A 62-year-old woman was admitted to receive bone marrow ablative chemotherapy for acute myeloid leukemia. On day seven of admission, she was noted to be profoundly neutropenic (peripheral white blood cell count 900 cells/µL [normal range 3500 cells/µL–10,500 cells/µL]; absolute neutrophil count (ANC) 10 cells/µL [normal ANC range 1700 cells/µL–7000 cells/µL). She continued to be neutropenic on day 17 of admission when she developed sudden onset of severe abdominal pain. An abdominal CT scan showed inflammation of the cecum and ascending colon, consistent with neutropenic enterocolitis, but no signs of perforation. Several hours later, she developed profound hemodynamic instability and clinical signs of sepsis. Three sets of blood cultures were obtained at this time. Nine hours later, the anaerobic bottle from each set flagged positive; Gram-positive bacilli were seen on Gram stain of the blood culture broth. Subcultures from the blood bottles grew within 24 hours on CDC anaerobic sheep blood agar, with grey-white colonies exhibiting swarming on the plate (Figure 1). Gram stain of the colonies was as shown (Figure 2; structures marked with arrows are a hint). The organism was identified by MALDI-TOF mass spectrometry.
Andrew Norgan, M.D., Ph.D.
Resident, Clinical Pathology
Audrey Schuetz, M.D.
Consultant, Clinical Microbiology