Quantitative proteomic analysis of differential proteins in Streptococcus agalactiae piscine strain and human strain using iTRAQ

Zebrafish and macrophages were used as in vivo and in vitro infection models to evaluate the pathogenetic characteristics of Streptococcus agalactiae piscine strain (GD201008-001) and human strain (A909). iTRAQ and LC-MS/MS technology was used to identify differentially expressed proteins in GD201008-001 and A909, and provide new clues for exploring the pathogenic mechanism of S. galactiae strains isolated from different hosts. The pathogenetic characteristics of GD201008-001 and A909 were evaluated by analyzing LD₅₀ to zebrafish and phagocytosis of macrophages. Cellular proteins were extracted from cultures of GD201008-001 and A909, and labelled with iTRAQ reagent. Differentially expressed proteins were identified with LC-MS/MS. The mass spectrometry data was analyzed by Mascot2.2 and Proteome Discoverer1.4, and then subjected to biological information analysis of GO (gene ontology) and KEGG pathway. The result of pathogenicity difference analysis indicated that the virulence of GD201008-001 was higher than that of A909. Differentially expressed proteins were identified in S. galactiae piscine strain compared with human strain. A total of 368 differentially expressed proteins were revealed (P<0.05), among which 193 proteins were up-regulated (ratio>1.5) and 175 proteins were down-regulated (ratio<0.667) in GD201008-001. Bioinformatics analysis predicted that these proteins are mainly involved in 26 biological functions and 14 pathways. It is speculated that ClpX, GlmS and CpsIVK may play an important role in the pathogenicity of GD201008-001 and A909. These results may shed light on the pathogenic mechanism ofS. galactiae strains isolated from different hosts.