Cons of Probiotics?

The use of probiotics as a therapeutic treatment for human disease and illness has long been established. Pioneered by Élie Metchnikoff in 1907, probiotics now form the basis of a multi-million, if not billion pound industry, which has now been applied in aquaculture. A vast array of literature has been published focussing on probiotics, with researchers claiming a diverse range of benefits; reduction of gastrointestinal pathology, protection of biomacromolecules from oxidative damage and improvement of the immune system, to name a few. Probiotics are can be defined as live micro-organisms which confer benefits to the host when consumed.The term, and relative definition of probiotic has been subject to much conjecture in the literature; the original definition fails to take into account the viability of the microbial consortia constituting the probiotic. It has been reported that even non-viable microbes can confer benefits to the host-organism; thus the term paraprobiotic was conceived –  non-viable microbial cells, which confer benefits to the host in sufficient amounts. Recently, Dash et al. (2015) investigated the effect of probiotics, specifically paraprobiotics on the immune response in the prawn, Macrobrachium rosenbergii.

The paraprobiotic strain, Lactobacillus plantarum was heat-killed and added to the diet of the shrimp, M. rosenbergii at three concentrations; 10⁷, 10⁸ and 10⁹ cfu g^-1 diet. These were compared to a control group of shrimp, which had no supplementation with paraprobiotics. Standard aquaculture feed trial measures, such as weight gain, growth rate, feed conversion ratio and food conversion ratios were taken at the end of the 90-day investigation period. Through extraction of haemolymph, immunological/biochemical assays were undertaken including; haemocyte counts, phenoloxidase activity, respiratory burst activity and bacterial clearance efficiency. M. rosenbergii were immune challenged with the pathogenic bacteria, Aeromonas hydrophilia.

A. hydrophilia is a problem for a diverse range of organisms (particularly crustaceans) because of their ability to produce cytoxic enterotoxins that can induce tissue damage. This bacterium is also considered to be resistant to a number of antibiotics, thus finding a way to manage infection of this bacterium, without causing deleterious changes in the host’s microflora is greatly beneficial.

Phenoloxidase activity (an antimicrobial phenol and component of the invertebrate immune system, hemocyte count, respiratory burst activity (rapid release of ROS; proxy of immune cell activity) and bacterial clearance efficiency of M. rosenbergii all increased when supplemented  with paraprobiotics. Also, reduction in mortality was observed in organisms supplemented with the paraprobiotic; those subject to higher concentrations of the paraprobiotic displayed less mortality, thus showing an increased disease resistance capacity. Little change in the growth parameters was observed throughout the investigation.

 A definitive mechanistic understanding as to how probiotics enhance immunity in invertebrates is non-existent. That said, it is evident that probiotics do provide benefits to the host particularly immunological function and disease resistance. Elucidating the host-microflora-probiotic cross-talk would be incredibly interesting and revealing, furthermore observing how this cross-talk changes in response to a number of factors, from pollutants to xenobiotics to other bacterial strains could introduce a novel use for probiotic supplementation. However, in a more ecological context, do ‘natural’ probiotics exist and have existing studies merely designated these as constituents of the microflora? 

Jack 

Dash, G., Raman, R.P., Prasad, K.P., Makesh, M., Pradeep, M.A. and Sen, S. (2015). Evaluation of paraprobiotic applicability of Lactobacillus plantarum in improving the immune response and disease protection in giant freshwater prawn, Macrobrachium rosenbergii (de Man, 1879), Fish & Shellfish Immunology, 43(1). p167-174.