Immunosenescence refers to the development of weakened and/or dysfunctional immune responses associated with aging. Several commensal bacteria can be pathogenic in immunosuppressed individuals. AlthoughKlebsiella pneumoniaeis a commensal bacterium that colonizes human mucosal surfaces, the gastrointestinal tract, and the oropharynx, it can cause serious infectious diseases, such as pneumonia, urinary tract infections, and liver abscesses, primarily in elderly patients. However, the reason whyK.pneumoniaeis a more prevalent cause of infection in the elderly population remains unclear. This study aimed to determine how the host’s intestinal immune response toK.pneumoniaevaries with age. To this end, the study analyzed anin vivo K.pneumoniaeinfection model using aged mice, as well as anin vitro K.pneumoniaeinfection model using a Transwell insert co-culture system comprising epithelial cells and macrophages. In this study, we demonstrate that growth arrest-specific 6 (Gas6), released by intestinal macrophages that recognizeK.pneumoniae, inhibits bacterial translocation from the gastrointestinal tract by enhancing tight-junction barriers in the intestinal epithelium. However, in aging mice, Gas6 was hardly secreted underK.pneumoniaeinfection due to decreasing intestinal mucosal macrophages; therefore,K.pneumoniaecan easily invade the intestinal epithelium and subsequently translocate to the liver. Moreover, the administration of Gas6 recombinant protein to elderly mice prevented the translocation ofK.pneumoniaefrom the gastrointestinal tract and significantly prolonged their survival. From these findings, we conclude that the age-related decrease in Gas6 secretion in the intestinal mucosa is the reason whyK.pneumoniaecan be pathogenic in the elderly, thereby indicating that Gas6 could be effective in protecting the elderly against infectious diseases caused by gut pathogens.