Distribution of insertion- and deletion-associated genetic polymorphisms among four Mycobacterium tuberculosis phospholipase C genes and associations with extrathoracic tuberculosis: a population-based study

Roles of Lipolytic enzymes in Mycobacterium tuberculosis pathogenesis

Mycobacterium tuberculosis (Mtb) is a bacterial pathogen that can endure for long periods in an infected patient, without causing disease. There are a number of virulence factors that increase its ability to invade the host. One of these factors is lipolytic enzymes, which play an important role in the pathogenic mechanism of Mtb. Bacterial lipolytic enzymes hydrolyze lipids in host cells, thereby releasing free fatty acids that are used as energy sources and building blocks for the synthesis of cell envelopes, in addition to regulating host immune responses. This review summarizes the relevant recent studies that used in vitro and in vivo models of infection, with particular emphasis on the virulence profile of lipolytic enzymes in Mtb. A better understanding of these enzymes will aid the development of new treatment strategies for TB. The recent work done that explored mycobacterial lipolytic enzymes and their involvement in virulence and pathogenicity was highlighted in this study. Lipolytic enzymes are expected to control Mtb and other intracellular pathogenic bacteria by targeting lipid metabolism. They are also potential candidates for the development of novel therapeutic agents.

IS6110 Copy Number in Multi-Host Mycobacterium bovis Strains Circulating in Bovine Tuberculosis Endemic French Regions

IS6110 is an insertion sequence found in the Mycobacterium tuberculosis complex, to which Mycobacterium bovis belongs, which can play a role in genome plasticity and in bacterial evolution. In this study, the abundance and location of IS6110 on M. bovis genomic data of French animal field strains were studied. A first analysis was performed on a panel of 81 strains that reflect the national M. bovis population’s genetic diversity. The results show that more than one-third of them are IS6110 multicopy and that 10% have IS6110 in a high copy number (more than 6 copies). Multicopy strains are those circulating in the regions where prevalence was above the national average. Further study of 93 such strains, with an IS6110 copy number of 10-12, showed stability of IS6110 copy number and genome location over time and between host species. The correlation between M. bovis multicopy strains and high bovine tuberculosis (bTB) prevalence leads us to consider whether their epidemiological success could be partly due to genetic changes originated by IS6110 transposition.

Lipid metabolism and intracellular bacterial virulence: key to next-generation therapeutics

Lipid metabolism is thought to play a key role in the pathogenicity of several intracellular bacteria. Bacterial lipolytic enzymes hydrolyze lipids from the host cell to release free fatty acids which are used as an energy source and building blocks for the synthesis of cell envelope and also to modulate host immune responses. In this review, we discussed the role of lipid metabolism and lipolytic enzymes in the life cycle and virulence of Mycobacterium tuberculosis and other intracellular bacteria. The lipolytic enzymes appear to be potential candidates for developing novel therapeutics by targeting lipid metabolism for controlling M. tuberculosis and other intracellular pathogenic bacteria.

[Formula: see text]

The truncated Rv2820c of Mycobacterium tuberculosis Beijing family augments intracellular survival of M. smegmatis by altering cytokine profile and inhibiting NO generation

