Objective: Our purpose was to determine whether intrauterine bacterial inoculation leads to preterm delivery in mice.
Study design: Fifty-four female CD-1 mice at 75% of the length of the gestational period (14.5 days) received either an intrauterine bacterial inoculum of 2 to 10 x 10(3) Escherichia coli (n = 33), an intraperitoneal bacterial inoculum (n = 7), or an intrauterine injection of a sterile solution (n = 14).
Results: Delivery within 48 hours of surgery occurred in 91% of mice after intrauterine bacteria, in 0% after intraperitoneal bacteria, and in 7% after sterile intrauterine injection (p < 0.001). Intrauterine bacterial inoculation produced systemic infection (i.e., recovery of organisms from culture of the heart) in 50% of animals post partum. Intraperitoneal bacteria and intrauterine saline solution injections resulted in systemic infection rates of 20% and 0%, respectively, 48 hours after surgery. Five of seven animals injected with bacteria into the uterus had histologic evidence of metritis, mild in all cases. Intrauterine bacterial inoculation resulted in induction of ribonucleic acid transcripts for tumor necrosis factor-alpha, interleukin-1 alpha, interleukin-1 beta, and cyclooxygenase-2.
Conclusions: Intrauterine inoculation with Escherichia coli in mice leads to preterm delivery and the local induction of factors known to be involved in human preterm labor with infection. The observation that intraperitoneal bacterial inoculation does not result in preterm delivery suggests that in this model labor is the product of a local (uterine) stimulus.