# P-1264. The Long View: Tracking Gram-negative Susceptibility Trends from 2010-2024 to Inform Stewardship

## TL;DR

This study tracks changes in antibiotic resistance among Gram-negative bacteria at UK HealthCare from 2010 to 2024, showing worsening resistance in some species and stable resistance in others.

## Contribution

The study provides a 15-year longitudinal analysis of Gram-negative bacterial susceptibility trends to inform antimicrobial stewardship and empirical treatment strategies.

## Key findings

- Susceptibility to cefepime, piperacillin-tazobactam, and other antibiotics declined significantly in K. pneumoniae and E. coli over 15 years.
- P. aeruginosa and S. marcescens showed stable or slightly improved susceptibility to key antibiotics during the same period.
- The findings emphasize the need for data-driven antimicrobial stewardship and rapid diagnostics to combat rising resistance.

## Abstract

The rise in antimicrobial resistance (AMR) among Gram-negative bacteria poses significant treatment challenges. This study evaluated susceptibility trends over a 15-year period for key Gram-negative organisms at UK HealthCare (UKHC) to guide stewardship strategies and empirical therapy.

A retrospective review of cumulative antimicrobial susceptibility data from 2010 to 2024 was conducted for K. aerogenes, E. coli, K. pneumoniae, P. aeruginosa, S. marcescens, and E. cloacae. Susceptibility to cefepime, piperacillin-tazobactam, levofloxacin, ceftriaxone, trimethoprim-sulfamethoxazole (TMP-SMX), and meropenem were analyzed. Trend lines were generated using linear regression to assess changes over time.

Over the 15-year period, notable declines in susceptibility were observed among Enterobacterales, particularly K. pneumoniae and E. coli. Cefepime susceptibility declined from 98% to 81% (R² = 0.8291) in K. pneumoniae and from 95% to 83% (R² = 0.7809) in E. coli. For K. pneumoniae, susceptibilities fell for piperacillin-tazobactam (90% to 74%, R² = 0.5163), ceftriaxone (91% to 81%, R² = 0.7448) and TMP-SMX (95% to 80%, R² = 0.6504). E. coli also showed declining susceptibility to ceftriaxone (R² = 0.4627) and cefepime (R² = 0.7809) though piperacillin-tazobactam susceptibility remained stable above 90%. K. aerogenes exhibited declines across all agents, particularly levofloxacin and cefepime. In contrast, P. aeruginosa demonstrated stable or slightly improving susceptibility to cefepime, meropenem, and piperacillin-tazobactam. S. marcescens showed minimal variability in susceptibility, while E. cloacae experienced modest declines, especially to ceftriaxone and piperacillin-tazobactam.

At UKHC, antimicrobial resistance among Enterobacterales, especially K. pneumoniae and E. coli, continues to worsen, driven by declining susceptibility to key beta-lactams and fluoroquinolones. Meanwhile, susceptibility among P. aeruginosa and S. marcescens has remained relatively stable. These findings highlight the critical need for robust antimicrobial stewardship interventions and local, data-driven empiric prescribing, supported by ongoing surveillance and rapid diagnostics.

All Authors: No reported disclosures