Bap, a <i>Staphylococcus aureus</i> Surface Protein Involved in Biofilm Formation

TLDR

New genes involved in biofilm formation are needed to elucidate strain variation and chronic staphylococcal infection mechanisms, and the bap locus encodes a novel 2,276‑amino‑acid cell‑wall protein with structural similarities to surface proteins of both gram‑negative and gram‑positive bacteria. The authors created biofilm‑negative Tn917 insertion mutants from a biofilm‑producing *S. aureus* strain, characterized the Bap protein core as 52 % of the sequence composed of 13 nearly identical 86‑residue repeats, and surveyed its presence in bovine mastitis versus human isolates.

Abstract

ABSTRACT Identification of new genes involved in biofilm formation is needed to understand the molecular basis of strain variation and the pathogenic mechanisms implicated in chronic staphylococcal infections. A biofilm-producing Staphylococcus aureus isolate was used to generate biofilm-negative transposon (Tn917) insertion mutants. Two mutants were found with a significant decrease in attachment to inert surfaces (early adherence), intercellular adhesion, and biofilm formation. The transposon was inserted at the same locus in both mutants. This locus ( bap [for biofilm associated protein]) encodes a novel cell wall associated protein of 2,276 amino acids (Bap), which shows global organizational similarities to surface proteins of gram-negative ( Pseudomonas aeruginosa and Salmonella enterica serovar Typhi) and gram-positive ( Enteroccocus faecalis ) microorganisms. Bap's core region represents 52% of the protein and consists of 13 successive nearly identical repeats, each containing 86 amino acids. bap was present in a small fraction of bovine mastitis isolates (5% of the 350 S. aureus isolates tested), but it was absent from the 75 clinical human S. aureus isolates analyzed. All staphylococcal isolates harboring bap were highly adherent and strong biofilm producers. In a mouse infection model bap was involved in pathogenesis, causing a persistent infection.