A microtitre plate-based assay for the screening of beta-lactams.

A simple, rapid, sensitive and automatizable method for the detection and quantification of bacterial cell wall inhibitors has been developed. The procedure is characterized by the use of a micro-organism hypersensitive to beta-lactam antibiotics that contains an inducible cytosolic beta-galactosidase; this enzyme is released when the micro-organism cell wall is disrupted by the antibiotic action, and then measured by the use of a chromogenic substrate. The present method allows the detection of beta-lactam traces in other non-beta-lactam antibiotics, and has been successfully applied in the detection of small amounts of beta-lactams in biological fluids such as milk and Actinomycetes fermentation broths. The easy automatization of this method makes it specially suitable for the screening of new antibiotics of natural origin.