Screening and selection of stress resistant Lactobacillus spp. isolated from the marine oyster (Crassostrea gigas)

We attempted to isolate Lactobacillus spp. from the marine oyster (Crassostrea gigas) and select stress resistant strains for development of a future marine aquaculture feed adjuvant. A total of 83 lactobacilli strains were isolated from oyster. They were all Gram-positive, rod-shaped and catalase-negative. By performing a stress resistance assay, we selected eighteen isolates. Based on 16S rRNA gene sequencing, Lactobacillus paracasei was the most prevalent species among the selected isolates. The in vitro antagonistic effect of the selected strains against fish pathogens was assayed by measurement of inhibition diameters. Except for MH44, MH51, MH53 and MH62, most of the isolates showed inhibition of Vibrio alginolyticus and Vibrio proteolyticus (diameters over 15 mm). Lactobacillus rhamnosus MH22 was selected as the most stress resistant strain showing the MICs of 1.8 M NaCl, 14% ethanol and 0.014% hydrogen peroxide. L. rhamnosus MH22 isolated from oyster has a potential to be applied as a microbial feed adjuvant for marine aquaculture.