Stress and disease-related alterations of the intestinal microflora across the life span of rhesus monkeys

The intestines harbor a complex microflora of over 400 different species of bacteria, many of which provide protection to the host by limiting pathogen colonization and proliferation. This type of nonspecific defense may be particularly important at points in the life span when the immune system may not be fully functional, such as infancy and old age. This dissertation research was designed to assess the impact of stressors and disease on the intestinal microflora across the life span of rhesus monkeys.; In the initial study, prenatal stress significantly altered the development of the intestinal microflora. Lactobacilli and Bifidobacteria concentrations were higher in monkeys born from mothers undisturbed during gestation in comparison to prenatally stressed infants. Moreover, the prevalence of subclinical Shigella infection tended to be higher in prenatally stressed infants in comparison to control infants. Although the mechanisms causing the prenatal stressor to affect the intestinal microflora are unclear, anaerobic bacterial concentrations were associated with fewer maternal solicitous behaviors toward the infants.; The intestinal microflora of rhesus monkeys are fully mature by 6 months of age. However, separating the infants from their mothers reduced the concentration of Lactobacilli in the intestines. Moreover, animals that became naturally infected with intestinal pathogens tended to have lower Lactobacilli levels. In addition to being associated with pathogenic bacterial concentrations, Lactobacilli were associated with stress-indicative behaviors. In general, those monkeys showing the strongest reaction to separation also had the lowest concentrations of Lactobacilli.; Microflora concentrations remain stable throughout healthy adulthood, but are thought to naturally decline with advanced age. However, in the final study, the microflora were not altered in old, healthy monkeys, but were altered in older monkeys with the age-associated disease endometriosis. Like the effects of stress, monkeys with endometriosis had significantly lower Lactobacilli concentrations than healthy, age-matched controls.; These studies demonstrate that although the intestinal microflora reside at their set point concentrations during quiescent and healthy periods, stress and disease disrupt this stability, resulting in enhanced susceptibility to infectious diseases. This dissertation research offers a new way of thinking about bacteria in the complex host/illness relationship.