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

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 [+ or -] 10.8 nm long) are usually in a lateral position on the cells. Fibriilar ([Fib.sup.+]) and nonfibrillar ([Fib.sup.-]) 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.sup.-] cells and the less hydrophobic cells from the buffer phase entirely comprised [Fib.sup.-] cells. The [Fib.sup.+] and [Fib.sup.-] subpopulations did not revert on subculture (34 times) on solid medium. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of cell surface proteins from WT, [Fib.sup.+], and [Fib.sup.-] cells revealed two high-molecular-mass proteins (280 kDa and 230 kDa) on the WT and [Fib.sup.+] cells that were absent from the [Fib.sup.-] 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. Immunogoid staining with anti-Aap antibodies labeled tuft fibrils of the WT and [Fib.sup.+] cells but not the cell surface of Fibcells. 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.sup.+] S. epidermidis NCTC 11047 populations. Reverse transcriptionPCR showed that aap was transcribed in both [Fib.sup.+] and [Fib.sup.-] 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.