A problem which every farmer faces is the onset of disease.
Medication such as antibiotics can be used to fight infection, particularly in
young stock, however this can help further drive antibiotic resistance. Probiotics
are a means to help promote healthy growth in the selected organism, and so may
also help combat disease.
A recent paper by Skjermo et al. (2015) has looked into the previously understudied
colonisation of probiotic bacteria in the microbiota of cod larvae (Gadus morhua L), in order to determine
the most effective time to introduce the strains, and how they grow over time. Four
strains were cultivated over a period of weeks and were used to inoculate cod
larvae: Microbacterium (ID3-10), Ruegeria (RA4-1), Pseudoalteromonas (RA7-14) and Vibrio
(RD5-30). These strains were previously identified in another paper from cod intestines,
and were introduced to the live feed in the water over a period of 24 hours for
each treatment time: 0, 2, 4, 8, 16, 30, 45 days post-hatching. No repeat doses
were given.
The strains were measured using 16S rRNA sequencing and
DNA extraction of randomly selected fish, as well as real-time PCR, so that they
could be quantified and identified. The results were interesting, as only
ID3-10 was still present in significantly high amounts after 45 days, while the
other three strains were significantly less after 11, and had faded to
background levels. It was also interesting to see greater concentrations of
ID3-10 after only one day post-hatching in the larvae than in the surrounding
water or feed. This had suggested that the strain had taken hold in the gut;
however the levels soon dropped after around four days.
None of the strains could establish themselves in
the microbiota during any stage, as the levels decreased steadily. This may
have been due to the selective pressures the larvae face whilst developing, as
well as competition within the microbial community itself. These results have
shed light on how difficult it is to introduce new strains of probiotics to a
system, especially without continuous doses. Unless repeated inoculation occurs,
it is hard to create new strains within the cod larvae. It also appeared that
introducing the strains later on in larvae development yielded the best
results, however it would require intensive and continuous administration of
the probiotics, which would be labour intensive and potentially costly.
While it seems that using probiotics could be the
solution to antibiotic overuse, the problems with introducing an effective
strain to a species are yet to be solved. A few studies have provided promising
results, however this paper highlights the need for further optimisation of
these methods in order to increase the use of microbes in aquaculture. I believe
that this study has pointed out the difficulties in a way that is beneficial
and so others can build upon this research to forward this growing industry.
Skjermo, J., Bakke, I., Dahle, S.W. and
Vadstein, O., 2015. Probiotic strains introduced through live feed and rearing
water have low colonizing success in developing Atlantic cod larvae. Aquaculture, 438,
pp.17-23.
Hi Lucy, is there any mention as to why there seem to be better results when the probiotics are introduced later on in development?
ReplyDeleteDo you think it is issues with the larvae actually taking up the probiotics or could it possibly be because the 'normal' larval microbiota is still establishing itself?
Also do you think if repeat doses had been given in this experiment the results would have been different?
Hi Laura, the fact that the larvae are still adapting to other extremes at such a young stage, for example the uptake of oxygen, maybe the gut microbiota as you said is establishing itself but also is taking a backseat until the other, more important needs are taken care of. Maybe this is why the strains don't take hold until much later. I agree, repeat doses would likely see a change in the results, hopefully shifting towards more of the strains taking hold in the gut. But of course, this could just be more costly and require more optimisation; maybe if only the ID3-10 strain is used it could save on costs.
DeleteVery interesting study, it's good that there's research being done that takes into account time taken for probiotics to become established into the gut microbiota of larvae. What Laura was saying about the larval microbiota still establishing itself is a good point - there is a possibility that depending on the developmental stage of the larvae, certain probiotics may not be able to 'stay' in the gut and this causes a shift in the gut microbiota altogether. I believe there have been studies that show how at different developmental stages of shellfish, the microbiota changes - so this may answer the question as to why none of the strains could establish themselves for a reasonable time period. This would then cause problems with adding probiotics to aquaculture systems because you'd have to constantly change the mix of strains depending on the age of fish. Further studies could be done where the strains were added at different times of development, also taking into account other variables such as temperature etc. which may also change this level of establishment.
ReplyDeleteI agree with your point that the strains would need to constantly be mixed, this would be time-consuming and expensive in order to find the right amount for each stage in the life cycle. Even more frustrating would be the fact that the money that you have just spent making a specific blend of strains would not likely take hold, and you'd need to start again with the next stage of development.
DeleteAs Laura had asked, perhaps repeat doses given at different stages of development may show an improvement, so that the populations of the strains added would stand a better chance of taking hold early on. However, it may just be more cost-effective to optimise the strain that did work in some way, ID3-10, and focus on this in the future but with repeat doses.
Experimenting with different factors such as temperatures and repeated doses may yield better results, but perhaps the strains may take hold, then when exposed to variable temperatures later on in the life of the cod, would they be able to cope?