Exopolysaccharides from Lactobacillus delbrueckii ssp. bulgaricus OLL1073R-1 prevent influenza virus infection and attenuate secondary bacterial infection risk

The present study assessed the inhibitory action of exopolysaccharides (EPS) produced by Lactobacillus delbrueckii ssp. bulgaricus OLL1073R-1 against influenza virus infection followed by secondary bacterial infection. We found that the presence of 200 or 400 μg ml-1 of EPS significantly protected against influenza virus infection in a dose-dependent manner when A549 cells were treated with EPS before infection but not after it. The expression of carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM-1), an adhesion molecule for bacteria adherence, on A549 cells was significantly enhanced during influenza virus infection compared with viral-non-infected A549 cells. However, this upregulated CEACAM-1 expression was significantly decreased by EPS treatment before viral infection in association with the reduction in the virus titre in A549 cells. In a bacterial adhesion assay using Staphylococcus aureus, the bacterial adherence to viral-infected A549 cells was significantly greater than that to viral-non-infected A549 cells, and the increased bacterial adherence induced by influenza virus infection tended to be decreased by EPS treatment before the infection. Our findings show that EPS treatment before viral infection can inhibit influenza virus infection and alleviate secondary bacterial infection through decreased CEACAM-1 expression.