Genetic diversity of Staphylococcus aureus wall teichoic acid glycosyltransferases affects immune recognition

Abstract

Staphylococcus aureus (S. aureus) is a leading cause of skin and soft tissue infections and (hospital-acquired) systemic infections. Wall teichoic acids (WTAs) are cell wall-anchored glycopolymers that are important for S. aureus nasal colonization, endocarditis, and antibiotic resistance. WTAs consist of a polymerized ribitol phosphate (RboP) chain that can be glycosylated with N-acetylglucosamine (GlcNAc) by three glycosyltransferases: TarS, TarM, and TarP. TarS and TarP modify WTA with β-linked GlcNAc on the C-4 (β1,4-GlcNAc) and the C-3 position (β1,3-GlcNAc) of the RboP subunit, respectively, whereas TarM modifies WTA with α-linked GlcNAc at the C-4 position (α1,4-GlcNAc). Importantly, these WTA glycosylation patterns impact immune recognition and clearance of S. aureus. Previous studies suggest that tarS is near-universally expressed within the S. aureus population, whereas a smaller proportion co-express either tarM or tarP. To gain more insight in the presence and genetic variation of tarS, tarM, and tarP in the S. aureus population, we analyzed a collection of 25,652 S. aureus genomes within the PubMLST database. Over 99% of isolates contained tarS. Co-expression of tarS/tarM or tarS/tarP occurred in 37% and 7% of isolates, respectively, and was associated to specific S. aureus clonal complexes. We also identified 26 isolates (0.1%) that contained all three glycosyltransferase genes. At sequence level, we identified tar alleles with amino acid substitutions in critical enzymatic residues or with premature stop codons. Several tar variants were expressed in a S. aureus tar-negative strain. Analysis using specific monoclonal antibodies and human langerin showed that WTA glycosylation was severely attenuated or absent. Overall, our data provide a broad overview of the genetic diversity of the three WTA glycosyltransferases in the S. aureus population and the functional consequences for immune recognition.

Glycan-specific IgM is critical for human immunity toStaphylococcus aureus

“…In this study, we conducted antibody profiling of glycosylated S. aureus RboP-WTA, a prominent glycopolymer expressed by nearly all S. aureus strains (20,28). For this work, we took advantage of synthetic glycosylated RboP-WTA oligomers, which resemble bacteria-expressed WTA as previously confirmed by WTA-specific monoclonal antibodies and recognition by the C-type lectin receptor langerin (15,29).…”

“…Since IgM-mediated complement activation is not affected by SpA and plays a critical role S. aureus killing (figure 2), we hypothesized that impaired bacterial opsonization due to low WTA-specific IgM responses could contribute to this association. To align the patient's antibody response with the WTA glycoprofile of the infecting S. aureus strain, we determined the genetic presence of tar glycosyltransferases and the pattern of WTA glycoslyation in available clinical isolates (20).…”

“…Confirmation of the expressed glycoprofile with GlcNAc-WTA specific Fab fragments is key, since we have recently shown that some S. aureus strains harbor inactivating mutations of the encoded Tar enzymes (20). We obtained original isolates from eight patients within the S. aureus ICU cohort; four that survived the infection (patient 4, 10, 18 and 27) and four that passed away in the ICU (patient 12, 16, 20 and 35).…”

“…Three WTA glycotypes have been identified, each requiring a dedicated glycosyltransferase enzyme (TarM, TarS or TarP) to add the GlcNAc to the ribitol phosphate WTA backbone subunits in an 1,4-(TarM), 1,4-(TarS) or 1,3-(TarP) position (17)(18)(19). All S. aureus isolates possess the tarS gene, while approximately 40% of strains co-express tarM or tarP (20). The specific WTA glycoprofile of a particular S. aureus strain is determined by the presence of corresponding tar genes, enzymatic activity, and environmental conditions, leading to glycovariation (21).…”