A new study suggests the composition of a cancer patient’s intestinal microbiome before treatment may predict his risk of developing a bloodstream infection (BSI) after treatment.
Researchers analyzed fecal samples from patients with non-Hodgkin lymphoma who were set to receive an allogeneic hematopoietic stem cell transplant (allo-HSCT) with myeloablative conditioning.
The team found that patients with less diversity in their fecal samples before this treatment were more likely to develop a BSI after.
Emmanuel Montassier, MD, PhD, of Nantes University Hospital in France, and his colleagues conducted this study and reported the result in Genome Medicine.
A previous study suggested that intestinal domination—when a single bacterial taxon occupies at least 30% of the microbiota—is associated with BSIs in patients undergoing allo-HSCT. However, the role of the intestinal microbiome before treatment was not clear.
So Dr Montassier and his colleagues set out to characterize the fecal microbiome before treatment. To do this, they sequenced the bacterial DNA of fecal samples from 28 patients with non-Hodgkin lymphoma.
The team collected the samples before patients began a 5-day myeloablative conditioning regimen (high-dose carmustine, etoposide, aracytine, and melphalan), followed by allo-HSCT on the seventh day.
Eleven of these patients developed a BSI at a mean of 12 days after sample collection. Two patients (18.2%) developed Enterococcus BSI, 4 (36.4%) developed Escherichia coli BSI, and 5 (45.5%) developed other Gammaproteobacteria BSI.
The researchers said that alpha diversity in samples from these patients was significantly lower than alpha diversity from patients who did not develop a BSI, with reduced evenness (Shannon index, Monte Carlo permuted t-test two-sided P value = 0.004) and reduced richness (Observed species, Monte Carlo permuted t-test two-sided P value = 0.001)
The team also noted that, compared to patients who did not develop a BSI, those who did had decreased abundance of Barnesiellaceae, Coriobacteriaceae, Faecalibacterium, Christensenella, Dehalobacterium, Desulfovibrio, and Sutterella.
Using this information, the researchers developed a BSI risk index that could predict the likelihood of a BSI with 90% sensitivity and specificity.
“This method worked even better than we expected because we found a consistent difference between the gut bacteria in those who developed infections and those who did not,” said study author Dan Knights, PhD, of the University of Minnesota in Minneapolis.
“This research is an early demonstration that we may be able to use the bugs in our gut to predict infections and possibly develop new prognostic models in other diseases.”
Still, the researchers said these findings are based on a limited number of patients treated with the same regimen at a single clinic. So the next step for this research is to validate the findings in a much larger cohort including patients with different cancer types, different treatment types, and from multiple treatment centers.
“We still need to determine if these bacteria are playing any kind of causal role in the infections or if they are simply acting as biomarkers for some other predisposing condition in the patient,” Dr Montassier said.
