Monday, 31 March 2014

The potential of Lactic Acid Bacteria for use as probiotics in aquaculture

Aquaculture is important, obviously. It has the potential to make a significant contribution to the ever increasing demand for seafood worldwide. However it faces many problems, one of which is disease control. The widespread use of antibiotics as a disease control measure has lead to the emergence of antibiotic-resistant pathogens, and has thus lead to a ban in Europe and more stringent regulations worldwide. Alternative methods of disease control have included better husbandry practices, vaccinations, immunostimulants, use of bacteriophages to target pathogens, quorum sensing disruption, prebiotics and probiotics.

Recently, a probiotic culture has been authorised for the first time for use in aquaculture by the EU, using Pediococcus acidilactici, a LAB. For a bacterium to be deemed safe for use as a feed additive in the EU, it must receive Qualified Presumption of Safety (QPS) status, show an absence of resistance to human and veterinary antibiotics, and also prove its effectiveness in its intended use in the food chain. Most LAB have already received QPS status, demonstration of their suitability as aquaculture probiotics therefore only requires proof of their antimicrobial activity against fish pathogens and a lack of resistance to antibiotics, this was the aim of this study.

Lactic Acid Bacteria (LAB) are a clade of bacteria grouped together for their common metabolic characteristics. Currently, strains of LAB are the most commonly used bacteria in human probiotics, specifically members of the genera Lactobacillus and Bifidobacterium. In this study, 99 LAB strains were isolated from fish, seafood and fish products, 59 enterococci and 40 non-enterococci. Their antimicrobial activity was tested against 8 indicator fish pathogens. They were also tested for antibiotic resistance against 8 antibiotics, and those that do not already possess QPS status were tested for virulence factors and detrimental enzymatic activity.

They found that every species tested showed antimicrobial activity against at least 4 of the 8 fish pathogens, which is a very successful result, the majority showed resistance against 5-7 pathogens. However, genus-specific safety concerns were highlighted by antibiotic resistance tests and virulence factor tests. Antibiotic resistance was found in 60% of Weisella, 44% of Pediococcus and 33% of Lactobacillus. 86% of Enterococcus were found to be unsafe due to resistance or virulence factors. Of the non-enterococci LAB, only 7.5% showed antibiotic resistance. There were several examples of resistances being described for the first time in certain genera. Detrimental enzymatic activity was described in some two Enterococcus species, such as gelatinase activity and haemolytic activity. No genera showed bile deconjugation, mucin degradation or other detrimental enzymatic activity.

The main use of this study is as large-scale preliminary selection of safe LAB species, to identify and select the most suitable candidates to be further evaluated as probiotics for aquaculture. They also described novel antibiotic resistances and virulence factors in a range of LAB species. Ultimately they have shown that antimicrobial activity against fish pathogens is a widespread property of Lactic Acid Bacteria, that many species show resistance to antibiotics, but there are many other species that are perfectly safe and would be potential candidates for use as probiotics in aquaculture.

Muñoz-Atienza, E., Gómez-Sala, B., Araújo, C., Campanero, C., Del Campo, R., Hernández, P. E., ... & Cintas, L. M. (2013). Antimicrobial activity, antibiotic susceptibility and virulence factors of Lactic Acid Bacteria of aquatic origin intended for use as probiotics in aquaculture. BMC microbiology13(1), 15.


  1. The paper of my post on characterising fish gut microbiota seemed to condemn the use of lactic acid bacteria in fish probiotics, because the most prevalently used ones are those isolated from terrestrial mammals. But perhaps there are lactic acid bacteria found in the normal microbiota of fish.
    Seems like developing aquaculture probiotics is a long, difficult process; you have find the right strain with exactly the right properties to fit the legislature and the host's need.

    1. All of the LABs tested in this study were isolated from fish, seafood or fish products, and so are likely found in the normal microbiota of fish. Perhaps the paper you reviewed was arguing against the use of LABs used for human probiotics in aquaculture?
      It does seem difficult, if you begin with 99 LAB strains and insert them into a venn diagram selecting for beneficial qualities, safety for humans, safety for animals and the environment, viability as a probiotic and viability for industrial production, you may just have 1 LAB strain that fits all the criteria. Hopefully this study has taken the first step in narrowing the field.