Interaction between gut microbiota dysbiosis and lung infection as gut-lung axis caused by Streptococcus suis in mouse model

Streptococcus suis (S. suis) is an important zoonotic pathogen threatening the global pig farming industry. It causes respiratory and digestive tract infections simultaneously in pigs. The balanced gut microbiota not only affects the local mucosal immune response but also involves the regulation of the immune status of the distant lung tissues that is termed as "gut-lung" axis. Whether S. suis affects the gut during lung infection and how does the intestinal microbial disturbance play role in the development of lung infection during S. suis exposure is not clear yet. Therefore, in the current study, we constructed the animal model using six-week-old mice (N = 48) divided into four groups with S. suis serotype 2 (SS2)-induced lung infection and the antibiotic treated gut microbiota dysbiosis. By means of various techniques (like HE staining, RT-qPCR, Western Blot and ELISA and viability detection) we explored that S. suis can concurrently cause intestinal tissue damage and inflammation after lung infection. Moreover, gut microbiota dysbiosis changes the balance of Th1/Th2 cells that aggravates lung injury during the infection. Thus, "gut-lung" axis of the communication between the gut microbiota and lung infection was established through the spleen and blood. In addition, intestinal dysbacteriosis can affect alveolar macrophage activity for a long time and the balance of gut microbiota plays an important role in lung infection caused by S. suis. Hence, this study clarified the pulmonary infection caused by SS2 from the perspective of the intestinal microbiota providing novel theoretical basis for the treatment of related lung diseases.