Helicobacter pyloriResists the Antimicrobial Activity of Calprotectin via Lipid A Modification and Associated Biofilm Formation

ABSTRACTHelicobacter pyloriis one of several pathogens that persist within the host despite a robust immune response. H. pylorielicits a proinflammatory response from host epithelia, resulting in the recruitment of immune cells which manifests as gastritis. Relatively little is known about how H. pylorisurvives antimicrobials, including calprotectin (CP), which is present during the inflammatory response. The data presented here suggest that one way H. pylorisurvives the nutrient sequestration by CP is through alteration of its outer membrane. CP-treated H. pyloridemonstrates increased bacterial fitness in response to further coculture with CP. Moreover, CP-treated H. pyloricultures form biofilms and demonstrate decreased cell surface hydrophobicity. In response to CP, the H. pyloriLpx lipid A biosynthetic enzymes are not fully functional. The lipid A molecules observed in H. pyloricultures treated with CP indicate that the LpxF, LpxL, and LpxR enzyme functions are perturbed. Transcriptional analysis of lpxF, lpxL, and lpxRindicates that metal restriction by CP does not control this pathway through transcriptional regulation. Analyses of H. pylorilpx mutants reveal that loss of LpxF and LpxL results in increased fitness, similar to what is observed in the presence of CP; moreover, these mutants have significantly increased biofilm formation and reduced cell surface hydrophobicity. Taken together, these results demonstrate a novel mechanism of H. pyloriresistance to the antimicrobial activity of CP via lipid A modification strategies and resulting biofilm formation.IMPORTANCEHelicobacter pylorievades recognition of the host's immune system by modifying the lipid A component of lipopolysaccharide. These results demonstrate for the first time that the lipid A modification pathway is influenced by the host's nutritional immune response. H. pylori's exposure to the host Mn- and Zn-binding protein calprotectin perturbs the function of 3 enzymes involved in the lipid A modification pathway. Moreover, CP treatment of H. pylori, or mutants with an altered lipid A, exhibit increased bacterial fitness and increased biofilm formation. This suggests that H. pylorimodifies its cell surface structure to survive under the stress imposed by the host immune response. These results provide new insights into the molecular mechanisms that influence the biofilm lifestyle and how endotoxin modification, which renders H. pyloriresistant to cationic antimicrobial peptides, can be inactivated in response to sequestration of nutrient metals.