Prenatal Stress Alters Bacterial Colonization of the Gut in Infant Monkeys

Objective: The hypothesis that prenatal stress lowers the levels of protective microflora and increases the risk for postpartum Gram‐negative pathogens was tested in infant monkeys. Methods: Female monkeys were left undisturbed or were stressed during pregnancy using an acoustical startle paradigm for 6 weeks either early or late in their 24‐week gestation. Several types of intestinal microflora were repeatedly enumerated by fecal culture while infants were reared normally by their mothers. Results: Significant changes in microflora concentrations occurred during the first 6 months of life. The profile of total aerobes and facultative anaerobes was biphasic, with peak concentrations occurring between 2 and 16 weeks of age. The numbers of bifidobacteria and lactobacilli were low at 2 days after birth but rapidly increased to a peak between 8 and 16 weeks of age. Although similar temporal patterns were evident in all infants, prenatal stress reduced the overall numbers of bifidobacteria and lactobacilli. Conclusions: Moderate disturbance during pregnancy was sufficient to alter the intestinal microflora in the newborn infant. These alterations could result in enhanced susceptibility to infection and suggest a mechanism for some effects of maternal pregnancy conditions on infant health.