Impacts of salt-tolerant Staphylococcus nepalensis 5-5 on bacterial composition and biogenic amines accumulation in fish sauce fermentation.

High levels of biogenic amines (BAs) in fermented food can present a health risk to consumers. Microorganisms that can reduce BAs are widely used in fermented foods. However, the mechanism by which microorganisms reduce BAs in foods has not been explored. In this study, we investigated how Staphylococcus nepalensis 5-5 (S. nepalensis 5-5), which was a BA-degrading strain isolated from fish sauce, could reduce BA accumulation in the fish sauce. High-throughput sequencing and HPLC methods were sequentially used to determine the microbial community structure and BA content in fish sauce with/without S. nepalensis 5-5. The results showed that S. nepalensis 5-5 might be a safe strain that could improve the flavor of fish sauce while still exhibiting good BA degradation ability under a high salt environment. The content of BAs in fish sauce inoculated with S. nepalensis 5-5 was significantly decreased compared with the control fish sauce, achieving maximal reductions of 15.74, 14.18 and 16.65% in putrescine, cadaverine and histamine accumulation, respectively. According to high-throughput sequencing data, S. nepalensis 5-5 reduced the abundance of the genera positively associated with BAs, while increasing the number of bacterial genera negatively correlated with BAs in the sample and changed the correlation between some genera and BAs via species interaction. In addition, analysis of amino acid metabolism showed that S. nepalensis 5-5 might use histidine to produce metabolites other than histamine, thereby reducing the production of BAs. These findings not only explained the mechanisms by which the BA level in fish sauce could be reduced but also provided a potential means to control BA production in the fish sauce during the fermentation stage.