Differentiation of Amidase and β-Lactamase by Infrared Absorption

SUMMARY: The carbonyl-β-lactam absorption band of penicillins and cephalosporins at 1760 cm.−1 is detectable when the antibiotics are mixed with enzymes or bacterial protein. This band can therefore be used for differentiating the two inactivating enzymes β-lactamase and amidase. Examined thus, methicil- lin, cloxacillin, amino-cephalosporanic acid (7-ACA) and thienylacetamido- 7-AC A were stable to staphylococcal β-lactamase but less stable to coliform β-lactamase. Only quinacillin among a range of therapeutic derivatives tested resisted both types of β-lactamase. The other inactivating enzyme, amidase, can exist independently of β-lactamase in coliform organisms. When methicillin and cloxacillin were treated with amidase, they lost their stability to β-lactamase.