What is the general principle of rapid beta-lactamase tests in detecting enzyme activity?

• A. Turbidity increase
• B. Color change
• C. Gas production
• D. Fluorescence

Answer: (B)

Rapid beta-lactamase tests rely on a chromogenic substrate that changes color when the beta-lactam ring is hydrolyzed by the enzyme. When beta-lactamase acts on the substrate (such as nitrocefin), the chemical structure changes and a visible color shift occurs within minutes, signaling enzyme activity. This direct color readout reflects enzymatic action rather than bacterial growth, which is what turbidity would indicate; gas production would reflect fermentation, and fluorescence would require a different detection approach. The quick color change provides a rapid indication of beta-lactamase presence, aiding timely interpretation for antibiotic decision-making.