Exposure to stressful stimuli results in the activation of multiple physiological processes aimed at maintaining homeostasis within the body. These physiological processes also have the capacity to influence the composition of microbial communities, and research now indicates that exposure to stressful stimuli leads to gut microbiota dysbiosis. While the relative abundance of many different bacterial types can be altered during stressor exposure, findings in nonhuman primates and laboratory rodents, as well as humans, indicate that bacteria in the genus Lactobacillus are consistently reduced in the gut during stress. The gut microbiota, including the lactobacilli, have many functions that enhance the health of the host. This review presents studies involving germfree and antibiotic treated mice, as well as mice given Lactobacillus spp. to prevent stressor-induced reductions in lactobacilli, to provide evidence that the microbiota contribute to stressor-induced immunomodulation, both in gut mucosa as well as in systemic compartments. This review will also discuss the evidence that commensal gut microbes have bidirectional effects on gastrointestinal physiology during stressor exposure.
Keywords: Lactobacillus; anxiety; bacterial translocation; brain gut axis; colitis; dysbiosis; psychological stress; social defeat.