Possible impact of revisions in disc diffusion breakpoints for aminoglycosides and piperacillin/tazobactam in the 33rd edition of CLSI M100 document on clinical reporting and use in Indian settings with low susceptibility.

Purpose: The study explores the impact of significant interpretative breakpoint changes for aminoglycosides and piperacillin-tazobactam in Enterobacterales and Pseudomonas aeruginosa, considering PK/PD, clinical data, and susceptibility on clinical reporting and use.

Procedure: Between January 2021 and June 2023, a total of 189,583 samples were processed for bacterial pathogens and antimicrobial susceptibility testing was performed using disc diffusion method/VITEK® 2 Compact system/broth microdilution. WHONET software was utilised to capture and analyse the changes in the interpretation of disc diffusion method, following updates to CLSI M100 documents in comparison to previous editions. Antimicrobial consumption data was collected and interpreted as DDD/100 bed days using AMC tool software. Here, we present data for 13,615 members of Order Enterobacterales and 1793 Pseudomonas aeruginosa isolates.

Finding: Enterobacterales exhibited a significant susceptibility drop of 14.7% for gentamicin and 21.7% for amikacin. Pseudomonas aeruginosa showed an increase in isolates with intermediate tobramycin susceptibility, from 0.6% to 29.7%, with relatively minor changes in piperacillin-tazobactam interpretation.

Conclusion: The changes indicate a shift toward increased 'resistance' and 'intermediate susceptibility' for these antibiotics, emphasizing the need for cautious use and leveraging PK/PD knowledge for improved antibiotic utilization, patient outcomes, and antimicrobial stewardship.