Diarrheal diseases derived from enteric bacteria are one the most prominent health risks in the developing world. Enteric bacteria such as enterotoxigenic Escherichia coli (ETEC) and Salmonella enterica serovar Typhimurium (S. enterica) are known as two of the leading causes of diarrheal disease. They are noted to be of particular importance in cases involving children. An increase in pathogen abundance in coastal zones has been described in recent history. This is suggested to be attributed to anthropogenic activities such as sewage discharge and agricultural runoff.
Diarrheal pathogens such as ETEC and S. enterica are able to colonise numerous diverse environments, resulting in the widespread contamination of drinking water and food. Bivalves, such as mussels, clams and oysters are popular food stuffs and are frequently associated with the transmission of pathogens from the sea to humans. This occurs by the accumulation of pathogens by a bivalve, which is then transmitted to a human through consumption (oral-faecal route). In an attempt to break this transmission pathway, efforts have been made to determine how a population of enteric bacteria is sustained within an environment. By evaluating the behaviour and adaptation of enteric bacteria, as well as the complex factors which act upon them, a comprehensive understanding of the biocomplexity of a pathogen can be achieved.
Limited literature is available describing the incidence and diligence of ETEC in marine habitats. In order to determine its possible prevalence and influence in the marine environment, this study compared the growth response to various factors of ETEC to the better studied fecal contaminant S. enterica and the marine bacteria Vibrio parahaemolyticus. An evaluation of the uptake and behaviour of the bacteria in blue mussels is provided, along with an analysis of the effect of temperature, nutrient supply, bivalve immune response and UV illumination on the viability of the bacteria.
Most parameters were assessed by culturing each species on agar plates and incubating in seawater for 8 weeks. However, to investigate the influence of bivalve immune response, an in vitro experiment was devised where the bactericidal capacity of haemocytes was measured. Haemocytes were harvested from the haemolymph of four different bivalves.
Noted results that should be highlighted from this paper include; V. parahaemolyticus was negatively affected by low temperature, whilst ETEC was positively affected. The growth of ETEC was observed in high-nutrient conditions, whilst no affect was noted in any other bacteria. In samples where blue mussels were nourished with each species of bacteria, lower ingestion rates were observed for V. parahaemolyticus when compared to other enterobacteria. Additionally in these conditions, V. parahaemolyticus is advocated to reduce the filtration activity of blue mussels.
Investigation of the influence of bivalve immune response suggested that the bactericidal capacity of bivalve hemocytes differed both on a species level as well as between each species. Results indicated that V. parahaemolyticus showed increased resistance to haemocytes from different bivalves, whilst ETEC and S. enterica were efficiently terminated by the haemocytes. It is advocated that mussels are less proficient at eliminating V. parahaemolyticus, as the haemocytes of three different species of bivalve were unable to eliminate the strain of V. parahaemolyticus used in this analysis. However, this pathway is advocated as a successful method of eradicating ETEC and S. enterica.
This paper emphasizes that the role of ETEC in the transmission of enteric diseases from an oceanic source is currently underestimated. Subsequently, it is suggested that ETEC, V. parahaemolyticus and S. enterica should be considered and measured as analogous sources of infection, when assessing the role of the marine environment as a source in the spread of enteric diseases. Nevertheless, the transmission of these pathogens to human populations is dependent upon a great number of factors, to which a lot of details are unknown. In order to successfully manage waterborne infections, a profound understanding of the relative sources and pathways of transmission are required. Further studies should concentrate on the persistence of ETEC in the marine environment.
4 comments:
so have these diseases came from humans via diarrhoea in the sea or did they originate in the sea and adapt to infect humans because that would effect how long they can survive in the marine environment? did the paper not mention ways of eliminating the disease from the shellfish by maybe introducing disease control technologies when in the sea or after harvest? To further the seriousness of the diseases they may pick up antibiotic resistance from aquaculture antibiotic use as discussed in my last blog as a point of interest.
Hey alice,
The salmonella and E.coli will be coming from the sewage sources and are non-indigenous in the marine environment but the vibrios will be indigenous. There are many measures after harvest like depuration and heat treatment but depuration isnt very effective against indigenous bacteria like vibrios and heat treatment changes the texture of the shellfish so a lot of people wont buy them. There are other methods as well but are expensive. In reality of you cook the shellfish they shouldnt do any harm but a lot of people eat them raw for some crazy reason. Its interesting that ETEC was positively affected by lower temperatures. Its also interesting that so many papers end with 'we have to monitor vibrios' yet no ones actually developed a realistic method to do so.
Thanks for your question Alice, and a nice reply Matt. A good answer from my reading, and I concur with your thoughts.
i see they should just say how disgusting it is to eat stuff raw i guess, we dont eat sausages raw!
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