Inactivation of the dlt operon in Staphylococcus aureus confers sensitivity to defensins, protegrins, and other antimicrobial peptides

Positively charged antimicrobial peptides with membrane-damaging activity a re produced by animals and humans as components of their innate immunity ag ainst bacterial infections and also by many bacteria to inhibit competing m icroorganisms. Staphylococcus aureus and Staphylococcus xylosus, which tole rate high concentrations of several antimicrobial peptides, were mutagenize d to identify genes responsible for this insensitivity. Several mutants wit h increased sensitivity were obtained, which exhibited an altered structure of teichoic acids, major components of the Gram-positive cell wall. The mu tant teichoic acids lacked D-alanine, as a result of which the cells carrie d an increased negative surface charge. The mutant cells bound fewer anioni c, but more positively charged proteins, They were sensitive to human defen sin HNP1-3, animal-derived protegrins, tachyplesins, and magainin II, and t o the bacteria-derived peptides gallidermin and nisin, The mutated genes sh ared sequence similarity with the dlt genes involved in the transfer of D-a lanine into teichoic acids from other Gram-positive bacteria. Wild-type str ains bearing additional copies of the dlt operon produced teichoic acids wi th higher amounts of D-alanine esters, bound cationic proteins less effecti vely and were less sensitive to antimicrobial peptides. We propose a role o f the D-alanine-esterified teichoic acids which occur in many pathogenic ba cteria in the protection against human and animal defense systems.