By: Olaspers Sara Eriksson

Title: Pathogenic Neisseria: single cell motility, multicellular dynamics and antimicrobial susceptibility

Opponent: Associate Professor Matthew Francis, Department of Molecular Biology, Umeå University



Neisseria meningitidis and Neisseria gonorrhoeae can colonize humans without causing any symptoms. However, gonorrhea and invasive meningococcal disease are serious health concerns. An essential virulence factor for neisserial adhesion to host cells, twitching motility and microcolony formation/aggregation is the retractile type IV pili (Tfp). The scope of this thesis stretches from the motility of single Neisseria cells, via the multicellular dynamics of N. meningitidis microcolonies, to the bactericidal and endotoxin-inhibiting activity of a novel anti-meningococcal peptide.

The Tfp machinery in pathogenic Neisseria is highly conserved. Nevertheless, our data demonstrate species-specific expression levels of the Tfp retraction ATPase PilT. By using live-cell microscopy and particle tracking together with visualization of pili, differences between N. gonorrhoeae and N. meningitidis were also observed in piliation and twitching motility speed. However, these differences could not be attributed to the contrasting PilT expressions per se (Paper I). The importance of PilT for pilus dynamics is well established in the literature while comprehensive knowledge of the paralog PilU is lacking. In Paper II, results suggest that PilU promotes timely formation of microcolonies. Furthermore, both PilU and PilT were required for full virulence of meningococci in vivo.

The meningococcal response upon adhesion to host cells includes upregulation of the novel virulence factor Neisseria anti-aggregation factor A (NafA). Our data indicate that NafA limits microcolony formation by preventing excessive formation of Tfp bundles (Paper III). Microcolony dispersal is a prerequisite for close adhesion and mucosal invasion. Dispersal progressed rapidly on host cells and upon induction with host cell-conditioned medium (Paper IV). The dispersal phase was not altered in NafA-deficient meningococci. However, NafA may be important after microcolony dispersal on host cells for maintaining bacteria in a single cell state (Paper IV).

In Paper V, a screen of cell-penetrating peptides for antimicrobial activity towards meningococci demonstrated that transportan-10 (TP10) exhibited rapid membrane-disruptive and bactericidal activity. TP10 also decreased bacteraemia levels in a murine model of meningococcal disease. Furthermore, TP10 reduced the proinflammatory effect of endotoxin on macrophages. Thus, TP10 displays two properties that may be utilized for the development of a peptide-based treatment against pathogens.