# P-1265. Tracking Resistance: Four years of Pseudomonas aeruginosa and its Battle with Antibiotics

## TL;DR

This study tracks antibiotic resistance in Pseudomonas aeruginosa over four years, showing high resistance rates and the effectiveness of newer beta-lactam drugs.

## Contribution

A four-year analysis of Pseudomonas aeruginosa resistance patterns and susceptibility to beta-lactam antibiotics in a single medical center.

## Key findings

- Respiratory isolates showed the highest rates of non-susceptibility to beta-lactams.
- Newer beta-lactam agents like ceftolozane-tazobactam and ceftazidime-avibactam had high in vitro activity.
- Over 18% of isolates were multidrug-resistant, with resistance increasing over time.

## Abstract

Pseudomonas aeruginosa is a difficult Gram-negative pathogen due to its intrinsic and acquired resistance. As beta-lactams remain central to treatment, local susceptibility is vital. This study evaluated susceptibility to first-line agents and newer beta-lactam agents over a 4-year period at our academic medical center.

Non-duplicate P. aeruginosa isolates from January 2021 through December 2024 were analyzed. Susceptibility was determined by BD Phoenix™ or E-test and interpreted according to CLSI breakpoints. Antimicrobials analyzed included aztreonam (AZT), cefepime (CFP), piperacillin-tazobactam (PTZ), meropenem (MEM), ceftolozane-tazobactam (C/T), ceftazidime-avibactam (C/A), ciprofloxacin (CIP) and levofloxacin (LEV). Resistance phenotypes including MDR, XDR, DTR, and PDR were defined per CDC criteria. Culture source and hospital location were also recorded.

A total of 1,509 non-duplicate P. aeruginosa isolates were analyzed. The overall prevalence of resistance phenotypes was: MDR 18.2%, XDR 16.8%, DTR 5.0%, and PDR 0.9%. Respiratory specimens comprised the largest proportion of isolates (39.6%) compared to urine (23.7%), wound (12.9%), blood (12.6%), and other sources (9.1%).

Overall susceptibility rates were as follows: C/T 98.5%, C/A 97.8%, MEM 84.7%, CFP 83.9%, PTZ 79.6%, AZT 75.9%, CIP 72.3%, and LEV 69.9%. Of all isolates, 63.0% were susceptible to all first-line beta-lactams, 30.8% were non-susceptible to at least one, and 6.2% were non-susceptible to all. Among isolates non-susceptible to at least one beta-lactam, 41.7% were resistant to a single agent, 19.4% to two agents, 17.6% to three, and 21.3% to four. Respiratory isolates consistently demonstrated the highest rates of non-susceptibility across all agents tested.

This analysis highlights the persistent challenge of P. aeruginosa resistance, particularly among respiratory isolates. The high in vitro activity of newer beta-lactams such as C/T and C/A supports their role in treatment algorithms for resistant infections. Continued local surveillance, antimicrobial stewardship, and individualized therapy remain essential for preserving the efficacy of beta-lactams in the management of P. aeruginosa.

All Authors: No reported disclosures