Genetic variations among genes of Mycobacterium tuberculosis may be associated with antigenic variation and immune evasion, which complicates the pathogenesis of M. tuberculosis. The hyper-virulent M. tuberculosis Beijing strains harbored several large sequence deletions, among which RD207 attributed to the deletion of CRISPR loci and several Cas genes. RD207 also gave rise to a truncated gene Rv2820c-Bj with 60% deletion in length at the 3'-end and a new 3'-end of five amino acid mutations. It has been reported that Rv2820c-Bj correlated with enhanced intracellular survival of M. smegmatis in macrophages when compared to its full-length counterpart Rv2820c in M. tuberculosis, however, the respective contribution of the truncation and the new 3'-end of Rv2820c-Bj to this enhancement was unclear. Here, by infecting THP-1 macrophages with Ms_Rv2820c-Bj, Ms_Rv2820c and MS_Rv2820c-Tr (expressing the truncated Rv2820c without five amino acid mutations at 3'-end), we found only Ms_Rv2820c-Bj was responsible for the enhancement of survival of M. smegmatis in macrophages. Furthermore, we detected that Ms_Rv2820c-Tr and Ms_Rv2820c-Bj induced similar cytokine profile and NO production after infection of macrophages, which was distinctly different from Ms_Rv2820c. However, Ms_Rv2820c-Bj evoked higher levels of interleukin-10 (IL-10) and lower levels of interleukin- 6 (IL-6), interleukin-1β (IL-1β) and interleukin-12 (IL-12) in infected THP-1 macrophages than Ms_Rv2820c-Tr. Accordingly, we concluded that the new 3'-end of Rv2820c-Bj was important to dampen host defense and enhance the intracellular survival of M. smegmatis.

The Troika Host-Pathogen-Extrinsic Factors in Tuberculosis: Modulating Inflammation and Clinical Outcomes

The already enormous burden caused by tuberculosis (TB) will be further aggravated by the association of this disease with modern epidemics, as human immunodeficiency virus and diabetes. Furthermore, the increasingly aging population and the wider use of suppressive immune therapies hold the potential to enhance the incidence of TB. New preventive and therapeutic strategies based on recent advances on our understanding of TB are thus needed. In particular, understanding the intricate network of events modulating inflammation in TB will help to build more effective vaccines and host-directed therapies to stop TB. This review integrates the impact of host, pathogen, and extrinsic factors on inflammation and the almost scientifically unexplored complexity emerging from the interactions between these three factors. We highlight the exciting data showing a contribution of this troika for the clinical outcome of TB and the need of incorporating it when developing novel strategies to rewire the immune response in TB.

The predominance of Ethiopian specific Mycobacterium tuberculosis families and minimal contribution of Mycobacterium bovis in tuberculous lymphadenitis patients in Southwest Ethiopia

BACKGROUND

Ethiopia has an extremely high rate of extrapulmonary tuberculosis, dominated by tuberculous lymphadenitis (TBLN). However, little is known about Mycobacterium tuberculosis complex (MTBc) lineages responsible for TBLN in Southwest Ethiopia.

METHODS

A total of 304 MTBc isolates from TBLN patients in Southwest Ethiopia were genotyped primarily by spoligotyping. Isolates of selected spoligotypes were further analyzed by 15-loci mycobacterial interspersed repetitive unit-variable number tandem repeat (MIRU-VNTR) (n=167) and qPCR-based single nucleotide polymorphism (n=38). Isolates were classified into main phylogenetic lineages and families by using the reference strain collections and identification tools available at MIRU-VNTRplus data base. Resistance to rifampicin was determined by Xpert MTB/RIF.

RESULTS

The majority of isolates (248; 81.6%) belonged to the Euro-American lineage (Lineage 4), with the ill-defined T and Haarlem as largest families comprising 116 (38.2%) and 43 (14.1%) isolates respectively. Of the T family, 108 isolates were classified as being part of the newly described Ethiopian families, namely Ethiopia_2 (n=44), Ethiopia_3 (n=34) and Ethiopia_H₃₇Rv-like (n=30). Other sub-lineages included URAL (n=18), S (n=17), Uganda I (n=16), LAM (n=13), X (n=5), TUR (n=5), Uganda II (n=4) and unknown (n=19). Lineage 3 (Delhi/CAS) was the second most common lineage comprising 44 (14.5%) isolates. Interestingly, six isolates (2%) were belonged to Lineage 7, unique to Ethiopia. Lineage 1 (East-African Indian) and Lineage 2 (Beijing) were represented by 3 and 1 isolates respectively. M. bovis was identified in only two (0.7%) TBLN cases. The cluster rate was highest for Ethiopia_3 isolates showing clonal similarity with isolates from North Ethiopia. Lineage 3 was significantly associated with rifampicin resistance.

