The probiotic potential against vibriosis of the indigenous microflora of rainbow trout

Abstract

The antibacterial properties of the indigenous microflora of rainbow trout (Oncorhynchus mykiss Walbaum) and the potential use of inhibitory bacteria as fish probiotics were investigated. A total of 1018 bacteria and yeasts were isolated on tryptone soy agar (TSA) from skin, gills and intestine. Forty-five of these inhibited growth of the fish pathogenic bacterium Vibrio anguillarum in a well diffusion assay. The antagonism was most prominent among Pseudomonas spp., as 28 (66%) of the antagonistic bacteria belonged to this genus, despite constituting only 15% of the total tested flora. As pseudomonads are typically siderophore producers, chrome azurol S (CAS) agar was used as a semi-selective medium for isolation of antagonistic bacteria. On this medium, 75% of the iron-chelating strains were inhibitory to V. anguillarum. Eight strains out of a subset of 11 antagonists caused a 3-6 log unit reduction in the density of V. anguillarum [measured by polymerase chain reaction (PCR) detection in a most probable number (MPN) regimen] in a broth co-culture assay. Survival of rainbow trout infected with vibriosis was improved 13-43% by six out of nine antagonistic strains tested in vivo. All disease-protecting strains were pseudomonads, isolated from CAS plates, whereas two Carnobacterium spp. that were antagonistic in in vitro well diffusion assays did not alter the accumulated mortality of rainbow trout. The addition of live bacterial cultures to fish-rearing water may thus improve survival of the fish; however, in vitro antagonism could not completely predict an in vivo effect. Further studies on the underlying mechanism of activity are required to design appropriate selection criteria for fish probiotic bacteria.

Elucidating the Probiotic Potential of Malaysian Paenibacillus pabuli Against Vibrio alginolyticus in Artemia Culture

“…1). This finding was in accordance with a previous study reported by Spanggaard et al (2001), which showed that a complete inhibition was discovered in V. anguillarum growth when co-cultured in TSB with five strains (E174, E156, AH2 and E102) of antagonistic Pseudomonas isolated from rainbow trout. Conversely, they also reported that two out of three respective Pseudomonas strains and Carnobacterium strains D4 and D5 were not able to inhibit target strains in M9GC broth and TSA diffusion assay, thus suggesting that substrate compositions significantly influenced the production of secondary metabolites.…”

Gnotobiotic zebrafish reveal evolutionarily conserved responses to the gut microbiota

“…For example, Lactococcus lactis and Pseudomonas spp. can inhibit growth of Vibrio anguillarum (55,56). Because of the absence of an adaptive immune response during the larval-juvenile stages in zebrafish, incorporation of these bacterial species into the gut microbiota may be important for maintaining their health during this free-living period.…”

An Overview of the Immunological Defenses in Fish Skin

“…This definition is being constantly refined. Probiotics are associated with healthpromoting properties [320,321] and also with other benefits [322,323]. However, in aquaculture systems the interaction between the microbiota and the host is not limited to the intestinal tract, and given the nature of fish farming and the fact that water harbours microbial communities, a distinctive definition of probiotic for aquatic animals is accepted [324].…”