Restricted structural gene polymorphism in the Mycobacterium tuberculosis complex indicates evolutionarily recent global dissemination

Simple multiplex PCR assay for identification of Beijing family Mycobacterium tuberculosis isolates with a lineage-specific mutation in Rv0679c

The Beijing genotype of Mycobacterium tuberculosis is known to be a worldwide epidemic clade. It is suggested to be a possibly resistant clone against BCG vaccination and is also suggested to be highly pathogenic and prone to becoming drug resistant. Thus, monitoring the prevalence of this lineage seems to be important for the proper control of tuberculosis. The Rv0679c protein of M. tuberculosis has been predicted to be one of the outer membrane proteins and is suggested to contribute to host cell invasion. Here, we conducted a sequence analysis of the Rv0679c gene using clinical isolates and found that a single nucleotide polymorphism, C to G at position 426, can be observed only in the isolates that are identified as members of the Beijing genotype family. Here, we developed a simple multiplex PCR assay to detect this point mutation and applied it to 619 clinical isolates. The method successfully distinguished Beijing lineage clones from non-Beijing strains with 100% accuracy. This simple, quick, and cost-effective multiplex PCR assay can be used for a survey or for monitoring the prevalence of Beijing genotype M. tuberculosis strains.

Characterization of mutations in multi- and extensive drug resistance among strains of Mycobacterium tuberculosis clinical isolates in Republic of Korea

In order to characterize molecular mechanisms of first- and second-line drug resistance in Mycobacterium tuberculosis and to evaluate the use of molecular markers of resistance, we analyzed 62 multidrug-resistant, 100 extensively drug-resistant, and 30 pan-susceptible isolates from Korean tuberculosis patients. Twelve genome regions associated with drug resistance, including katG, ahpC, and inhA promoter for isoniazid (INH); embB for ethambutol (EMB), rpoB for rifampin (RIF), pncA for pyrazinamide (PZA), gyrA for fluoroquinolones; rpsL, gidB, and rrs for streptomycin; rrs and eis for kanamycin (KM); rrs and tylA for capreomycin (CAP); and rrs for amikacin (AMK) were amplified simultaneously by polymerase chain reaction, and the DNA sequences were determined. We found mutations in 140 of 160 INH-resistant isolates (87.5%), 159 of 162 RIF-resistant isolates (98.15%), 127 of 143 EMB-resistant isolates (88.8%), 108 of 123 ofloxacin-resistant isolates (87.8%), and 107 of 122 PZA-resistant isolates (87.7%); 43 of 51 STM-resistant isolates (84.3%), 15 of 17 KM-resistant isolates (88.2%), and 14 of 15 (AMK and CAP)-resistant isolates (93.3%) had mutations related to specific drug resistance. In addition, the sequence analyses of the study revealed many novel mutations involving these loci. This result suggests that mutations in the rpoB531, katGSer315Thr, and C-15T in the inhA promoter region, and gyrA94, embB306, pncA159, rpsL43, and A1401G in the rrs gene could serve as useful markers for rapid detection of resistance profile in the clinical isolates of M. tuberculosis in Korea, with potentials for the new therapeutic benefits in actual clinical practice.

Advances in tuberculosis diagnostics: the Xpert MTB/RIF assay and future prospects for a point-of-care test

Rapid progress has been made in the development of new diagnostic assays for tuberculosis in recent years. New technologies have been developed and assessed, and are now being implemented. The Xpert MTB/RIF assay, which enables simultaneous detection of Mycobacterium tuberculosis (MTB) and rifampicin (RIF) resistance, was endorsed by WHO in December, 2010. This assay was specifically recommended for use as the initial diagnostic test for suspected drug-resistant or HIV-associated pulmonary tuberculosis. By June, 2012, two-thirds of countries with a high tuberculosis burden and half of countries with a high multidrug-resistant tuberculosis burden had incorporated the assay into their national tuberculosis programme guidelines. Although the development of the Xpert MTB/RIF assay is undoubtedly a landmark event, clinical and programmatic effects and cost-effectiveness remain to be defined. We review the rapidly growing body of scientific literature and discuss the advantages and challenges of using the Xpert MTB/RIF assay in areas where tuberculosis is endemic. We also review other prospects within the developmental pipeline. A rapid, accurate point-of-care diagnostic test that is affordable and can be readily implemented is urgently needed. Investment in the tuberculosis diagnostics pipeline should remain a major priority for funders and researchers.