CONCLUSIONS

In TBLN in Southwest Ethiopia, the recently described Ethiopia specific Lineage 4 families were predominant, followed by Lineage 3 and Lineage 4-Haarlem. The contribution of M. bovis in TBLN infection is minimal.

Biological and Epidemiological Consequences of MTBC Diversity

Tuberculosis is caused by different groups of bacteria belonging to the Mycobacterium tuberculosis complex (MTBC). The combined action of human factors, environmental conditions and bacterial virulence determine the extent and form of human disease. MTBC virulence is a composite of different clinical phenotypes such as transmission rate and disease severity among others. Clinical phenotypes are also influenced by cellular and immunological phenotypes. MTBC phenotypes are determined by the genotype, therefore finding genotypes responsible for clinical phenotypes would allow discovering MTBC virulence factors. Different MTBC strains display different cellular and clinical phenotypes. Strains from Lineage 5 and Lineage 6 are metabolically different, grow slower, and are less virulent. Also, at least certain groups of Lineage 2 and Lineage 4 strains are more virulent in terms of disease severity and human-to-human transmission. Because phenotypic differences are ultimately caused by genotypic differences, different genomic loci have been related to various cellular and clinical phenotypes. However, defining the impact of specific bacterial genomic loci on virulence when other bacterial determinants, human and environmental factors are also impacting the phenotype would contribute to a better knowledge of tuberculosis virulence and ultimately benefit tuberculosis control.

Revisiting the role of phospholipases C in virulence and the lifecycle of Mycobacterium tuberculosis

Mycobacterium tuberculosis, the agent of human tuberculosis has developed different virulence mechanisms and virulence-associated tools during its evolution to survive and multiply inside the host. Based on previous reports and by analogy with other bacteria, phospholipases C (PLC) of M. tuberculosis were thought to be among these tools. To get deeper insights into the function of PLCs, we investigated their putative involvement in the intracellular lifestyle of M. tuberculosis, with emphasis on phagosomal rupture and virulence, thereby re-visiting a research theme of longstanding interest. Through the construction and use of an M. tuberculosis H37Rv PLC-null mutant (ΔPLC) and control strains, we found that PLCs of M. tuberculosis were not required for induction of phagosomal rupture and only showed marginal, if any, impact on virulence of M. tuberculosis in the cellular and mouse infection models used in this study. In contrast, we found that PLC-encoding genes were strongly upregulated under phosphate starvation and that PLC-proficient M. tuberculosis strains survived better than ΔPLC mutants under conditions where phosphatidylcholine served as sole phosphate source, opening new perspectives for studies on the role of PLCs in the lifecycle of M. tuberculosis.

Beijing clades of Mycobacterium tuberculosis are associated with differential survival in HIV-negative Russian patients

We conducted a prospective study to establish factors associated with survival in tuberculosis patients in Russia including social, clinical and pathogen-related genetic parameters. Specifically we wished to determine whether different strains/clades of the Beijing lineage exerted a differential effect of survival. HIV-negative culture-confirmed cases were recruited during 2008-2010 across Samara Oblast and censored in December 2011. Molecular characterization was performed by a combination of spoligotyping, multilocus VNTR typing and whole genome sequencing (WGS). We analyzed 2602 strains and detected a high prevalence of Beijing family (n=1933; 74%) represented largely by two highly homogenous dominant clades A (n=794) and B (n=402) and non-A/non-B (n=737). Multivariable analysis of 1366 patients with full clinical and genotyping data showed that multi- and extensive drug resistance (HR=1.86; 95%CI: 1.52, 2.28 and HR=2.19; 95%CI: 1.55, 3.11) had the largest impact on survival. In addition older age, extensive lung damage, shortness of breath, treatment in the past and alcohol abuse reduced survival time. After adjustment for clinical and demographic predictors there was evidence that clades A and B combined were associated with poorer survival than other Beijing strains (HR=0.48; 95%CI 0.34, 0.67). All other pathogen-related factors (polymorphisms in genes plcA, plcB, plcC, lipR, dosT and pks15/1) had no effect on survival. In conclusion, drug resistance exerted the greatest effect on survival of TB patients. Nevertheless we provide evidence for the independent biological effect on survival of different Beijing family strains even within the same defined geographical population. Better understanding of the role of different strain factors in active disease and their influence on outcome is essential.

