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Free Content Time to detection of Mycobacterium tuberculosis in BACTEC systems as a viable alternative to colony counting

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OBJECTIVE: To investigate whether time to detection (TTD) of Mycobacterium tuberculosis in BACTEC Mycobacteria Growth Indicator Tube (MGIT) 960 and BACTEC 460 TB systems can be used as an alternative to colony-forming unit (cfu) counting.

DESIGN: A single sputum sample recovered from each of 22 patients with tuberculosis (TB) was cultured on Middlebrook 7H11 agar and in BACTEC MGIT 960 and BACTEC 460 to investigate the relationship between cfu/ml and TTD. The relationship between TTD and treatment response was investigated by culturing a single sputum sample from each of 125 patients with TB in the BACTEC 460 system and comparing TTD values with their treatment response.

RESULTS: An inverse correlation between TTD and bacterial number, as assessed by inoculum size and cfu/ml, was observed. For the 125 patients followed up during treatment, TTD values at diagnosis correlated with smear conversion rates at 2 months and treatment outcomes. Drug resistance of the infecting strain was associated with decreased killing, as indicated by the delayed increase in TTD during the first few days of treatment.

CONCLUSION: The TTD of M. tuberculosis in BACTEC MGIT 960 and BACTEC 460 TB systems is a viable alternative to colony counting. TTD in liquid culture will facilitate mycobacterial quantification, especially in the evaluation of early bactericidal activity.
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Keywords: BACTEC; colony forming units; early bactericidal activity; time to detection; tuberculosis

Document Type: Regular Paper

Affiliations: 1: Desmond Tutu TB Centre, Department of Paediatrics and Child Health, Faculty of Health Sciences, Stellenbosch University, Tygerberg, South Africa 2: Centre for Molecular Microbiology and Infection, Imperial College, London, UK

Publication date: 2008-07-01

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  • The International Journal of Tuberculosis and Lung Disease publishes articles on all aspects of lung health, including public health-related issues such as training programmes, cost-benefit analysis, legislation, epidemiology, intervention studies and health systems research. The IJTLD is dedicated to the continuing education of physicians and health personnel and the dissemination of information on tuberculosis and lung health world-wide.

    Certain IJTLD articles are selected for translation into French, Spanish, Chinese or Russian. They are available on the Union website

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