Current trends of Mycobacterium tuberculosis molecular epidemiology in Saudi Arabia and associated demographical factors

Data are scarce on demographical factors related to the population structure of Mycobacterium tuberculosis in Saudi Arabia. A study was conducted on 902 clinical isolates to explore current trends in the phylogeography and associated demographical factors of tuberculosis by using spoligotyping and 24 loci based MIRU-VNTR typing. Young male patients (aged 16-29 and 30-44) were predominant in this cohort. The phylogenetic diversity among M. tuberculosis isolates was found high, as almost all known genetic lineages were identified. Delhi/CAS (26.4%), EAI (13.7%) and Haarlem (11.3%) were the most common lineages observed, particularly among the low age groups (16-29 and 30-44 years), whereas elderly patients (>60 years) showed a predominance in the lineages S, Ghana, TUR and Uganda-I. A statistically significant association was observed between gender of the patients and lineages of EAI (p value 0.026) and LAM (p value 0.005). Overall, molecular strain cluster rate was 34.4% with an elevated rate among patients aged below 15 years (43.1%), while cases among the elderly (>60 years) showed the lowest degree of clustering (12.5%). The largest level of clustering was noticed among cases caused by strains of the lineages Haarlem (59.8%), Beijing (55.8%) and LAM (42.8%). The current population structure of M. tuberculosis in Saudi Arabia is highly diverse with significant associations to demography, transmission dynamics and origin of the patients. The difference in genotype distributions among low and high aged patients reflects the ongoing change in the strain population structure in the country.

HIV infection disrupts the sympatric host-pathogen relationship in human tuberculosis

The phylogeographic population structure of Mycobacterium tuberculosis suggests local adaptation to sympatric human populations. We hypothesized that HIV infection, which induces immunodeficiency, will alter the sympatric relationship between M. tuberculosis and its human host. To test this hypothesis, we performed a nine-year nation-wide molecular-epidemiological study of HIV–infected and HIV–negative patients with tuberculosis (TB) between 2000 and 2008 in Switzerland. We analyzed 518 TB patients of whom 112 (21.6%) were HIV–infected and 233 (45.0%) were born in Europe. We found that among European-born TB patients, recent transmission was more likely to occur in sympatric compared to allopatric host–pathogen combinations (adjusted odds ratio [OR] 7.5, 95% confidence interval [95% CI] 1.21–infinity, p = 0.03). HIV infection was significantly associated with TB caused by an allopatric (as opposed to sympatric) M. tuberculosis lineage (OR 7.0, 95% CI 2.5–19.1, p<0.0001). This association remained when adjusting for frequent travelling, contact with foreigners, age, sex, and country of birth (adjusted OR 5.6, 95% CI 1.5–20.8, p = 0.01). Moreover, it became stronger with greater immunosuppression as defined by CD4 T-cell depletion and was not the result of increased social mixing in HIV–infected patients. Our observation was replicated in a second independent panel of 440 M. tuberculosis strains collected during a population-based study in the Canton of Bern between 1991 and 2011. In summary, these findings support a model for TB in which the stable relationship between the human host and its locally adapted M. tuberculosis is disrupted by HIV infection.

