Training Manual Application of Genetics and Biotechnology in ...

survival. It could have been due to the probiotic effect or an effect on the water
quality by degradation of organic matter. As regards its effect as a probiotic on the
possible intestinal transience it brings about, more studies are required to be camed
out.
Results of the experiments of Moriarty (1998) suggest the Bacillus spp is
used as a biocontrol agent. The effects could possibly have been due to production of
antibiotics in relation to sporulation or during proteolysis of the vegetative cells.
The inclusion of nitrifying bacteria under the term probiotic is rather incorrect.
This concept is considered as bioremediation which is defined as "Treatment of any
waste by use of microbes that break down the undesirable substance". Other
commercial preparations of lactic acid bacteria and Streptococcus faeciunr have also
been tried in aquaculture but there is not much evidence of its ability to colonise the
gut. There has been limited success in extending the use of probiotics of terrestrial
animals to aquaculture. The survival of microbes in the gastrointestinal tract of
aquatic animals is uncertain, therefore there has been a shift in the research by
scientists who are now looking for autochthonous strains residing in the
gastrointestinal tract adhering to the mucus, as possible candidates.
Antagonism, commonly observed among marine bacteria may be mediated
by antibiotics, organic acids, hydrogen peroxide and siderophores. However, the in
vitro activity seen, should be extended to in vivo studies in order to consider it as a
probiotic. Intestinal colonization is an important potential to consider in a probiotic.
In a study, it was observed that autochthonous intestinal bacteria adhere specifically
to intestinal mucus and their adherence potential to mucus was found to be stronger
than to control surface bacteria. Yeasts are reported to have a greater ability to adhere
to intestine and colonise by specific adhesions and their application as probionts is
promising.
In conclusion one can.see the advantages of probiotics over other chemicals used
in aquaculture. It is to be expected that probiotic-resistant pathogens will emerge. To
avoid this situation, one must take care to ensure that probiotics with diversified
antagonistic properties are used. It is also important to consider the stimulation of the
immune system by the probiotic. Molecular approaches to analyze bacterial
communities in the gut may help to look at the influence of specific probiotics on the
gastrointestinal microbiota.