# Antimicrobial Activity of Aztreonam-Avibactam and Other β-Lactamase Inhibitor Combinations Tested Against Enterobacterales Isolates from Pediatric Patients from United States Medical Centers (2019–2023)

## TL;DR

This study found that certain antibiotic combinations are highly effective against bacteria causing infections in children, with lower resistance rates compared to adults.

## Contribution

The study provides new insights into the antimicrobial susceptibility of pediatric Enterobacterales isolates and evaluates the effectiveness of β-lactamase inhibitor combinations.

## Key findings

- Aztreonam–avibactam, ceftazidime–avibactam, and meropenem–vaborbactam showed high activity against resistant pediatric isolates.
- Carbapenem resistance was significantly lower in pediatric isolates compared to adults.
- ESBL-producing bacteria in children were mostly CTX-M +/− OXA-1/30 gene carriers, similar to adults.

## Abstract

Objective: To evaluate the antimicrobial susceptibility of Enterobacterales isolated from pediatric patients. Methods: A total of 5723 isolates were consecutively collected (1/patient) from pediatric patients (<18 years old [yo]) from 82 United States medical centers in 2019–2023 and susceptibility-tested by broth microdilution method. Susceptibility was stratified by infection type and patient age: ≤1 yo (n = 2275), 2–5 yo (n = 1130), 6–12 yo (n = 1213), and 13–17 yo (n = 1105) and compared to adults (18–64 yo; n = 17,712). Results: Pediatric isolates were mainly from pneumonia (21.8%), bloodstream (BSI; 15.3%), and urinary tract infection (UTI; 51.8%). Aztreonam–avibactam, ceftazidime–avibactam, and meropenem–vaborbactam were active against ≥99.4% of ceftriaxone-nonsusceptible (99.4–100.0% susceptible), multidrug-resistant (MDR; 99.7–100.0% susceptible), and ESBL producer (99.7–100.0% susceptible) isolates from pediatric patients. Susceptibility to imipenem–relebactam varied from 97.1% (ceftriaxone-nonsusceptible) to 100.0% (ESBL producers). Ceftolozane–tazobactam showed good activity against ESBL producers (91.8% susceptible), but limited activity against ceftriaxone-nonsusceptible (75.8% susceptible) and MDR isolates (80.9% susceptible). The MDR phenotype varied from 14.3% (13–17 yo) to 19.7% (6–12 yo) among pediatric isolates (15.8% overall) and was 20.7% among adult Enterobacterales. Carbapenem resistance rates were markedly lower in pediatric (0.1%) isolates compared to adult isolates (1.3%). The ESBL profiles were similar among pediatric and adult isolates; 90.1% of ESBL producers from pediatric patients and 88.5% from adults carried a CTX-M +/− an OXA-1/30 gene. Conclusions: Antimicrobial resistance was generally lower among Enterobacterales from pediatric patients compared to adults. ESBL-producing Enterobacterales, mainly CTX-M, remain an important cause of infection in children. Aztreonam–avibactam, ceftazidime–avibactam, and meropenem–vaborbactam were highly active against isolates from both pediatric and adult population.