Sara Sigurlássdóttir, MBW, Stockholm University
Ann-Beth Jonsson, MBW, Stockholm University
Ute Römling, Dept. of Microbiology, Tumor and Cell Biology, Karolinska Institute
Sanna Koskiniemi, Dept. of Cell- and Microbiology, Uppsala University
Öjar Melefors, Department of Laboratory Medicine, Karolinska Institute
Edmund Loh, Dept. of Microbiology, Tumor and Cell Biology, Karolinska Institute
Ann-Kristin Lindås, MBW, Stockholm University

Influence of host and bacterial factors during Neisseria meningitidis colonization

The human-restricted pathogen Neisseria meningitidis is a major cause of bacterial meningitis and sepsis worldwide. Colonization of the mucosal layer in the upper respiratory tract is essential to establish an asymptomatic carrier state and invasive disease. N. meningitidis encounters diverse environmental challenges during colonization and has evolved multiple strategies and virulence factors to survive and adapt within the host.

Upon initial adhesion to the host epithelial cells, N. meningitidis forms pilus-mediated aggregates called microcolonies, which are characterized by interbacterial and host-cell interactions. Microcolonies promote long-term asymptomatic colonization within the host. However, the dispersal of single bacteria from microcolonies can help N. meningitidis to develop close contact with host cells and facilitate the invasion of mucosal surfaces or transmission to a new host.

This thesis focuses on understanding how the interplay between the host, environment, and virulence factors influences N. meningitidis colonization. Paper I shows that the host-derived metabolite lactate induces rapid dispersal of N. meningitidis microcolonies. Further molecular characterization in Paper II revealed that lactate-induced dispersal is mediated by pilus retraction, occurs in a density-dependent manner, and is responsive to temperature. Paper III shows that the deletion of D-lactate dehydrogenase LdhA in N. meningitidis promotes aggregation and biofilm formation through an increase in the autolysis-mediated release of extracellular DNA. Finally, Paper IV examines the role of polynucleotide phosphorylase (PNPase) in the virulence of N. meningitidis. The deletion of PNPase resulted in a pilus-dependent increase in the aggregation and adhesion to epithelial cells. A PNPase mutant was growth deficient and highly attenuated in an in vivo mouse model. Transcriptional analysis revealed that PNPase plays a role as a major regulator in N. meningitidis.

Keywords: Neisseria meningitidis, Colonization, Host-bacteria interactions, Lactate, Biofilms, Polynucleotide phosphorylase.