Theoretical basis for reducing time-lines to the determination of positive Mycobacterium tuberculosis cultures using thy
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Theoretical basis for reducing time-lines to the determination of positive Mycobacterium tuberculosis cultures using thymidylate kinase (TMK) assays Misaki Wayengera1,2,3 Address: 1Division of Molecular Pathology, Dept of Pathology, School of Biomedical Sciences, College of Health Sciences, Makerere University, PO Box 7072, Kampala, Uganda, 2Restrizymes Biotherapeutics Uganda Limited, PO Box 16606, Kampala, Uganda and 3School of Health Sciences, Kampala International University Western Campus, PO Box 71, Ishaka, Uganda Email: Misaki Wayengera - [email protected]
Published: 18 March 2009 Theoretical Biology and Medical Modelling 2009, 6:4
doi:10.1186/1742-4682-6-4
Received: 19 December 2008 Accepted: 18 March 2009
This article is available from: http://www.tbiomed.com/content/6/1/4 © 2009 Wayengera; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract Background: In vitro culture of pathogens on growth media forms a "pillar" for both infectious disease diagnosis and drug sensitivity profiling. Conventional cultures of Mycobacterium tuberculosis (M.tb) on Lowenstein Jensen (LJ) medium, however, take over two months to yield observable growth, thereby delaying diagnosis and appropriate intervention. Since DNA duplication during interphase precedes microbial division, "para-DNA synthesis assays" could be used to predict impending microbial growth. Mycobacterial thymidylate kinase (TMKmyc) is a phosphotransferase critical for the synthesis of the thymidine triphosphate precursor necessary for M.tb DNA synthesis. Assays based on high-affinity detection of secretory TMKmyc levels in culture using specific antibodies are considered. The aim of this study was to define algorithms for predicting positive TB cultures using antibody-based assays of TMKmyc levels in vitro. Methods and results: Systems and chemical biology were used to derive parallel correlation of "M.tb growth curves" with "TMKmyc curves" theoretically in four different scenarios, showing that changes in TMKmyc levels in culture would in each case be predictive of M.tb growth through a simple quadratic curvature, |tmk| = at2+ bt + c, consistent with the "S" pattern of microbial growth curves. Two drug resistance profiling scenarios are offered: isoniazid (INH) resistance and sensitivity. In the INH resistance scenario, it is shown that despite the presence of optimal doses of INH in LJ to stop M.tb proliferation, bacilli grow and the resulting phenotypic growth changes in colonies/units are predictable through the TMKmyc assay. According to our current model, the areas under TMKmyc curves (AUC, calculated as the integral ∫(at2+ bt + c)dt or ~1/3 at3+ 1/2 bt2+ct) could directly reveal the extent of prevailing drug resistance and thereby aid decisions about the usef
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