Probiotics: challenges and outlook

A Review of: 'Probiotics in Aquaculture: Challenges and Outlook'. 2008. By Wang, Li and Lin. Aquaculture 281, pp. 1-4

Many modern aquaculture operations require hydrobionts to be cultured at high densities, resulting in elevated stress levels, disease and deterioration of environmental conditions, leading to economic losses. In recent decades, disease prevention and control have led to substantial increase in the use of chemical additives and Vetinary medicines, however their wide spread use is now recognized as causing environmental problems and so the need for alternative techniques is increasing. The contribution of probiotics is considerable and widely accepted, having been introduced to molluscan, shrimp and fish farming as feed additives.

Intensified research efforts in recent years confirm the importance of microbials in the digestive tract. Compared to water, the digestive tract of hydrobionts is an ecosystem far richer in nutrients and therefore more favorable for growth of the majority of bacteria. Gastrointestinal bacteria take part in the decomposition of nutrients, provide the macroorganisms with physiologically active materials, such as enzymes, amino acids, and vitamins, and play an  important role in the resistance to infectious diseases, producing antibacterial materials pathogenic to 'harmful' bacteria. Antiviral effects have also been reported although the exact mechanism by which these bacteria do this is not known.

To be effective and confer health benefits, probiotic cultures must be able to retain their probiotic properties after processing, and with sufficient numbers surviving during shelf life/ storage for efficacy. The retention of high viability during preparation and storage presents particular challenges and can be regarded as a ‘major bottleneck’ in commercial probiotic production. Stability is also critical to guarantee the efficacy and can be influenced by various factors, including species, strain biotype, water activity, temperature, pH, osmotic pressure, mechanical friction and oxygen. Consequently, special attention and techniques are needed during probiotic production.

Safety considerations have been neglected for a long time but are now taken into account for the development and marketing of probiotics: new strains are carefully assessed and evaluated for both safety and efficacy prior to incorporation into products and not assumed to share the historical safety of tested or traditional strains. The safety profile of a potential probiotic strain is of critical importance in the selection process and its testing should include the determination of strain resistance to a wide variety of common classes of antibiotics such as quinolones and macrolides, and subsequent confirmation of non-transmission of drug resistance genes of virulence plasmids. Modern molecular techniques should be applied to ensure that the species of probiotics used in aquaculture are correctly identified, for quality assurance as well as safety.

I thought this was a great little paper. The authors clearly support the use and need for probiotics in aquaculture especially instead of antibiotics. However they are clearly concerned about a few main points and discuss them clearly, such as their safety, thorough testing before application and the growing need to further identify the mechanisms by which they work and further understanding of the composition and interactions that occur between the microbial populations in the GI tract.

[Could be quite a useful paper for an exam question asking for a critical evaluation of probiotics??]