Isolation and screening of lactic acid bacteria associated with the gastrointestinal tracts of abalone at various life stages for probiotic candidates

Members of lactic acid bacteria (LAB) have been well-known for probiotic agents owing to their ability to produce diverse beneficial compounds for cultured species, as well as for having a status of generally recognized as safe microorganisms. Considering these facts, the current study investigated the presence of cultivable LAB associated with the gastrointestinal tracts (GIT) of hybrid abalone (Haliotis laevigata x H. rubra Brown 1992) at various life stages (larvae, juvenile, and adult), and screened them for their probiotic properties. GITs of 90 hybrid abalone (30 larvae, 30 juveniles, and 30 adult stages) were dissected out aseptically and then inoculated into de Man Rogosa Sharp (MRS) broth and agar. The result revealed that no LAB was isolated from the GITs of abalone at the larval stage. LAB were firstly recorded at the juvenile stage (44 isolates) and the adult stage (49 isolates). Based on partial sequences of the 16S rRNA gene, the 44 LAB in the juvenile stage were identified as five genera and belonged to 10 ribotypes. While the 49 LAB isolates from the adult stage were identified as three genera and belonged to eight ribotypes. Of the 93 LAB, five strains which were Enterococcus faecium MA002, Enterococcus lactis MA056, Leuconostoc mesenteroides MA064, Enterococcus lactis MA068, and Enterococcus lactis MA084, exhibited antagonistic activities against bacterial pathogens (Vibrio alginolyticus and Listeria mono- cytogenes ). The five LAB strains did not show any hemolytic activity, possibly indicating that they were non - pathogen. These results confirmed that LAB colonized the intestinal tract of abalone at juvenile and adult stages and were capable of producing antimicrobial compounds. Acknowledging the presence of indigenous LAB in GITs of abalone, a prebiotic application can be considered for another strategy to modify the healthy microbiome of abalone.