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A putative heat-labile enterotoxin expressed by strains of Aeromonas media
1Department of Microbiology, Institute of Medical Sciences, Banaras Hindu University, Varanasi 221 005, India.
Abstract:
Fifteen isolates of Aeromonas media (seven from diarrhoeal stools, four from water and four from superficial skin ulcers of catfish) were examined for enterotoxin production. Ten of these isolates (six diarrhoeal, one from water and three from fish) caused accumulation of fluid in the initial rabbit ileal loop (RIL) tests. Isolates from diarrhoeal stools and fish caused relatively more fluid accumulation than those from water. Those strains that caused little or no fluid accumulation in the initial experiments became enterotoxin producers after one passage through RILs, regardless of source, and also showed gradual enhancement of fluid outpouring after each subsequent passage. Inocula of c. 1 x 10(4) viable cells and 0.25 ml of culture filtrate (CF) caused fluid accumulation similar to that of toxigenic Vibrio cholerae 569B. The enterotoxic factor(s) were inactivated when held at 56 degrees C for 20 min or 65 degrees C for 10 min and showed biological activity over a wide range of pH values. These results suggest that strains of A. media, whether from diarrhoeal stools, water or infected fish, are potentially enterotoxigenic and may have the potential to produce a heat-labile and pH-stable diarrhoeagenic factor in the same way as other known heat-labile and pH-stable enterotoxins.
Insights
Aeromonas media strains from various sources, including diarrheal stools, water, and catfish, can produce heat-labile enterotoxins. These toxins, similar to Vibrio cholerae, cause fluid accumulation and may pose a public health risk.
Area of Science:
- Microbiology
- Bacteriology
- Food Safety
Background:
- Aeromonas media is a bacterium found in various environments, including aquatic ecosystems and as a potential pathogen.
- Enterotoxigenicity of A. media strains, particularly those isolated from clinical and environmental sources, requires further investigation.
Purpose of the Study:
- To investigate the enterotoxin production capabilities of Aeromonas media isolates from diverse origins.
- To characterize the properties of the enterotoxic factors produced by A. media.
Main Methods:
- Enterotoxin production was assessed using the rabbit ileal loop (RIL) assay.
- Isolates were tested before and after passage through RILs to evaluate toxin enhancement.
- The heat stability and pH activity of the enterotoxic factors were determined.
Main Results:
- Ten out of fifteen A. media isolates exhibited enterotoxigenicity in RIL tests, with strains from diarrheal stools and fish showing higher fluid accumulation.
- Enterotoxin production was enhanced after serial passage in RILs, irrespective of the isolate's source.
- The enterotoxic factor(s) were heat-labile (inactivated at 56°C for 20 min or 65°C for 10 min) and biologically active across a wide pH range.
Conclusions:
- A. media strains from diarrheal stools, water, and infected fish possess the potential to produce enterotoxins.
- These enterotoxins are heat-labile and pH-stable, similar to known diarrhoeagenic factors from other bacteria.