Characterization and Comparative Analysis of the Staphylococcus aureus Genomic Island v Saβ: an In Silico Approach

Abstract

With the rapid increase of available sequencing data on clinically relevant bacterial species such as S. aureus, the genomic basis of clinical phenotypes can be investigated in much more detail, allowing a much deeper understanding of the mechanisms involved in disease. We characterized in detail the S. aureus genomic island vSaβ and defined a superordinate system to categorize S. aureus strains based on their vSaβ type, providing information about the strains’ virulence-associated genes and clinical potential.

Pathogenicity and virulence of Staphylococcus aureus

“…The accessory genome also contains genomic islands (νSAα, νSAβ, νSAγ), which encode a series of virulence factors and appear to have originated from MGEs, but lost the ability to be transferred other than by non-MGE-specific modes of transfer. They are thus quite stable and so widespread that their contents can be considered characteristic for the entire species, although specific subtypes are associated with different lineages [212]. This contrasts the isolate-specific MGEs, which are often linked to specific diseases ("toxinoses") due to the encoding of the respective responsible toxins, such as TSST-1 or the food poisoning enterotoxins [210,211].…”

Staphylococcal Enterotoxin Gene Cluster: Prediction of Enterotoxin (SEG and SEI) Production and of the Source of Food Poisoning on the Basis of v Saβ Typing

“…to SFPO strains (35). Out of the 75 strains, 60 were allocated to the 15 previously defined vSaβ types (30). The remaining strains could be grouped into newly defined vSaβ types ( Figure 1).…”

“…In the pubMLST database program (41), the sequence types (STs) from the MLST were used to allocate each strain to a clonal complex (CC), for ST504 in the actual pubMLST database no corresponding CC is available, in consequence, this ST was allocated to CC705 as also described in literature (43). vSaβ islands were identified in the genome by applying the method described by Kläui et al (30). Briefly, if the vSaβ island of a strain had a sequence similarity of ≥ 90 % to the reference strain of any existing vSaβ type, it was considered of the same type (30).…”

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“…Pathogenicity islands are an example of extrachromosomal elements that possess different degree of stability. This genetic element is likely a result of phage integration into the host genome of S. aureus, which later underwent a number or recombination, as well as insertion/excision eventsand that now is considered to be stable [49]. This extrachromosomal element is the result of a horizontal gene transfer and integration into the S. aureus genome.…”

“…The lineages possessing this island demonstrate strong sequence conservation suggesting a common origin [50]. lukE and lukD represent a small fraction of the genes located on vSaβ [49], among the other genes there are different virulence factors such as serine proteases, enterotoxins, bacteriocins and a hyaluronate lyase [49].…”