Bronchoalveolar lavage fluid microbiota dysbiosis in infants with protracted bacterial bronchitis

Abstract

Background: Protracted bacterial bronchitis (PBB) is a chronic purulent bronchitis which could cause recurrent coughing and wheezing in infants. Based on previous reports, main pathogens which caused PBB were identified in the patients, but their impacts on lung microbiota dysbiosis remain unclear.

Methods: In this study, bronchoalveolar lavage fluid (BALF) was collected from PBB infants and tracheomalacia (TM) infants younger than 3 years old under the instruction of Shenzhen Children's Hospital, and 12 samples were randomly selected for 16S rDNA analysis in each group. Based on the results of bacterial composition, the microbiota diversity and co-occurrence network in PBB and TM group were detected and compared.

Results: Microbiota diversity was significantly lower in PBB group than it in TM group (P<0.001 for the comparison of Shannon and Simpson indexes). The PBB group was found to harbor 25 accumulated bacterial agents by comparison with TM group, including Haemophilus (P<0.001) and Bacteroides (P<0.001). Whilst, the populations of Lactococcus (P<0.001) and Lactobacillus (P<0.001) were dramatically smaller in PBB group. The co-occurrence network in PBB group also differed from that of TM group. It contained four core nodes in PBB patients, including Haemophilus, Parabacteroides, Porphyromonas, and Cronobacter. Haemophilus was found to be negatively associated with most counterparts, including Clostridium and Bacillus.

Conclusions: PBB infants contained discrepant lung genera and co-occurrence network when compared with TM infants. This retrospective study may deepen our understanding of PBB pathogenesis, and it also provided a foundation for bacterial adjunctive therapy of infantile PBB in accordance with clinical treatment.

Keywords: Protracted bacterial bronchitis (PBB); bronchoalveolar lavage fluid (BALF); co-occurrence network; lung microbiota; tracheomalacia (TM).

Figure 1

PCA and microbial diversity of PBB infants and TM infants. (A) PCA was performed based on weighted UniFrac distances, and the samples from PBB group clustered apart from TM group; (B) distribution of Shannon and Simpson indexes in PBB group and TM group. The microbial diversity was significantly higher in PBB infants than it in TM infants (P=0.006 and P=1×10⁻⁵ for Shannon and Simpson indexes respectively). **, P value smaller than 0.01. PCA, principal component analysis; PBB, protracted bacterial bronchitis; TM, tracheomalacia.

Figure 2

Microbial co-occurrence network in infants with PBB and TM. The green and red edges stand for the positive and negative correlations among lung bacteria, and the P values were indicated by asterisks (one, two and three asterisks stand for the P value smaller than 0.05, 0.01 and 0.001 respectively). Green or red spots indicated the genera were significantly enriched in PBB or TM cohorts, while the diameters respond to their relative abundances. The bacterial network in PBB group was more complicated than that of TM group, and most bacterial relationships in TM group was disrupted. Meanwhile direct negative correlation between Haemophilus and other genera, including Bacillus, Lactococcus, Clostridium and Acinetobacter, was determined for PBB group. PBB, protracted bacterial bronchitis; TM, tracheomalacia.

Figure S1

Differentially enriched taxa between PBB infants and TM infants. (A) A total of 25 taxa, including Bacillus, Haemophilus, Pseudomonas and Enterococcus, were found significantly enriched in PBB group, while levels of Lactococcus and Lactobacillus were lower than they in TM group; (B) biomarkers on phylum, class, order, family and genus levels were exhibited from inner to outer. PBB and TM groups were shown in green and red respectively. PBB, protracted bacterial bronchitis; TM, tracheomalacia.