The population structure of Neisseria meningitidis was investigated by MLEE and REA. Using MLEE 107 strains were characterised studying 6 loci. Clones were defined as 5 loci were identical in the strains studied. Seventy two strains fell into twenty six multimember clones. The clones identified contained between 2 and 6 members. The remaining (n=35) strains were regarded as unique. The genetic diversity of the population was estimated as 0.700. This high degree of diversity seems to be because the majority of the strains were isolated from sporadic cases. Isolates within multimember clones contain isolates of outbreaks and sporadic cases. Clones were also identified in a collection of serogroup C. Neisseria meningtidis (n=34) strains by REA using endonuclease StuI. Eleven multimember clones were recognised containing between 2 and 15 members. Seven strains were regarded as unique. The largest multimember clone (n=15) contained 6 rifampicin resistant meningococci and also strains sensitive to rifampicin. This finding seems to be in the favour of this hypothesis that the resistant phenotype arose once and spread through the United Kingdom. Similarly matrices between 11 serogroup C and 5 serogroup B meningococcal strains were determined. The extensive Dice similarity coefficient between strains of serogroup C and B and also close genetic distance between these two serogroups, on the one hand, and very low Dice similarity coefficient (>50%) and distant genetic relations between serogroups C meningococcal isolates, on the other, demonstrated serogrouping cannot be regarded as a reflection of overall genetic similarity; although its practicality in epidemics and its convenience renders it useful as a first step in hierarchical typing system.

Macrophages are dynamic, plastic, and heterogeneous immune cells that play an important role in host immune defense against bacterial infection. Various bacterial pathogens, such as Neisseria meningitidis and Mycobacterium tuberculosis, can modulate host immune responses by interfering with macrophage differentiation and polarization. The focus of this thesis was to understand the role of macrophages in the pathogenesis of bacteria-induced diseases, which has important implications in the search for novel therapeutic strategies to control those infectious diseases. In Paper I, we found that NhhA, a conserved meningococcal outer membrane protein, can activate macrophages through both Toll-like receptor 4 (TLR4)-dependent and -independent pathways. In Paper II, we demonstrated that NhhA activates monocytes through TLR2 and triggers autocrine IL-10 and TNF production through the ERK and JNK pathways, which skew monocyte differentiation into CD200Rhi macrophages. These immune homeostatic macrophages are associated with nasopharyngeal carriage of meningococci. In Paper III, we examined the role of human CD46, a ubiquitous transmembrane protein, in regulating macrophage apoptosis, differentiation, and functional polarization. We revealed that macrophages expressing CD46 exhibit an M1 phenotype and are prone to generate proinflammatory cytokines, such as IL-6, TNF, and IL-12, upon lipopolysaccharide challenge or meningococcal infection. The important role of these macrophages in the development of septic shock was further confirmed by in vivo studies using a CD46 transgenic mouse disease model. M. tuberculosis, a gram-positive bacterium, remains an important cause of death in developing countries. In Paper IV, we reported that murine macrophages expressing human CD46 exhibit enhanced viability and bactericidal capacity and are prone to form granulomas following chronic mycobacterial infection. Increased understanding of host factor roles in the physiopathology of tuberculosis is critical for the design of effective vaccines and new drugs. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>

MSc (Med), Faculty of Health Sciences, University of the Witwatersrand, 2011 / Despite being a fulminant pathogen, Neisseria meningitidis (meningococcus) is part of the commensal flora of the human nasopharynx. Globally, five meningococcal serogroups (A, B, C, Y and W135) cause the majority of invasive disease. Most serogroup B cases occur sporadically but may be endemic or epidemic within a geographic region. In South Africa, there are limited data on invasive serogroup B clones and the antigenic diversity of certain meningococcal outer membrane proteins. This study examined the molecular epidemiology of serogroup B meningococci in South Africa from 2002 through 2006. Invasive meningococcal isolates were submitted to a national laboratory-based surveillance system. For this study, serogroup B isolates were characterised by pulsed-field gel electrophoresis (PFGE), PorA, FetA and multilocus sequence (MLST) typing. PorA, FetA and multilocus sequence (MLST) typing were performed on all 2005 isolates (n=58) and randomly selected isolates from other years (n=25). A total of 2144 invasive cases were reported over the study period. Of these, 76% (1627/2144) had viable isolates available for serogrouping and 307 (19%) were serogroup B. Serogroup B cases were reported from across the country however the majority were from the Western Cape province. The highest incidence of serogroup B was in children less than 5 years of age. Isolates displayed a high level of diversity by PFGE. Despite this diversity the majority of serogroup B meningococci collected over the 5-year period could be grouped into several clonal clusters representative of global invasive MLST clonal complexes. Overall, the most predominant MLST clones in South Africa were ST-32/ET-5 and ST-41/44/lineage 3. In addition, at least 19 PorA types and 16 FetA types were determined among selected isolates. Globally invasive serogroup B disease is caused by heterogeneous strains however, prolonged outbreaks in several countries have been due to strains of the ST-32/ET-5 and ST-41/44/lineage 3 clonal complexes. At present, serogroup B disease in South Africa is not dominated by an epidemic clone, however, global clonal complexes ST-32/ET-5 and ST-41/44/lineage 3 are circulating in Western Cape and Gauteng, respectively.