Laribacter hongkongensis : novel bacterium associated with gastroenteritis

by Teng, Lee-lee

Abstract (Summary)
(Uncorrected OCR) Abstract of thesis entitled ?aribacter 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 37? in ambient air. Growth also occurs on MacConkey agar, at 25? and 42? 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 ?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 ?/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 (P<0.005). Gastroenteritis with recovery of L. hongkongensis was associated with recent travel (P<0.001), fish consumption (P<0.01), and minced freshwater fish meat consumption (P<0.05). Twenty-seven additional L. hongkongensis isolates were recovered from intestinal samples in 25% of freshwater fish and 15% of minced freshwater fish meat from retail markets in Hong Kong. In 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 virulent. ------ Total word count: 485 ------ 4
Bibliographical Information:


School:The University of Hong Kong

School Location:China - Hong Kong SAR

Source Type:Master's Thesis

Keywords:neisseriaceae china hong kong gastroenteritis laribacter hongkongensis


Date of Publication:01/01/2005

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