Febrile neutropenia caused by the rare organism Phytobacter: first Case Report from India

Phytobacter diazotrophicus is an emerging opportunistic, Gram-negative bacterium, originally recognized as a nitrogen-fixing, plant-associated organism and increasingly implicated in nosocomial infections. We report the first documented case of bloodstream infection due to P. diazotrophicus in an elderly female breast cancer patient with chemotherapy-induced febrile neutropenia.

A 62-year-old woman with HER2-positive, cT4bN2M0 breast cancer receiving neoadjuvant trastuzumab, carboplatin, and docetaxel presented with fever, headache, profound fatigue, pallor, and retinal hemorrhages. Laboratory evaluation revealed severe pancytopenia, with a platelet count of 5 × 10⁹/L, an absolute neutrophil count of 0.294 × 10⁹/L, a total leukocyte count of 1.05 × 10⁹/L, and a hemoglobin level of 3.7 g/dL. Blood cultures grew non-lactose-fermented Gram-negative bacilli, initially identified as Pantoea species by the VITEK-2 system; however, 16S rDNA sequencing confirmed the organism as Phytobacter species. The patient was managed with blood component transfusions, filgrastim, and empirical piperacillin-tazobactam. Antimicrobial therapy was stopped on day 8, with recovery of blood counts noted by day 7. Subsequently, chemotherapy was resumed with trastuzumab and single-agent taxane at a reduced dose.

Gram-negative infections caused by phytobacteria are likely underreported with the automated VITEK-2 identification system. This first molecularly confirmed case of Phytobacter diazotrophicus identified by 16S rDNA sequencing in India underscores the need for heightened clinical awareness, prompt and accurate microbiological identification, and vigilance regarding antimicrobial resistance, especially in the immunocompromised population.