Chapter 18 Antimicrobial activity of lactic acid bacteria isolated from aquatic animals and the use of lactic acid bacteria in aquaculture

Abstract

This chapter focuses on the antagonistic ability of lactic acid bacteria (LAB), the effect of LAB administration on intestinal microbiota, in vivo challenge tests, and the use of commercial preparations of live LAB in aquaculture. The intestine and its associated microbiota are a complex ecosystem. Interactions and competition within the resident population, and dietary inputs, environmental conditions, and possibly the host immune system, influence the composition of the enteric community and its ability to inhibit pathogens. LAB with antagonistic activity against fish pathogens are potential candidate probiotics in future aquaculture. Numerous autogenic factors generated by some members of the GIT microbiota influence the capacity of other microorganisms to associate with epithelial surfaces. The presence of bacteria associated with mucus capable of inhibiting the growth of pathogenic bacteria, constitute a barrier against colonization and proliferation by pathogens. Techniques proposed as in vitro antagonism tests are (1) the disc diffusion method, (2) the diametric-streak technique, (3) the double-layer method, (4) liquid growth medium, and (5) the microtiter plate assay. Opportunistic infections of fish pathogens may be reduced by manipulation of the gut flora either by adding antagonistic bacteria to the diet or by dietary manipulation, in order to increase the proportion of health-promoting bacteria in the gut microflora. Further studies on how LAB can improve the disease resistance in challenge tests with pathogenic bacteria and the influence of LAB on the GIT microbiota are necessary.