Comparative Exoproteomics and Host Inflammatory Response in Staphylococcus aureus Skin and Soft Tissue Infections, Bacteremia, and Subclinical Colonization

Abstract

The exoproteome of Staphylococcus aureus contains enzymes and virulence factors that are important for host adaptation. We investigated the exoprotein profiles and cytokine/chemokine responses obtained in three different S. aureus-host interaction scenarios by using two-dimensional gel electrophoresis (2-DGE) and two-dimensional immunoblotting (2D-IB) combined with tandem mass spectrometry (MS/MS) and cytometric bead array techniques. The scenarios included S. aureus bacteremia, skin and soft tissue infections (SSTIs), and healthy carriage. By the 2-DGE approach, 12 exoproteins (the chaperone protein DnaK, a phosphoglycerate kinase [Pgk], the chaperone GroEL, a multisensor hybrid histidine kinase, a 3-methyl-2-oxobutanoate hydroxymethyltransferase [PanB], cysteine synthase A, an N-acetyltransferase, four isoforms of elongation factor Tu [EF-Tu], and one signature protein spot that could not be reliably identified by MS/MS) were found to be consistently present in more than 50% of the bacteremia isolates, while none of the SSTI or healthy-carrier isolates showed any of these proteins. By the 2D-IB approach, we also identified five antigens (methionine aminopeptidase [ Staphylococcus aureus is capable of causing a wide range of infections, including skin and soft tissue infections (SSTIs), bacteremia, osteomyelitis, and more. However, certain sequence types (STs) of S. aureus may better colonize and infect patients. For instance, necrotizing pneumonia or sepsis is commonly associated with ST1 of clonal cluster 1 (CC1) (1). In addition, the burden of multidrug-resistant (MDR) S. aureus renders infection control challenging in hospital settings. Furthermore, non-MDR strains may also cause severe staphylococcal infections (2-4).In S. aureus, exoproteins play a major role in virulence, particularly during invasion and host tissue damage. S. aureus produces exogenous phenol-soluble modulins that exhibit strong cytolytic activity against human neutrophils, erythrocytes, and monocytes (5). The exoprotein LukGH was recently reported to exhibit synergistic effects with Panton-Valentine leukocidin on human neutrophil lysis (6). Similarly, the exoprotein SasX facilitates intercellular aggregation and promotes biofilm formation (7). A continuous search for new S. aureus virulence factors is ongoing, and comparative exoproteomics of strains isolated from different infection types may help in the identification of additional virulence factors.Several studies have reported heterogeneous virulence gene expression in strains from different infection types and different clones (8,9). These studies also reported exoproteome heterogeneity likely due to genetic regulation, posttranslational modification, or targeted protein degradation or stabilization. Such heterogeneity complicates the identification of potential biomarkers or vaccine candidates for S. aureus.It is well known that some exoproteins are antigenic. This antigenicity has been shown in both S. aureus-infected patients and healthy carriers (10, 11). The exoproteins Hla, I...

Elongation factor Tu is a multifunctional and processed moonlighting protein

“…Notably, antibodies against Ef-Tu are induced during infections caused by Staphylococcus aureus 39 , 40 Mycoplasma capricolum 41 , Mycoplasma ovipneumoniae 37 , Chlamydia trachomatis 42 , Burkholderia pseudomallei 43 and Mycoplasma hyopneumoniae 44 . Ef-Tu has been identified in six surfacome studies (excludes cell membrane and envelope isolations) 45 – 50 performed on S. aureus and Ef-Tu is one of twelve proteins consistently identified in the exoproteome of S. aureus from patients with bacteraemia 51 . The major staphylococcal autolysin Alt is implicated in playing a role in secreting cytosolic proteins including Ef-Tu into the extracellular milieu 24 .…”

DEBS – a unification theory for dry eye and blepharitis

“…It is well known that exotoxins are extremely immunogenic, many of which are classified as super-antigens capable of activating large amounts of T cells resulting in immense release of cytokines, and thus, excessive inflammation. Important exotoxins include toxic shock syndrome toxin responsible for toxic shock syndrome, staphylococcal enterotoxins A, B, C, D, E, G, H, and I responsible for food poisoning and exfoliative toxins A and B responsible for scalded skin syndrome 39,40. The enzymes produced consist of nucleases, proteases, lipases, hyaluronidase, and collagenase, all capable of destroying host tissue 41.…”

From Immunologically Archaic to Neoteric Glycovaccines

“…Only the addition of several staphylococcal proteins leads to a protective immunity, thus raising the question of whether the T cell response elicited by a vaccine needs to be pathogen-specific [77], at least for certain pathogens. A pure protein vaccine against S. aureus is not available despite a multitude of studies [68,78,79,80]. Probably, the combination of infection proteomics [81] with PS biosynthesis will lead to successful staphylococcal vaccines.…”