Human tuberculosis (TB) caused by Mycobacterium tuberculosis kills 1.5 million people each year. M. tuberculosis has been affecting humans for millennia, suggesting that different strain lineages may be adapted to specific human populations. The combination of a particular strain lineage and its corresponding patient population can be classified as sympatric (e.g. Euro-American lineage in Europeans) or allopatric (e.g. East-Asian lineage in Europeans). We hypothesized that infection with the human immunodeficiency virus (HIV), which impairs the human immune system, will interfere with this host–pathogen relationship. We performed a nation-wide molecular-epidemiological study of HIV–infected and HIV–negative TB patients between 2000 and 2008 in Switzerland. We found that HIV infection was associated with the less adapted allopatric lineages among patients born in Europe, and this was not explained by social or other patient factors such as increased social mixing in HIV–infected individuals. Strikingly, the association between HIV infection and less adapted M. tuberculosis lineages was stronger in patients with more pronounced immunodeficiency. Our observation was replicated in a second independent panel of M. tuberculosis strains collected during a population-based study in the Canton of Bern. In summary, our study provides evidence that the sympatric host–pathogen relationship in TB is disrupted by HIV infection.

Comparative genomic analysis of Mycobacterium tuberculosis drug resistant strains from Russia

Tuberculosis caused by multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mycobacterium tuberculosis (MTB) strains is a growing problem in many countries. The availability of the complete nucleotide sequences of several MTB genomes allows to use the comparative genomics as a tool to study the relationships of strains and differences in their evolutionary history including acquisition of drug-resistance. In our work, we sequenced three genomes of Russian MTB strains of different phenotypes--drug susceptible, MDR and XDR. Of them, MDR and XDR strains were collected in Tomsk (Siberia, Russia) during the local TB outbreak in 1998-1999 and belonged to rare KQ and KY families in accordance with IS6110 typing, which are considered endemic for Russia. Based on phylogenetic analysis, our isolates belonged to different genetic families, Beijing, Ural and LAM, which made the direct comparison of their genomes impossible. For this reason we performed their comparison in the broader context of all M. tuberculosis genomes available in GenBank. The list of unique individual non-synonymous SNPs for each sequenced isolate was formed by comparison with all SNPs detected within the same phylogenetic group. For further functional analysis, all proteins with unique SNPs were ascribed to 20 different functional classes based on Clusters of Orthologous Groups (COG). We have confirmed drug resistant status of our isolates that harbored almost all known drug-resistance associated mutations. Unique SNPs of an XDR isolate CTRI-4(XDR), belonging to a Beijing family were compared in more detail with SNPs of additional 14 Russian XDR strains of the same family. Only type specific mutations in genes of repair, replication and recombination system (COG category L) were found common within this group. Probably the other unique SNPs discovered in CTRI-4(XDR) may have an important role in adaptation of this microorganism to its surrounding and in escape from antituberculosis drugs treatment.

Genomic analysis of smooth tubercle bacilli provides insights into ancestry and pathoadaptation of Mycobacterium tuberculosis

Global spread and limited genetic variation are hallmarks of M. tuberculosis, the agent of human tuberculosis. In contrast, Mycobacterium canettii and related tubercle bacilli that also cause human tuberculosis and exhibit unusual smooth colony morphology are restricted to East Africa. Here, we sequenced and analyzed the whole genomes of five representative strains of smooth tubercle bacilli (STB) using Sanger (4-5× coverage), 454/Roche (13-18× coverage) and/or Illumina DNA sequencing (45-105× coverage). We show that STB isolates are highly recombinogenic and evolutionarily early branching, with larger genome sizes, higher rates of genetic variation, fewer molecular scars and distinct CRISPR-Cas systems relative to M. tuberculosis. Despite the differences, all tuberculosis-causing mycobacteria share a highly conserved core genome. Mouse infection experiments showed that STB strains are less persistent and virulent than M. tuberculosis. We conclude that M. tuberculosis emerged from an ancestral STB-like pool of mycobacteria by gain of persistence and virulence mechanisms, and we provide insights into the molecular events involved.

Pathogen typing in the genomics era: MLST and the future of molecular epidemiology

Multi-locus sequence typing (MLST) is a high-resolution genetic typing approach to identify species and strains of pathogens impacting human health, agriculture (animals and plants), and biosafety. In this review, we outline the general concepts behind MLST, molecular approaches for obtaining MLST data, analytical approaches for MLST data, and the contributions MLST studies have made in a wide variety of areas. We then look at the future of MLST and their relative strengths and weaknesses with respect to whole genome sequence typing approaches that are moving into the research arena at an ever-increasing pace. Throughout the paper, we provide exemplar references of these various aspects of MLST. The literature is simply too vast to make this review comprehensive, nevertheless, we have attempted to include enough references in a variety of key areas to introduce the reader to the broad applications and complications of MLST data.

