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台灣結核病醫學會 91 年南區研討會-92.01.11-成大醫學院第三會議室 |
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Improvement in Laboratory Diagnosis of Mycobacterial Infections by Molecular Testing |
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Jing-Jou Yan ( 顏經洲 )
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The genus Mycobacterium consists of a diverse group of acid-fast bacilli which included Mycobacterium tuberculosis and more than 80 species of nontuberculous mycobacteria. The laboratory diagnosis of mycobacterial diseases depends on the detection and recovery of mycobacteria from clinical specimens. Conventional culture methods with solid media and phenotypic identification methods are time-consuming, requiring more than two months of processing. In the past decade, the development of automated, continuously monitored culture system and nucleic acid technology has remarkably shortened the processing time for recovery and identification of acid-fast bacilli, thus have limited the role of conventional identification methods. Two basic approaches to the laboratory diagnosis of mycobacterial diseases have been employed: signal amplification with species-specific probes or nucleic amplification with species-specific primers is used for detection or identification of a particular micro-organism; amplification of a nucleotide sequence universal to targeted organisms. The universal amplification system normally relies on further characterization of the amplified sequence, such as a subsequent round of selective amplification or hybridization of the universal amplification product with a specific probe, or nucleotide sequencing amplified products. 16S ribosomal DNA sequence analysis, the most commonly used universal amplification system, could allow identification, for reasons including its universal distribution among bacteria and the presence of species-specific variable regions. The assay has been favorably compared to computer-assisted cell wall fatty acid analysis and computer-assisted biochemical profile analysis of aerobic gram-negative bacilli and coryneform isolates. The results of nucleic acid amplification procedures and the results of culture or serology mean different things. Nucleic acid amplification procedures determine whether DNA or RNA from a particular organism is present in the specimen. They reveal nothing about the viability of the organism or whether the organism is involved in an infectious process. Culture, on the other hand, clearly demonstrates the viability of the organism, while a rise in titer of antibody to a specific organism agent strongly suggests involvement in infection. Cross contamination in molecular testing can also cause a serious problem. Therefore, at present, nucleic acid amplification procedures will not replace conventional diagnostic techniques.
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