Dynamics of the shedding of bacterial and ultrafine forms of mycobacteria during the chemotherapy of patients with pulmonary tuberculosis

The specific features of bacterial excretion by patients with pulmonary tuberculosis in the process of chemotherapy, depending on the duration of treatment, have been studied, and the time-course of the excretion of ultramicro forms of mycobacteria by patients with and without caverns in the lungs in the process of chemotherapy has been followed. The results of the detection of M. tuberculosis ultramicro forms with the use of the biological and bacteriological methods indicate that both these methods are highly effective and informative. The method of the direct reversion of ultramicro forms into coccoid ones in Shkol'nikova's culture medium with 10% of plasma added has proved to be the simplest. The injection of sputum filtrates containing filter-passing (ultramicro) forms of mycobacteria into experimental animals induced the development of specific minor tuberculous inflammation of a productive character without the caseation of granulomas or progressing; such inflammation coursed as a latent lympho-hematogenous process.     

ATP content of Mycobacterium tuberculosis grown in vivo and in vitro

In order to determine the reason for the slow growth of Mycobacterium leprae either in a host or in vitro, the growth characteristics of Mycobacterium tuberculosis were studied. The ATP content of in vitro-grown M. tuberculosis was about 520 pg/10(6) viable organisms. The ATP levels from in vivo-derived organisms obtained from liver and spleen of mice was about 130 pg (in cases of chronic infection) and about 270 pg (in cases of acute infection). When the in vivo-derived organisms were inoculated into culture medium, the growth rates for both types of organisms, acute as well as chronic infection, were the same and the maximum growth was reached during the fifth subculture. Although the maximum ATP content for both types of organism was the same, it was attained during the 4th subculture for organisms obtained during acute infection and during the 6th subculture for those obtained during chronic infection. The comparison between the ATP content of M. leprae and of M. tuberculosis indicates the reason for the slow growth of M. leprae.     

Comparative effectiveness of different methods for the microbiological study of resected pulmonary tuberculomas

Wide-range microbiological study (bacterioscopy, inoculation, biological assays) of 114 lung tuberculomas excised from 107 patients has revealed a pronounced variability and sharply decreased viability of mycobacterial populations vegetating in caseous foci. Differences in the frequency and character of the detection of Mycobacterium tuberculosis and their altered forms, arising from the use of three above-mentioned methods of microbiological investigation, were noted. Bacterioscopy proved to be more informative with respect to the detection of the bacterial forms of M. tuberculosis. Biological assay was highly sensitive with respect to the L-forms of M. tuberculosis and permitted the detection of the persisting forms of this infective agent, contained in caseous foci and not detected by the method of inoculations. To evaluate the actual state of the mycobacterial population in the focus of tuberculous lesion, the use of a complex of microbiological methods for the detection of typical and biologically altered forms of M. tuberculosis is necessary.     

Cloning of the gene encoding a protective Mycobacterium tuberculosis secreted protein detected in vivo during the initial phases of the infectious process

The existence of therapeutic agents and the bacille Calmette-Guérin (BCG) vaccine have not significantly affected the current tuberculosis pandemic. BCG vaccine protects against serious pediatric forms of tuberculosis but not against adult pulmonary tuberculosis, the most common and contagious form of the disease. Several vaccine candidates, including Mycobacterium tuberculosis recombinant proteins formulated in newer adjuvants or delivered in bacterial plasmid DNA have recently been described. An attractive source of vaccine candidates has been M. tuberculosis Ags present in culture supernatants of the initial phases of the bacterial growth in vitro. In this study we describe an Ag discovery approach to select for such Ags produced in vivo during the initial phases of the infection. We combined RP-HPLC and mass spectrometry to identify secreted or shed M. tuberculosis proteins eliminated in animal urine within 14 days after the infection. A peptide containing sequence homology with a hypothetical M. tuberculosis protein was identified and the recombinant protein produced in Escherichia coli. The protein was recognized by Ab (IgG2a and IgG1) and T cells (Th1) of mice infected with M. tuberculosis and by lymphoid cells from healthy donors who had a positive purified protein derivative skin test but not from tuberculosis patients. Moreover, this Ag induced protection in mice against M. tuberculosis at levels comparable to protection induced by BCG vaccine. These results validate the Ag discovery approach of M. tuberculosis proteins secreted or shed in vivo during the early phases of the infection and open new possibilities for the development of potential vaccine candidates or of markers of active mycobacterial multiplication and therefore active disease.     

