Differential fadE28 expression associated with phenotypic virulence of Mycobacterium tuberculosis

Potential impact of efflux pump genes in mediating rifampicin resistance in clinical isolates of Mycobacterium tuberculosis from India

Despite the consideration of chromosomal mutations as the major cause of rifampicin (RIF) resistance in M. tuberculosis, the role of other mechanisms such as efflux pumps cannot be ruled out. We evaluated the role of four efflux pumps viz., MmpL2 (Rv0507), MmpL5 (Rv0676c), Rv0194 and Rv1250 in providing RIF resistance in M. tuberculosis. The real time expression of the efflux pumps was analyzed in 16 RIF resistant and 11 RIF susceptible clinical isolates of M. tuberculosis after exposure to RIF. Expression of efflux pumps in these isolates was also correlated with mutations in the rpoB gene and MICs of RIF in the presence and absence of efflux pump inhibitors. Under RIF stress, Rv0194 was induced in 8/16 (50%) RIF resistant and 2/11 (18%) RIF susceptible isolates; mmpL5 in 7/16 (44%) RIF resistant and 1/11 (9%) RIF susceptible isolates; Rv1250 in 4/16 (25%) RIF resistant and 2/11 (18%) RIF susceptible isolates; and mmpL2 was upregulated in 2/16 (12.5%) RIF resistant and 1/11 (9%) RIF susceptible isolates. This preliminary study did not find any association between Rv0194, MmpL2, MmpL5 and Rv1250 and RIF resistance. However, the overexpression of Rv0194 and mmpL5 in greater number of RIF resistant isolates as compared to RIF susceptible isolates and expression of Rv0194 in wild type (WT) resistant isolates suggests a need for further investigations.

Identification of FadAB Complexes Involved in Fatty Acid β-Oxidation in Streptomyces coelicolor and Construction of a Triacylglycerol Overproducing strain

Oleaginous microorganisms represent possible platforms for the sustainable production of oleochemicals and biofuels due to their metabolic robustness and the possibility to be engineered. Streptomyces coelicolor is among the narrow group of prokaryotes capable of accumulating triacylglycerol (TAG) as carbon and energy reserve. Although the pathways for TAG biosynthesis in this organism have been widely addressed, the set of genes required for their breakdown have remained elusive so far. Here, we identified and characterized three gene clusters involved in the β-oxidation of fatty acids (FA). The role of each of the three different S. coelicolor FadAB proteins in FA catabolism was confirmed by complementation of an Escherichia coliΔfadBA mutant strain deficient in β-oxidation. In S. coelicolor, the expression profile of the three gene clusters showed variation related with the stage of growth and the presence of FA in media. Flux balance analyses using a corrected version of the current S. coelicolor metabolic model containing detailed TAG biosynthesis reactions suggested the relevance of the identified fadAB genes in the accumulation of TAG. Thus, through the construction and analysis of fadAB knockout mutant strains, we obtained an S. coelicolor mutant that showed a 4.3-fold increase in the TAG content compared to the wild type strain grown under the same culture conditions.

Microbial Offense vs Host Defense: Who Controls the TB Granuloma?

The granuloma is the hallmark of tuberculosis and simultaneously signifies acquisition of an infection and induction of a host immune response. But who benefits more from the development of the granuloma, the host or the pathogen? Is microbe or man dictating disease course and progression? Mycobacterial diseases affect humans and animals alike, and the concepts presented in this review reflect host-pathogen interactions that influence not only mycobacterial granulomas in humans and animals but also other infectious granulomatous diseases that are encountered in veterinary medicine. Current dogma supports that an organized granuloma is a mark of an adequate and “restrictive” host immune response. However, the formation of a granuloma also provides a niche for the maturation, growth, and persistence of numerous infectious agents, and these pathogens devote some portion of their genetic machinery to ensuring these structures’ form. An understanding of pathogens’ contributions to granuloma formation can aid the development of host-directed therapies and other antimicrobial and antiparasitic therapies that can tip this balance in favor of a restrictive host response and elimination—not just containment—of the infectious organism. This review discusses animal models that have aided our understanding of pathogens’ contribution to the host response and how mycobacterial virulence genes direct host pathology in ways that may aid disease transmission and/or persistence in the form of latent infection.

Secretome profile analysis of hypervirulent Mycobacterium tuberculosis CPT31 reveals increased production of EsxB and proteins involved in adaptation to intracellular lifestyle

Epidemiological information and animal models have shown various Mycobacterium tuberculosis phenotypes ranging from hyper- to hypovirulent forms. Recent genomic and proteomic studies suggest that the outcome of infection depends on the M. tuberculosis fitness, which is a direct consequence of its phenotype. However, little is known about the molecular and cellular mechanisms used by mycobacteria to survive, replicate and persist during infection. The aim of this study was to perform a comprehensive proteomic analysis of culture filtrate from hypo- (CPT23) and hypervirulent (CPT31) M. tuberculosis isolates. Using two-dimensional electrophoresis we observed that 70 proteins were unique, or more abundant in culture filtrate of CPT31, and 15 of these were identified by mass spectrometry. Our analysis of protein expression showed that most of the proteins identified are involved in lipid metabolism (FadA3, FbpB and EchA3), detoxification and adaptation (GroEL2, SodB and HspX) and cell wall processes (LprA, Tig and EsxB). These results suggest that overrepresented proteins in M. tuberculosis CPT31 secretome could facilitate mycobacterial infection and persistence.