Mixed-strain mycobacterium tuberculosis infections and the implications for tuberculosis treatment and control

Numerous studies have reported that individuals can simultaneously harbor multiple distinct strains of Mycobacterium tuberculosis. To date, there has been limited discussion of the consequences for the individual or the epidemiological importance of mixed infections. Here, we review studies that documented mixed infections, highlight challenges associated with the detection of mixed infections, and discuss possible implications of mixed infections for the diagnosis and treatment of patients and for the community impact of tuberculosis control strategies. We conclude by highlighting questions that should be resolved in order to improve our understanding of the importance of mixed-strain M. tuberculosis infections.

Genetic diversity in Mycobacterium tuberculosis

Recent years have witnessed an increased appreciation of the extent and relevance of strain-to-strain variation in Mycobacterium tuberculosis. This paradigm shift can largely be attributed to an improved understanding of the global population structure of this organism, and to the realisation that the various members of the M. tuberculosis complex (MTBC) harbour more genetic diversity than previously realised. Moreover, many studies using experimental models of infection have demonstrated that MTBC diversity translates into significant differences in immunogenecity and virulence . However, linking these experimental phenotypes to relevant clinical phenotypes has been difficult, and to date, largely unsuccessful. Nevertheless, emerging high-throughput technologies, in particular next-generation sequencing , offer new opportunities, and have already lead to important new insights. Given the complexity of the host-pathogen interaction in tuberculosis, systems approaches will be key to define the role of MTBC diversity in the fight against one of humankind's most important pathogens.

Significance of the identification in the Horn of Africa of an exceptionally deep branching Mycobacterium tuberculosis clade

Molecular and phylogeographic studies have led to the definition within the Mycobacterium tuberculosis complex (MTBC) of a number of geotypes and ecotypes showing a preferential geographic location or host preference. The MTBC is thought to have emerged in Africa, most likely the Horn of Africa, and to have spread worldwide with human migrations. Under this assumption, there is a possibility that unknown deep branching lineages are present in this region. We genotyped by spoligotyping and multiple locus variable number of tandem repeats (VNTR) analysis (MLVA) 435 MTBC isolates recovered from patients. Four hundred and eleven isolates were collected in the Republic of Djibouti over a 12 year period, with the other 24 isolates originating from neighbouring countries. All major M. tuberculosis lineages were identified, with only two M. africanum and one M. bovis isolates. Upon comparison with typing data of worldwide origin we observed that several isolates showed clustering characteristics compatible with new deep branching. Whole genome sequencing (WGS) of seven isolates and comparison with available WGS data from 38 genomes distributed in the different lineages confirms the identification of ancestral nodes for several clades and most importantly of one new lineage, here referred to as lineage 7. Investigation of specific deletions confirms the novelty of this lineage, and analysis of its precise phylogenetic position indicates that the other three superlineages constituting the MTBC emerged independently but within a relatively short timeframe from the Horn of Africa. The availability of such strains compared to the predominant lineages and sharing very ancient ancestry will open new avenues for identifying some of the genetic factors responsible for the success of the modern lineages. Additional deep branching lineages may be readily and efficiently identified by large-scale MLVA screening of isolates from sub-Saharan African countries followed by WGS analysis of a few selected isolates.

First insights into the phylogenetic diversity of Mycobacterium tuberculosis in Nepal

Background

Tuberculosis (TB) is a major public health problem in Nepal. Strain variation in Mycobacterium tuberculosis may influence the outcome of TB infection and disease. To date, the phylogenetic diversity of M. tuberculosis in Nepal is unknown.

