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Korean J Clin Pathol. 1997 Feb;17(1):89-98. Korean. Original Article.
Lee GI .

BACKGROUND: The recent surge of tuberculosis in association with AIDS and multi-drug resistant tuberculosis in the world has made even apparent the need for more rapid and accurate technologies of detecting and characterizing mycobacteria in the clinical microbiology laboratory. The BACTEC radiometric method which is known rapid alternative to traditional culture methods has been reported to be useful for the rapid detection and identification of mycobacteria from clinical specimens. I report the experience for the use of the BACTEC 460TB for detection of mycobacteria from clinical specimens. METHODS: All clinical specimens received in the department of clinical pathology from July 1993 through August 1994 were used for this study. Smears were prepared and stained for acid-fast bacilli(AFB) by Ziehl-Neelson method Middlebrook 7H12 medium(BACTEC 12A) containing a 14C-labeled palmitic acid was used as the basal medium. Quantitation of the liberated 14CO2 was used as a measure of cell growth. A BACTEC 460TB instrument was used for the detection and quantitation of 14CO2 liberated in the culture bottle. NAP tests for differentiating the M. tuberculosis complex from mycobacteria other than tuberculosis(MOTT) were performed. RESULTS: A total of 111(9.6%) mycobacterial isolates were recovered from 1.151 clinical specimens. The sensitivity of the BACTEC 460TB for detecting M. tuberculosis in acid-fast smear-positive specimens was 93.8%. The mean time required for the primary isolation of mycobacteria(GI of > or =10) was 9.8 days and the mean detection time of M. tuberculosis complex was 19.3 days. In according to the acid-fast smear results, the mean detection times of M tuberculosis complex in smear-positive and smear-negative specimens were 14.9 days and 20.9 days, respectively. The mean detection time of M. tuberculosis complex in smear-positive specimens was better for respiratory specimens(14.7 days) than for extrapulmonary specimens(21 days). All 111 isolates were susceptible to rho-nitro-alpha-acetylamino-beta-hydroxypropiophenone(NAP) and the contamination rate was 4%. CONCLUSIONS: The BACTEC radiometric method for detecting and characterizing mycobacteria requires expensive instrument and reagents using radioisotope and additional expenditure of time and effort, but The BACTEC 460TB is extremely useful for the rapid detection, isolation and identification of clinically important mycobacteria in clinical laboratory.

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