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

Abstract

ABSTRACT 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 a ccumulation- a ssociated p rotein (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.