A new subfamily of short bacterial adenylate kinases with the Mycobacterium tuberculosis enzyme as a model: A predictive and experimental study.

The adk gene from Mycobacterium tuberculosis codes for an enzyme of 181 amino acids. A sequence comparison with 52 different forms of adenylate kinases (AK) suggests that the enzyme from M. tuberculosis belongs to a new subfamily of "short" bacterial AKs. The recombinant protein, overexpressed in Escherichia coli, exhibits a low catalytic activity and an unexpectedly high thermal stability (Tm = 64.8 degrees C). Based on various spectroscopic data, on the known three-dimensional structure of the AK from E. coli and on secondary structure predictions for various sequenced AKs, we propose a structural model for AK from M. tuberculosis (AKmt). Proteins 1999;36:238-248.     

Characteristics of the filterable forms of Mycobacterium tuberculosis and their significance in pathology

The results of the present investigation indicate that antituberculosis therapy for a period of 6 months leads to qualitative changes in M. tuberculosis population. This is manifested by the appearance of the filterable forms of M. tuberculosis in pathological material. At the same time these forms retain the initial pathogenicity of M. tuberculosis and induce not only tuberculous, but also nonspecific inflammation. Among the population of these filterable forms organisms carrying the genetic information of the species and capable of replication processes have been detected.     

The structure and computational analysis of Mycobacterium tuberculosis protein CitE suggest a novel enzymatic function

Fatty acid biosynthesis is essential for the survival of Mycobacterium tuberculosis and acetyl-coenzyme A (acetyl-CoA) is an essential precursor in this pathway. We have determined the 3-D crystal structure of M. tuberculosis citrate lyase beta-subunit (CitE), which as annotated should cleave protein bound citryl-CoA to oxaloacetate and a protein-bound CoA derivative. The CitE structure has the (beta/alpha)(8) TIM barrel fold with an additional alpha-helix, and is trimeric. We have determined the ternary complex bound with oxaloacetate and magnesium, revealing some of the conserved residues involved in catalysis. While the bacterial citrate lyase is a complex with three subunits, the M. tuberculosis genome does not contain the alpha and gamma subunits of this complex, implying that M. tuberculosis CitE acts differently from other bacterial CitE proteins. The analysis of gene clusters containing the CitE protein from 168 fully sequenced organisms has led us to identify a grouping of functionally related genes preserved in M. tuberculosis, Rattus norvegicus, Homo sapiens, and Mus musculus. We propose a novel enzymatic function for M. tuberculosis CitE in fatty acid biosynthesis that is analogous to bacterial citrate lyase but producing acetyl-CoA rather than a protein-bound CoA derivative.     

Culturability of Mycobacterium tuberculosis cells isolated from murine macrophages: a bacterial growth factor promotes recovery

Very little is known about the culturability and viability of mycobacteria following their phagocytosis by macrophages. We therefore studied populations of the avirulent 'Academia' strain of Mycobacterium tuberculosis isolated from murine peritoneal macrophage lysates several days post-infection in vivo. The resulting bacterial suspensions contained a range of morphological types including rods, ovoid forms and coccoid forms. Bacterial viability measured using the MPN method (dilution to extinction in liquid medium) was often much higher than that measured by CFU (plating on solid medium). Viability in the MPN assay was further enhanced when the Micrococcus luteus protein, Rpf, was incorporated into the liquid culture medium at picomolar concentrations. Rpf is an example of a family of autocrine growth factors found throughout the high G+C cohort of Gram-positive bacteria including M. tuberculosis. M. tuberculosis cells obtained from macrophages had altered surface properties, as compared with bacteria grown in vitro. This was indicated by loss of the ability to adsorb bacteriophage DS6A, a reduced tendency to form clumps, acquisition of ethidium bromide stainability following heat treatment, and loss of Rpf-mediated resuscitation following freezing and thawing. These results indicate that a proportion of 'unculturable' M. tuberculosis cells obtained from macrophages is either injured or dormant and that these cells may be recovered or resuscitated using Rpf in liquid medium.     