Genetic diversity and drug susceptibility profile of Mycobacterium tuberculosis isolated from different regions of India

OBJECTIVES

Molecular genotyping profiles of Mycobacterium tuberculosis (MTB) provide a valuable insight into the evolution and transmission of the bacilli. Due to the lack of comprehensive national level data from India on this subject, we performed this study to determine the recent trends and distribution of various MTB lineages circulating in India.

METHODS

A total of 628 MTB isolates were obtained from North, West, South, Central and Eastern India. Spoligotyping and drug susceptibility testing was performed by using manufacturer's instructions.

RESULTS

Spoligotyping detected 102 distinct spoligo-patterns. A total of 536 (85.3%) isolates were distributed into 85 SITs which matched the pre-existing database, whereas 17 SITs were newly created for 34 (5.4%) isolates. Overall, CAS family genotype was predominant, comprising 222 (35.4%) isolates, followed by EAI in 152 (24.2%), Beijing in 108 (17.2%), Manu in 41 (6.5%), T in 30 (4.8%), H in 6 (0.9%), X in 3 (0.5%) and one (0.2%) each in Ural and AFRI. Drug susceptibility testing identified 134 (21.3%) isolates as multi drug resistant (MDR).

CONCLUSIONS

The CAS lineage had a pan India presence but EAI lineage was confined to southern parts of India. Beijing genotype of MTB was significantly associated (p-value <0.0001) with MDR.

To Be or Not to Be a Pseudogene: A Molecular Epidemiological Approach to the mclx Genes and Its Impact in Tuberculosis

Tuberculosis presents a myriad of symptoms, progression routes and propagation patterns not yet fully understood. Whereas for a long time research has focused solely on the patient immunity and overall susceptibility, it is nowadays widely accepted that the genetic diversity of its causative agent, Mycobacterium tuberculosis, plays a key role in this dynamic. This study focuses on a particular family of genes, the mclxs (Mycobacteriumcyclase/LuxR-like genes), which codify for a particular and nearly mycobacterial-exclusive combination of protein domains. mclxs genes were found to be pseudogenized by frameshift-causing insertion(s)/deletion(s) in a considerable number of M. tuberculosis complex strains and clinical isolates. To discern the functional implications of the pseudogenization, we have analysed the pattern of frameshift-causing mutations in a group of M. tuberculosis isolates while taking into account their microbial-, patient- and disease-related traits. Our logistic regression-based analyses have revealed disparate effects associated with the transcriptional inactivation of two mclx genes. In fact, mclx2 (Rv1358) pseudogenization appears to be primarily driven by the microbial phylogenetic background, being mainly related to the Euro-American (EAm) lineage; on the other hand, mclx3 (Rv2488c) presents a higher tendency for pseudogenization among isolates from patients born on the Western Pacific area, and from isolates causing extra-pulmonary infections. These results contribute to the overall knowledge on the biology of M. tuberculosis infection, whereas at the same time launch the necessary basis for the functional assessment of these so far overlooked genes.

Consequences of genomic diversity in Mycobacterium tuberculosis

The causative agent of human tuberculosis, Mycobacterium tuberculosis complex (MTBC), comprises seven phylogenetically distinct lineages associated with different geographical regions. Here we review the latest findings on the nature and amount of genomic diversity within and between MTBC lineages. We then review recent evidence for the effect of this genomic diversity on mycobacterial phenotypes measured experimentally and in clinical settings. We conclude that overall, the most geographically widespread Lineage 2 (includes Beijing) and Lineage 4 (also known as Euro-American) are more virulent than other lineages that are more geographically restricted. This increased virulence is associated with delayed or reduced pro-inflammatory host immune responses, greater severity of disease, and enhanced transmission. Future work should focus on the interaction between MTBC and human genetic diversity, as well as on the environmental factors that modulate these interactions.

