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.