The lipooligosaccharide-modifying enzyme LptA enhances gonococcal defence against human neutrophils.

Infection with Neisseria gonorrhoeae (Gc) is marked by an influx of neutrophils to the site of infection. Despite a robust immune response, viable Gc can be recovered from neutrophil-rich gonorrhoeal secretions. Gc enzymatically modifies the lipid A portion of lipooligosaccharide by the addition of phosphoethanolamine to the phosphate group at the 4' position. Loss of lipooligosaccharide phosphoethanolamine transferase A (LptA), the enzyme catalysing this reaction, increases bacterial sensitivity to killing by human complement and cationic antimicrobial peptides. Here, we investigated the importance of LptA for interactions between Gc and human neutrophils. We found that lptA mutant Gc was significantly more sensitive to killing by human neutrophils. Three mechanisms underlie the increased sensitivity of lptA mutant Gc to neutrophils. (i) lptA mutant Gc is more likely to reside in mature phagolysosomes than LptA-expressing bacteria. (ii) lptA mutant Gc is more sensitive to killing by components found in neutrophil granules, including CAP37/azurocidin, human neutrophil peptide 1 and the serine protease cathepsin G. (iii) lptA mutant Gc is more susceptible to killing by antimicrobial components that are exocytosed from neutrophils, including those decorating neutrophil extracellular traps. By increasing the resistance of Gc to the bactericidal activity of neutrophils, LptA-catalysed modification of lipooligosaccharide enhances survival of Gc from the human inflammatory response during acute gonorrhoea.

The MtrCDE Efflux Pump Contributes to Survival of Neisseria gonorrhoeae From Human Neutrophils and Their Antimicrobial Components.

The mucosal inflammatory response to Neisseria gonorrhoeae (Gc) is characterized by recruitment of neutrophils to the site of infection. Gc survives exposure to neutrophils by limiting the ability of neutrophils to make antimicrobial products and by expressing factors that defend against these products. The multiple transferable resistance (Mtr) system is a tripartite efflux pump, comprised of the inner membrane MtrD, the periplasmic attachment protein MtrC, and the outer membrane channel MtrE. Gc MtrCDE exports a diverse array of substrates, including certain detergents, dyes, antibiotics, and host-derived antimicrobial peptides. Here we report that MtrCDE contributes to the survival of Gc after exposure to adherent, chemokine-treated primary human neutrophils, specifically in the extracellular milieu. MtrCDE enhanced survival of Gc in neutrophil extracellular traps and in the supernatant from neutrophils that had undergone degranulation (granule exocytosis), a process that releases antimicrobial proteins into the extracellular milieu. The extent of degranulation was unaltered in neutrophils exposed to parental or mtr mutant Gc. MtrCDE expression contributed to Gc defense against some neutrophil-derived antimicrobial peptides but not others. These findings demonstrate that the Mtr system contributes to Gc survival after neutrophil challenge, a key feature of the host immune response to acute gonorrhea.