SUMMARY With an estimated 9.4 million new cases globally, tuberculosis (TB) continues to be a major public health concern. Eighty percent of all cases worldwide occur in 22 high-burden, mainly resource-poor settings. This devastating impact of tuberculosis on vulnerable populations is also driven by its deadly synergy with HIV. Therefore, building capacity and enhancing universal access to rapid and accurate laboratory diagnostics are necessary to control TB and HIV-TB coinfections in resource-limited countries. The present review describes several new and established methods as well as the issues and challenges associated with implementing quality tuberculosis laboratory services in such countries. Recently, the WHO has endorsed some of these novel methods, and they have been made available at discounted prices for procurement by the public health sector of high-burden countries. In addition, international and national laboratory partners and donors are currently evaluating other new diagnostics that will allow further and more rapid testing in point-of-care settings. While some techniques are simple, others have complex requirements, and therefore, it is important to carefully determine how to link these new tests and incorporate them within a country's national diagnostic algorithm. Finally, the successful implementation of these methods is dependent on key partnerships in the international laboratory community and ensuring that adequate quality assurance programs are inherent in each country's laboratory network.

SummaryProtein tyrosine kinases and tyrosine phosphatases from several bacterial pathogens have been shown to act as virulence factors by modulating the phosphorylation and dephosphorylation of host proteins. The identification and characterization of two tyrosine phosphatases namely MptpA and MptpB from Mycobacterium tuberculosis has been reported earlier.MptpB is secreted by M. tuberculosis into extracellular mileu and exhibits a pH optimum of 5.6, similar to the pH of the lysosomal compartment of the cell. To determine the role of MptpB in the pathogenesis of M. tuberculosis , we constructed a mptpB mutant strain by homologous recombination and compared the ability of parent and the mutant strain to survive intracellularly. We show that disruption of the mptpB gene impairs the ability of the mutant strain to survive in activated macrophages and guinea pigs but not in resting macrophages suggesting the importance of its role in the host-pathogen interaction. Infection of guinea pigs with the mutant strain resulted in a 70-fold reduction in the bacillary load of spleens in infected animals as compared with the bacillary load in animals infected with the parental strain. Upon reintroduction of the mptpB gene into the mutant strain, the complemented strain was able to establish infection and survive in guinea pigs at rates comparable to the parental strain. These observations demonstrate a role of MptpB in the pathogenesis of M. tuberculosis .

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We had recently reported that the mymA operon (Rv3083 to Rv3089) of Mycobacterium tuberculosis is regulated by AraC/XylS transcriptional regulator VirS (Rv3082c) and is important for the cell envelope of M. tuberculosis. In this study, we further show that a virS mutant (Mtb⌬virS) and a mymA mutant (Mtbmym::hyg) of M. tuberculosis exhibit reduced contents and altered composition of mycolic acids along with the accumulation of saturated C 24 and C 26 fatty acids compared to the parental strain. These mutants were markedly more susceptible to major antitubercular drugs at acidic pH and also showed increased sensitivity to detergent (sodium dodecyl sulfate) and to acidic stress than the parental strain. We show that disruption of virS and mymA genes impairs the ability of M. tuberculosis to survive in activated macrophages, but not in resting macrophages, suggesting the importance of the mymA operon in protecting the bacterium against harsher conditions. Infection of guinea pigs with Mtb⌬virS, Mtbmym::hyg, and the parental strain resulted in an ϳ800-fold-reduced bacillary load of the mutant strains compared with the parental strain in spleens, but not in the lungs, of animals at 20 weeks postinfection. Phenotypic traits were fully complemented upon reintroduction of the virS gene into Mtb⌬virS. These observations show the important role of the mymA operon in the pathogenesis of M. tuberculosis at later stages of the disease.Mycobacterium tuberculosis, the etiological agent of extremely serious human infections, is a highly successful intracellular pathogen because it can adapt itself to various hostile environments. The cell envelope of mycobacteria is known to play a major role in their virulence and resistance to hostile environments. Besides, interaction of the mycobacterial cell envelope with host cell receptors facilitates uptake of the bacterium and modulation of host immune responses (12). Mycobacterium tuberculosis has approximately 250 genes involved in its lipid metabolism, and the lipid contents of the pathogen contribute to 60% of the cell dry weight (10,12). A number of genes involved in the synthesis of essential components of the cell envelope for maintaining appropriate cell wall architecture of M. tuberculosis have been identified, and their requirement for the virulence of M. tuberculosis has been established, suggesting their importance as targets for the development of new antitubercular drugs (4,8,19,22,57). Genes responsible for the biosynthesis of oxygenated mycolic acids and cyclopropanated mycolic acids were shown to be important for the in vivo growth and persistence of M. tuberculosis (19,22,57). The gene cluster involved in the biosynthesis of major complex lipids phthiocerol and phenolphthiocerol dimycocerosates of M. tuberculosis have been shown to play an important role in its virulence (11). Induction of various genes involved in fatty acid metabolism in caseous granuloma (9) or human macrophages (20) or after exposure to sodium dodecyl sulfate (SDS) (37, 57) or acidic stress (21) su...

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