Determining the optimal ceftriaxone MIC for triggering extended-spectrum β-lactamase confirmatory testing

Area of Science:

• Clinical microbiology
• Antimicrobial resistance

Background:

• Routine testing for extended-spectrum β-lactamase (ESBL) production is no longer mandated by the Clinical and Laboratory Standards Institute (CLSI).
• Clinical microbiology laboratories require alternative methods for identifying ESBL-producing bacteria.

Purpose of the Study:

• To evaluate the utility of ceftriaxone Minimum Inhibitory Concentration (MIC) values as a proxy for detecting ESBL production in clinical isolates.
• To determine an optimal ceftriaxone MIC cutoff for predicting ESBL presence.

Main Methods:

• Analysis of ceftriaxone MIC data from 1,386 clinical bacterial isolates.
• Statistical evaluation of predictive values for a proposed ceftriaxone MIC cutoff.

Main Results:

• A ceftriaxone MIC cutoff of 8 μg/ml demonstrated high accuracy in predicting ESBL production.
• Positive predictive value approached 100%, and negative predictive value approached 99.5% for this cutoff.

Conclusions:

• Ceftriaxone MIC testing serves as an effective and efficient surrogate method for identifying potential ESBL producers in clinical settings.
• This approach can streamline laboratory workflows following updated CLSI guidelines.