An Improved Extended-Spectrum-β-Lactamase Detection Test Utilizing Aztreonam plus Clavulanate

Area of Science:

• Clinical Microbiology
• Antimicrobial Resistance
• Infectious Diseases

Background:

• Extended-spectrum β-lactamases (ESBLs) are crucial targets for epidemiological surveillance and infection control.
• Standard ESBL testing methods face challenges, including potential false negatives with co-produced AmpC or metallo-β-lactamases.
• Boronic acid-supplemented tests and aztreonam's inhibition of AmpCs offer potential improvements in ESBL detection.

Purpose of the Study:

• To compare the diagnostic accuracy of three ESBL detection methods: CLSI disk test, CLSI plus boronic acid (BA), and aztreonam plus clavulanate (ATM plus CA).
• To evaluate the performance of these tests, particularly in isolates co-producing AmpC or metallo-β-lactamases.

Main Methods:

• Evaluated 100 characterized isolates of Enterobacteriaceae, Acinetobacter baumannii, and Pseudomonas aeruginosa.
• Included isolates producing TEM, SHV, or CTX-M ESBLs, with or without co-produced AmpC or metallo-β-lactamases, and ESBL-negative controls.
• Compared CLSI, CLSI plus BA, and ATM plus CA disk tests using CLSI methodology, with inhibition zones ≥5 mm indicating a positive result.

Main Results:

• The ATM plus CA test demonstrated the highest overall ESBL detection rate (95.7%), followed by CLSI plus BA (88.6%) and CLSI (78.6%).
• ATM plus CA achieved 100% sensitivity for ESBL detection in AmpC co-producers, outperforming CLSI (60%) and CLSI plus BA (93.3%).
• ATM plus CA also detected ESBLs in 90.1% of metallo-β-lactamase co-producers, with no falsely positive results.

Conclusions:

• The aztreonam plus clavulanate (ATM plus CA) disk test offers superior accuracy for ESBL detection compared to standard CLSI and boronic acid-supplemented methods.
• ATM plus CA is particularly effective in identifying ESBLs in isolates co-producing AmpC or metallo-β-lactamases, addressing limitations of current testing protocols.
• This enhanced detection capability is vital for accurate epidemiological data and effective infection control strategies in clinical laboratories.