Resilience and the Gut Microbiome: Insights from Chronically Socially Stressed Wild-Type Mice

The microbiome is an important player within physiological homeostasis of the body but also in pathophysiological derailments. Chronic social stress is a challenge to the organism, which results in psychological illnesses such as depression in some individuals and can be counterbalanced by others, namely resilient individuals. In this study, we wanted to elucidate the potential contribution of the microbiome to promote resilience. Male mice were subjected to the classical chronic social defeat paradigm. Defeated or undefeated mice were either controls (receiving normal drinking water) or pre-treated with antibiotics or probiotics. Following social defeat, resilient behavior was assessed by means of the social interaction test. Neither depletion nor probiotic-shifted alteration of the microbiome influenced stress-associated behavioral outcomes. Nevertheless, clear changes in microbiota composition due to the defeat stress were observed such as elevated Bacteroides spp. This stress-induced increase in Bacteroides in male mice could be confirmed in a related social stress paradigm (instable social hierarchy) in females. This indicates that while manipulation of the microbiome via the antibiotics- and probiotics-treatment regime used here has no direct impact on modulating individual stress susceptibility in rodents, it clearly affects the microbiome in the second line and in a sex-independent manner regarding Bacteroides.