Research progress on comorbidity between gastrointestinal and pulmonary diseases from the perspective of the gut-lung axis

Table 1 Association between the gut microbiome and several common lung diseases

Diseases	Details	Ref.
COPD	Fecal microbiological profiles were analyzed using 16S rRNA gene sequencing. The results showed a distinct difference in the bacterial community composition between the AECOPD, COPD, and healthy control groups. The COPD and AECOPD groups had higher levels of Firmicutes but lower levels of Bacteroidetes compared with the healthy control group at the phylum level. At the genus level, there was an increased abundance of Lachnoclostridium, Alistipes, Streptococcus, and Prevotella in patients with COPD and AECOPD. Increasing levels of Lachnoclostridium and Prevotella may indicate an acute exacerbation of COPD	[62]
Asthma	Gut microbial species and metabolites primarily SCFAs may either worsen or reduce airway inflammation by regulating the balance of Th1/Th2 and other immune mediators	[63]
ARDS	The major characteristic of the intestinal flora in patients with ARDS/CAP was higher abundances of Gram-negative bacteria than normal controls. The gut microbiota derived from patients with ARDS/CAP promoted neuroinflammation and behavioral dysfunction in mice. Mice who underwent fecal transplant from patients with ARDS/CAP had increased systemic LPS, systemic inflammation, and increased colonic barrier permeability	[64]
VAP	The fungal genus Alternaria spp. is associated with the occurrence of VAP. The composition of the gut microbiota differs between patients who are critically ill patients and subsequently develop VAP and those who do not	[65]

AECOPD: Acute exacerbation of chronic obstructive pulmonary disease; CAP: Community-acquired pneumonia; COPD: Chronic obstructive pulmonary disease; SCFAs: Short-chain fatty acids; Th1: Helper T cell 1; ARDS: Acute respiratory distress syndrome; LPS: Lipopolysaccharide; VAP: Ventilator-associated pneumonia.