Polysaccharide intercellular adhesin (PIA) protects Staphylococcus epidermidis against major components of the human innate immune system

TLDR

Staphylococcus epidermidis, a skin commensal and leading cause of nosocomial and biofilm-associated infections, has poorly understood mechanisms for evading the human innate immune system. Scanning electron microscopy revealed that the exopolysaccharide intercellular adhesin (PIA) forms fibrous strands on the bacterial surface, and its absence eliminates the extracellular matrix thought to mediate immune evasion. Loss of PIA markedly increased phagocytosis and killing by polymorphonuclear leukocytes and heightened susceptibility to antimicrobial peptides β‑defensin 3, LL‑37, and dermcidin, establishing PIA as the first defined biofilm matrix component protecting S.

Abstract

The skin commensal and opportunistic pathogen Staphylococcus epidermidis is the leading cause of nosocomial and biofilm-associated infections. Little is known about the mechanisms by which S. epidermidis protects itself against the innate human immune system during colonization and infection. We used scanning electron microscopy to demonstrate that the exopolysaccharide intercellular adhesin (PIA) resides in fibrous strands on the bacterial cell surface, and that lack of PIA production results in complete loss of the extracellular matrix material that has been suggested to mediate immune evasion. Phagocytosis and killing by human polymorphonuclear leucocytes was significantly increased in a mutant strain lacking PIA production compared with the wild-type strain. The mutant strain was also significantly more susceptible to killing by major antibacterial peptides of human skin, cationic human β-defensin 3 and LL-37, and anionic dermcidin. PIA represents the first defined factor of the staphylococcal biofilm matrix that protects against major components of human innate host defence.