SNIF - Survey of Nasal InFection

It is becoming increasingly clear that the communities of microorganisms that populate the surfaces exposed to the external environment, or microbiota, are key players in the regulation of pathogen-host cross-talk affecting onset as well as the outcome of infectious diseases. We have recently performed a multicenter, prospective, observational study, in which nasal and oropharyngeal swabs were collected for microbiota-predicting risk of invasive fungal infections (IFI) in patients with hematological malignancies. The previously published results on the oropharyngeal microbiota have demonstrated that the communities of bacteria associated to IFI-high risk were characterized by low diversity, loss of beneficial bacteria, expansion of potential pathogenic taxa, in the presence of reduced levels of tryptophan (Trp) and beneficial microbial-derived Trp metabolites. We herein demonstrate that the nasal microbiota of the same cohort of patients is different from the oropharyngeal microbiota although similar characteristics differentiate high risk from low risk samples. In addition, the low Trp levels, observed in high risk samples, associated with defective host-derived kynurenine production, were indicative of reduced tolerance mechanisms at the nasal mucosal surface. Thus, the nasal and pharyngeal microbiome of hematologic patients provide complementary information that could improve predictive tools for the risk of IFI in hematological patients.