Pyridinium 2-azo-p-dimethylaniline chromophore, a chromogenic reagent for beta-lactamase testing compared to nitrocefin.

Pyridinium-2-azo-p-dimethylaniline chromophore was evaluated as a test tube, filter paper and spectrophotometric assay for detection of beta-lactamases from gram-positive and gram-negative organisms. Although useful for detection of TEM beta-lactamases in Haemophilus influenzae and Neisseria gonorrhoeae, it was a poor agent for detecting TEM, OXA and PSE enzymes in Enterobacteriaceae. It also proved poor for detecting cephalosporinases in Pseudomonas aeruginosa and Enterobacteriaceae, and penicillinases in Staphylococcus aureus when compared to nitrocefin. As a spectrophotometric substrate it was equivalent to nitrocefin and cephaloridine with various beta-lactamases.