Mapping IS6110 in high-copy number Mycobacterium tuberculosis strains shows specific insertion points in the Beijing genotype

BACKGROUND

Mycobacterium tuberculosis Beijing strains are characterized by a large number of IS6110 copies, suggesting the potential implication of this element in the virulence and capacity for rapid dissemination characteristic of this family. This work studies the insetion points of IS6110 in high-copy clinical isolates specifically focusing on the Beijing genotype.

RESULTS

In the present work we mapped the insertion points of IS6110 in all the Beijing strains available in the literature and in the DNA sequence databases. We generated a representative primer collection of the IS6110 locations, which was used to analyse 61 high-copy clinical isolates. A total of 440 points of insertion were identified and analysis of their flanking regions determined the exact location, the direct repeats (DRs), the orientation and the distance to neighboring genes of each copy of IS6110. We identified specific points of insertion in Beijing strains that enabled us to obtain a dendrogram that groups the Beijing genotype.

CONCLUSIONS

This work presents a detailed analysis of locations of IS6110 in high-copy clinical isolates, showing points of insertion present with high frequency in the Beijing family and absent in other strains.

Ethnicity and mycobacterial lineage as determinants of tuberculosis disease phenotype

BACKGROUND

Emerging evidence suggests that Mycobacterium tuberculosis (Mtb) lineage and host ethnicity can determine tuberculosis (TB) clinical disease patterns but their relative importance and interaction are unknown.

METHODS

We evaluated prospectively collected TB surveillance and Mtb strain typing data in an ethnically heterogeneous UK population. Lineage assignment was denoted using 15-loci mycobacterial interspersed repetitive units containing variable numbers of tandem repeats (MIRU-VNTR) and MIRU-VNTRplus. Geographical and ethnic associations of the six global Mtb lineages were identified and the influence of lineage and demographic factors on clinical phenotype were assessed using multivariate logistic regression.

RESULTS

Data were available for 1070 individuals with active TB which was pulmonary only, extrapulmonary only and concurrent pulmonary-extrapulmonary in 52.1%, 36.9% and 11.0% respectively. The most prevalent lineages were Euro-American (43.7%), East African Indian (30.2%), Indo-Oceanic (13.6%) and East Asian (12.2%) and were geo-ethnically restricted with, for example, Indian subcontinent ethnicity inversely associated with Euro-American lineage (OR 0.23; 95% CI 0.14 to 0.39) and positively associated with the East African-Indian lineage (OR 4.04; 95% CI 2.19 to 7.45). Disease phenotype was most strongly associated with ethnicity (OR for extrathoracic disease 21.14 (95% CI 6.08 to 73.48) for Indian subcontinent and 14.05 (3.97 to 49.65) for Afro-Caribbean), after adjusting for lineage. With East Asian lineage as the reference category, the Euro-American (OR 0.54; 95% CI 0.32 to 0.91) and East-African Indian (OR 0.50; 95% CI 0.29 to 0.86) lineages were negatively associated with extrathoracic disease, compared with pulmonary disease, after adjusting for ethnicity.

CONCLUSIONS

Ethnicity is a powerful determinant of clinical TB phenotype independently of mycobacterial lineage and the role of ethnicity-associated factors in pathogenesis warrants investigation.

Genomic stability over 9 years of an isoniazid resistant Mycobacterium tuberculosis outbreak strain in Sweden

In molecular epidemiological studies of drug resistant Mycobacterium tuberculosis (TB) in Sweden a large outbreak of an isoniazid resistant strain was identified, involving 115 patients, mainly from the Horn of Africa. During the outbreak period, the genomic pattern of the outbreak strain has stayed virtually unchanged with regard to drug resistance, IS6110 restriction fragment length polymorphism and spoligotyping patterns. Here we present the complete genome sequence analyses of the index isolate and two isolates sampled nine years after the index case as well as experimental data on the virulence of this outbreak strain. Even though the strain has been present in the community for nine years and passaged between patients at least five times in-between the isolates, we only found four single nucleotide polymorphisms in one of the later isolates and a small (4 amino acids) deletion in the other compared to the index isolate. In contrast to many other evolutionarily successful outbreak lineages (e.g. the Beijing lineage) this outbreak strain appears to be genetically very stable yet evolutionarily successful in a low endemic country such as Sweden. These findings further illustrate that the rate of genomic variation in TB can be highly strain dependent, something that can have important implications for epidemiological studies as well as development of resistance.

