SACI both in macro and micro EIA assay which allows the processing of numerous samples with minimum hand ling. The sensitivity of the EIA is comparable with radioassay (EIA 2ng-RIA 4ng) which uses SACI in place of second antibody. The inhibition test can be performed in 4 hours time. These results suggest that the stability of SACl when combined with that of enzyme labeled antigens can widen the use of EIA, both for investigative and clinical studies.
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