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Factors affecting detection of Yersinia enterocolitica heat-stable enterotoxin by the infant mouse test
Abstract:
With regard to the assay of heat-stable enterotoxin (ST) from Yersinia enterocolitica, we made a comparative study of the conventional infant mouse test read at 4 h and a modified infant mouse test read at 2 h. The influence of several factors, such as the medium used to prepare ST, lysing of bacterial cells from the broth cultures used to prepare ST, and the temperature at which the inoculated mice were kept during the test, was also investigated. Thus, with a few exceptions, Pai-Mors medium was more suitable than Casamino Acids-yeast extract medium, for the preparation of yersinial ST. Gut/carcass weight ratios obtained with lysed supernatants or with supernatants from whole cultures of Y. enterocolitica were similar, suggesting that most of the ST produced by this microorganism in broth cultures is extracellular. The amount of ST produced by Y. enterocolitica, as well as the ambient temperature at which inoculated mice were kept during the assay, was found to influence gut/carcass weight ratios obtained with both tests. Enterotoxigenicity and the temperature at which mice were kept were interrelated, such that for weakly enterotoxigenic strains there were no significant differences among gut/carcass weight ratios for the conventional and modified infant mouse tests carried out at 18 or 25 degrees C, but at 30 degrees C the values in the modified test were higher for most ST preparations with Pai-Mors medium. The influence of ambient temperature was more pronounced at 37 degrees C, since most strains produced negative results in the conventional test at this temperature. We conclude that the conventional infant mouse test is adequate for assaying yersinial ST, provided that the temperature at which mice are kept during the assay is fixed at around 25 degrees C.
Insights
This study compared conventional and modified infant mouse tests for heat-stable enterotoxin (ST) from Yersinia enterocolitica. A 25°C ambient temperature is recommended for accurate ST detection using the conventional infant mouse assay.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Gastroenterology
Background:
- Yersinia enterocolitica produces heat-stable enterotoxin (ST), a significant cause of bacterial gastroenteritis.
- Accurate detection of ST is crucial for diagnosing infections and understanding disease mechanisms.
Purpose of the Study:
- To compare the efficacy of a conventional infant mouse assay (4-hour read) with a modified assay (2-hour read) for detecting Yersinia enterocolitica ST.
- To investigate the impact of culture media, bacterial cell lysis, and incubation temperature on ST assay sensitivity.
Main Methods:
- Comparative analysis of conventional (4h) and modified (2h) infant mouse bioassays for ST detection.
- Evaluation of different culture media (Pai-Mors vs. Casamino Acids-yeast extract) for ST production.
- Assessment of bacterial cell lysis and incubation temperatures (18°C, 25°C, 30°C, 37°C) on assay results.
Main Results:
- Pai-Mors medium generally proved more suitable for preparing yersinial ST compared to Casamino Acids-yeast extract.
- Gut/carcass weight ratios were similar for lysed and unlysed supernatants, indicating extracellular ST production.
- Ambient temperature significantly influenced assay outcomes, with 25°C optimal for the conventional test and higher temperatures favoring the modified test for certain preparations.
Conclusions:
- The conventional infant mouse assay is adequate for quantifying Yersinia enterocolitica ST.
- Maintaining a consistent ambient temperature of approximately 25°C during the assay is critical for reliable results.
- Optimizing culture media and understanding temperature effects enhance the accuracy of ST detection.