Probiotics and Prebiotics: Concepts, Definitions and History - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 174

Office of Vaccines Research and Review (Vaillancourt 2005). They may include bacteria or
yeasts to be used in disease prevention or treatment. In parallel, the International Study Group
on New Antimicrobial Strategies (ISGNAS) has proposed the distinction between medical,
pharmaceutical and alimentary probiotics (Rusch 2002).
As many people now refer to all the previously discussed microbial applications as probiotic
treatments ( sensu lato ), it is important to be aware that the term may be used quite liberally.
7.2.2 Probiotic selection criteria
Previous researchers have published varied opinions on what are considered to be important
characteristics for the selection of probionts for applications in aquaculture (e.g. Spanggaard
et al . 2001; Gram and Ringø 2005; Balcázar et al . 2006; Vine et al . 2006; Farzanfar 2006;
Gómez and Balcázar 2008). Merrifield et al . (2010) collated such characteristics and extended
them to produce the following comprehensive list of criteria (where E indicates an essential
criterion and F indicates a favourable criterion). The probiont:
• must not be pathogenic, not only with regards to the host species but also with regards to
aquatic animals in general and human consumers (E)
• must be free of plasmid-encoded antibiotic resistance genes (E)
• must be resistant to bile salts and low pH (E)
• should be able to adhere to and/or grow well within intestinal mucus (F)
• should be able to colonize the intestinal epithelial surface (F)
• should be recognized as safe for use as a feed additive (F)
• should display advantageous growth characteristics (e.g. a short lag period, a short doubling
time and/or growth at host rearing temperatures) (F)
• should exhibit antagonistic properties towards one or more key pathogens (F)
• should produce relevant extracellular digestive enzymes (e.g. chitinase if chitin-rich ingre-
dients are to be incorporated into the diet, or cellulase if the diet is rich in plant ingredients)
and/or vitamins (F)
• should be indigenous to the host or the rearing environment (F)
• should remain viable under normal storage conditions and be robust enough to survive
industrial processes (F).
From a practical and commercial perspective, it is clearly recognized that bacterial species
from the US FDA's Generally Recognized as Safe (GRAS) list and/or the EFSA's Qualified
Presumption of Safety (QPS) list will be favourable with respect to commercialization of pro-
biotic products, as further discussed in Chapter 12 . It is clear that finding a specific microbe
that has all, or even most, of these characteristics is highly unlikely, and therefore a number of
researchers, and commercial products, have embraced the simultaneous application of a num-
ber of microbial species/strains in 'multi-species' preparations in order to extend the number
of beneficial characteristics that can be achieved with the application.
7.3 THE PREBIOTIC CONCEPT AND DEFINITION
The use of probiotics in many cases is difficult in the feed production industry because of
the low viability of the bacteria after pelleting, during storage, as well as problems with