Mycobacterium tuberculosis cells growing in macrophages are filamentous and deficient in FtsZ rings

FtsZ, a bacterial homolog of tubulin, forms a structural element called the FtsZ ring (Z ring) at the predivisional midcell site and sets up a scaffold for the assembly of other cell division proteins. The genetic aspects of FtsZ-catalyzed cell division and its assembly dynamics in Mycobacterium tuberculosis are unknown. Here, with an M. tuberculosis strain containing FtsZ(TB) tagged with green fluorescent protein as the sole source of FtsZ, we examined FtsZ structures under various growth conditions. We found that midcell Z rings are present in approximately 11% of actively growing cells, suggesting that the low frequency of Z rings is reflective of their slow growth rate. Next, we showed that SRI-3072, a reported FtsZ(TB) inhibitor, disrupted Z-ring assembly and inhibited cell division and growth of M. tuberculosis. We also showed that M. tuberculosis cells grown in macrophages are filamentous and that only a small fraction had midcell Z rings. The majority of filamentous cells contained nonring, spiral-like FtsZ structures along their entire length. The levels of FtsZ in bacteria grown in macrophages or in broth were comparable, suggesting that Z-ring formation at midcell sites was compromised during intracellular growth. Our results suggest that the intraphagosomal milieu alters the expression of M. tuberculosis genes affecting Z-ring formation and thereby cell division.     

Microarrays for public health: genomic epidemiology of tuberculosis

In response to a large local school-based outbreak of tuberculosis, we have been evaluating the utility of microarray bacterial genomic analysis in outbreak management. After initial comparison of the isolate from the index case with Mycobacterium tuberculosis H37Rv, it was possible to design robust PCRs directed towards strain-specific deletions. Rapid PCR analysis of isolates proved valuable in determining whether or not other isolates were compatible with the outbreak strain and further microarray studies revealed genetic markers that could be used to discriminate between locally circulating strains.We suggest that this approach forms the basis for developing rapid local genotyping schemes applicable to M. tuberculosis and that application to other pathogens warrants consideration.     

Virulent Mycobacterium tuberculosis strains evade apoptosis of infected alveolar macrophages

Human alveolar macrophages (AMphi) undergo apoptosis following infection with Mycobacterium tuberculosis in vitro. Apoptosis of cells infected with intracellular pathogens may benefit the host by eliminating a supportive environment for bacterial growth. The present study compared AMphi apoptosis following infection by M. tuberculosis complex strains of differing virulence and by Mycobacterium kansasii. Avirulent or attenuated bacilli (M. tuberculosis H37Ra, Mycobacterium bovis bacillus Calmette-Guérin, and M. kansasii) induced significantly more AMphi apoptosis than virulent strains (M. tuberculosis H37Rv, Erdman, M. tuberculosis clinical isolate BMC 96.1, and M. bovis wild type). Increased apoptosis was not due to greater intracellular bacterial replication because virulent strains grew more rapidly in AMphi than attenuated strains despite causing less apoptosis. These findings suggest the existence of mycobacterial virulence determinants that modulate the apoptotic response of AMphi to intracellular infection and support the hypothesis that macrophage apoptosis contributes to innate host defense in tuberculosis.     

The antilysozyme activity of Mycobacterium tuberculosis L forms

The method for the detection of antilysozyme activity (ALA) in M. tuberculosis L forms was developed. The level of ALA in M. tuberculosis L forms isolated from patients with different clinical forms of the disease varied within 1-5 micrograms. M. tuberculosis L forms with the ALA level > 4 micrograms were isolated from patients with the progressing course of the disease. The method for the prognostication of the course of the tuberculous process in the lungs by the results of the antilysozyme test was proposed.     

