title: [Identification and detection of trag: a new infection-related gene expressed in vivo from isolates of Streptococcus suis].
abstract: OBJECTIVE
  The trag (transfer gene G) was one of the novel infection-related factors identified by in vivo-induced antigen technology (IVIAT) from Streptococcus suis type 2 expression libraries with swine convalesecent sera in our former research. We detected the distribution of trag in different Streptococcus suis isolates and identify the differential expression of the new infection-related factor between in vivo and in vitro condition.
  
  
  METHODS
  According to the sequence of trag of North American strain 89/1591, a pair of primers were designed to detect the distribution of trag in total 43 SS isolates. Another pair of primers were designed to amplify the ORF of trag of 5 SS representive strains (ZY05719, HA9801, 98012, SH040805, SH040917). Partial gene of trag was cloned and inserted into expression vector pET28a(+), and induced by IPTG to express recombinant TRAG. The recombinant protein was probed with swine convalescent sera and immune sera respectively.
  
  
  RESULTS
  The trag was detected in the most of SS2 isolates (30/32), in SS9 isolates (4/6), and 1 isolate of SS7, while it was not found in SS2 European strain ATCC43765, avirulent strain SS2 T15, 1 isolates of SS1, 1 isolates of SS1/2 and 2 isolates of group C streptococcal strains from pigs. Comparisons between the sequences of TRAG of 5 isolates with that of SS isolates, showed a high homology (>97%) with North American strain 89/1589 and China strains 98HAH33, 05ZYH33. The immunoreactivity was only presented with convalescent sera.
  
  
  CONCLUSIONS
  The trag was detected from virulent SS isolates but not from avirulent strain, which suggested that this gene may be related to the pathogenicity of SS. The special reactivity was only present with convalescent sera, and it indicated that TRAG might play a role during SS2 invasive course.
authors.affiliation: Key Laboratory ofAnimal Disease Diagnostics and Immunology of the Ministry of Agriculture, Nanjing Agricultural University, Nanjing 210095, China.
authors.forename: Haodan
authors.initials: H
authors.lastname: Zhu
authors.forename: Hongwei
authors.initials: H
authors.lastname: Gu
authors.forename: Chengping
authors.initials: C
authors.lastname: Lu
mesh_terms: D000818:Animals; D002681:China; D004195:Disease Models, Animal; D015870:Gene Expression / Q000235:genetics*; D008969:Molecular Sequence Data; D013290:Streptococcal Infections / Q000235:genetics* / Q000378:metabolism; D017011:Streptococcus suis / Q000235:genetics / Q000276:immunology / Q000472:pathogenicity; D013552:Swine