Localized tufts of fibrils on Staphylococcus epidermidis NCTC 11047 are comprised of the accumulation-associated protein

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 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. Copyright © 2007, American Society for Microbiology. All Rights Reserved.