Methods and Findings

We analyzed 261 M. tuberculosis isolates recovered from pulmonary TB patients recruited between August 2009 and August 2010 in Nepal. M. tuberculosis lineages were determined by single nucleotide polymorphisms (SNP) typing and spoligotyping. Drug resistance was determined by sequencing the hot spot regions of the relevant target genes. Overall, 164 (62.8%) TB patients were new, and 97 (37.2%) were previously treated. Any drug resistance was detected in 50 (19.2%) isolates, and 16 (6.1%) were multidrug-resistant. The most frequent M. tuberculosis lineage was Lineage 3 (CAS/Delhi) with 106 isolates (40.6%), followed by Lineage 2 (East-Asian lineage, includes Beijing genotype) with 84 isolates (32.2%), Lineage 4 (Euro-American lineage) with 41 (15.7%) isolates, and Lineage 1 (Indo-Oceanic lineage) with 30 isolates (11.5%). Based on spoligotyping, we found 45 different spoligotyping patterns that were previously described. The Beijing (83 isolates, 31.8%) and CAS spoligotype (52, 19.9%) were the dominant spoligotypes. A total of 36 (13.8%) isolates could not be assigned to any known spoligotyping pattern. Lineage 2 was associated with female sex (adjusted odds ratio [aOR] 2.58, 95% confidence interval [95% CI] 1.42–4.67, p = 0.002), and any drug resistance (aOR 2.79; 95% CI 1.43–5.45; p = 0.002). We found no evidence for an association of Lineage 2 with age or BCG vaccination status.

Conclusions

We found a large genetic diversity of M. tuberculosis in Nepal with representation of all four major lineages. Lineages 3 and 2 were dominating. Lineage 2 was associated with clinical characteristics. This study fills an important gap on the map of the M. tuberculosis genetic diversity in the Asian region.

Single nucleotide polymorphisms in Mycobacterium tuberculosis and the need for a curated database

Recent advances in DNA sequencing have led to the discovery of thousands of single nucleotide polymorphisms (SNPs) in clinical isolates of Mycobacterium tuberculosis complex (MTBC). This genetic variation has changed our understanding of the differences and phylogenetic relationships between strains. Many of these mutations can serve as phylogenetic markers for strain classification, while others cause drug resistance. Moreover, SNPs can affect the bacterial phenotype in various ways, which may have an impact on the outcome of tuberculosis (TB) infection and disease. Despite the importance of SNPs for our understanding of the diversity of MTBC populations, the research community currently lacks a comprehensive, well-curated and user-friendly database dedicated to SNP data. First attempts to catalogue and annotate SNPs in MTBC have been made, but more work is needed. In this review, we discuss the biological and epidemiological relevance of SNPs in MTBC. We then review some of the analytical challenges involved in processing SNP data, and end with a list of features, which should be included in a new SNP database for MTBC.

Population structure and circulating genotypes of drug-sensitive and drug-resistant Mycobacterium tuberculosis clinical isolates in São Paulo state, Brazil

São Paulo is the most populous Brazilian state and reports the largest number of tuberculosis cases in the country annually (over 18,500). This study included 193 isolates obtained during the 2nd Nationwide Survey on Mycobacterium tuberculosis Drug Resistance that was conducted in São Paulo state and 547 isolates from a laboratory based study of drug resistance that were analyzed by the Mycobacteria Reference Laboratory at the Institute Adolfo Lutz. Both studies were conducted from 2006 to 2008 and sought to determine the genetic diversity and pattern of drug resistance of M. tuberculosis isolates (MTC) circulating in São Paulo. The patterns obtained from the spoligotyping analysis demonstrated that 51/740 (6.9%) of the isolates corresponded to orphan patterns and that 689 (93.1%) of the isolates distributed into 144 shared types, including 119 that matched a preexisting shared type in the SITVIT2 database and 25 that were new isolates. A total of 77/144 patterns corresponded to unique isolates, while the remaining 67 corresponded to clustered patterns (n=612 isolates clustered into groups of 2-84 isolates each). The evolutionarily ancient PGG1 lineages (Beijing, CAS1-DEL, EAI3-IND, and PINI2) were rarely detected in São Paulo and comprised only 13/740, or 1.76%, of the total isolates; all of the remaining 727/740, or 98.24%, of the MTC isolates from São Paulo state were from the recent PGG2/3 evolutionary isolates belonging to the LAM, T, S, X, and Haarlem lineages, i.e., the Euro-American group. This study provides the first overview of circulating genotypes of M. tuberculosis in São Paulo state and demonstrates that the clustered shared types containing seven or more M. tuberculosis isolates that are spread in São Paulo state included both resistant and susceptible isolates.

