Rapid evolution of virulence and drug resistance in the emerging zoonotic pathogen Streptococcus suis.
BACKGROUND
Streptococcus suis is a zoonotic pathogen that infects pigs and can occasionally cause serious infections in humans. S. suis infections occur sporadically in human Europe and North America, but a recent major outbreak has been described in China with high levels of mortality. The mechanisms of S. suis pathogenesis in humans and pigs are poorly understood.


RESULTS
The sequencing of whole genomes of S. suis isolates provides opportunities to investigate the genetic basis of infection. Here we describe whole genome sequences of three S. suis strains from the same lineage: one from European pigs, and two from human cases from China and Vietnam. Comparative genomic analysis was used to investigate the variability of these strains. S. suis is phylogenetically distinct from other Streptococcus species for which genome sequences are currently available. Accordingly, approximately 40% of the approximately 2 Mb genome is unique in comparison to other Streptococcus species. Finer genomic comparisons within the species showed a high level of sequence conservation; virtually all of the genome is common to the S. suis strains. The only exceptions are three approximately 90 kb regions, present in the two isolates from humans, composed of integrative conjugative elements and transposons. Carried in these regions are coding sequences associated with drug resistance. In addition, small-scale sequence variation has generated pseudogenes in putative virulence and colonization factors.


CONCLUSIONS
The genomic inventories of genetically related S. suis strains, isolated from distinct hosts and diseases, exhibit high levels of conservation. However, the genomes provide evidence that horizontal gene transfer has contributed to the evolution of drug resistance.
Holden
Matthew T G
MT
The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom. mh3@sanger.ac.uk
Hauser
Heidi
H
Sanders
Mandy
M
Ngo
Thi Hoa
TH
Cherevach
Inna
I
Cronin
Ann
A
Goodhead
Ian
I
Mungall
Karen
K
Quail
Michael A
MA
Price
Claire
C
Rabbinowitsch
Ester
E
Sharp
Sarah
S
Croucher
Nicholas J
NJ
Chieu
Tran Bich
TB
Mai
Nguyen Thi Hoang
NT
Diep
To Song
TS
Chinh
Nguyen Tran
NT
Kehoe
Michael
M
Leigh
James A
JA
Ward
Philip N
PN
Dowson
Christopher G
CG
Whatmore
Adrian M
AM
Chanter
Neil
N
Iversen
Pernille
P
Gottschalk
Marcelo
M
Slater
Josh D
JD
Smith
Hilde E
HE
Spratt
Brian G
BG
Xu
Jianguo
J
Ye
Changyun
C
Bentley
Stephen
S
Barrell
Barclay G
BG
Schultsz
Constance
C
Maskell
Duncan J
DJ
Parkhill
Julian
J
D000818:Animals; D004269:DNA, Bacterial / Q000235:genetics; D004196:Disease Outbreaks; D004352:Drug Resistance, Microbial / Q000235:genetics*; D016680:Genome, Bacterial; D006801:Humans; D010802:Phylogeny; D013290:Streptococcal Infections / Q000453:epidemiology / Q000382:microbiology; D017011:Streptococcus suis / Q000145:classification / Q000187:drug effects / Q000235:genetics / Q000472:pathogenicity*; D014774:Virulence / Q000235:genetics*; D015047:Zoonoses / Q000382:microbiology*
D004269:DNA, Bacterial