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This dissertation, Molecular Epidemiology of Anaerobic Gram-positive Bacilli Bacteremia and Discovery of Six Novel Anaerobic Gram-positive Bacilli by Kei-sheng, Gibson, Woo, 吳基昇, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled Molecular Epidemiology of Anaerobic Gram-positive Bacilli Bacteremia and Discovery of Six Novel Anaerobic Gram-positive Bacilli Submitted by Woo Kei Sheng, Gibson for the degree of Master of Philosophy at The University of Hong Kong in December 2003 Owing to their fastidious growth requirements and limitations in phenotypic identification, the epidemiology, clinical significance and pathogenesis of many anaerobic Gram-positive bacilli remain poorly understood. Although reports of bacteremia caused by individual genera of anaerobic Gram-positive bacilli were available, most have relied on phenotypic methods of identification. Besides, no study has been carried out to investigate the relative importance of the different genera and species of anaerobic Gram-positive bacilli in causing bacteremia using 16S ribosomal RNA (rRNA) gene sequencing, the new gold standard for bacterial classification and identification. In this study, with the aid of 16S rRNA gene sequencing, 165 anaerobic Gram-positive bacilli recovered from the blood cultures of 165 patients during a 4-year period were identified to the species level. Six strainsof novel anaerobic Gram-positive bacilli were also discovered. Of the 165 isolates, 68 were identified as Clostridium species, 91 as known species of non-sporulating Gram-positive bacilli (75 Propionibacterium, 7 Lactobacillus, 5 Eggerthella, 2 Eubacterium, 1 each of Bifidobacterium and Olsenella), 5 as novel Eggerthella species (4 Eggerthella hongkongensis sp. nov. and 1 Eggerthella sinensis sp. nov.), and 1 as novel genus and species (Catabacter hongkongensis gen. nov. sp. nov.), which forms a distinct lineage among the anaerobic Gram-positive bacilli, with clusters I, III, and XIVb of the clostridia as the neighbouring clusters by phylogenetic analysis. Thirty-eight (56%) of the 68 Clostridium isolates, 11 (12%) of the 91 isolates of known non-sporulating Gram-positive bacilli, and all 6 novel bacteria were associated with clinically significant bacteremia. Despite the rarity of Eggerthella bacteremia reported in the literature, the present study showed that Eggerthella is responsible for 18% (10/55) of clinically significant bacteremia caused by anaerobic Gram-positive bacilli. The first cases of Olsenella uli bacteremia and Clostridium disporicum infection in humans were also uncovered and described. Underlying hepatobiliary tract disease was associated with clinically significant Clostridium bacteremia (P

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