Phaeobacter inhibens as biocontrol agent against Vibrio vulnificus in oyster models

• The study investigates a new option for biocontrol of human pathogenic bacteria in molluscan shellfish.
• TDA producing Roseobacter-clade bacteria, Phaeobacter inhibens, could antagonize human pathogenic Vibrio species.
• A sterile model system simulating oysters (oyster juice) was developed.
• P. inhibens killed Vibrio. vulnificus in the oyster model system.
• P. inhibens could be established in oysters, however, numbers were too low to prevent V. vulnificus colonization.

Molluscan shellfish can cause food borne diseases and here we investigated if addition of Vibrio-antagonising bacteria could reduce Vibrio vulnificus in model oyster systems and prevent its establishment in live animals. Phaeobacter inhibens, which produces an antibacterial compound, tropodithietic acid (TDA), inhibited V. vulnificus as did pure TDA (MIC of 1–3.9 μM). P. inhibens DSM 17395 (at 106 cfu/ml) eradicated 105 cfu/ml V. vulnificus CMCP6 (a rifampicin resistant variant) from a co-culture oyster model system (oyster juice) whereas the pathogen grew to 107 cfu/ml when co-cultured with a TDA negative Phaeobacter mutant. P. inhibens grew well in oyster juice to 108 CFU/ml and sterile filtered samples from these cultures were inhibitory to Vibrio spp. P. inhibens established itself in live European flat oysters (Ostrea edulis) and remained at 105 cfu/g for five days. However, the presence of P. inhibens could not prevent subsequently added V. vulnificus from entering the live animals, likely because of too low levels of the biocontrol strain. Whilst the oyster model studies provided indication that P. inhibens DSM 17395 could be a good candidate as biocontrol agent against V. vulnificus further optimization is need in the actual animal rearing situation.