d -Alanine Modification of a Protease-Susceptible Outer Membrane Component by the Bordetella pertussis dra Locus Promotes Resistance to Antimicrobial Peptides and Polymorphonuclear Leukocyte-Mediated Killing

Bordetella pertussis is the causative agent of pertussis, a highly contagious disease of the human respiratory tract. Despite very high vaccine coverage, pertussis has reemerged as a serious threat in the United States and many developing countries. Thus, it is important to pursue research to discover unknown pathogenic mechanisms ofB. pertussis . We have investigated a previously uncharacterized locus inB. pertussis , thedra locus, which is homologous to thedlt operons of Gram-positive bacteria. The absence of thedra locus resulted in increased sensitivity to the killing action of antimicrobial peptides (AMPs) and human phagocytes. Compared to the wild-type cells, the mutant cells bound higher levels of cationic proteins and peptides, suggesting thatdra contributes to AMP resistance by decreasing the electronegativity of the cell surface. The presence ofdra led to the incorporation ofd -alanine into an outer membrane component that is susceptible to proteinase K cleavage. We conclude thatdra encodes a virulence-associated determinant and contributes to the immune resistance ofB. pertussis . With these findings, we have identified a new mechanism of surface modification inB. pertussis which may also be relevant in other Gram-negative pathogens.