[Analysis of correlation between fecal and alveolar lavage fluid flora of ventilator-associated pneumonia patients based on 16S rRNA sequencing technology].

Objective: To investigate the changes and correlation of intestinal and pulmonary microecological structures in patients with ventilator-associated pneumonia (VAP).
Methods: A prospective observational study was conducted. Thirty-one patients with VAP admitted to the department of critical care medicine of General Hospital of Ningxia Medical University from May 1st 2019 to May 1st 2020 were enrolled. Feces and alveolar lavage fluid samples from patients with the same day, feces and alveolar lavage specimen flora composition and the structure of biological information analysis by 16S rRNA sequencing technologies, the comprehensive sequencing results, and clinical data of patients were analyzed.
Results: (1) The diversity (abundance and diversity) of flora in the alveolar lavage fluid of VAP patients was higher than that of fecal flora. Among them, Ace index, Chao index and Shannon index describing the abundance of flora showed statistically significant differences [Ace index: 305.89 (214.39, 458.66) vs. 204.51 (165.15, 247.61), Chao index: 259.83 (194.20, 459.31) vs. 187.67 (153.28, 234.01), Shannon index: 3.01 (2.39, 3.54) vs. 2.55 (1.86, 2.95), all P < 0.05], but there was no significant difference in Simpson index describing diversity [0.14 (0.08, 0.27) vs. 0.19 (0.10, 0.33), P > 0.05]. (2) In the sequencing results of feces and alveolar lavage fluid of VAP patients, there were some intestinal related bacteria groups with high abundance, such as Escherichia-Shigella, Faecalibacterium, Bacteroides, and Lachnospira, etc. (3) In 31 VAP patients, suspicious pathogenic bacteria was found in 20 cases (6 cases of Streptococcus viridans, 5 cases of Escherichia coli, 3 cases of Klebsiella pneumoniae, 3 cases of Acinetobacter baumannii, 2 cases of Staphylococcus aureus, 1 case of Pseudomonas aeruginosa), and the same suspected pathogens also existed in the 17 patients' alveolar lavage and waste sequencing. (4) Fourteen VAP patients combined with sepsis, 14 patients without sepsis were selected for sample size matching. The results showed that, Jaccard similarity index to describe lung-correlation of intestinal flora in VAP with sepsis group was significantly elevated, and the difference was statistically significant (0.24±0.08 vs. 0.19±0.06, P < 0.01).
Conclusions: There is a certain correlation between pulmonary and intestinal flora in VAP patients. In addition to the exclusion of pulmonary infection caused by environmental and upper respiratory micro-inhalation, the lower digestive tract may also be source of infection.