Evolution of the
Staphylococcus argenteus
ST2250 Clone in Northeastern Thailand Is Linked with the Acquisition of Livestock-Associated Staphylococcal Genes
Authors: Moradigaravand Danesh , Jamrozy Dorota , Mostowy Rafal , Anderson Annaliesa , Nickerson Emma K. , Thaipadungpanit Janjira , Wuthiekanun Vanaporn , Limmathurotsakul Direk , Tandhavanant Sarunporn , Wikraiphat Chanthiwa , Wongsuvan Gumphol , Teerawattanasook Nittaya , Jutrakul Yaowaruk , Srisurat Nuttiya , Chaimanee Prajuab , Eoin West T. , Blane Beth , Parkhill Julian , Chantratita Narisara , Peacock Sharon J. 
Published: July 2017

Staphylococcus argenteus
is a newly named species previously described as a divergent lineage of
Staphylococcus aureus
that has recently been shown to have a global distribution. Despite growing evidence of the clinical importance of this species, knowledge about its population epidemiology and genomic architecture is limited. We used whole-genome sequencing to evaluate and compare
S. aureus
(
n
= 251) and
S. argenteus
(
n
= 68) isolates from adults with staphylococcal sepsis at several hospitals in northeastern Thailand between 2006 and 2013. The majority (82%) of the
S. argenteus
isolates were of multilocus sequence type 2250 (ST2250).
S. aureus
was more diverse, although 43% of the isolates belonged to ST121. Bayesian analysis suggested an
S. argenteus
ST2250 substitution rate of 4.66 (95% confidence interval [CI], 3.12 to 6.38) mutations per genome per year, which was comparable to the
S. aureus
ST121 substitution rate of 4.07 (95% CI, 2.61 to 5.55).
S. argenteus
ST2250 emerged in Thailand an estimated 15 years ago, which contrasts with the
S. aureus
ST1, ST88, and ST121 clades that emerged around 100 to 150 years ago. Comparison of
S. argenteus
ST2250 genomes from Thailand and a global collection indicated a single introduction into Thailand, followed by transmission to local and more distant countries in Southeast Asia and further afield.
S. argenteus
and
S. aureus
shared around half of their core gene repertoire, indicating a high level of divergence and providing strong support for their classification as separate species. Several gene clusters were present in ST2250 isolates but absent from the other
S. argenteus
and
S. aureus
study isolates. These included multiple exotoxins and antibiotic resistance genes that have been linked previously with livestock-associated
S. aureus
, consistent with a livestock reservoir for
S. argenteus
. These genes appeared to be associated with plasmids and mobile genetic elements and may have contributed to the biological success of ST2250.

IMPORTANCE
In this study, we used whole-genome sequencing to understand the genome evolution and population structure of a systematic collection of ST2250
S. argenteus
isolates. A newly identified ancestral species of
S. aureus
,
S. argenteus
has become increasingly known as a clinically important species that has been reported recently across various countries. Our results indicate that
S. argenteus
has spread at a relatively rapid pace over the past 2 decades across northeastern Thailand and acquired multiple exotoxin and antibiotic resistance genes that have been linked previously with livestock-associated
S. aureus
. Our findings highlight the clinical importance and potential pathogenicity of
S. argenteus
as a recently emerging pathogen.