Which substrate is most sensitive for detecting beta-lactamase activity?

Which substrate is most sensitive for detecting beta-lactamase activity?

• A. Penicillin
• B. Cefoxitin
• C. Nitrocefin
• D. Amoxicillin

Answer: (C)

Detecting beta-lactamase activity is easiest when the substrate provides a clear, rapid signal as soon as the enzyme acts. Nitrocefin is a chromogenic cephalosporin that changes color—from yellow to red—when the beta-lactam ring is hydrolyzed by beta-lactamase. That visible color shift happens quickly and reliably, making it highly sensitive for detecting even low levels of enzyme across a wide range of beta-lactamases. Penicillin and amoxicillin are antibiotics rather than designed colorimetric substrates, so they don’t provide as immediate or as easy-to-read a signal of beta-lactamase activity. Cefoxitin can be useful for identifying certain enzymes like AmpC, but its sensitivity is more limited to specific mechanisms, whereas nitrocefin offers broad, rapid detection.

Detecting beta-lactamase activity is easiest when the substrate provides a clear, rapid signal as soon as the enzyme acts. Nitrocefin is a chromogenic cephalosporin that changes color—from yellow to red—when the beta-lactam ring is hydrolyzed by beta-lactamase. That visible color shift happens quickly and reliably, making it highly sensitive for detecting even low levels of enzyme across a wide range of beta-lactamases.

Penicillin and amoxicillin are antibiotics rather than designed colorimetric substrates, so they don’t provide as immediate or as easy-to-read a signal of beta-lactamase activity. Cefoxitin can be useful for identifying certain enzymes like AmpC, but its sensitivity is more limited to specific mechanisms, whereas nitrocefin offers broad, rapid detection.