Phosphatidylcholine in membrane ofEscherichia colichanges bacterial antigenicity

This study reports that Escherichia coli phosphatidylcholine-positive (PC+) strain Top10/ptac66 (PC+ PE+), in which borrelial PC synthase (PCS) directly condenses exogenous choline with CDP-diacylglycerol (CDP-DAG) to form PC, displayed not only stronger resistance to antimicrobial peptides cecropin P1 and indolicidin, but also decreased ability to attract macrophages to the abdominal cavity of infected mice in the 36 h following infection, compared with the control strain Top10/ptac85 (PC- PE+). Rabbit sera raised against the PC+ strains Top10/ptac66 (PC+ PE+) and AD93/ptac67 (PC+ PE-) recognized a different set of periplasmic proteins and lipopolysaccharides,compared with those detected by antisera to the PC- strains Top10/ptac85 and AD93 (PC- PE-) . Electron microscopy also showed that the morphology of cell wall of Top10/ptac66 was different from that of the control strain Top10/ptac85. Enhancement of bacterial resistance to antimicrobe peptides, alteration of bacterial antigenicity and evasion of macrophage attacks in mice suggest that PC in the bacterial membrane may play a role in bacterial evasion of the innate or adaptive immune response of the host.