Conlon BP, Geoghegan JA, Waters EM, McCarthy H, Rowe SE, Davies JR, Schaeffer CR, Foster TJ, Fey PD, O'Gara JP
Polysaccharide intercellular adhesin or the cell wall-anchored accumulation associated protein (Aap) mediate cellular accumulation during Staphylococcus epidermidis biofilm maturation. Mutation of sortase, which anchors up to 11 proteins (including Aap) to the cell wall, blocked biofilm development by the cerebrospinal fluid isolate CSF41498. Aap was implicated in this phenotype when Western blots and 2D electrophoresis revealed increased levels of the protein in culture supernatants. Unexpectedly, reduced levels of primary attachment were associated with impaired biofilm formation by CSF41498 srtA and aap mutants. In contrast to previous studies, which implicated Aap proteolytic cleavage and specifically the Aap B-domains in biofilm accumulation, the CSF41498 Aap protein was unprocessed. Furthermore, aap appeared to play a less important role in the biofilm phenotype of S. epidermidis 1457, in which the Aap protein is processed. Anti-Aap A-domain IgG inhibited primary attachment and biofilm formation in CSF41498 but not in 1457. The nucleotide sequences of the aap gene A-domain region and cleavage site were identical in CSF41498 and 1457, implicating altered protease activity in differential Aap processing in the two strains. These data reveal a new role for the A-domain of unprocessed Aap in the attachment phase of biofilm formation and suggest that extracellular protease activity can influence whether Aap contributes to the attachment or accumulation phases of the S. epidermidis biofilm phenotype.
Keyword: Biofilm, Microbiology