RESUMO
Respiratory microbiome is extensively involved in human life activities and affects lung health and disease states through metabolism and immune regulation. Based on 16S rRNA gene sequencing and other methods, it is obvious that the diversity and the changes in the structure of respiratory microbiome and the dominant proliferation of pathogens are strongly related to the occurrence, development and clinical prognosis of ventilator-associated pneumonia (VAP). The mechanism by which respiratory microbiota promotes the clearance of pathogens may include the following aspects: ① pre-stimulating innate immune system to increase the number of immune effector cells; ② regulating pattern recognition receptor (PRR) to moderately promote the production of cytokines; ③ inducing the differentiation of neutrophils into specific subtypes and increasing the expression of antimicrobial genes; ④ producing free fatty acids and organic compounds that are capable of positively modulating the immune system. In conclusion, intervention of microbiome is beneficial to VAP patients. Therefore, this review illustrates the changes of respiratory flora in VAP and its effect on host immunity. At the same time, based on the review of the adjuvant treatment of VAP with probiotics, we put forward the prospect of respiratory commensal bacteria as a new clinical probiotic, in order to deepen the clinical understanding of the role of respiratory flora in VAP, and then provide new ideas for the evaluation of treatment and prognosis.
RESUMO
Heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria are aerobic microorganisms that can remove nitrogen under high-salt conditions, but their performance in practical applications are not satisfactory. As a compatible solute, trehalose helps microorganisms to cope with high salt stress by participating in the regulation of cellular osmotic pressure, and plays an important role in promoting the nitrogen removal efficiency of microbial populations in the high-salt environment. We investigated the mechanism of exogenous-trehalose-enhanced metabolism of HN-AD community under high-salt stress by starting up a membrane aerobic biofilm reactor (MABR) to enrich HN-AD bacteria, and designed a C150 experimental group with 150 μmol/L trehalose addition and a C0 control group without trehalose. The reactor performance and the community structure showed that NH4+-N, total nitrogen (TN) and chemical oxygen demand (COD) removal efficiency were increased by 29.7%, 28.0% and 29.1%, respectively. The total relative abundance of salt-tolerant HN-AD bacteria (with Acinetobacter and Pseudofulvimonas as the dominant genus) in the C150 group reached 66.8%, an 18.2% increase compared with that of the C0 group. This demonstrated that trehalose addition promoted the enrichment of salt-tolerant HN-AD bacteria in the high-salt environment to enhance the nitrogen removal performance of the system. In-depth metabolomics analysis showed that the exogenous trehalose was utilized by microorganisms to improve proline synthesis to increase resistance to high-salt stress. By regulating the activity of cell proliferation signaling pathways (cGMP-PKG, PI3K-Akt), phospholipid metabolism pathway and aminoacyl-tRNA synthesis pathway, the abundances of phosphoethanolamine, which was one of the glycerophospholipid metabolites, and purine and pyrimidine were up-regulated to stimulate bacterial aggregation and cell proliferation to promote the growth of HN-AD bacteria in the high-salt environment. Meanwhile, the addition of trehalose accelerated the tricarboxylic acid (TCA) cycle, which might provide more electron donors and energy to the carbon and nitrogen metabolisms of HN-AD bacteria and promote the nitrogen removal performance of the system. These results may facilitate using HN-AD bacteria in the treatment of high-salt and high-nitrogen wastewater.