# 629. Investigating the Molecular Epidemiology of Extended-Spectrum β-Lactamase Producing Enterobacterales Among Patients Admitted to the Intensive Care Unit

## TL;DR

This study finds that 5% of ICU patients in the U.S. are colonized with antibiotic-resistant bacteria called ESBL-E, mostly E. coli and K. pneumoniae, and highlights the importance of molecular testing to avoid overestimating resistance.

## Contribution

The study provides contemporary U.S. data on ESBL-E colonization in ICU patients using whole-genome sequencing to confirm resistance genes.

## Key findings

- 5% of ICU admissions were confirmed to be colonized with ESBL-producing Enterobacterales.
- Escherichia coli (72%) and Klebsiella pneumoniae (19%) were the most common ESBL-E species.
- blaCTX-M-15 was the most prevalent ESBL gene variant (63%).

## Abstract

Colonization with extended-spectrum β-lactamase-producing Enterobacterales (ESBL-E) is increasingly recognized in critically ill patients and impacts infection prevention practices and empiric antibiotic selection. However, contemporary United States estimates of ESBL-E prevalence at the time of ICU admission are limited.Table 1.ICU-Specific Prevalence of ESBL Colonization at Admission Confirmed by Whole Genome SequencingFigure 1.Distribution of ESBL Gene Variants Among ESBL-Producing Enterobacterales Isolates by Bacterial Species (n = 173)

ICU-Specific Prevalence of ESBL Colonization at Admission Confirmed by Whole Genome Sequencing

Distribution of ESBL Gene Variants Among ESBL-Producing Enterobacterales Isolates by Bacterial Species (n = 173)

We conducted a prospective molecular epidemiology study of ESBL-E colonization among adult and pediatric patients admitted to nine ICUs at The Johns Hopkins Hospital between March and August 2023. Routine rectal surveillance swabs (Copan Eswab) collected at ICU admission were plated on selective chromogenic media (HardyCHROM™ ESBL) to identify third-generation cephalosporin-resistant Enterobacterales (3GCRE). Species identification was performed using MALDI-TOF MS, and ceftriaxone resistance was confirmed by broth microdilution. Whole-genome sequencing (WGS) was performed on the first isolate of each species per patient to confirm ESBL gene carriage and assess molecular features.

Among 3,278 ICU admissions, 328 (10%) had 3GCRE isolated on admission swabs. Of these isolates, 173 (5% of all admissions) were confirmed by WGS to harbor at least one ESBL gene—representing approximately 53% of all 3GCRE isolates. ESBL-E colonization was most prevalent in the medical (10%) and cardiac (8%) ICUs. The most common ESBL-E species were Escherichia coli (72%) and Klebsiella pneumoniae (19%). Dominant E. coli sequence types were ST131 (36%), ST1193 (7%), and ST38 (6%). Nearly all ESBL genes belonged to the blaCTX-M family (95%), with blaCTX-M-15 as the predominant allele (63%). Other ESBL genes included blaCTX-M-27 (17%), blaCTX-M-14 (5%), blaCTX-M-55 (5%), and blaSHV-12 (3%).

In this large, prospective cohort, 5% of ICU patients were colonized with ESBL-E at admission, most commonly E. coli and K. pneumoniae harboring blaCTX-M genes. Phenotypic detection of 3GCRE overestimated ESBL-E prevalence by nearly 90%, highlighting the need for molecular confirmation to accurately characterize resistance. These findings suggest ESBL-E colonization remains uncommon in the U.S., even at a major referral center, supporting non-carbapenem empiric therapy in low-risk patients and reinforcing the need for targeted surveillance.

All Authors: No reported disclosures