Does M. tuberculosis genomic diversity explain disease diversity?

The outcome of tuberculosis infection and disease is highly variable. This variation has been attributed primarily to host and environmental factors, but better understanding of the global genomic diversity in the M. tuberculosis complex (MTBC) suggests that bacterial factors could also be involved. Review of nearly 100 published reports shows that MTBC strains differ in their virulence and immunogenicity in experimental models, but whether this phenotypic variation plays a role in human disease remains unclear. Given the complex interactions between the host, the pathogen and the environment, linking MTBC genotypic diversity to experimental and clinical phenotypes requires an integrated systems epidemiology approach embedded in a robust evolutionary framework.

Evidence for a rapid rate of molecular evolution at the hypervariable and immunogenic Mycobacterium tuberculosis PPE38 gene region

BACKGROUND

PPE38 (Rv2352c) is a member of the large PPE gene family of Mycobacterium tuberculosis and related mycobacteria. The function of PPE proteins is unknown but evidence suggests that many are cell-surface associated and recognised by the host immune system. Previous studies targeting other PPE gene members suggest that some display high levels of polymorphism and it is thought that this might represent a means of providing antigenic variation. We have analysed the genetic variability of the PPE38 genomic region on a cohort of M. tuberculosis clinical isolates representing all of the major phylogenetic lineages, along with the ancestral M. tuberculosis complex (MTBC) member M. canettii, and supplemented this with analysis of publicly available whole genome sequences representing additional M. tuberculosis clinical isolates, other MTBC members and non tuberculous mycobacteria (NTM). Where possible we have extended this analysis to include the adjacent plcABC and PPE39/40 genomic regions.

RESULTS

We show that the ancestral MTBC PPE38 region comprises 2 homologous PPE genes (PPE38 and PPE71), separated by 2 esat-6 (esx)-like genes and that this structure derives from an esx/esx/PPE duplication in the common ancestor of M. tuberculosis and M. marinum. We also demonstrate that this region of the genome is hypervariable due to frequent IS6110 integration, IS6110-associated recombination, and homologous recombination and gene conversion events between PPE38 and PPE71. These mutations result in combinations of gene deletion, gene truncation and gene disruption in the majority of clinical isolates. These mutations were generally found to be IS6110 strain lineage-specific, although examples of additional within-lineage and even within-cluster mutations were observed. Furthermore, we provide evidence that the published M. tuberculosis H37Rv whole genome sequence is inaccurate regarding this region.

CONCLUSION

Our results show that this antigen-encoding region of the M. tuberculosis genome is hypervariable. The observation that numerous different mutations have become fixed within specific lineages demonstrates that this genomic region is undergoing rapid molecular evolution and that further lineage-specific evolutionary expansion and diversification has occurred subsequent to the lineage-defining mutational events. We predict that functional loss of these genes could aid immune evasion. Finally, we also show that the PPE38 region of the published M. tuberculosis H37Rv whole genome sequence is not representative of the ATCC H37Rv reference strain.

IS6110 in oriC affects the morphology and growth of Mycobacterium tuberculosis and attenuates virulence in mice

The IS6110 element is widely used in studies of molecular epidemiology of tuberculosis and it is considered the gold standard for genotyping Mycobacterium tuberculosis strains. Because of its high frequency of transposition, IS6110 is probably a major contributor to the evolution of M. tuberculosis. Nevertheless, very few studies of the effect of IS6110 insertions on the virulence of M. tuberculosis have been reported. We analysed two isogenic groups of M. tuberculosis strains isolated from the sputa of two patients. Strains belonging to the same isogenic group differed from one another by one IS6110-oriC hybridising band, but they showed identical spoligo and MIRU-VNTR profiles. Isogenic strains containing the IS6110 element in oriC exhibited a diminished growth rate and average dimensions of the bacilli were modified; moreover, they were less virulent in a mouse model.