Genotype of a historic strain of Mycobacterium tuberculosis

The use of ancient DNA in paleopathological studies of tuberculosis has largely been restricted to confirmation of disease identifications made by skeletal analysis; few attempts at obtaining genotype data from archaeological samples have been made because of the need to perform different PCRs for each genetic locus being studied in an ancient DNA extract. We used a next generation sequencing approach involving hybridization capture directed at specific polymorphic regions of the Mycobacterium tuberculosis genome to identify a detailed genotype for a historic strain of M. tuberculosis from an individual buried in the 19th century St. George's Crypt, Leeds, West Yorkshire, England. We obtained 664,500 sequencing by oligonucleotide ligation and detection (SOLiD) reads that mapped to the targeted regions of the M. tuberculosis genome; the coverage included 218 of 247 SNPs, 10 of 11 insertion/deletion regions, and the repeat elements IS1081 and IS6110. The accuracy of the SOLiD data was checked by conventional PCRs directed at 11 SNPs and two insertion/deletions. The data placed the historic strain of M. tuberculosis in a group that is uncommon today, but it is known to have been present in North America in the early 20th century. Our results show the use of hybridization capture followed by next generation sequencing as a means of obtaining detailed genotypes of ancient varieties of M. tuberculosis, potentially enabling meaningful comparisons between strains from different geographic locations and different periods in the past.

The genotypic population structure of Mycobacterium tuberculosis complex from Moroccan patients reveals a predominance of Euro-American lineages

BACKGROUND

Tuberculosis (TB) remains a major health problem in Morocco. Characterization of circulating Mycobacterium tuberculosis genotypic lineages, important to understand the dynamic of the disease, was hereby addressed for the first time at a national level.

METHODOLOGY/PRINCIPAL FINDINGS

Spoligotyping was performed on a panel of 592 M. tuberculosis complex strains covering a 2-year period (2004-2006). It identified 129 patterns: 105 (n = 568 strains) corresponded to a SIT number in the SITVIT2 database, while 24 patterns were labeled as orphan. A total of 523 (88.3%) strains were clustered vs. 69 or 11.7% unclustered. Classification of strains within 3 large phylogenetical groups was as follows: group 1- ancestral/TbD1+/PGG1 (EAI, Bovis, Africanum), group 2- modern/TbD1-/PGG1 group (Beijing, CAS), group 3- evolutionary recent/TbD1-/PGG2/3 (Haarlem, X, S, T, LAM; alternatively designated as the Euro-American lineage). As opposed to group 3 strains (namely LAM, Haarlem, and T) that predominated (86.5% of all isolates), 6 strains belonged to group 2 (Beijing n = 5, CAS n = 1), and 3 strains (BOV_1 n = 2, BOV_4-CAPRAE) belonged to ancestral group 1 (EAI and AFRI lineage strains were absent). 12-loci MIRU-VNTR typing of the Casablanca subgroup (n = 114 strains) identified 71 patterns: 48 MITs and 23 orphan patterns; it allowed to reduce the clustering rate from 72.8% to 29.8% and the recent transmission rate from 64% to 20.2%.

CONCLUSION

The M. tuberculosis population structure in Morocco is highly homogeneous, and is characterized by the predominance of the Euro-American lineages, namely LAM, Haarlem, and T, which belong to the "evolutionary recent" TbD1-/PGG2/3 phylogenetic group. The combination of spoligotyping and MIRUs decreased the clustering rate significantly, and should now be systematically applied in larger studies. The methods used in this study appear well suited to monitor the M. tuberculosis population structure for an enhanced TB management program in Morocco.