Latent tuberculosis infection: myths, models, and molecular mechanisms

The aim of this review is to present the current state of knowledge on human latent tuberculosis infection (LTBI) based on clinical studies and observations, as well as experimental in vitro and animal models. Several key terms are defined, including "latency," "persistence," "dormancy," and "antibiotic tolerance." Dogmas prevalent in the field are critically examined based on available clinical and experimental data, including the long-held beliefs that infection is either latent or active, that LTBI represents a small population of nonreplicating, "dormant" bacilli, and that caseous granulomas are the haven for LTBI. The role of host factors, such as CD4(+) and CD8(+) T cells, T regulatory cells, tumor necrosis factor alpha (TNF-α), and gamma interferon (IFN-γ), in controlling TB infection is discussed. We also highlight microbial regulatory and metabolic pathways implicated in bacillary growth restriction and antibiotic tolerance under various physiologically relevant conditions. Finally, we pose several clinically important questions, which remain unanswered and will serve to stimulate future research on LTBI.

Gene expression profiling of Mycobacterium avium subsp. paratuberculosis in simulated multi-stress conditions and within THP-1 cells reveals a new kind of interactive intramacrophage behaviour

BACKGROUND

Recent studies have identified in Mycobacterium avium subsp. paratuberculosis (MAP), already known as a pathogen in ruminants, a potential zoonotic agent of some autoimmune diseases in humans. Therefore, considering the possible risk for public health, it is necessary a thorough understanding of MAP's gene expression during infection of human host as well as the identification of its immunogenic and/or virulence factors for the development of appropriate diagnostic and therapeutic tools.

RESULTS

In order to characterize MAP's transcriptome during macrophage infection, we analyzed for the first time the whole gene expression of a human derived strain of MAP in simulated intraphagosomal conditions and after intracellular infection of the human macrophage cell line THP-1 by using the DNA-microarray technology. Results showed that MAP shifts its transcriptome to an adaptive metabolism for an anoxic environment and nutrient starvation. It up-regulates several response factors to oxidative stress or intracellular conditions and allows, in terms of transcription, a passive surface peptidoglycan spoliation within the macrophage along with an intensification of the anabolic activity for lipidic membrane structures.

CONCLUSIONS

These results indicate a possible interactive system between MAP and its host cell based on the internal mimicry unlike other intracellular pathogens, bringing new hypothesis in the virulence and pathogenicity of MAP and its importance in human health.

Cholesterol metabolism in Mycobacterium smegmatis

The metabolism of cholesterol in Mycobacterium smegmatis mc(2) 155 has been investigated by using a microarray approach. The transcriptome of M. smegmatis growing in cholesterol was compared with that of cells growing in glycerol as the sole carbon and energy sources during the middle exponential phase. Microarray analyses revealed that only 89 genes were upregulated at least threefold during growth on cholesterol compared with growth on glycerol. The upregulated genes are scattered throughout the 7 Mb M. smegmatis genome and likely reflect a general physiological adaptation of the bacterium to grow on this highly hydrophobic polycyclic compound. Nevertheless, 39 of the catabolic genes are organized in three specific clusters. These results not only supported the role of KstR and KstR2 as auto-regulated repressors of cholesterol catabolism, and revealed some metabolic similarities and differences on actinobacteria, but more important, they have facilitated the identification of new catabolic genes, opening a research scenario that might provide important clues on the role of cholesterol in tuberculosis infection.

Burkholderia cenocepacia ShvR-regulated genes that influence colony morphology, biofilm formation, and virulence

Burkholderia cenocepacia is an opportunistic pathogen that primarily infects cystic fibrosis (CF) patients. Previously, we reported that ShvR, a LysR regulator, influences colony morphology, virulence, and biofilm formation and regulates the expression of an adjacent 24-kb genomic region encoding 24 genes. In this study, we report the functional characterization of selected genes in this region. A Tn5 mutant with shiny colony morphology was identified with a polar mutation in BCAS0208, predicted to encode an acyl-coenzyme A dehydrogenase. Mutagenesis of BCAS0208 and complementation analyses revealed that BCAS0208 is required for rough colony morphology, biofilm formation, and virulence on alfalfa seedlings. It was not possible to complement with BCAS0208 containing a mutation in the catalytic site. BCAS0201, encoding a putative flavin adenine dinucleotide (FAD)-dependent oxidoreductase, and BCAS0207, encoding a putative citrate synthase, do not influence colony morphology but are required for optimum levels of biofilm formation and virulence. Both BCAS0208 and BCAS0201 contribute to pellicle formation, although individual mutations in each of these genes had no appreciable effect on pellicle formation. A mutant with a polar insertion in BCAS0208 was significantly less virulent in a rat model of chronic lung infection as well as in the alfalfa model. Genes in this region were shown to influence utilization of branched-chain fatty acids, tricarboxylic acid cycle substrates, l-arabinose, and branched-chain amino acids. Together, our data show that the ShvR-regulated genes BCAS0208 to BCAS0201 are required for the rough colony morphotype, biofilm and pellicle formation, and virulence in B. cenocepacia.