This dissertation, "Laribacter Hongkongensis: Novel Bacterium Associated With Gastroenteritis" by Lee-lee, Jade, Teng, 鄧莉莉, 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 "Laribacter hongkongensis, a novel bacterium associated with gastroenteritis" Submitted by Teng Lee Lee for the degree of Doctor of Philosophy at The University of Hong Kong in September 2005 In the first part of the study, a novel bacterium was isolated from the blood culture and empyema in a cirrhotic patient. The cells were facultative anaerobic, non-sporulating, Gram negative, spiral shaped rods. It grows on sheep blood agar as non-hemolytic, gray colonies of 1 mm in diameter after 24 hours of incubation at 37C in ambient air. Growth also occurs on MacConkey agar, at 25C and 42C and in 1% and 2% NaCl. This strain is aflagellated and non-motile. It is oxidase, catalase, urease, and arginine dihydrolase positive, and it reduces nitrate to nitrite but does not reduce nitrite. It does not ferment, oxidize, or assimilate any sugar tested. 16S ribosomal RNA gene sequencing showed that there were 6.2% difference between the bacterium and Microvirgula aerodenitrificans. The G + C content of it (mean SD) was 68.0 2.43%. Its genomic size was about 3 Mb. It belongs to the Neisseriaceae family of the β-subclass of Proteobacteria. This bacterium was named Laribacter hongkongensis gen. nov., sp. nov. In the second part of the study, L. hongkongensis was isolated in pure culture on 2 charcoal cefoperazone deoxycholate agar from the stool of six patients with diarrhea. Unlike L. hongkongensis type strain HKU1, all the six strains were motile with bipolar flagellae. Sequencing of the 16S ribosomal RNA genes showed that they all had sequences with only 0-2 base differences to that of the type strain. Pulsed-field gel electrophoresis of the SpeI digested genomic DNA of the six isolates and that of the type strain revealed that the seven isolates were genotypically unrelated strains. In the third part of the study, a new selective medium, cefoperazone MacConkey agar containing 32 μg/ml cefoperazone, was developed for primary isolation of L. hongkongensis from stool. The performance of this medium on the quantitative recovery of L. hongkongensis and suppression of standard aerobic enteric bacteria was superior to charcoal cefoperazone deoxycholate agar. In the fourth part of the study, a prospective study to determine the association of L. hongkongensis with gastroenteritis, the associated risk factors and the source of L. hongkongensis was carried out. During a four-month period, L. hongkongensis was recovered from 17 out of 3788 patients with community-acquired gastroenteritis, but none of 1894 controls (PIn the last part of my study, a territory-wide eco-epidemiology study was carried out. In this surveillance study, L. hongkongensis was isolated solely from freshwater 3 fish (60% grass carps, 53% bighead carps and 25% mud carps). Comparing the pulsed-field gel electrophoresis patterns of fish and patient isolates revealed that most patient isolates were clustered together, suggesting that some clones could be more virulen