Antimicrobial Resistance and Genomic Characterization of an Escherichia coli Strain Harboring p0111 and an IncX1-Type Plasmid, Isolated from the Brain of an Ostrich

An outbreak characterized by clinical signs of diarrhea and paralysis, occasionally progressing to fatal outcomes, occurred at an ostrich breeding facility. Conventional antibiotic treatments proved ineffective. To investigate the etiology of the disease, brain and liver specimens were collected for diagnostic analysis. An <i>Escherichia coli</i> (<i>E. coli</i>) isolate, designated strain HZDC01, was obtained from cerebral tissues, and whole-genome sequencing was performed for genomic characterization. Genomic analysis revealed that the chromosomal DNA harbors numerous resistance genes, conferring multidrug resistance through complex mechanisms. Furthermore, a p0111-type plasmid carrying the <i>bla_CTX-M-55</i> gene and an IncX1-type plasmid harboring <i>rmtB</i>, <i>sul1</i>, <i>APH(6)-Id</i>, <i>tet(A)</i>, <i>AAC(3)-IIc</i>, <i>aadA2</i>, <i>bla_TEM-1B</i>, and <i>floR</i> genes were identified. These plasmids carry numerous mobile genetic elements that can disseminate via horizontal gene transfer, thereby amplifying the risk of resistance-gene spread within bacterial populations. Additionally, the <i>ibeB</i> and <i>ibeC</i> genes, which encode proteins involved in the invasion of brain microvascular endothelial cells, were identified. These genes may facilitate <i>E. coli</i> penetration of the blood-brain barrier, potentially leading to meningitis and posing a life-threatening risk to the host. This is the first report of the isolation and characterization of extended-spectrum beta-lactamase <i>E. coli</i> from the brain of an ostrich with paralysis. The findings provide valuable genomic insights into the antimicrobial resistance profiles and pathogenic mechanisms of ostrich-derived <i>E. coli</i> isolates.