Heat-killed probiotic Lactobacillus plantarum modulates the functionality of neutrophils but does not improve survival in a murine burn injury model

Probiotics have become of interest as therapeutics in trauma or sepsis-induced inflammation due to their ability to modulate the immune response. However, their use is still under debate due to the potential risk of septicemia. Therefore, heat-killed probiotics offer a potential alternative, with recent research suggesting a comparable immunomodulating potential and increased safety. In a previous study, we demonstrated decreased mortality by administration of live Lactobacillus plantarum in a mouse burn-sepsis model. Neutrophils are an essential innate defense against pathogens. Therefore, our present study aims to understand the modulating impact of heat-killed probiotic L. plantarum (HKLP) on neutrophil function. Utilizing an in vitro stimulation with HKLP and a burn-infection in vivo model, we determined that administration of HKLP induced significant release of granulocyte-colony stimulating factor (G-CSF) and stimulated the release of pro-and anti-inflammatory cytokines. HKLP had no impact on neutrophil functionalities, such as phagocytosis, oxidative burst, and NETosis, but increased apoptosis and activated neutrophils. HKLP did not improve survival. Together, contrary to our hypothesis, heat-killed probiotics did not improve neutrophil function and survival outcome in a murine severe burn injury model. • In mice treated with Pseudomonas aeruginosa following severe burn injury, heat-killed probiotic did not have a the same protective effect as live Lactobacillus plantarum which improves survival. • Heat-killed Lactobacillus plantarum (HKLP) administration led to the augmentation of hematopoietic stem cell growth factor, G-CSF. • HKLP led to the increase of pro-and anti-inflammatory cytokines, but did not increase functionality of neutrophils.