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Localized Tufts of Fibrils on Staphylococcus epidermidis NCTC 11047 Are Comprised of the Accumulation-Associated Protein

Faculty of Life Sciences, 1.800 Stopford Building, The University of Manchester, Oxford Road, Manchester M13 9PT, United Kingdom,¹ Wirral Hospital NHS Trust, Arrowe Park Hospital, Arrowe Park Road, Upton, Wirral, Merseyside LH49 5PE, United Kingdom,² Department of Microbiology, Moyne Institute of Preventative Medicine, Trinity College, Dublin 2, Ireland,³ Institut für Medizinische Mikrobiologie, Virologie und Hygiene, Zentrum für Klinische Pathologie, Universitätsklinikum Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany,⁴ Medical Microbiology and Infectious Diseases, The School of Medicine, University of Wales Swansea, Singleton Park, Swansea SA2 8PP, United Kingdom,⁵ NeuTec Pharma PLC, Clinical Sciences Building 1, Manchester Royal Infirmary, Oxford Road, Manchester M13 9WL, United Kingdom,⁶ Faculty of Life Sciences, MIB Building, North Campus, The University of Manchester, Manchester, United Kingdom,⁷ Division of Laboratory and Regenerative Medicine, School of Medicine, The University of Manchester, Clinical Sciences Building 1, Manchester Royal Infirmary, Oxford Road, Manchester M13 9WL, United Kingdom⁸

Received 30 June 2006/ Accepted 16 January 2007

Staphylococcus epidermidis is both a human skin commensal and an opportunistic pathogen, causing infections linked to implanted medical devices. This paper describes localized tufts of fibrillar appendages on a subpopulation (25%) of wild-type (WT) S. epidermidis NCTC 11047 cells. The fibrils (122.2 ± 10.8 nm long) are usually in a lateral position on the cells. Fibrillar (Fib⁺) and nonfibrillar (Fib^–) subpopulations were separated (enriched) by 34 sequential partitions of WT cells between a buffer phase and a hexadecane phase. Following enrichment, hydrophobic cells from the hexadecane phase comprised 70% Fib⁺ cells and the less hydrophobic cells from the buffer phase entirely comprised Fib^– cells. The Fib⁺ and Fib^– subpopulations did not revert on subculture (34 times) on solid medium. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of cell surface proteins from WT, Fib⁺, and Fib^– cells revealed two high-molecular-mass proteins (280 kDa and 230 kDa) on the WT and Fib⁺ cells that were absent from the Fib^– cells. Amino acid sequencing revealed that fragments of both the 280- and 230-kDa proteins had 100% identity to the accumulation-associated protein (Aap). Aap is known to cause biofilm formation if it is truncated by loss of the terminal A domain. Immunogold staining with anti-Aap antibodies labeled tuft fibrils of the WT and Fib⁺ cells but not the cell surface of Fib^– cells. The tufts were labeled with N-terminally directed antibodies (anti-A domain), showing that the fibrillar Aap was not truncated on the cell surface. Thus, the presence of full-length Aap correlated with the low biofilm-forming abilities of both WT and Fib⁺ S. epidermidis NCTC 11047 populations. Reverse transcription-PCR showed that aap was transcribed in both Fib⁺ and Fib^– cells. We therefore propose that full-length Aap is expressed on cells of S. epidermidis NCTC 11047 as tufts of short fibrils and that fibril expression is regulated at a posttranscriptional level.

Published ahead of print on 2 February 2007.

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