Enzyme immunoassays in which biotinillated β-lactamase is used for the detection of microbial antigens

The performance characteristics of enzyme immunoassays are determined to a great extent by the enzyme-substrate system utilized for the immunoassay. Beta-lactamases (penicillin amido-beta-lactamhydrolase EC 3.5.2.6) offer a number of advantages which might make them useful in immunoassay systems. We linked beta-lactamase from Bacillus cereus with biotin and used the biotinillated enzyme to devise immunoassay systems for the detection of a number of microbial antigens. An assay system in which antibodies to the polyribitol phosphate antigen of Haemophilus influenzae type b were used was capable of detecting between 0.4 and 1.6 ng of that antigen. Similarly, an assay in which antibodies to the common antigens of adenoviruses and biotin-linked beta-lactamase were used was capable of detecting between 1 and 10 50% tissue culture infective doses of a strain of enteric-type adenovirus. When applied to the detection of rotavirus, a similar system in which biotinillated beta-lactamase was used was capable of detecting small amounts of antigen in a standard rotavirus preparation. This assay could also detect virus in 36 of 37 stool specimens from children with rotavirus gastroenteritis. The positive specimens could easily be distinguished from negative ones by the naked eye, and a permanent record of the qualitative results could be obtained by the use of a standard office photocopying machine. Beta-lactamases have promise for use in practical enzyme immunoassay systems, especially in situations in which expensive colorimetric instrumentation is not available.