Canadian impact of CLSI aminoglycoside breakpoint changes for selected gram-negative bacteria

Area of Science:

• Clinical microbiology
• Antimicrobial resistance
• Infectious diseases

Background:

• The Clinical and Laboratory Standards Institute (CLSI) periodically updates antimicrobial susceptibility testing (AST) breakpoints.
• Aminoglycosides are crucial antibiotics for treating serious Gram-negative infections.
• Enterobacterales and Pseudomonas aeruginosa are common causes of hospital-acquired infections.

Purpose of the Study:

• To assess the impact of recent CLSI aminoglycoside breakpoint revisions on Enterobacterales and Pseudomonas aeruginosa susceptibility.
• To identify specific bacterial subgroups disproportionately affected by the breakpoint changes.

Main Methods:

• Retrospective analysis of AST data from a Canadian academic hospital.
• Comparison of susceptibility rates before and after CLSI breakpoint implementation.
• Stratification of results by bacterial species and key resistance mechanisms (e.g., beta-lactamase production).

Main Results:

• Overall aminoglycoside susceptibility for Enterobacterales and Pseudomonas aeruginosa remained largely unchanged post-revision.
• A significant impact was observed in the susceptibility of beta-lactamase producing Enterobacterales.
• Specific aminoglycosides may show varying degrees of impact depending on the resistance phenotype.

Conclusions:

• Recent CLSI aminoglycoside breakpoint revisions have a limited effect on the overall susceptibility of Enterobacterales and Pseudomonas aeruginosa.
• Clinicians should be aware of the potential for altered susceptibility interpretations in beta-lactamase producing Enterobacterales.
• Continued monitoring of antimicrobial susceptibility patterns following breakpoint changes is essential.