Abstract
BackgroundStreptococcus suis serotype 2 (SS2) is a zoonotic agent that causes death and disease in both humans and swine. A better understanding of SS2-host molecular interactions is crucial for understanding SS2 pathogenesis and immunology. Conventional genetic and biochemical approaches used to study SS2 virulence factors are unable to take into account the complex and dynamic environmental stimuli associated with the infection process. In this study, in vivo-induced antigen technology (IVIAT), an immunoscreening technique, was used to identify the immunogenic bacterial proteins that are induced or upregulated in vivo during SS2 infection.ResultsConvalescent-phase sera from pigs infected with SS2 were pooled, adsorbed against in vitro antigens, and used to screen SS2 genomic expression libraries. Upon analysis of the identified proteins, we were able to assign a putative function to 40 of the 48 proteins. These included proteins implicated in cell envelope structure, regulation, molecule synthesis, substance and energy metabolism, transport, translation, and those with unknown functions. The in vivo-induced changes in the expression of 10 of these 40 genes were measured using real-time reverse transcription (RT)-PCR, revealing that the expression of 6 of the 10 genes was upregulated in the in vivo condition. The strain distribution of these 10 genes was analyzed by PCR, and they were found in the most virulent SS2 strains. In addition, protein sequence alignments of the newly identified proteins demonstrate that three are putative virulence-associated proteins.ConclusionCollectively, our results suggest that these in vivo-induced or upregulated genes may contribute to SS2 disease development. We hypothesize that the identification of factors specifically induced or upregulated during SS2 infection will aid in our understanding of SS2 pathogenesis and may contribute to the control SS2 outbreaks. In addition, the proteins identified using IVIAT may be useful potential vaccine candidates or virulence markers.
Highlights
Streptococcus suis serotype 2 (SS2) is a zoonotic agent that causes death and disease in both humans and swine
Sera selection and adsorption in vivo-induced antigen technology (IVIAT) depends on the presence of antibodies directed against pathogen antigens expressed in vivo, so the selection of convalescent sera for use in IVIAT must be carefully considered
When we determined the locations of the 48 in vivo-induced (IVI) genes identified by IVIAT, we found five IVI genes located in four pathogenicity islands in SS2 reference strain P1/7
Summary
Streptococcus suis serotype 2 (SS2) is a zoonotic agent that causes death and disease in both humans and swine. Streptococcus suis (S. suis) infections have been considered a major problem in the swine industry worldwide, over the past 20 years. S. suis is a gram-positive, facultatively anaerobic coccus, and 35 serotypes (1-34 and 1/ 2) have been described based on their capsular antigens. Serotype 2 (SS2) is the causative agent of many different syndromes worldwide, including meningi-. Two recent large-scale outbreaks of human streptococcal toxic shock syndrome (STSS) caused by SS2 in China in 1998 and in 2005 have increased public health concerns worldwide. A total of 215 cases of human S. suis infection were reported, and the outbreak resulted in 38 deaths and massive economic losses [4,5]
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