Identification of tetrodotoxin-producing Shewanella spp. from feces of food poisoning patients and food samples
© Wang et al.; licensee BioMed Central Ltd. 2013
Received: 9 April 2013
Accepted: 15 June 2013
Published: 20 June 2013
Shewanella spp. is infrequently recovered from clinical specimens. Following two outbreaks of food poisoning, eight Shewanella spp. strains were obtained from the fecal specimens of patients, food and food processing-related materials. Tetrodotoxin (TTX) was identified in the culture supernatants of these strains, and the toxin’s biological activity was detected using a mouse bioassay. This study suggested that Shewanella strains can colonize and survive in human intestines. The study also raises the issues of the accumulation of TTX produced by Shewanella in food and the possible role of TTX-producing Shewanella in food poisoning.
KeywordsTetrodotoxin Shewanella Food poisoning
Shewanella spp. is Gram-negative, motile bacilli that belong to the order Alteromonadales and the family Alteromonadceae, within the gamma subdivision of the Proteobacteria. Human infections with members of the genus Shewanella are rare and mainly involve the ears  and soft tissue [2–5]. The isolation of Shewanella spp. from patients with diarrhea, poultry and livestock has also been reported . In most instances, the isolation of has occurred in the absence of clinical disease and has been considered to involve only colonization, rather than an active infection . However, in recent years, it was found that Shewanella spp. can produce tetrodotoxin (TTX) . TTX and its analogs (TTXs) have been detected in a wide variety of marine animals . It has been suggested that TTX is a secondary metabolite produced by symbiotic bacteria in marine organisms that gradually accumulates in the bodies of marine organisms through the food chain [8, 10]. With the source of TTX still a controversial issue, the exact origin of TTX in the food chain is unknown.
Study design and results
Mouse bioassay of the toxicity of TTX extracts from the Shewanella spp. isolates
TTX extracts from cells
(overnight culture, 8 isolates)
TTX extracts from supernatants
(overnight culture, 8 isolates)
TTX extracts from cells (7-day
culture, 8 strains)
TTX extracts from supernatants
(7-day culture, 8 isolates)
TTX standard, 2.2 μ g/ml
0.1% acetic acid
The Shewanella strains recovered from the fecal samples of the food poisoning patients may present evidence of the survival of TTX-producing Shewanella in human intestines. To date, there is still no direct evidence to show that TTX produced by Shewanella spp. is related to food poisoning. Considering a previous report of Shewanella isolation from food poisoning patients  and our investigation, in which strains were also obtained from food, hand swabs of a restaurant chef and a knife, these findings suggest contamination with Shewanella through the fecal-oral route and indicate the need for detection and studies of Shewanella in food poisoning, especially if caused by TTX. The limitations of this study are that no blood samples were obtained for the detection of anti-TTX antibody, and no food sample was screened for TTX. Studies indicate that TTX accumulation in the puffer fish occurs through the food chain, consisting of several steps and starting with marine bacteria as the primary source . In this study, very weak, slow TTX production by the Shewanella strains under common culture conditions was also observed. We suspected that weak accumulation of TTX in seafood might have caused the poisoning symptoms of the patients, as the recovered Shewanella strains were in fact the bacteria colonizing the seafood.
This work was supported by grants from the National High Technology R&D Program of China (863 Program) (2006AA02Z425), the NSFC of China (30872260), and the National Priority Program for Prevention and Control of Infectious Diseases (2008ZX10004-012).
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