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Heat-stable enterotoxin produced by Shigella flexneri
Abstract:
Filtrates and ultrasonics extracts of Shigella flexneri showed rapid permeability factor (PF) test and proved positive in suckling mice and ligated rabbit loop tests within 4 hr. Delayed PF was not detected and the rabbit loop dilatation test read after 18 to 24 hr, the mouse pad oedema reaction, the test for elongation effect of CHO cells were also negative. In the delayed PF test a strong "blanching" effect was observed. A filtrate of an Ent-Escherichia coli strain was positive only in the rapid PF test, while filtrate and ultrasonic extract prepared from the Ent+ E. coli strain showed a positive reaction in all tests for enterotoxins (ST and LT) including the rapid PF test. Ultrasonic extracts of a S. flexneri and an Ent- E. coli strain concentrated by freeze-drying were fractionated on Sephadex G-100 column. S. flexneri fractions of 60--70ml were positive for rapid PF, dilation capacity in suckling mice, and the blanching effect in the delayed PF test. No positive reaction was found in the delayed PF test and in CHO cell culture. Similar fractions of Ent- E. Coli carried substances responsible for the rapid PF and the blanching effect, but without suckling mice positivity.
Insights
Shigella flexneri and E. coli extracts showed rapid permeability factor (PF) activity. Specific fractions demonstrated enterotoxin properties in mouse models, highlighting distinct toxin profiles.
Area of Science:
- Microbiology
- Bacteriology
- Toxicology
Background:
- Enterotoxins produced by bacterial pathogens like Shigella flexneri and Escherichia coli are critical virulence factors.
- Assessing the activity and characteristics of these toxins is crucial for understanding pathogenesis and developing diagnostics.
Purpose of the Study:
- To characterize the enterotoxic properties of Shigella flexneri and Escherichia coli extracts.
- To compare the efficacy of rapid and delayed permeability factor (PF) tests in detecting enterotoxins.
- To investigate the specific fractions responsible for enterotoxin activity.
Main Methods:
- Preparation of filtrates and ultrasonic extracts from bacterial strains.
- Application of rapid and delayed permeability factor (PF) tests.
- In vivo assays: suckling mouse and ligated rabbit loop tests.
- In vitro assays: Chinese Hamster Ovary (CHO) cell elongation test.
- Fractionation of extracts using Sephadex G-100 column chromatography.
Main Results:
- Shigella flexneri extracts exhibited rapid PF activity and positive results in suckling mouse and rabbit loop tests.
- A strong blanching effect was observed in the delayed PF test for S. flexneri.
- Enterotoxigenic (Ent+) E. coli extracts showed positive reactions in all enterotoxin assays, including rapid PF.
- Non-enterotoxigenic (Ent-) E. coli extracts were positive only in the rapid PF test.
- Fractionated S. flexneri extracts were positive for rapid PF, mouse dilation, and delayed PF blanching effect, but negative in CHO cell assays.
- Fractionated Ent- E. coli extracts showed rapid PF and blanching effects, but lacked suckling mouse positivity.
Conclusions:
- Rapid permeability factor (PF) testing is a sensitive indicator for bacterial enterotoxins.
- Shigella flexneri produces toxins with distinct properties, including a rapid PF and a blanching effect.
- Fractionation studies reveal specific molecular weight ranges associated with enterotoxic activities.