Bacillus cereus Sepsis in the Treatment of Acute Myeloid Leukemia

Fatal sepsis during chemotherapy-induced neutropenia is the most severe complication of which physicians must be keenly aware. Common bacterial pathogens in neutropenic patients usually include gram-positive cocci such as coagulase-negative staphylococci, Staphylococcus aureus, Enterococcus species, and gram-negative rods such as Escherichia coli, Klebsiella species, Enterobacter species, and Pseudomonas aeruginosa (Wisplinghoff, et al 2003). Thus, clinical practice guidelines for the use of antibiotics are likely to be aimed at targeting these pathogens including antibiotic-resistant strains (Freifeld, et al 2011). In the absence of effector cells for these pathogens, the rapid progression of invasive bacterial infections may occur; therefore, antibiotics are a life-saving measure during severe neutropenia. Bacillus cereus (B. cereus) is an aerobic gram-positive, spore-forming, and rod-shaped bacterium that is widely distributed in the environment. Although B. cereus is a common cause of food-poisoning, abdominal distress such as vomiting and diarrhea is usually mild and self-limiting unless the host is immunocompromised. Some patients that undergo prolonged hospitalization have Bacillus species as a part of the normal flora in their intestine (Drobniewski 1993). Therefore, identification of this microorganism in clinical cultures has usually been considered to be due to contamination. For example, 78 patients were found to have cultures positive for B. cereus in a single center in the United States; however, only 6% of them resulted in clinically significant infections (Weber, et al 1989). On the other hand, B. cereus is a growing concern as a cause of life-threatening infections in patients with hematologic malignancies, including septic shock, brain abscess, meningitis, colitis, respiratory infections, endocarditis, and infection-related coagulopathy and hemolysis. The risk factors for patients with unfavorable outcomes, however, have not been totally elucidated. In addition, B. cereus sepsis generally does not respond to any antibiotics in spite of their in vitro efficacy (Drobniewski 1993). Akiyama et al. reviewed 16 case reports of B. cereus sepsis in patients with leukemia, and consequently reported only 3 survivors (Akiyama, et al 1997). Therefore, physicians should identify specific risk factors of B. cereus sepsis during chemotherapy for leukemia patients and establish a proper strategy to overcome this life-threatening sepsis.