Genomic analysis of a clinical Enterobacter hormaechei isolate from a postoperative left atrial myxoma patient

Enterobacter hormaechei is an opportunistic pathogen increasingly implicated in healthcare-associated infections, including bloodstream infections. However, the genomic and pathogenic features of clinical isolates from specific surgical settings remain incompletely characterized.

We performed whole-genome sequencing and comprehensive genomic analysis of a clinical E. hormaechei isolate (strain FLZ) recovered from a patient who developed fatal septic shock following left atrial myxoma resection. Antimicrobial resistance genes and virulence factors were identified using curated databases with stringent thresholds. The in vivo virulence of FLZ was assessed using a murine peritonitis model.

The FLZ genome comprised 4,609,213 bp with a GC content of 55.3%, encoding 4377 predicted genes. Phylogenomic analysis confirmed its classification as E.hormaechei subsp. xiangfangensis (99.09% ANI with the type strain). The isolate carried resistance-associated genes and efflux pump components. Virulence gene profiling identified 61 curated virulence-associated genes, most notably the complete enterobactin biosynthesis and uptake system. At the intermediate infection dose of 108 CFU/mL, the FLZ strain demonstrated significantly higher pathogenicity compared to the reference strain, with a median survival time of 3.3 days (95% Confidence Interval: 0.5-6.1) compared to 8.7 days for the reference strain (P = 0.02, 95% Confidence Interval: 6.3-11.1).

This study provides genomic and in vivo evidence characterizing the pathogenic potential of an E. hormaechei clinical isolate from a rare postoperative setting. The findings highlight the need for enhanced surveillance and further functional studies to elucidate the virulence mechanisms of this emerging pathogen.