A 23-month-old girl with relapsed acute myeloid leukemia (AML) was admitted in partial remission for matched-unrelated donor umbilical cord stem cell transplantation. She received intense pretransplant conditioning with cytarabine (on day 11 pretransplant [here referred to as day −11] to day −6), clofarabine (on days −10 to −6), hydrocortisone (on days −10 to −6), intravenous immunoglobulin (on day −8), rabbit anti-thymocyte globulin (on days −6 to −3), and total body irradiation without cranial boost (on days −5 to −3). While profoundly immunocompromised on day −1, the patient developed septic shock, with Escherichia coli isolated from multiple blood cultures. The patient was treated with cefepime, gentamicin, and vancomycin, and this treatment was narrowed to cefepime when susceptibility results were available for the E. coli. Her symptoms resolved, and she remained clinically stable for several days posttransplant.
While still on cefepime, and on day 10 posttransplant (here referred to as day +10), the patient developed low-grade fevers to 38.3°C. Also on day +10, blood collected on day +3 in a Myco/F Lytic (BD, Sparks, MD) fungal blood culture bottle was flagged as positive by the Bactec system (BD). The remaining surveillance bacterial and fungal blood cultures remained negative after their incubation periods of 5 and 15 days, respectively. The Gram stain revealed large Gram-positive bacilli, initially thought to be a possible bacillus. Given the patient's myelosuppression, fevers, lethargy, and irritability, the patient's parenteral cefepime treatment was broadened to piperacillin-tazobactam initially for 48 h and then to imipenem, with subsequent clinical improvement. On subculture, the organism grew poorly on sheep's blood agar and chocolate agar at 35°C in a CO2 incubator, displaying only pinpoint colonies after 48 h of incubation. The organism was subcultured to Sabouraud agar (SAB) and grown at 30°C in ambient air, which revealed coral pink-pigmented colonies (Fig. 1A); a Gram stain of the colonies demonstrated slightly curved, vacuolated, and mostly Gram-negative bacilli (Fig. 1B). Conclusive identification of the bacterium was performed with partial 16S rRNA gene sequencing.
FIG 1.
(A) Coral pink-pigmented colonies on SAB agar; (B) Gram stain showing Gram-variable vacuolated rods.
(For answer and discussion, see page 1788 in this issue [doi:10.1128/JCM.01356-13].)