Modulation of gut microbiota protects against viral respiratory tract infections: a systematic review of animal and clinical studies

Abstract

Background Earlier studies suggest that probiotics have protective effects in the prevention of respiratory tract infections (RTIs). Whether such benefits apply to RTIs of viral origin and mechanisms supporting the effect remain unclear. Aim To determine the role of gut microbiota modulation on clinical and laboratory outcomes of viral RTIs. Methods We conducted a systematic review of articles published in Embase and MEDLINE through 20 April 2020 to identify studies reporting the effect of gut microbiota modulation on viral RTIs in clinical studies and animal models. The incidence of viral RTIs, clinical manifestations, viral load and immunological outcomes was evaluated. Results We included 58 studies (9 randomized controlled trials; 49 animal studies). Six of eight clinical trials consisting of 726 patients showed that probiotics administration was associated with a reduced risk of viral RTIs. Most commonly used probiotics were Lactobacillus followed by Bifidobacterium and Lactococcus. In animal models, treatment with probiotics before viral challenge had beneficial effects against influenza virus infection by improving infection-induced survival (20/22 studies), mitigating symptoms (21/21 studies) and decreasing viral load (23/25 studies). Probiotics and commensal gut microbiota exerted their beneficial effects through strengthening host immunity. Conclusion Modulation of gut microbiota represents a promising approach against viral RTIs via host innate and adaptive immunity regulation. Further research should focus on next generation probiotics specific to viral types in prevention and treatment of emerging viral RTIs. Supplementary Information The online version contains supplementary material available at 10.1007/s00394-021-02519-x.

The role of microbiota in pathogenesis and development of viral infections

“…Compared with healthy individuals, the airway microbiome in COVID-19 patients was characterized by less diversity, which can be related to a lower lymphocyte to neutrophil ratio [22]. Among COVID19 patients, opportunistic pathogens such as Salmonella, Pseudomonadaceae, Bacteroidetes, Streptococcus, Staphylococcus, Haemophilus, parainfluenzae, Neisseria, Human influenza virus, Respiratory syncytial viruses were detected in the airway while Bacteroides and Bifidobacterium were at lower concentrations in the airway [23].…”

The relationship among avian influenza, gut microbiota and chicken immunity: an updated overview

“…Various interactions among pathogens and the commensal microbiome have been reported in the literature. For instance, the gut microbiome prevents the development of bacterial infection by generating biosurfactants, competing for attachment and nutrients, secreting metabolites with antimicrobial activities, and promoting the action of secondary intestinal lymphoid organs, which are the first line of defense in the gut mucosa ( Hooper et al, 2012 ; Meijerink et al, 2021 ; Shi et al, 2021 ).…”

Respiratory tract infections and gut microbiome modifications: A systematic review

“…Known as the ‘ gut-lung axis ’, this bi-directional system is complex and involved in both health, disease and secondary disease outcomes [ 17 ]. For example, gut microbiome derived short chain fatty acids (SCFAs) such as acetate, propionate and butyrate from dietary fermentation, in combination with host-derived cytokines and chemokines, travel via the bloodstream and lymphatic system and are directly associated with a protective response [ 5 ]. Infections can also influence this.…”

“…Microbial communities are associated with many human body niches, including the gut, skin, lungs, and mucosal surface [4][5][6]. The gut is the most densely and diversely colonised organ, with a bacterial to host cell ratio of 1:1 [7].…”