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.
Highlights
Our data indicate that saprophyticus surface protein F (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
The corresponding region in S. saprophyticus ATCC 15305 is longer (26 kb) and contains an arsenic resistance operon arsRBC and a putative lipase, both absent from pSSAP2. This region is framed by two copies of the IS element IS431, which is frequently involved in the recombination-mediated integration of transposons and plasmids in methicillin-resistant S. aureus (MRSA) chromosomes [21,22]
This region is likely to be an integrative plasmid of strain ATCC 15305; positioned upstream is a truncated integrase (SSP1642), for which an intact copy can be found in the S. saprophyticus MS1146 chromosome (Figure 1)
Summary
The 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. Three cell wall-anchored proteins, featuring a conserved characteristic C-terminal LPXTG motif, have previously been identified in S. saprophyticus. These proteins (i.e. SdrI, UafA and UafB) are all involved in adhesion [7,8,9], a crucial first step in the colonisation process. S. saprophyticus possesses non-covalently surface-associated Aas [10,11]
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