Clinical, experimental, and genomic differences between intermediately pathogenic, highly pathogenic, and epidemic Streptococcus suis.
BACKGROUND
Streptococcus suis emerged to cause an unusual outbreak of streptococcal toxic-shock-like syndrome (STSLS) in 2005. The mechanisms involved are unknown.


METHODS
Clinical, laboratory, and epidemiologic data on patients infected with culture-confirmed S. suis were analyzed. The strain involved in the outbreak, "epidemic" strain ST7, was compared with both a classical highly pathogenic strain, ST1, and an intermediately pathogenic strain, ST25, to determine both its capacity to induce cytokines in experimentally infected mice and its genomic difference.


RESULTS
Of 38 patients infected with culture-confirmed S. suis, 14 presented with STSLS. During the early phase of the disease, serum levels of interleukin (IL)-1beta, IL-6, IL-8, IL-12p70, interferon-gamma, and tumor necrosis factor-alpha were more elevated in patients with STSLS than in those with meningitis only. Serum levels of proinflammatory cytokines were significantly higher in mice infected with ST7 than in those infected with either ST1 or ST25. Genomic comparisons with ST25 showed that ST1 had acquired 132 genomic islands, including 5 pathogenicity islands, and that ST7, the epidemic strain, had acquired an additional 5 genomic islands.


CONCLUSIONS
Intermediately pathogenic strain ST25 has evolved to become highly pathogenic strain ST1, which, in turn, has more recently evolved to become epidemic strain ST7. ST7 has the ability to stimulate the production of massive amounts of proinflammatory cytokines, leading to STSLS.
Ye
Changyun
C
State Key Laboratory for Infectious Disease Prevention and Control, China.
Zheng
Han
H
Zhang
Ji
J
Jing
Huaiqi
H
Wang
Lei
L
Xiong
Yanwen
Y
Wang
Wei
W
Zhou
Zhemin
Z
Sun
Qiangzheng
Q
Luo
Xia
X
Du
Huamao
H
Gottschalk
Marcelo
M
Xu
Jianguo
J
D002681:China / Q000453:epidemiology; D004196:Disease Outbreaks / Q000706:statistics & numerical data; D016680:Genome, Bacterial; D006801:Humans; D013290:Streptococcal Infections / Q000097:blood / Q000453:epidemiology* / Q000401:mortality / Q000503:physiopathology; D017011:Streptococcus suis / Q000235:genetics* / Q000472:pathogenicity*; D016019:Survival Analysis; D017741:Survivors; D014774:Virulence