Mycobacterium tuberculosis strains potentially involved in the TB epidemic in Sweden a century ago

A hundred years ago the prevalence of tuberculosis (TB) in Sweden was one of the highest in the world. In this study we conducted a population-based search for distinct strains of Mycobacterium tuberculosis complex isolated from patients born in Sweden before 1945. Many of these isolates represent the M. tuberculosis complex population that fueled the TB epidemic in Sweden during the first half of the 20^th century.

Single nucleotide polymorphisms in the Mycobacterium bovis genome resolve phylogenetic relationships

Mycobacterium bovis isolates carry restricted allelic variation yet exhibit a range of disease phenotypes and host preferences. Conventional genotyping methods target small hypervariable regions of the M. bovis genome and provide anonymous biallelic information that is insufficient to develop phylogeny. To resolve phylogeny and establish trait-allele associations, we interrogated 75 M. bovis and 61 M. tuberculosis genomes for single nucleotide polymorphisms (SNPs), using iPLEX MassArray (Sequenom Inc., CA) technology. We indexed nucleotide variations in 306 genic and 44 intergenic loci among isolates derived from outbreaks in the United States from 1991 to 2010 and isolated from a variety of mammalian hosts. Two hundred six variant SNPs classified the 136 isolates and 4 previously sequenced strains (AF2122/97, BCG Pasteur, H37Rv, and CDC1551) into 5 major "SNP cluster groups." M. bovis isolates clustered into three major lineages based on 118 variant SNPs, while 84 SNPs differentiated the M. bovis BCG lineage from the virulent isolates. Forty-nine of the 51 human M. tuberculosis isolates were identical at all 350 loci studied. Thus, SNP-based analyses resolved the genotypic differences within M. bovis strains and differentiated these strains from M. tuberculosis strains representing diversity in time and space, providing population genetic frameworks that may aid in identifying factors responsible for the wide host range and disease phenotypes of M. bovis.

Next-generation ion torrent sequencing of drug resistance mutations in Mycobacterium tuberculosis strains

A novel protocol for full-length Mycobacterium tuberculosis gene analysis of first- and second-line drug resistance was developed using the Ion Torrent Personal Genome Machine (PGM). Five genes-rpoB (rifampin), katG (isoniazid), pncA (pyrazinamide), gyrA (ofloxacin/fluoroquinolone), and rrs (aminoglycosides)-were amplified and sequenced, and results were compared to those obtained by genotypic Hain line probe assay (LPA) and phenotypic Bactec MGIT 960 analysis using 26 geographically diverse South African clinical isolates collected between July and November 2011. Ion Torrent sequencing exhibited 100% (26/26) concordance to phenotypic resistance obtained by MGIT 960 culture and genotypic rpoB and katG results by LPA. In several rifampin-resistant isolates, Ion Torrent sequencing revealed uncommon substitutions (H526R and D516G) that did not have a defined mutation by LPA. Importantly, previously uncharacterized mutations in rpoB (V194I), rrs (G878A), and pncA (Q122Stop) genes were observed. Ion Torrent sequencing may facilitate tracking and monitoring geographically diverse multidrug-resistant and extensively drug-resistant strains and could potentially be integrated into selected regional and reference settings throughout Africa, India, and China.