结核分枝杆菌毒素-抗毒素系统与生物膜

结核分枝杆菌(Mycobacterium tuberculosis)是引起结核病的病原菌。其处于持续生存的休眠状态时,可导致长期无症状感染,称为结核潜伏感染。研究显示,结核分枝杆菌染色体中存在大量 “毒素-抗毒素系统”(toxin-antitoxin system,TAS),某些TAS在潜伏感染中发挥作用,可调节细菌生长和诱导细菌进入休眠状态;某些TAS参与生物膜形成和应激反应,但其影响生物膜形成的机制尚未阐明。生物膜中的结核分枝杆菌对多种抗结核药物耐药,且能抵抗宿主免疫系统防御;休眠状态的结核分枝杆菌对抗结核药物通常也是耐受的,给结核病治疗带来了巨大挑战。本文就近年来结核分枝杆菌TAS与生物膜的研究及抗结核药物对生物膜形成的影响进行综述。     

Requirement of gene fadD33 for the growth of Mycobacterium tuberculosis in a hepatocyte cell line

Gene fadD33 of Mycobacterium tuberculosis, one of the 36 homologues of gene fadD of Escherichia coli identified in the M. tuberculosis genome, predictively encodes an acyl-CoA synthase, an enzyme involved in fatty acids metabolism. The gene is underexpressed in the attenuated strain M. tuberculosis H37Ra relative to virulent H37Rv and plays a role in M. tuberculosis virulence in BALB/c mice by supporting mycobacterial replication in the liver. In the present paper, we investigated the role of fadD33 expression in bacterial growth within the hepatocyte cell line HepG2, as well as in human monocyte-derived THP-1 cells and peripheral blood mononuclear cells. M. tuberculosis H37Rv proved able to grow within HepG2 cells, while the intracellular replication of M. tuberculosis H37Ra was markedly impaired; complementation of strain H37Ra with gene fadD33 restored its replication to the levels of H37Rv. Moreover, disruption of gene fadD33 by allelic exchange mutagenesis reduced the intracellular growth of M. tuberculosis H37Rv, and complementation of the fadD33-disrupted mutant with gene fadD33 restored bacterial replication. Conversely, fadD33 expression proved unable to influence M. tuberculosis growth in human phagocytes, as fadD33-disrupted M. tuberculosis H37Rv mutant, as well as fadD33-complemented M. tuberculosis H37Ra, grew within THP-1 cells and peripheral monocytes basically at the same rates as parent H37Rv and H37Ra strains. The results of these experiments indicate that gene fadD33 expression confers growth advantage to M. tuberculosis in immortalized hepatocytes, but not in macrophages, thus emphasizing the importance of fadD33 in liver-specific replication of M. tuberculosis.     

The influence of host and bacterial genotype on the development of disseminated disease with Mycobacterium tuberculosis

The factors that govern the development of tuberculosis disease are incompletely understood. We hypothesized that some strains of Mycobacterium tuberculosis (M. tuberculosis) are more capable of causing disseminated disease than others and may be associated with polymorphisms in host genes responsible for the innate immune response to infection. We compared the host and bacterial genotype in 187 Vietnamese adults with tuberculous meningitis (TBM) and 237 Vietnamese adults with uncomplicated pulmonary tuberculosis. The host genotype of tuberculosis cases was also compared with the genotype of 392 cord blood controls from the same population. Isolates of M. tuberculosis were genotyped by large sequence polymorphisms. The hosts were defined by polymorphisms in genes encoding Toll-interleukin 1 receptor domain containing adaptor protein (TIRAP) and Toll-like receptor-2 (TLR-2). We found a significant protective association between the Euro-American lineage of M. tuberculosis and pulmonary rather than meningeal tuberculosis (Odds ratio (OR) for causing TBM 0.395, 95% confidence intervals (C.I.) 0.193-0.806, P = 0.009), suggesting these strains are less capable of extra-pulmonary dissemination than others in the study population. We also found that individuals with the C allele of TLR-2 T597C allele were more likely to have tuberculosis caused by the East-Asian/Beijing genotype (OR = 1.57 [95% C.I. 1.15-2.15]) than other individuals. The study provides evidence that M. tuberculosis genotype influences clinical disease phenotype and demonstrates, for the first time, a significant interaction between host and bacterial genotypes and the development of tuberculosis.     

