This paper studies the occurrence but more importantly the pathogenicity of three vibrios species on the south coast of Sweden. The species were V. cholerae, V. vulnificus (associated with sepsis) and V. parahaemolyticus (associated with gastroenteritis). The main reason why I like this paper is it doesn’t just concentrate on the occurrence of vibrios like many papers do, but also tries to differentiate between pathogenetic and non-pathogenetic strains.
Their method is very thorough and they used many different methods of which some I have left out. They used mussels as natural filters and collected them from the Sound between Sweden and Denmark over the summer. The occurrence of vibrios was measured by PCR based methods using species-specific and virulent genetic markers coupled with enrichment cultivation methods using TCBS agar. They also performed a cell toxicity test by exposing eukaryotic cell cultures to the isolated vibrios and recording the killing index.
In the PCR based method 53% of samples contained the V. cholerae specific toxR gene of which none were positive for the virulent ctx gene. 63% of samples were positive for the V. vulnificus species specific viuB gene and virulent vvh gene. 79% were positive for the V .parahaemolyticus tlh gene of which 53% were positive for the virulent tdh gene. There were no positive results for any genes when the water temperature was below 17⁰C. In the enrichment method all three vibrios were isolated additionally with V. alginolyticus. These were identified with an API 20NE test kit followed by PCR. All of the isolates were present for the species specific genes stated above but none were positive for any of the tested virulent genes. In the cell toxicity test the killing indices were 78%, 85% and 79% for V. cholerae, V. vulnificus and V. parahaemolyticus respectively.
Overall I thought the paper was really good and the variety of methods used was pretty impressive. They suggest that pathogenic vibrios are common during the summer months possibly even more so than other areas due to the brackish water of the Sound. I found it quite interesting that the virulence genes tested were not present in the isolated vibrios yet they still had a killing index higher than clinical strains. This shows how important it is to use different methods. It also shows that the genes tested aren’t completely necessary for cytotoxicity. Although the cytotoxicity test was using Chinese hamster ovary cells which is very different to the human body and most of the genes tested are suppose to code for haemolysins or toxins which wouldn’t normally affect this sort of cell. The paper shows that the pathogenicity of vibrios is incredibly complex and variable and many different methods should be used to test for it.
A review of: Betty Collin & Ann-Sofi Rehnstam-Holm (2011) Occurrence and potential pathogenesis of Vibrio cholera, Vibrio parahaemolyticus and Vibrio vulnificus on the South Coast of Sweden. FEMS Microbiol Ecol 78: 306–313
2 comments:
The relationship between environmental statins and clinical strains, and the production of different virulence factors, is very complex in Vibrio Sep. and we will be looking at this in lectures. There is a big interest in the emergence of vibrios as a significant health problems in th Baltic Sea, due to the rapid warming here (almost 1 degree per decade).
The CHO assay is widely used to test for cytotoxicity ( we use it here for studies on V. parahaemolyticus). Incidentally, haemolysis is just a convenient assay for cell damage - haemolysins usually affect a wide range of cel membranes.
yea they said there had been three deaths caused by vibrios in sweden over one summer and many nasty wound infections but the paper seemed to suggest that this was more to do with the salinity there than temperature. The production of virulence factors does seem pretty intense but is there a reason why they rarely seem to test for pathogenicity after finding vibrios? or is it just by chance because of the papers ive read?
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