A review of: Periera, C. et al (2011) Bacteriophages with Potential for Inactivation of Fish Pathogenic Bacteria: Survival, Host Specificity and Effect on Bacterial Community Structure, Marine Drugs, 9: 2236-2255.
The aquaculture industry is very fast-growing, with an average 6% increase in production per year reported over the last decade, but incidences of disease caused by pathogenic bacteria have led to great financial losses. Solutions to this problem have included the use of vaccinations and antibiotics, but these are not without their drawbacks. Vaccinations are of limited use owing to the range of different diseases present in a variety of fish species, and overuse of antibiotics has led to the emergence of multidrug resistant bacteria.
Previous studies have shown that the use of bacteriophages to control bacterial disease in fish aquaculture has great potential, but the success of phage therapy depends upon the ability of the viruses to survive and remain infective in the water, and their effects on non-pathogenic bacteria, which have an important role in aquaculture, particularly in semi-intensive systems.
The aim of the study was to isolate Aeromonas salmonicida phages (AS-1) and Vibrio parahaemolyticus phages (VP-1) and investigate their survival, specificity, and impact on natural bacterial communities within a semi-intensive system in Ria de Aveiro, on the North-Western coast of Portugal.
Analysis of the host range of the phages showed that AS-1 was also able to infect Vibrio anguillarum (98.87% efficacy) and V. parahemolyticus (96.03%), and VP-1 also infected V. anguillarum (83.27%) as well as A. salmonicida (64.75%).
Survival of the phages was determined using quantification through the soft agar overlay technique. AS-1 phage had a survival period of 91 days, whereas the survival period of VP-1 was much lower, at 16 days.
Analysis of DGGE profiles of PCR-amplified 16s rRNA gene fragments showed that bacterial ribotype diversity was not significantly altered by the addition of the phages to aquaculture water samples, after ten hours of incubation.
As fish aquaculture continues to grow and concerns about the widespread use of antibiotics within the industry increase, it is important that viable alternatives are found to control disease caused by pathogenic bacteria. The two bacteriophages isolated in this study show long term viability and an ability to infect a range of hosts without having a detrimental effect on natural bacterial communities. The results of the study suggest that more research should be conducted in order to devise an effective combination of phages for use in phage therapy. The authors also point out that owing to the seasonal variation within bacterial communities, careful monitoring should take place so suitable phages are selected.
7 comments:
Hi Helen. Just curious when you say that "bacterial ribotype diversity was not significantly altered by the addition of phages" is this only refering to the bacterial communities not targeted by the phages? Also does the paper go on to talk about changes in bacterial community structure beyond the 10 hour mark? If the phages are capable of surviving for much longer periods I would have assumed that they would still have some impact on the bacteria.
Hi Dave, yes I should have clarified that the effect on ribotype diversity referred to the non-pathogenic bacterial community, which is not targeted by the phages, thanks for pointing that out.
The authors did not investigate changes in community structure beyond 10 hours of incubation, but they did point out that more extensive studies should be performed. They also suggested that because phages are both self-replicating and self-limiting, their abundance will increase and decrease along with bacterial abundance, implying that their will be little ecological impact. The paper briefly mentioned the implications of seasonal variation, and the paper you just reviewed seems to follow on nicely from this one. I hope you manage to find the next paper, I am sure it will make an interesting read.
Thanks Helen, it would be very interesting to see the results of a long term study.
I have had another look for this follow up paper but no luck......I will keep looking though.
Hey Helen I found the paper! I started reading it and it sounded very familiar.......then I realised it was the paper that you have just reviewed here. That is obviously why they went so nicely together.
Hey Helen I found the paper! I started reading it and it sounded very familiar.......then I realised it was the paper that you have just reviewed here. That is obviously why they went so nicely together.
Oh ok, how funny...that makes sense now!
Hopefully they will do some more studies as it would still be nice to see results of a long term study.
Hi Helen, I'm guessing that this subject has been an irritating and recurrent problem for applied marine microbiologists for years. I guess that, even though antibiotics and phage are effective when treating disease, the way in which antimicrobial agents are applied and the way the environment is managed could prove most important. One major concern when investigating the use of antibiotics is that, in many cases, the most effective antibiotics are those that also impact on the bacterial community. This bacterial community may be important in outcompeting more opportunistic pathogens that may cause disease when commensal organisms are affected. Also, even though phage treatment would be more selective for the pathogen, misuse would still confer resistance in pathogens over time as seen with antibiotic use. Therefore, as you pointed out, the use of multiple specific phage alongside, in my opinion, more specific antibiotics targeting the same pathogen would be a major breakthrough in treating not only aquaculture but natural environments such as reefs and lakes. However, one thing that would make treating aquaculture more effective is seasonality. The commercial nature of aquaculture would lead to less extreme conditions found in nature with more optimum environments maintained for longer periods of time allowing bacterial community diversity to remain constant.
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