[Broad spectrum beta-lactamases and the API ATB 244 system: the need for detection]

Area of Science:

• Microbiology
• Clinical Diagnostics
• Antimicrobial Resistance

Background:

• Automated systems like API ATB 24H are used for bacterial antibiotic sensitivity testing.
• Extended-spectrum beta-lactamases (ESBLs) confer resistance to beta-lactam antibiotics, including oxy-iminocephalosporins.
• Enterobacteriaceae producing specific ESBLs (CTX-1, SHV-3, SHV-4) pose a significant challenge in clinical settings.

Purpose of the Study:

• To evaluate the efficacy of the API ATB 24H automated system in detecting acquired resistance to oxy-iminocephalosporins.
• To compare the detection rates across different API system types, beta-lactam antibiotics, and beta-lactamase types.
• To identify a reliable method for detecting oxy-imini beta-lactamases.

Main Methods:

• Testing bacterial isolates of Enterobacteriaceae with known ESBL production using the API ATB 24H system.
• Utilizing different configurations of the API ATB system (ATB G-, ATB PSE).
• Employing a double disk synergy test with Augmentin and an oxy-iminocephalosporin disk.

Main Results:

• The API ATB 24H system demonstrated limitations in fully detecting acquired resistance to oxy-iminocephalosporins.
• Detection frequency varied based on the specific API system used, the antibiotic tested (cefotaxime, ceftazidime), and the type of beta-lactamase produced.
• The double disk synergy test proved effective in detecting oxy-imini beta-lactamases.

Conclusions:

• The API ATB 24H system requires improvement for accurate detection of certain ESBL-mediated resistance mechanisms.
• Clinical laboratories should be aware of the limitations of automated systems for detecting emerging resistance.
• A double disk synergy test serves as a simple and effective method for identifying oxy-imini beta-lactamase production.