Spoilage potential of Vagococcus salmoninarum in preservative-free, MAP-stored brown shrimp and differentiation from B. thermosphacta on streptomycin thallous acetate actidione (STAA) agar

Aims

During a previous study concerning brown shrimp (Crangon crangon), selective streptomycin thallous acetate actidione (STAA) agar was used to determine the growth of Brochothrix thermosphacta. However, the growth of Vagococcus salmoninarum on this medium was also noticed. This study explores the spoilage potential of this organism when inoculated on sterile shrimp.
Methods and Results

Isolates growing on STAA were identified using (GTG)5 clustering followed by partial 16S rRNA gene sequence analysis. Their biochemical spoilage potential was analysed for H2S production and enzymatic activities were tested using an APIZYM test. Headspace solid phase micro-extraction (SPME) and gas chromatography-mass spectrometry (GC-MS) were used to analyse the volatile organic compounds (VOCs) produced during storage of inoculated shrimp.
Conclusion

Fifty-five per cent of isolates taken from STAA could be identified as V. salmoninarum, while no apparent morphological difference with B. thermosphacta isolates was identified upon the prescribed incubation conditions. For isolates identified as V. salmoninarum, production of 2-heptanone, 2-nonanone, 2-undecanone was found, as was the possibility to form H2S.
Significance and impact of the Study

When using the STAA medium for detecting B. thermosphacta, one should consider the possible abundant presence of V. salmoninarum as well. Based on this study, V. salmoninarum does not exhibit great spoilage potential, although it can produce H2S and formed VOCs which are also found in other spoiled seafood products.