A modified infant mouse assay for bacterial enterotoxins.

Area of Science:

• Microbiology
• Animal models
• Bacterial pathogenesis

Background:

• The infant mouse assay is a standard method for detecting enterotoxins produced by bacteria such as Escherichia coli and Aeromonas spp.
• Current classification relies heavily on the intestinal weight to remaining body weight ratio (IW/RBW), which can be unreliable.
• Profuse diarrhea in test animals can skew IW/RBW results, leading to misclassification of enterotoxigenic strains.

Purpose of the Study:

• To improve the reproducibility and accuracy of the infant mouse assay for bacterial enterotoxins.
• To develop a more reliable method for classifying enterotoxigenic strains of E. coli and Aeromonas spp.
• To enhance the utility of the assay by incorporating multiple assessment criteria.

Main Methods:

• Utilized a scoring system that integrates the intestinal weight to remaining body weight ratio (IW/RBW) with the observed amount of diarrhea.
• Tested pooled and single supernatants from broth cultures of E. coli strains.
• Evaluated the classification accuracy of the new scoring system compared to using IW/RBW alone.

Main Results:

• Using IW/RBW alone misclassified 15% of ST-producing E. coli from pooled supernatants and 25% from single supernatants.
• The proposed scoring system demonstrated improved separation between positive and negative enterotoxigenic strains.
• The scoring system is adaptable for use with older mice, expanding the age range for testing and increasing animal facility utilization.

Conclusions:

• A combined assessment of IW/RBW and diarrhea significantly enhances the reliability of the infant mouse assay.
• The developed scoring system provides a more accurate method for identifying enterotoxigenic bacterial strains.
• This improved assay methodology allows for broader application and more efficient use of animal resources in research.