Use of inhibitors in reporter assays

A method for increasing the signal-to-noise ratio of a β-lactamase assay, comprising:

• a) contacting a sample comprising a membrane compartment containg a gene encoding a beta lactamase reporter enzyme operably linked to an inducible promoter which exhibits background expression of beta lactamase actvity with clavulanic acid,
• b) incubating said sample with said clavulanic acid so as to inhibit said background beta lactamase activity,
• c) contacting said sample with a class C beta-lactamase activity that degrades said clavulanic acid, and
• d) inducing expression of a beta lactamase reporter enzyme activity,
• e) contacting said sample with a substrate for said beta-lactamase reporter enzyme activity,
• f) determining the activity of said beta-lactamase reporter enzyme activity,
• wherein said beta-lactamase assay is homogeneous,
• further wherein the signal-to-noise ratio of said beta-lactamase assay is increased.

A method for screening test compounds for activity as an inducer of a beta lactamase reporter enzyme activity, comprising:

• a) contacting a sample comprising a membrane compartment containg a gene encoding a beta lactamase reporter enzyme operably linked to an inducible promoter which exhibits background expression of beta lactamase actvity with clavulanic acid,
• b) incubating said sample with said clavulanic acid so as to inhibit said background beta lactamase activity,
• c) incubating said membrane compartment in media without said clavulanic acid, or contacting said sample with a class C beta-lactamase activity to degrade said clavulanic acid,
• d) contacting said sample with at least one test chemical,
• e) contacting said sample with a substrate for said beta lactamase reporter enzyme activity, and
• f) determining the activity of said beta lactamase reporter enzyme activity,
• g) optionally comparing the activity of said beta lactamase reporter enzyme activity in the presence and absence of said test chemical.