Dysbiosis in SARS-CoV-2–infected patients

Gastrointestinal symptoms are frequently observed in patients with coronavirus disease 2019 (COVID-19), but only limited knowledge is available regarding the ability of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to influence the host microbiota composition. The entry of SARS-CoV-2 into intestinal cells down-regulates angiotensin-converting 2 receptors and causes microbial dysbiosis.1 , 2 An alteration of the microbial composition may impact the pulmonary defense mechanisms through the so-called gut–lung axis.3 We have read with interest the articles by Zuo et al4 confirming the impact of COVID-19 on the gastrointestinal tract's microbial community composition. Remarkably, their article represents, to our knowledge, the first publication exploring the complex association between SARS-CoV-2 infection and fungi, a neglected component of the gut microbiota. Gut bacteria inhibit the growth of Candida albicans and other gut fungi via the target of rapamycin signaling pathway and through those tryptophan metabolites, which are responsible for an interleukin-22–dependent mucosal response.5 , 6 Bacteria and fungi compete for some nutrients and, in this context, bacteria with probiotic properties may control Candida overgrowth. In healthy volunteers, a commercially available probiotic product has induced a significant fecal anti-Candida activity associated with the augmented production of interferon-alfa in the gastrointestinal tract.7 Another probiotic formulation administered to patients with COVID-19 has induced a significantly faster remission of gastrointestinal symptoms and other symptoms, such as fever, cough, dyspnea, headache, myalgia, and a decreased risk of evolving respiratory failure compared with nontreated patients.8 These preliminary data should encourage the scientific community to investigate the possible use of probiotics in patients with COVID-19, keeping in mind that not all probiotic formulations are equivalent for efficacy and safety in these fragile patients.