Expression, purification, and characterization of a functionally active Mycobacterium tuberculosis UDP-glucose pyrophosphorylase

Tuberculosis, which is caused by Mycobacterium tuberculosis, remains to be a global health problem. The thick and complex cell envelope has been implicated in many aspects of the pathogenicity of M. tuberculosis. M. tuberculosis UDP-glucose pyrophosphorylase (UGP, coded by galU, Rv0993) is involved in cell envelope precursor synthesis. UGP catalyzes the reversible formation of UDP-glucose and inorganic pyrophosphate from UTP and glucose 1-phosphate (Glc-l-P). Bacterial UGPs are completely unrelated to their eukaryotic counterparts. This enzyme is recognized as a virulence factor in several bacterial species and is conserved among mycobacterial species, which makes it a good target for mycobacterial pathogenicity research. The recombinant M. tuberculosis UGP (rMtUGP) was purified in Escherichia coli and found to be stable and catalytically active. The effects of pH, temperature and Mg2+ on enzyme activity were characterized. In addition, subcellular localization studies revealed that most of M. tuberculosis UGP protein was located in the cell wall. The purification and characterization of M. tuberculosis UGP may help to decipher the pathogenicity of M. tuberculosis.     

Cloning and characterization of GTP-binding proteins of Mycobacterium tuberculosis H(37)Rv

GTP-binding proteins (G-proteins) are highly conserved signaling molecules that participate in cellular signaling and bacterial pathogenesis by regulating the activity of cognate GTPases. However, the exact role of G-proteins in the pathogenesis of Mycobacterium tuberculosis is poorly understood. The complete genome sequence of M. tuberculosis H(37)Rv, suggests the presence of several homologs of bacterial G-proteins. In the present study, three G-proteins, Era, Obg and LepA of M. tuberculosis H(37)Rv were cloned and expressed in Escherichia coli. Purified proteins showed GTP-binding and hydrolyzing activities. A point mutation in the conserved GTP-binding motif, AspXXGly (Asp to Ala) in Era (Asp-258) and Obg (Asp-212) proteins resulted in the loss of the associated activities, confirming that known key residues in well-established G-proteins are also conserved in mycobacterial homologs. This study confirms that Era, Obg and LepA of M. tuberculosis H(37)Rv possess GTPase activity and provide a platform to understand the physiological significance of these proteins in associated pathogenesis.     

A family of autocrine growth factors in Mycobacterium tuberculosis

Mycobacterium tuberculosis and its close relative, Mycobacterium bovis (BCG) contain five genes whose predicted products resemble Rpf from Micrococcus luteus. Rpf is a secreted growth factor, active at picomolar concentrations, which is required for the growth of vegetative cells in minimal media at very low inoculum densities, as well as the resuscitation of dormant cells. We show here that the five cognate proteins from M. tuberculosis have very similar characteristics and properties to those of Rpf. They too stimulate bacterial growth at picomolar (and in some cases, subpicomolar) concentrations. Several lines of evidence indicate that they exert their activity from an extra-cytoplasmic location, suggesting that they are also involved in intercellular signalling. The five M. tuberculosis proteins show cross-species activity against M. luteus, Mycobacterium smegmatis and M. bovis (BCG). Actively growing cells of M. bovis (BCG) do not respond to these proteins, whereas bacteria exposed to a prolonged stationary phase do. Affinity-purified antibodies inhibit bacterial growth in vitro, suggesting that sequestration of these proteins at the cell surface might provide a means to limit or even prevent bacterial multiplication in vivo. The Rpf family of bacterial growth factors may therefore provide novel opportunities for preventing and controlling mycobacterial infections.     

Cell-cell interactions during formation and reactivation of "nonculturable" mycobacteria

To date, the possible existence of "nonculturable" (NC) but potentially viable forms has been shown for some bacteria. NC mycobacteria have attracted particular interest due to the assumption that the latent form of tuberculosis is associated with the conversion of its causative agent, Mycobacterium tuberculosis, into the NC state. A number of approaches have been developed to obtain NC forms of mycobacteria, but the mechanisms of transition into or from this state have been insufficiently studied. This review considers cell-cell communications involved in the formation and reactivation of NC forms of the bacteria M. smegmatis and M. tuberculosis. Special attention has been paid to the secreted Rpf family proteins, which belong to peptidoglycan hydrolases and participate in the resuscitation of NC mycobacteria.