Thursday, August 18, 2011

Laboratory Diagnosis of Mycobacterium Tuberculosis

The gold standard for TB diagnosis is the cultivation of M. tuberculosis. It can be performed on a variety of specimens, such as sputum and bronchial washings, and also other nonpulmonary samples. It is much more sensitive than microscopy and it allows the recovery of the bacteria for other studies, such as drug susceptibility testing and genotyping. In some cases, the diagnosis of TB becomes even more problematic due to several factors associated with immunosuppresion in patients as it occurs in HIV infected persons or in the case of latent infection or extrapulmonary TB. Due to its nonspecific clinical presentation, diagnosis of TB is also problematic in children.
Recent advances in the field of molecular biology and progress in the understanding of the molecular basis of DR in M. tuberculosis have provided new tools for its rapid diagnosis by molecular methods 6. However
the high cost of most of these techniques, and their requirement for sophisticated equipment or highly skilled personnel, have precluded their implementation on a routine basis, especially in low-income countries 7. Other nonconventional approaches recently proposed include the search for biochemical markers, detection of immunological response and early detection of M. tuberculosis by methods other than colony counting. In the present article, some of these approaches will be reviewed and the feasibility for their implementation in diagnostic laboratories will be discussed.
Remarkable efforts have been made globally to accelerate the development and expansion of new diagnostic technologies. However, tuberculosis case detection still remains dependent upon sputum smear and culture, radiography and clinical symptomatology, and currently 57% of global tuberculosis patients receive a bacteriological diagnosis. Therefore, efforts to improve the quality of existing methods are necessary, and there actually have been certain achievements in this direction.
Samples for Mycobacterium Tuberculosis
Samples for bacteriological diagnosis usually depends on the affected anatomical sites by infections. The commenest lesion in Mycobacterium tuberculosis is oulmonary infection. Sputum is usually an acceptable sample for diagnosis.
If a patient cannot produce sputum, any method for sputum induction is encouraged. This is especially beneficial to ensure high sensitivity of sputum smear tests in resource-poor settings where such drastic methods as gastric washing or fibro-optic bronchoscopy cannot be used.143 It was shown that induction performed well in developing countries with little added costs.144 Recently, a new device for sputum induction called the ‘lung flute’ has been developed and may be worth trying145 (refer to Table 2 for collecting and processing specimens for the diagnosis of tuberculosis)

need more Read: Mycobacterium tuberculosis: Current status in rapid Laboratory Diagnosis

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