Karunasagar, I., Shivu, M.M., Girisha, S.K., Krohne, G., Karunasagar, I., 2007. Biocontrol of pathogens in shrimp hatcheries using bacteriophages. Aquaculture. 268, 288–292
Luminous Vibrio harveyi cause most of the mass mortalities in larval stages of shrimp, Penaeus monodon. Antibiotics are no longer an option for controlling disease in aquaculture, therefore new technologies are being developed. Bacteriophages have a potential to control bacterial pathogens. The authors of this paper are the first to explore this.
Twenty different V. harveyi isolates obtained from shrimp hatchery water, shrimp farm water, shrimp larvae and coastal seawater were used as hosts for isolation of bacteriophages. An area of lysis at an inoculated spot, on a lawn culture, indicated susceptibility of the host to the bacteriophage. Further a V. harveyi biofilm was developed on high-density polyethylene (HDPE) template. Experimental trials were carried out in triplicate to determine the effect of the bacteriophage on the biofilm. Treatment of 105, 106 , 107 and 108 pfu ml−1 of bacteriophage was given at 12 and 18 h to study the effect of repeated phage treatment. The most effective phages were then also tested in a hatchery system.
The bacteriophages isolated had a broad host range, lysing around 55–70% of the V. harveyi strains obtained from diverse environments. It was observed that most of the strains that were not lysed by one particular bacteriophage (Viha10) were lysed by another (Viha8) and using a combination of these phages, 94% of the strains could be lysed. This suggests that biocontrol of V. harveyi is possible using a combination of bacteriophages. Electron microscopy revealed that both the phages were members of Siphoviridae.
One of the strategies used by V. harveyi to survive in hatchery environments is to form biofilms. Studies have shown that antibiotics are less effective on biofilms and therefore new treatments are required. Treatment of the biofilm in this study, with 108 pfu ml−1 bacteriophage Viha10 led to 1 log reduction in bacterial numbers at 6 h and 3 log at 18 h. The effect of the bacteriophage was clearly dose dependent. It has been suggested that phage may produce polysaccharide lyases that remove polysaccharide from a biofilm, which is important in biofilm architecture. Other studies by these authors have shown production of polysaccharides by V. harveyi in biofilms using ruthenium red staining. The results of the phages added to shrimp hatcheries are promising giving increases in survival over 20% more than antibiotic treatments.
So overall this study is one of the first to discover that we can also potentially use bacteriophages to protect aquaculture from disease. Of course using bacteriophages could be dangerous as they can mutate quickly and may add to the virulence of the pathogen. However the hatchery trials showed that the bacteriophages used in this study are not associated with virulence of V. harveyi but are effective in controlling the populations of these bacteria in hatchery systems.
3 comments:
Great post as always Alice. I am currently reading a paper on bacteriophages and they are really praising the use of them to control bacterial pathogens. When you say that the bacteriophages could mutate and "add to the virulence of the pathogen". Does this mean they would change their target and possibly attack other bacteria that could be beneficial?
The paper I am reading is from 2011 and it suggests that some of the greatest aspects of the bacteriophage control are that they are species specific and self-limiting two things that would make them very safe for use in aquaculture. Possibly this is because of new discoveries of more effective bacteriophages. What do you think?
Thankyou :). That is true that bacteriophages are very species specific, that is shown by some strains being lysed by one bacteriophage but not by another in this experiment. I was just thinking that some bacteriophages cut and paste DNA into bacteria which could add virulence factors but looking back i dont think that is how these ones work. They may mutate and attack other bacteria but im not sure how long the added bacteriophages remain.
I just did a quick search on bacteriophage longevity and it seems that it varies considerably so maybe some species could be capable of causing this problem. It is also possible that becuase of bacteriophages ability to self-replicate it could make this problem realistic even if they do not remain for long period.
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