The microbiota in induced sputum

Recent research has shown that the bacterial constituents of lungs from patients with asthma differ markedly from their non-asthma comparators.  Specifically, asthma lungs have increased predominance of Proteobacteria as well as higher bacterial load.  These findings came from subjects on chronic ICS therapy, which is known to be immunosuppressive.  Marri et al. in this month’s issue present important results from their investigation on lung bacteria from asthma patients not on ICS therapy (J Allergy Clin Immunol 2013; 131(2): 346-352).

The authors analyzed induced sputum from 10 asthma subjects and 10 non-asthma subjects.  Bacterial 16s rRNA was sequenced and compared to data from the Ribosomal Database Project.  All samples contained 5 phyla of bacteria, Firmicutes, Proteobacteria, Actinobacteria, Fusobacteria, and Bacteroides.  Sputum from asthma subjects had significantly higher percentages of Proteobacteria with a concordant drop in Firmicutes prevalence as compared to sputum from non-asthma subjects.  They also found increased bacterial load in the asthma subjects as well as increased bacterial diversity.   Marri et al. report a higher relative abundance of bacterial families that contain Moraxella catarrhalis and  Haemophilus influenza in asthma subjects, potentially implicating these pathogens in asthma pathogenesis.  They also note that atopic status did not influence the results.

 The authors conclude that an altered lung bacterial community in asthma patients is not attributable to ICS therapy or atopy, though further investigations are required to determine if the differential bacterial components are causal or consequential.  Antibacterial therapeutics aimed at Proteobacteria might be one of the ways to reduce the bacterial load in asthmatics.