Catheter-associated Ochrobactrum anthropi Bacteremia in Immunocompromised Children: Navigating Clinical Uncertainty

To the Editor: Ochrobactrum anthropi is an aerobic, motile, Gram-negative bacillus found in environmental and hospital water sources. While phenotypically similar to Brucella spp., taxonomic studies confirm its distinction, though misidentification remains possible.1 Typically regarded as a low-virulence opportunist, O anthropi has nevertheless been implicated in invasive pediatric disease, particularly among children with malignancies or central venous catheters.2,3 We describe 2 cases identified at our center within 9 months and highlight interpretive challenges in their management. Case 1 A 14-month-old girl with immunodeficiency (ICF-3, CDCA7 mutation) was admitted for hematopoietic stem cell transplantation. Five days after central line insertion, she developed fever (38.5 °C). Catheter-drawn blood cultures grew Gram-negative bacilli at 36 hours, while a synchronous peripheral sample remained negative. Empiric cefepime was escalated to meropenem plus amikacin, with rapid defervescence. The isolate was identified as O anthropi with high minimum inhibitor concantration (MIC)s to many β-lactams and intermediate imipenem (Table 1). The catheter was removed; subsequent cultures were sterile. She completed 14 days of empiric therapy with an uncomplicated recovery. TABLE 1. - Antimicrobial Susceptibility Results of the Ochrobactrum anthropi Isolate (Case 1) Antimicrobial Agent MIC/Zone Interpretation* Tetracycline 8 Intermediate Rifampin Zone: 14 mm Resistant Cefepime >256 Resistant Cefotaxime >256 Resistant Ceftazidime >256 Resistant Gentamicin >256 Resistant Imipenem 4 Intermediate Piperacillin/tazobactam >256 Resistant Methods: MICs by broth microdilution; disk diffusion, where zone diameters are reported.*Interpretive criteria: CLSI M100 (34th ed.); where species‑specific breakpoints are unavailable, non‑Enterobacterales/other nonfermenters criteria were applied. Case 2 A 4-year-old girl with newly diagnosed B-cell acute lymphoblastic leukemia developed febrile neutropenia during induction. Piperacillin–tazobactam was started empirically. Cultures from both the port (17 hours) and a peripheral vein (24 hours) grew O anthropi. Despite elevated MICs to several β-lactams (Table 2), the patient became afebrile within 24 hours and completed 14 days of the initial regimen without modification. Chemotherapy resumed uneventfully. TABLE 2. - Antimicrobial Susceptibility Results of Ochrobactrum anthropi Isolate (Case 2) Antimicrobial Agent MIC Interpretation* Cefepime >256 Resistant Ciprofloxacin 0.094 Susceptible Gentamicin 0.50 Susceptible Imipenem 0.75 Susceptible Piperacillin/tazobactam >256 Resistant Amikacin 16 Intermediate Trimethoprim/sulfamethoxazole 0.25 Susceptible Meropenem >32 Resistant Methods: MICs by broth microdilution.*Interpretive criteria: CLSI M100 (34th ed.); as in Table 1. These cases illustrate the diagnostic and therapeutic dilemmas posed by O anthropi in immunocompromised hosts. Although in vitro resistance to multiple β-lactams is frequently observed—often linked to inducible AmpC—clinical responses may not align with susceptibility data.4 Both of our patients improved without targeted therapy: in case 1, after catheter removal and broad empiric coverage, and in case 2, despite high MICs to the empiric regimen. Differential time-to-positivity supported a catheter-associated source (catheter-only in case 1, earlier catheter signal in case 2). Taken together, these findings suggest that isolation of O anthropi from central line cultures should not prompt automatic escalation. True infection is possible, particularly in vulnerable hosts, but transient bacteremia or colonization must also be considered when the clinical course is mild and cultures sterilize following source control. Pragmatic management should include: confirmation of species identification (to exclude Brucella misassignment), assessment of time-to-positivity, removal of implicated devices when feasible, and close integration of clinical evolution before initiating prolonged pathogen-directed therapy. Current CLSI M100 guidelines (CLSI, 2024) should guide interpretation, in collaboration with microbiology.5 In conclusion, our experience supports a cautious, context-driven approach to O anthropi bacteremia in children with central lines. Further multicenter data are needed to optimize management strategies for this uncommon isolate. Acknowledgments We thank all the healthcare professionals involved in the diagnosis and treatment of this patient.