Isolation and characterization of Streptococcus parauberis from vacuum-packaging refrigerated seafood products

Streptococcus parauberis is known as an etiological agent of mastitis in cows and for producing streptococcosis in farmed fish, although its presence in foods has seldom been reported. In this work, two bacterial isolates were recovered from a spoiled vacuum-packaged refrigerated seafood product. Both isolates were identified by 16S rRNA gene sequencing, exhibiting 99% homology with respect to S. parauberis. Both isolates were also characterized by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS). Genetic analysis revealed the clonal homogeneity of the isolates and their grouping together with other S. parauberis strains in a different cluster with respect to Streptococcus uberis strains. Proteomic analysis by MALDI-TOF MS allowed for the identification of five mass peaks in the range of 2200-6000 m/z that resulted to be specific to the species S. parauberis and allowed its rapid and direct identification with respect to other pathogenic and spoilage bacteria potentially present in seafood and other food products. This study represents, to our knowledge, the first report of S. parauberis in seafood in general and in vacuum-packed food products in particular. Moreover, it provides a rapid method based on MALDI-TOF MS for the identification of S. parauberis.