Modeling Ascending Vaginal Infection, Preterm Birth, and Neonatal Morbidity in Mice
October 10th, 2025
Preterm birth (delivery < 37 weeks) is an urgent global health issue with suboptimal prevention and treatment options. We present a mouse model of ascending vaginal bacterial infection-induced preterm birth and outline how to analyze the resulting neonatal morbidity and mortality.
To begin, add 10 milliliters of antibiotic-treated Luria-Bertani, or LB broth, to a sterile 30-milliliter universal container. Retrieve a frozen glycerol stock of Escherichia coli for minus 80 degrees Celsius storage. Using a sterile pipette tip, scrape the surface of the frozen stock to lightly coat the tip with bacteria, then eject the tip directly into the universal container containing the LB broth.
Seal the container with parafilm, label it as a biohazard, and place it in an orbital shaker set at 200 RPM and 37 degrees Celsius overnight. The next morning, dilute the overnight bacterial culture 1 to 100 by adding 0.1 milliliters of the culture to 9.9 milliliters of fresh LB broth. Return the diluted culture to the orbital shaker at 200 RPM and 37 degrees Celsius for 1.5 to three hours.
Now, pipette 100 microliters of the culture and duplicate into a clear, flat-bottomed 96-well plate and measure the absorbance using a spectrophotometer with path length correction activated. When the optical density at 600 nanometers reaches between 0.5 and 0.7, remove 100 microliters of the bacterial culture. Dilute this in 900 microliters of sterile PBS.
Centrifuge the sample at 14, 000g for one minute to wash the bacterial pellet and remove the broth. Discard the supernatant, resuspend the pellet in sterile PBS, and then dilute the suspension 1 to 10, 000 in sterile PBS to achieve 100 to 1000 colony forming units. After anesthetizing the mouse, administer 20 microliters of mid-logarithmic phase E.coli suspension into the vagina using a sterile 200-microliter pipette tip.
Then, using a fresh sterile 200 microliter pipette tip, deliver 20 microliters of 20%Pluronic F-127 gel into the vagina to prevent bacterial leakage. Dab quinine powder onto the introitus using sterile gauze to prevent the mouse from cleaning the area. After launching the imaging software, click on Initialize and wait for the camera to reach the operating temperature indicated by a green and locked temperature bar.
After 48 hours, place the animal in the supine position on the heated stage of a bioluminescence imaging machine while maintaining anesthesia. Check the luminescent imaging box. Ensure the excitation filter is set to block and the emission filter is set to open.
Then, select auto-exposure time. This figure illustrates the time-dependent progression of bioluminescent E.coli infection from the vaginal tract to uterine and fetal tissues in pregnant mice. Bioluminescent E.coli reached the uterine horns within 48 hours post-infection, with strong luminescence signals detected at embryonic day 18.5, in contrast to the absence of signal at embryonic day 16.5.
Dissected uterine horns reveal clear bioluminescence signals as early as 18 hours after infection indicating rapid intrauterine colonization. Infection had also reached fetal compartments within 18 hours, as shown by luminescent signals in the placenta, fetal membranes, and amniotic fluid.
Overview
This study presents a mouse model for investigating preterm birth induced by ascending vaginal bacterial infection. It highlights the analysis of neonatal morbidity and mortality resulting from this condition.
Key Study Components
Area of Science
- Neuroscience
- Reproductive Biology
- Infectious Disease
Background
- Preterm birth is a significant global health concern.
- Current prevention and treatment options are inadequate.
- This model aims to better understand the mechanisms behind preterm birth.
- Infection during pregnancy can lead to adverse neonatal outcomes.
Purpose of Study
- To develop a reliable mouse model for studying preterm birth.
- To analyze the effects of bacterial infection on neonatal health.
- To provide insights into the timing and progression of infection.
Methods Used
- Preparation of bacterial cultures using Escherichia coli.
- Administration of bacterial suspension into the vaginal tract of pregnant mice.
- Monitoring of bioluminescent signals to track infection progression.
- Assessment of neonatal morbidity and mortality outcomes.
Main Results
- Bioluminescent E.coli reached uterine horns within 48 hours post-infection.
- Strong luminescence signals detected in fetal tissues by embryonic day 18.5.
- Rapid intrauterine colonization observed as early as 18 hours after infection.
- Infection impacted fetal compartments, including placenta and amniotic fluid.
Conclusions
- The model effectively demonstrates the impact of bacterial infection on preterm birth.
- Findings may inform future prevention and treatment strategies.
- Further research is needed to explore underlying mechanisms.
Frequently Asked Questions
Executive Industry Relevance
Modeling ascending vaginal infection and preterm birth in mice addresses a critical translational gap in understanding neonatal morbidity linked to infection-driven preterm delivery. This model enables mechanistic de-risking and predictive confidence for interventions targeting infection-induced preterm birth and its sequelae. Its reproducibility and clinical relevance support risk-adjusted portfolio decisions in early discovery and preclinical research.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Enables interrogation of infection-driven preterm birth mechanisms in a controlled, disease-relevant system.
- Supports functional validation of targets implicated in neonatal neuropathology and lung injury post-infection.
- Facilitates predictive confidence for candidate interventions addressing infection-induced morbidities.
Screening & Assay Development
- Provides a validated in vivo platform for evaluating anti-infective or anti-inflammatory compounds in the context of preterm birth.
- Enables quantitative assessment of infection progression using bioluminescent imaging.
- Supports reproducible measurement of neuropathological and pulmonary outcomes via standardized histology and immunohistochemistry.
Translational & Preclinical Research
- Aligns with human disease by recapitulating key neonatal morbidities observed in clinical preterm birth.
- Enables continuity from mechanistic discovery to preclinical efficacy and safety evaluation of novel interventions.
- Supports biomarker identification and validation for infection-associated neonatal outcomes.
Pipeline & Workflow Integration
This model integrates into the discovery-to-preclinical continuum by enabling hypothesis testing, target validation, and translational assessment of infection-driven preterm birth and neonatal morbidity.
- Discovery Biology: Supports mechanistic studies of ascending infection and its impact on fetal and neonatal tissues.
- Screening: Provides quantitative, reproducible infection and morbidity readouts for compound evaluation.
- Analytics: Delivers bioluminescent and histological data for comparative analysis across experimental conditions.
- Translational Research: Bridges preclinical findings to clinical scenarios by modeling human-relevant neonatal outcomes.
- Enterprise Reuse: Offers a reusable, standardized platform for diverse infection and preterm birth research programs.
Operational & Enterprise Impact
- Scientific Value: Increases predictive confidence and reduces mechanistic ambiguity in infection-driven preterm birth research.
- Operational Value: Enhances standardization, reproducibility, and scalability of in vivo infection models.
- Strategic Value: Informs go/no-go decisions and improves capital efficiency by de-risking early-stage programs.
- Portfolio Impact: Enables risk-adjusted prioritization of interventions targeting infection-associated neonatal morbidity.
Implementation Considerations
- Requires expertise in in vivo infection modeling and neonatal outcome assessment.
- Needs access to bioluminescent imaging systems and histopathological analysis infrastructure.
- Demands rigorous cross-team standardization for reproducibility of infection and outcome measures.
- Adaptation may be necessary for different bacterial strains or host genetic backgrounds.
- Limitations include species-specific differences and the need for careful interpretation of translational relevance.
