Possible Probiotic Lactic Acid Bacteria Isolated from Oysters (Crassostrea gigas)

we attempted to isolate lactic acid bacteria (lab) from the marine oyster (crassostrea gigas) and selected several environmental stress-resistant isolates for the development of a future probiotic adjuvant for marine aquaculture. twenty-six presumptive lab isolates were extracted from oysters and screened (by an agar diffusion assay) for antimicrobial activity toward various pathogens: vibrio parahaemolyticus, streptococcus iniae, and edwardsiella tarda. eight isolates had an antibacterial activity toward v. parahaemolyticus; in particular, 6 isolates showed a growth-inhibitory activity, with inhibition zone diameters > 15 mm. of these, 5 isolates (jl17, jl18, jl28, hl7, and hl32) were also active against s. iniae and e. tarda. enterococcus faecium hl7 was selected as the isolate most resistant to environmental stressors: the minimum nacl, ethanol, and hydrogen peroxide concentrations at which hl7 cells lost their viability were 1.9 m, 11%, and 0.013%, respectively. when an antibiotic sensitivity test was performed on e. faecium hl7, this isolate was found to be resistant to trimethoprim/sulfamethoxazole, cephalothin, ampicillin, rifampin, gentamicin, cefotaxime, cefepime, cefotetan, nalidixic acid, and kanamycin. while the oyster model studies provided indication that e. faecium hl7 could be a good candidate as biocontrol agent against v. vulnificus, further optimization is needed in the actual animal rearing situation.