ONR Mv/CDR/SD mouse study

Previous studies in our laboratory demonstrate that a heat-killed preparation of the immunoregulatory and anti-inflammatory environmental bacterium Mycobacterium vaccae NCTC 11659 (M. vaccae) is a potentially useful countermeasure that protects against negative outcomes of chronic psychosocial stress. These protective effects included ameliorations of stress-induced decreases in alpha diversity and increases in beta diversity of the gut microbiome, chemically induced colitis in a model of inflammatory bowel disease, and anxiety-like behavior. Here we utilized a 2 x 2 x 2 experimental design in 7 cohorts of juvenile male C57BL/6NCrl mice (N = 112) to determine if immunization with M. vaccae is an effective countermeasure in a murine model of chronic circadian disruption (CDR) and psychosocial stress using the social defeat (SD) test. Mice were implanted on pnd 36 with telemetric recording devices for monitoring 24-h rhythms of core body temperature and locomotor activity. We treated (3x weekly) adolescent male mice with a heat-killed preparation of M. vaccae or vehicle and evaluated the gut microbiome and fecal metabolome using 16S rRNA gene sequencing and untargeted LC-MS/MS, respectively, at three timepoints (day -1, 48, and 62). Briefly, CDR consisted of weekly 12-h light reversals of the normal 12:12h light:dark cycle every 7 days for 8 weeks. Single-housed mice immunized with vehicle and maintained on a non-manipulated 12-h light:dark cycle (lights on at ZT0 = 0700 h, lights off at ZT12 = 1400 h) for 8 weeks were used as controls.