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.

Tuberculosis, caused by the bacterium Mycobacterium tuberculosis, kills over 2 million people each year. It is estimated that approximately one-third of the world population is infected with M. tuberculosis, though the majority will never develop active disease. The most severe form of tuberculosis occurs when the bacterium spreads to the brain to cause meningitis. We examined whether the genetic variation of the person and the bacteria influenced the type of disease a person develops. We have previously shown that certain mutations in genes of the human immune system can predispose adults in Vietnam to developing tuberculous meningitis. In this study we show that some strains of M. tuberculosis commonly found in Europe and America are less likely to cause tuberculous meningitis in Vietnamese adults than strains predominantly found in Asia. We then looked at the interaction between M. tuberculosis strains and mutations in human immune genes and show that a particular mutation, TLR2 T597C, is more commonly found in patients infected with the East-Asian/Beijing strains of M. tuberculosis. This is the first study to look at both the host and pathogen genotypes together in tuberculosis infection, and the findings suggest that the outcome of exposure to M. tuberculosis can depend on both the human genotype and the bacterial genotype.

Using polymerase chain reaction with primers based on the plcB-plcC intergenic region to detect Mycobacterium tuberculosis in clinical samples

OBJECTIVE

To develop a system for the molecular diagnosis of tuberculosis by polymerase chain reaction (PCR), constructing primers based on the difference in gene organization of the intergenic region of phospholipase C (plcB-plcC region), which differentiates Mycobacterium tuberculosis from other mycobacteria.

METHODS

A PCR product of the expected size (432 bp) was obtained from M. tuberculosis and M. africanum only. A total of 33 mycobacterial isolates and 273 clinical samples from patients suspected of having tuberculosis were examined. These were used in the comparative study of the PCR technique versus culture.

RESULTS

For PCR versus culture, the data showed 93.8% accuracy (p < 0.0001), 93.1% sensitivity (CI: 88.7-96.0), and 96.4% specificity (CI: 96.1-99.4). The Kappa value (0.82) shows that there was a near-perfect concordance between the two tests.

CONCLUSION

The use of the plcB-plcC region in PCR amplification was found to be an important and reliable tool for the specific diagnosis of tuberculosis in the samples analyzed.

Association between Mycobacterium tuberculosis Beijing/W lineage strain infection and extrathoracic tuberculosis: Insights from epidemiologic and clinical characterization of the three principal genetic groups of M. tuberculosis clinical isolates

Clinical strains of Mycobacterium tuberculosis can be divided into three principal genetic groups based on the single-nucleotide polymorphisms at the katG gene codon 463 and the gyrA gene codon 95. One subgroup of genetic group 1, the Beijing/W lineage, has been widely studied because of its worldwide distribution and association with outbreaks. In order to increase our understanding of the clinical and epidemiological relevance of the genetic grouping of M. tuberculosis clinical strains and the Beijing/W lineage, we investigated the genetic grouping of 679 clinical isolates of M. tuberculosis, representing 96.3% of culture-confirmed tuberculosis cases diagnosed in Arkansas between January 1996 and December 2000 using PCR and DNA sequencing. We assessed the associations of infections by different genetic groups of M. tuberculosis strains and infection by the Beijing/W lineage strains with the clinical and epidemiological characteristics of the patients using chi-square tests and multivariate logistic regression analysis. Of the 679 study isolates, 676 fell into one of the three principal genetic groups, with 63 (9.3%) in group 1, 438 (64.8%) in group 2, and 175 (25.9%) in group 3. After adjusting for potential confounding of age, gender, race/ethnicity, human immunodeficiency virus serostatus, and plcD genotype in a multivariate logistic regression model, patients infected by the Beijing/W lineage isolates were nearly three times as likely as patients infected with the non-Beijing/W lineage isolates to have an extrathoracic involvement (odds ratio [95% confidence interval], 2.85 [1.33, 6.12]). Thus, the Beijing/W lineage strains may have some special biological features that facilitate the development of extrathoracic tuberculosis.

