Author: Yiu, Lap-san
Title: Identification of mycobacteria by computer-aided gas liquid chromatography
Degree: M.Sc.
Year: 1999
Subject: Mycobacteria -- Identification -- Technique
Gas chromatography
Tuberculosis -- Microbiology
Mycobacterial diseases -- Microbiology
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Department of Nursing and Health Sciences
Pages: ix, 82 leaves : ill. ; 30 cm
Language: English
Abstract: The performance of the Microbial Identification System (MIS) co-developed by the Hewlett-Packard Co. and Microbial ID. Inc., Newark, Del. for identification of clinically important mycobacteria was investigated. Ninety-one strains belonging to 11 mycobacterium species were studied. They were analysed using a gas-liquid chromatograph combined with MIS software. The identification was obtained by comparing the sample fatty acid composition with the MIS Library of mycobacteria. The MIS result obtained was compared with the identification of biochemical and molecular analysis. Sensitivity and specificity of MIS identification were determined. Under standard matching criteria for MIS library search, First rank Similarity Index (SI 1) >= 0.3 and SI 1 - SI 2 >= 0.1, the MIS sensitivity of MTB complex and NTM species were 77.5% (95%CI: 61.6- 89.2%) and 84.3% (95%CI: 71.4- 93.0%) respectively. The MIS specificity of MTB complex was 100% (95%CI: 97.5 - 100%). The major discrepancy was found in the identification of M. gastri. High specificity of MIS identification made it suitable for confirmatory purpose. Although the sensitivity was marginal, it could be raised by reducing the stringency of MIS library matching but additional tests were needed to confirm the identification result. The feasibility of using Mycobacteria Growth Indicator Tube (MGIT) and Lowenstein Jensen Medium (LJ) for Gas Liquid Chromatography (GLC) were investigated through cluster analysis. The samples cultured on Middlebrook 7H10 agar, MGIT and LJ were extracted and analysed by GLC. The fatty acid data were summarised by computer software and presented in two dimensional plot (2-D plot). Clusters of the same species were well defined in the diagrams of 7H10 and MGIT but not in the diagram of LJ. The cluster areas of Mycobacterium tuberculosis (MTB) complex and Mycobacterium avium-intracellulare (MAI) complex were estimated from the 2-D plots. Fatty acid composition variation of LJ organism was the largest, MGIT organism was the intermediate and 7H10 was the smallest. On the other hand, the nearest Euclidean distances among the clusters of MTB complex, MAI complex and Mycobacterium (M.) kansasii were measured from the 2-D plot of 7H10 and MGIT. It was found that the distances obtained from MGIT diagram were longer or comparable to those in the 7H10 diagram. The variability of fatty acid composition among the same species and the dissimilarity of different species indicated MGIT was a suitable method for GLC analysis. On the contrary, the fatty acid content of sterile LJ medium made it not suitable for GLC analysis. The minimal incubation time for MGIT organism for GLC analysis was investigated. Representatives of four Runyon group Non-tuberculosis mycobacteria (NTM) and MTB complex were analysed. The organism obtained one to three days after positive detection in MGIT was necessary for GLC detection.
Rights: All rights reserved
Access: restricted access

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