Vancomycin-resistance gene cluster, vanC, in the gut microbiome of acute leukemia patients undergoing intensive chemotherapy.

Two recent reports suggested that the less common, less virulent enterococcal species, Enterococcus gallinarum and E. casseliflavus, with low-level vancomycin resistance due to chromosomally encoded vanC1 and vanC2/3, may influence host immunity. We reported that peri-transplant gut colonization with E. gallinarum and E. casseliflavus is associated with lower mortality after allogeneic hematopoietic cell transplantation (HCT). Because most acute leukemia patients undergoing HCT have received intensive chemotherapy (usually requiring prolonged hospitalization) for their underlying disease before HCT, we hypothesized that some may have acquired vanC-positive enterococci during chemotherapy. Therefore, we evaluated the presence of the vanC gene cluster using vanC1 and vanC2/3 qPCR in thrice-weekly collected stool samples from 20 acute leukemia patients undergoing intensive chemotherapy. We found that an unexpectedly large proportion of patients have detectable vanC1 and vanC2/3 (15% and 35%, respectively) in at least one stool sample. Comparing qPCR results with 16S rRNA gene sequencing results suggested that E. gallinarum may reach high abundances, potentially persisting into HCT and influencing transplant outcomes.