Colonization with multidrug-resistant bacteria increases the risk of complications and a fatal outcome after allogeneic hematopoietic cell transplantation.

Composition of the gut microbiota seems to influence early complications of allogeneic hematopoietic cell transplantation (HCT) such as bacterial infections and acute graft-versus-host disease (GVHD). In this study, we assessed the impact of colonization with multidrug-resistant bacteria (MDRB) prior to HCT and the use of antibiotics against anaerobic bacteria on the outcomes of HCT. We retrospectively analyzed the data of 120 patients who underwent HCT for hematologic disorders between 2012 and 2014. Fifty-one (42.5%) patients were colonized with MDRB and 39 (32.5%) had infections caused by MDRB. Prior colonization was significantly correlated with MDRB infections (P < 0.001), especially bacteremia (P = 0.038). A higher incidence of MDRB infections was observed in patients with acute (P = 0.014) or chronic (P = 0.002) GVHD and in patients aged > 40 years (P = 0.002). Colonization had a negative impact on overall survival (OS) after HCT (64 vs. 47% at 24 months; P = 0.034) and infection-associated mortality (P < 0.001). Use of metronidazole was correlated with an increased incidence of acute GVHD (P < 0.001) and lower OS (P = 0.002). Patients colonized with MDRB are more susceptible to life-threatening infections. Colonization with virulent flora is the most probable source of neutropenic infection; therefore, information about prior positive colonization should be crucial for the selection of empiric antibiotic therapy. The use of metronidazole, affecting the biodiversity of the intestinal microbiome, seems to have a significant impact on OS and acute GVHD.