Bap, a Staphylococcus aureus surface protein involved in biofilm formation

Identification of new genes involved in biofilm formation is needed to unde rstand the molecular basis of strain variation and the pathogenic mechanism s implicated in chronic staphylococcal infections. A biofilm-producing Stap hylococcus aureus isolate was used to generate biofilm-negative transposon (Tn917) insertion mutants, Two mutants were found with a significant decrea se in attachment to inert surfaces (early adherence), intercellular adhesio n, and biofilm formation. The transposon was inserted at the same locus in both mutants. This locus (bap [for biofilm associated protein] encodes a no vel cell wall associated protein of 2,276 amino acids (Bap), which shows gl obal organizational similarities to surface proteins of gram-negative (Pseu domonas aeruginosa and Salmonella enterica serovar Typhi) and gram-positive (Enteroccocus faecalis) microorganisms. Bap's core region represents 52% o f the protein and consists of 13 successive nearly identical repeats, each containing 86 amino acids. bap was present in a small fraction of bovine ma stitis isolates (5% of the 350 S. aureus isolates tested), but it was absen t from the 75 clinical human S. aureus isolates analyzed. All staphylococca l isolates harboring bap were highly adherent and strong biofilm producers. In a mouse infection model bap was involved in pathogenesis, causing a per sistent infection.