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Open Access Highly Accessed Research article

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

Nathan P King1, Türkan Sakinç24, Nouri L Ben Zakour1, Makrina Totsika1, Begoña Heras3, Pavla Simerska1, Mark Shepherd15, Sören G Gatermann2, Scott A Beatson1 and Mark A Schembri1*

Author Affiliations

1 Australian Infectious Diseases Research Centre, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia

2 Department of Medical Microbiology, Institute for Hygiene and Microbiology, Ruhr-Universität Bochum, Universitätsstr. 150, D-44780 Bochum, Germany

3 Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD 4072, Australia

4 Center for Infectious Diseases and Travel Medicine, University Medical Center Freiburg, Freiburg, Germany

5 School of Biosciences, University of Kent, Canterbury, Kent CT2 7NJ, UK

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BMC Microbiology 2012, 12:8  doi:10.1186/1471-2180-12-8

Published: 15 January 2012

Abstract

Background

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. Indeed, S. saprophyticus UTI is usually preceded by perineal skin colonisation.

Results

In 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
.
    s
aprophyticus
    s
urface 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.

Conclusions

Our 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.