Characterisation of a cell wall-anchored protein of Staphylococcus saprophyticus associated with linoleic acid resistance

Abstract

BackgroundThe Gram-positive bacterium Staphylococcus saprophyticus is the second most frequent causative agent of community-acquired urinary tract infections (UTI), accounting for up to 20% of cases. A common feature of staphylococci is colonisation of the human skin. This involves survival against innate immune defenses including antibacterial unsaturated free fatty acids such as linoleic acid which act by disrupting bacterial cell membranes. Indeed, S. saprophyticus UTI is usually preceded by perineal skin colonisation.ResultsIn this study we identified a previously undescribed 73.5 kDa cell wall-anchored protein of S. saprophyticus, encoded on plasmid pSSAP2 of strain MS1146, which we termed S. saprophyticus surface protein F (SssF). The sssF gene is highly prevalent in S. saprophyticus clinical isolates and we demonstrate that the SssF protein is expressed at the cell surface. However, unlike all other characterised cell wall-anchored proteins of S. saprophyticus, we were unable to demonstrate a role for SssF in adhesion. SssF shares moderate sequence identity to a surface protein of Staphylococcus aureus (SasF) recently shown to be an important mediator of linoleic acid resistance. Using a heterologous complementation approach in a S. aureus sasF null genetic background, we demonstrate that SssF is associated with resistance to linoleic acid. We also show that S. saprophyticus strains lacking sssF are more sensitive to linoleic acid than those that possess it. Every staphylococcal genome sequenced to date encodes SssF and SasF homologues. Proteins in this family share similar predicted secondary structures consisting almost exclusively of α-helices in a probable coiled-coil formation.ConclusionsOur data indicate that SssF is a newly described and highly prevalent surface-localised protein of S. saprophyticus that contributes to resistance against the antibacterial effects of linoleic acid. SssF is a member of a protein family widely disseminated throughout the staphylococci.

Coagulase-Negative Staphylococci Pathogenomics

“…They also identified a unique uro-adaptative transport system and urease production as the two other factors that could be linked to the specific pathogenicity of S. saprophyticus . Since 2005, whole-genome virulence studies have been lacking, but adherence and persistence onto the urinary tract have been confirmed as the main factors that could be linked to pathogenicity [ 81 , 82 , 83 ]. Overall, S. saprophyticus , lacks many of the adhesion proteins and other virulence factors that have been identified in CoNS from the S. epidermidis group, S. caprae , and S. lugdunensis , which probably explains the differences that are observed at a clinical level.…”

Staphylococcus aureus Fibronectin-Binding Protein A Mediates Cell-Cell Adhesion through Low-Affinity Homophilic Bonds

“…In earlier work, the distribution of adhesins was mapped on the surface of staphylococcal cells. Immunogold electron microscopy was used to study the distribution of SssF and UafB adhesins on Staphylococcus saprophyticus ( 26 , 27 ). While the authors claimed that there was abundant labeling, the density was lower than that here, an effect that may reflect actual differences between species or variations in the sensitivity of the techniques.…”

Gram-Positive Uropathogens, Polymicrobial Urinary Tract Infection, and the Emerging Microbiota of the Urinary Tract

“…The first sequenced S. saprophyticus strain ATCC 15305 encodes only one sortase substrate on its chromosome, UafA [78]. S. saprophyticus MS1146 encodes UafA, as well as UafB and SssF, on two different plasmids [79, 80]. SdrI was characterized on the unsequenced S. saprophyticus 7108 [81].…”

“…Plasmid-encoded SssF is highly conserved among S. saprophyticus strains, is involved in resistance to linoleic acid, but does not play a role in uropathogenesis in a murine model. Instead, SssF has been postulated to be important prior to urethral exposure, in biological niches such as the perineum or periurethral area where polyunsaturated fatty acids such as linoleic acid are particularly abundant [80]. …”