Survival of infection with TEM ß-lactamase-producing Escherichia coli with Pan-ß-lactam resistance.

ABSTRACT

BACKGROUND: Antimicrobial resistance is a critical global health issue, significantly contributing to patient mortality. Recent antibiotic developments have aimed to counteract carbapenemase-producing Enterobacterales; however, the impact of their use on the emergence of antibiotic resistance is unknown. This study investigates the first case of a non-carbapenemase-producing, pan-ß-lactam-resistant Escherichia coli strain from a patient previously treated with ceftolozane-tazobactam and cefiderocol. METHODS: This study describes the clinical progression of a 39-year-old ICU patient who developed multiple infections, culminating in the isolation of a pan-ß-lactam-resistant E. coli strain (EC554). The resistance profile was characterised through MIC determination, whole-genome sequencing, the use of the ß-lactam inactivation method, RT-qPCR, efflux pump inhibition assays, outer membrane protein analysis, and blaTEM transformation. FINDINGS: The EC554 isolate displayed resistance to all tested ß-lactams and ß-lactam-ß-lactamase inhibitor combinations. Whole-genome sequencing revealed four plasmids in EC554, with the only ß-lactamase gene being blaTEM-252 on the pEC554-PBR-X1-X1 plasmid. We found that the extremely resistant phenotype was attributable to a combination of different mechanisms a high expression of TEM-252, efflux pump activity, porin loss, and PBP3 mutations. INTERPRETATION: The findings illustrate the complex interplay of multiple resistance mechanisms in E. coli, highlighting the potential for high-level resistance even without carbapenemase production. This study underscores the importance of comprehensively characterising resistance mechanisms in order to inform effective treatment strategies and mitigate the spread of resistant strains.