Tracking spoilage bacteria in the tuna necrobiome

International audienceLike other seafood products, tuna is highly perishable and sensitive to microbial spoilage. Its consumption, whether fresh or canned, can lead to severe food poisoning due to the presence of histamine-producing bacteria and other specific spoilage organisms (SSOs) found in the tuna microbiome. Such bacteria generally develop in dead fish after their capture if conservation conditions are deficient. However, many grey areas persist regarding their ecology, their conditions of emergence and proliferation, and their distribution within different organs. In this study, we used 16S rDNA barcoding to investigate post-mortem changes in the tuna necrobiome until the advanced stages of decomposition (i.e. 120 h). The analyses were performed on fresh and brine-frozen yellowfin tuna (Thunnus albacares) captured in the tropical Atlantic Ocean. The results revealed that despite standard refrigeration storage conditions (i.e. 4°C), a diverse and complex spoilage bacteriome continued to develop in the gut and liver. In general, the relative abundance of SSOs increased rapidly in both organs, representing 82% of the bacterial communities in fresh yellowfin tuna, and less than 30% in brine-frozen ones. Interestingly, Photobacterium was identified as a major bacterial genus, and its temporal dynamics were positively correlated with histamine concentrations, which ultimately, in fresh tunas, exceeded the recommended sanitary level of 50 ppm established by the United States Food and Drug Administration. Finally, the study of the tuna necrobiome shows that the sanitary risks associated with the consumption of this widely eaten fish is strongly influenced by the post-capture storage conditions