Immunoassay for detecting antibiotics

A method for detecting a beta-lactam antibiotic in a sample, said method comprising:

• a) contacting a liquid sample with a labeled antibiotic binding protein obtained from an antibiotic-sensitive Bacillus stearothermophilus and a labeled control reagent, wherein the labeled antibiotic binding protein and the labeled control reagent are present in a container, to form a liquid composition in the container,
• b) providing a test device having a proximal and a distal end, said test device configured to allow lateral flow from the proximal to the distal end, said test device comprising a solid support comprising the following regions in sequence from the proximal to the distal end:
• i. a sample receiving region,
• ii. a detection region, said detection region comprising at least two zones:
• A. a detection zone comprising an immobilized antibiotic capable of binding the labeled antibiotic binding protein, when said labeled antibiotic binding protein is unbound by antibiotic from the sample, and
• B. a control zone comprising an immobilized binding agent capable of binding the labeled control reagent,
• iii. an absorbing region, and
• iv. optionally, a handling region,
• c) contacting the liquid composition of part a) with the sample receiving region of the test device of part b),
• d) allowing the liquid composition to move from the sample receiving region through the detection region to the absorbing region, so as to allow the liquid composition comprising the labeled antibiotic binding protein and the labeled control reagent to contact the detection zone and the control zone,
• e) detecting a signal at the detection zone and a signal at the control zone, wherein
• i. an absence of antibiotic in the sample is indicated by a presence of a signal at the detection zone that is more intense than the signal at the control zone, and
• ii. a presence of antibiotic in the sample is indicated by an absence of a signal at the detection zone or a presence of a signal at the detection zone that is less intense than the signal at the control zone.