In a recent study published within the journal Access Microbiology, researchers explore the composition of the microbiome and interactions within the lower respiratory tract (LRT) in smokers. 

Study: Lower respiratory tract microbiome composition and community interactions in smokers. Image Credit: vchal / Shutterstock.com

The impact of smoking on the respiratory microbiome

Smoking has been shown to affect resident microbial communities present in numerous bodily regions. Previous studies have proposed various mechanisms answerable for this association, reminiscent of immunosuppression related to smoking, a rise in biofilm formation for specific species, and collection of species by the influence of local oxygen tension.

The upper airways and oral cavities might also directly interact with smoking chemicals, microbes, and warmth from cigarettes, which may alter microbiome content. Recent studies have hypothesized that dysbiosis noted within the oral microbiome related to smoking may result in a greater likelihood of experiencing complications within the respiratory tract amongst smokers. 

Concerning the study

In the current study, researchers compare the LRT microbiome profiles of lively smokers (AS), former smokers (FS), and non-smokers (NS) to explain the bacterial communities present within the lung.

The study involved volunteer subjects aged over 40 years of age who were either smokers of a minimum of 10 pack-years throughout their life or non-smokers. Former smokers qualified for the study in the event that they had abstained from using tobacco for at least 12 months, while AS smoked a minimum of 1 cigarette inside three days of recruitment.

All study participants were required to finish a pulmonary function examination and thorough demographic and clinical questionnaire. The sampling process was standardized for all participants. The team extracted total deoxyribonucleic acid (DNA) from the bronchoalveolar lavages (BALs) specimens.

A single polymerase chain response (PCR) assessment was conducted to amplify the V6-V8 region present on the 16S ribosomal ribonucleic acid (rRNA) gene from the metagenomic DNA extracts of the BAL samples. Alpha diversity was estimated using Chao richness and inverse Simpson diversity indices. The DESeq2 algorithm was also used to detect differentiating taxa for every cohort.

Study findings

All 46 smokers reported similar smoking exposure when it comes to pack-years, including the FS quitting smoking on a mean of about 10 years prior to enrollment. AS and FS exhibited reduced forced vital capability (FVC), diffusing capability for carbon monoxide (DL-CO), and compelled expiratory volume at second 1 (FEV₁); nevertheless, these variations weren’t remarkable in accordance with the evaluation of variance (ANOVA).

Over 3,600 reads with a mean length of about 479 nucleotides were documented in each participant’s BAL, which facilitated the outline of virtually 400 operational taxonomic units (OTUs) per participant. The NS profile was sufficiently balanced between the prevalent phyla Bacteroides, Firmicutes, Proteobacteria, and Actinobacteria with comparatively barely higher proportions. The FS cohort had a major increase in Proteobacteria with reduced Bacteroides and Firmicutes levels. This pattern was also true for AS, with Proteobacteria increasing to 75% and Firmicutes declining to 11%.

Genus-level assessments indicated that the majority of the enhancement in Proteobacteria in AS and FS compared to its high proportion in NS was as a result of the genus Ralstonia, which increased from 2% within the NS, 28% in AS, and 21% in FS.

From the Firmicutes phylum, the Streptococcus and Veillonella genera, in addition to Prevotella from the Bacteroidetes phyla exhibited the best decline in comparative abundance. Moreover, the Propionibacterium genus of the Actinobacteria phylum exhibited a slight improvement from 3% in AS and FS to 0.8% in NS.

With respect to the NS profile, a greater variety of upper-quartile taxa were distinguished from AS, whereas lower-quartile taxa were distinguished from FS.

NS exhibited a considerably higher mean diversity as in comparison with AS and FS. The mean diversity further increased when the participants were placed by declining richness, thus indicating that NS reported higher richness. Yet, the variety evaluated with the inverse Simpson index had only an intermediate association with richness estimates and the participant’s smoking status.

Conclusions

The present study provides recent insights into the complicated microbial communities present in the LRT and the way this microbiome could be modified under different smoking conditions. The researchers also observed that the oral microbiota can settle within the lungs of smokers, which makes the study of the upper airway microbiome interesting for future research.

The microbiomes of former smokers appear to exhibit similar properties to those of each AS and NS. In the longer term, integration of the current findings with next-generation analytical techniques would help establish the effect of such microbial communities on human health.