Abstract
BackgroundStaphylococcus argenteus and S. schweitzeri, were recently proposed as novel species within S. aureus complex (SAC). S. argenteus has been reported in many countries and can threaten human health. S. schweitzeri has not been associated with human infections, but has been isolated from non-human primates. Questions regarding the evolution of pathogenicity of these two species will remain elusive until an exploratory evolutionary framework is established.ResultsWe present genomic comparison analysis among members of SAC based on a pan-genome definition, which included 15 S. argenteus genomes (five newly sequenced), six S. schweitzeri genomes and 30 divergent S. aureus genomes. The three species had divergent core genomes and rare interspecific recombination was observed among the core genes. However, some subtypes of staphylococcal cassette chromosome mec (SCCmec) elements and prophages were present in different species. Of 111 tested virulence genes of S. aureus, 85 and 86 homologous genes were found in S. argenteus and S. schweitzeri, respectively. There was no difference in virulence gene content among the three species, but the sequence of most core virulence genes was divergent. Analysis of the agr locus and the genes in the capsular polysaccharides biosynthetic operon revealed that they both diverged before the speciation of SAC members. Furthermore, the widespread geographic distribution of S. argenteus, sequence type 2250, showed ambiguous biogeographical structure among geographically isolated populations, demonstrating an international spread of this pathogen.ConclusionsS. argenteus has spread among several countries, and invasive infections and persistent carriage may be not limited to currently reported regions. S. argenteus probably had undergone a recent host adaption and can cause human infections with a similar pathogenic potential.
Highlights
Staphylococcus argenteus and S. schweitzeri, were recently proposed as novel species within S. aureus complex (SAC)
For S. aureus, the genome sizes varied from 2.74 Mb to 2.99 Mb (TW20), the GC contents varied from 32.75% (MN8) to 32.96% (LGA251), and the number of coding sequences (CDS) per genome varied from 2399 (RKI4) to 3009 (TW20) (Fig. 1)
For S. argenteus, the genome sizes varied from 2.71 Mb (M051_MSHR) to 2.87 Mb (SJTU F21285), the GC contents varied from 32.20% (M051_MSHR) to 32.42% (SJTU F21285), and the number of CDSs per genome varied from 2490 (M051_MSHR) to 2662 (SH3) (Fig. 1)
Summary
Staphylococcus argenteus and S. schweitzeri, were recently proposed as novel species within S. aureus complex (SAC). Another S. aureus lineage has recently been recovered from nonhuman primates [18, 19] and bats [20] in Africa These two genetically divergent lineages have received formal taxonomic classification and were recognized as S. argenteus and S. schweitzeri, respectively, two novel species within the S. aureus complex (SAC) [16]. Considerable difficulties were observed in amplification of some multilocus sequence typing (MLST) gene loci from S. argenteus using standard MLST primers used for typing S. aureus [7, 21]. These difficulties may result in S. argenteus isolates being excluded from or misidentified as S. aureus. There is no doubt that S. argenteus is a threat to human health
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