Cerebrospinal Fluid Infection Caused by Mixta calida in a Patient With Sarcoma: Case Report With Whole-Genome Sequencing.

Mixta calida is a rare environmental Erwiniaceae organism with limited evidence of invasive human infection. We report cerebrospinal fluid infection in a 6-year-old girl with recurrent CIC-rearranged central nervous system sarcoma after neurosurgery, chemotherapy, stem-cell transplantation, and Ommaya reservoir access. Turbid cerebrospinal fluid showed severe neutrophilic inflammation and Gram-negative bacilli with leukocyte phagocytosis. Pure culture yielded an isolate identified by MALDI-TOF mass spectrometry. Four genomic 16S rRNA sequences showed 99.93% identity to the M. calida type strain, and whole-genome ANI was 99.59%. These findings support M. calida as a clinically significant opportunistic pathogen in immunocompromised patients.