Dysbiosis of gut microbiota in patients with severe COVID-19

Aim: Altered gut microbiota has been proposed as one of the causes of exacerbation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2/COVID-19) from the perspective of the gut-lung axis. We aimed to evaluate gut microbiota in mechanically ventilated patients with COVID-19 prior to using antibiotics.Methods: We retrospectively selected for enrollment COVID-19 patients who required mechanical ventilation on admission but who had not used antibiotics before admission to observe the influence of SARS-Cov-2 on gut microbiota. Fecal samples were collected serially on admission and were evaluated by 16S rRNA gene deep sequencing.Results: The phylum of Bacteroidetes decreased, and those of Firmicutes and Actinobacteria increased in COVID-19 patients compared with those in healthy controls (p < 0.001). The main commensals of Bacteroides, Faecalibacterium, and Blautia at the genus level were significantly decreased in the COVID-19 patients, and opportunistic bacteria including Corynebacterium, Anaerococcus, Finegoldia Peptoniphilus, Actinomyces, and Enterococcus were increased (p < 0.001). alpha-Diversity and beta-diversity in COVID-19 patients significantly changed compared with those in the healthy controls.Conclusion: The commensal gut microbiota were altered, and opportunistic bacteria increased in patients with severe COVID-19 who required mechanical ventilation on admission.