Rare Isolation of Pseudomonas Anguilliseptica in Blood Culture of a Patient With Acute Myeloid Leukemia: Diagnostic Challenge and Clinical Relevance

Acute leukemia is the most common cancer in children and adolescents. Among these, acute myeloid leukemia (AML) is particularly important because of the high risk of bacterial infections and high mortality, secondary to immunodeficiency generated by the underlying onco-hematologic disease, myelosuppressive chemotherapy with prolonged neutropenia, and disruption of mucosal barriers. Pseudomonas anguilliseptica is a non-fermenting Gram-negative bacterium commonly associated with infections in fish. This study aims to describe a rare infection due to P. anguilliseptica in an adolescent diagnosed with AML. Female patient, 16 years old, from São Paulo, Brazil, with type 2 diabetes mellitus. Admitted to our service to initiate treatment of AML secondary to myelodysplastic syndrome, presenting prolonged neutropenia during work-up. Due to fever and neutropenia on admission, empirical cefepime was started. After 48 hours, the Bactec PlusAerobic/F blood culture bottle showed bacterial growth. Initial identification by the automated VITEK® system was inconclusive, suggesting P. stutzeri or P. fluorescens (both with 50%). Mass spectrometry (MALDI-TOF), however, identified P. anguilliseptica with 99.9% confidence. In light of this result, and given worsening cough and respiratory discomfort, therapy was escalated to meropenem and teicoplanin. Respiratory virus panel revealed respiratory syncytial virus, and chest CT showed bilateral consolidations with small pleural effusions. A subsequent blood culture was negative. After 10 days of antibiotics, the patient remained clinically stable, with resolution of the infection, and continued oncologic treatment. Due to the rarity of this agent, the isolate was stored and awaits confirmation by 16S rRNA gene sequencing. This study reports the first case of invasive infection in humans due to Pseudomonas anguilliseptica, a rare pathogen, identified using advanced methods. There are no confirmed reports of its isolation in humans, which makes this finding clinically relevant in immunosuppressed patients.