Population-based study of deletions in five different genomic regions of Mycobacterium tuberculosis and possible clinical relevance of the deletions

Regions of difference (RDs) have been described in clinical isolates of Mycobacterium tuberculosis, but the potential epidemiological and clinical relevance of the genotypes of these RDs remains to be investigated. We screened a population-based sample of 648 isolates for the deletion of five RDs, designated RD105, RD181, RD142, RD150, and RD239, using microarray-based hybridization, PCR, and DNA sequencing and assessed the associations between the RD deletions and the clinical characteristics of the patients using chi-square analysis and multivariate logistic regression model. Of the 648 isolates, 18 (2.8%) had the RD239 deletion and 39 (6.0%) had the RD105 deletion. The deletions of RD142, RD150, and RD181 subdivided the isolates with the RD105 deletion into four groups comprising a group with concurrent deletions of RD105, RD181, and RD142 (n = 13); a group with concurrent deletions of RD105, RD181, and RD150 (n = 5); a group with concurrent deletions of RD105 and RD181 (n = 13); and a group with a deletion of RD105 only (n = 8). Extrathoracic tuberculosis is statistically significantly associated with infection with the isolates with concurrent deletions of RD105, RD181, and RD142 (adjusted odds ratio [OR] = 3.05; 95% confidence interval [CI] = 1.58, 5.90) and the isolates with concurrent deletions of RD105, RD181, and RD150 (adjusted OR = 11.09; 95% CI = 4.27, 28.80), after controlling for the previously identified risk factors for extrathoracic tuberculosis (human immunodeficiency virus serostatus, race, gender, and the genotype of the plcD gene). These two combinations of RD deletions have the potential for predicting the clinical presentation of M. tuberculosis infection in the human host.

Identification of an IS6110 insertion site in plcD, the unique phospholipase C gene of Mycobacterium bovis

The IS6110 repetitive element is present in multiple copies in most Mycobacterium tuberculosis complex bacteria, except for Mycobacterium bovis strains, which usually contain a single copy of IS6110 located on a 1·9 kb PvuII fragment of the direct repeat region. IS6110 transposition can disrupt coding regions and is a major force of genomic variation. In a previous work it was demonstrated that phospholipase C genes are preferential loci for IS6110 transposition in M. tuberculosis clinical strains. Bacterial phospholipase C enzymes participate in pathogenic mechanisms used by different organisms, and have been implicated in intracellular survival, cytolysis and cell-to-cell spread. Four phospholipase C genes (plcA, plcB, plcC and plcD) were detected in the genomes of M. tuberculosis, Mycobacterium africanum, Mycobacterium microti and ‘Mycobacterium canettii’. M. bovis and the vaccine strain M. bovis Bacillus Calmette–Guérin contain only the plcD gene. In the present work, the existence of IS6110 insertions within plcD, the unique phospholipase C gene of M. bovis, has been investigated by PCR, Southern blot hybridization and sequencing analysis. In 18 (7·3 %) of 245 isolates analysed, the plcD gene was interrupted by the insertion of one copy of IS6110, which in all cases was transposed in the same orientation and at the same position, 1 972 894, relative to the genome of M. bovis AF2122/97. These 18 isolates were distributed in 6 different spoligotype patterns and contained 4 to 8 IS6110 copies. In contrast, strains showing an intact plcD gene contained one (87 %), two (9·4 %) or three (2·4 %) IS6110 copies, and only a single isolate (1·2 %) had four IS6110 copies. The implications of plcD gene disruption in M. bovis have not been fully investigated, but no differences in the organ distribution of the disease were detected when animals infected with strains from the same spoligotype patterns bearing plcD : : IS6110 and intact plcD were compared.