Abstract
MICROBIOLOGY Catching an intractable disease while in the hospital is a worrying prospect and has become of greater concern mostly owing to persistent Staphylococcus epidermidis attaching to indwelling devices such as prosthetic heart valves. Its more aggressive relative S. aureus sports an arsenal of virulence factors, but how a ubiquitous skin commensal causes pathology is less clear. One useful defensive component appears to be poly-γ-DL-glutamic acid (PGA), which Kocianova et al. found is synthesized by all 74 strains of S. epidermidis they tested. In support of its commensal lifestyle, S . epidermidis relies on PGA to resist the wild swings in salt concentration that occur on human skin. PGA is known to protect other Gram-positive bacteria (such as Bacillus anthracis, which takes shelter in a capsule of PGA), from phagocytosis by host cells. PGA-nonproducing mutants of S. epidermidis, in which the cap gene locus was replaced, were wiped out by antibacterial peptides known as defensins and by neutrophil attack, whereas cap -intact bacteria survived. — CA J. Clin. Invest. 10.1172/JCI200523523 (2005).
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