Fluorogenic and chromogenic .beta.-lactamase substrates

A method of assaying for the presence of .beta.-lactamase in a sample comprising the steps of:

• a) contacting the sample with a chromogenic cephalosporin derivative having a group --CH.sub.2 --X--Y at position 3 of the cephalosporin, wherein X is ##STR9## and Y is selected from the group consisting of:
• ##STR10## N-methyl indoxyl, p-nitrophenol and o-nitrophenol, whereby X--Y is eliminated from the chromogenic cephalosporin derivative in the presence of .beta.-Lactamase and X--Y breaks down to X and Y, and;
• reacting Y with a reagent to produce a colored reaction product and detecting the colored reaction product as an indicator of the presence of .beta.-lactamase.

A kit for determining the presence of .beta.-lactamase in a sample comprising, in a first containing means, a cephalosporin derivative having a group --CH.sub.2 --X--Y at position 3 of the cephalosporin, wherein X is ##STR11## and Y is selected from the group consisting of:

• ##STR12## 1-naphthol, 2-naphthol, naphthylamine, fluorescein, N-methyl indoxyl, 4-methyl umbelliferone, 1-methyl-7-hydroxyquinolinium iodide, rhodamine, p-nitrophenol and o-nitrophenol;
• and in a second containing means, a .beta.-lactamase reagent suitable for standardization of an assay for .beta.-lactamase.