Highlights on molecular identification of closely related species

The term "complex" emerged in the literature at the beginning of the genomic era associated to taxonomy and grouping organisms that belong to different species but exhibited similar patterns according to their morphological, physiological and/or other phenotypic features. DNA-DNA hybridization values ~70% and high identity on 16S rRNA gene sequences were recommended for species delineation. Electrophoretic methods showed in some cases to be useful for species identification and population structure but the reproducibility was questionable. Later, the implementation of polyphasic approaches involving phenotypic and molecular methods brought new insights into the analysis of population structure and phylogeny of several "species complexes", allowing the identification of new closely related species. Likewise, the introduction of multilocus sequence typing and sequencing analysis of several genes offered an evolutionary perspective to the term "species complex". Several centres worldwide have recently released increasing genetic information on distinct microbial species. A brief review will be presented to highlight the definition of "species complex" for selected microorganisms, mainly the prokaryotic Acinetobacter calcoaceticus -Acinetobacter baumannii, Borrelia burgdorferi sensu lato, Burkholderia cepacia, Mycobacterium tuberculosis and Nocardia asteroides complexes, and the eukaryotic Aspergillus fumigatus, Leishmania donovani and Saccharomyces sensu stricto complexes. The members of these complexes may show distinct epidemiology, pathogenicity and susceptibility, turning critical their correct identification. Dynamics of prokaryotic and eukaryotic genomes can be very distinct and the term "species complex" should be carefully extended.

MLVA based classification of Mycobacterium tuberculosis complex lineages for a robust phylogeographic snapshot of its worldwide molecular diversity

Multiple-locus variable-number tandem repeat analysis (MLVA) is useful to establish transmission routes and sources of infections for various microorganisms including Mycobacterium tuberculosis complex (MTC). The recently released SITVITWEB database contains 12-loci Mycobacterial Interspersed Repetitive Units – Variable Number of Tandem DNA Repeats (MIRU-VNTR) profiles and spoligotype patterns for thousands of MTC strains; it uses MIRU International Types (MIT) and Spoligotype International Types (SIT) to designate clustered patterns worldwide. Considering existing doubts on the ability of spoligotyping alone to reveal exact phylogenetic relationships between MTC strains, we developed a MLVA based classification for MTC genotypic lineages. We studied 6 different subsets of MTC isolates encompassing 7793 strains worldwide. Minimum spanning trees (MST) were constructed to identify major lineages, and the most common representative located as a central node was taken as the prototype defining different phylogenetic groups. A total of 7 major lineages with their respective prototypes were identified: Indo-Oceanic/MIT57, East Asian and African Indian/MIT17, Euro American/MIT116, West African-I/MIT934, West African-II/MIT664, M. bovis/MIT49, M.canettii/MIT60. Further MST subdivision identified an additional 34 sublineage MIT prototypes. The phylogenetic relationships among the 37 newly defined MIRU-VNTR lineages were inferred using a classification algorithm based on a bayesian approach. This information was used to construct an updated phylogenetic and phylogeographic snapshot of worldwide MTC diversity studied both at the regional, sub-regional, and country level according to the United Nations specifications. We also looked for IS6110 insertional events that are known to modify the results of the spoligotyping in specific circumstances, and showed that a fair portion of convergence leading to the currently observed bias in phylogenetic classification of strains may be traced back to the presence of IS6110. These results shed new light on the evolutionary history of the pathogen in relation to the history of peopling and human migration.

Mycobacterium smegmatis Lsr2 physically and functionally interacts with a new flavoprotein involved in bacterial resistance to oxidative stress

Lsr2, a bacterial histone-like protein, has been shown to be clearly involved in modulating chromatin organization, compaction and global gene expression. However, the regulatory mechanism of its functions remains largely unclear. In this study, using bacterial two-hybrid technique and pull-down assays, the Mycobacterium smegmatis Lsr2 was detected to associate with a hypothetical flavoprotein, Ms4334. A further co-immunoprecipitation assay confirmed the physical interaction between these two proteins in vivo in mycobacteria. Importantly, the Ms4334 protein was also capable of enhancing the inhibitory effect of Lsr2 in vitro on the function of DNA topoisomerase I (MsTopA). Therefore, Lsr2 could physically and functionally interact with Ms4334. Further, the Ms4334 gene was confirmed to encode a new FAD-binding flavoprotein that displayed two characteristic absorption peaks at about 370 and 450 nm in a UV-visible spectra scanning assay. Interestingly, when comparing the growths of wild-type M. smegmatis with the Ms4334-knockout strain in response to H(2)O(2), Ms4334 was found to contribute to mycobacterial resistance to oxidative stress. The findings provided important clues for a further understanding of the regulation mechanism of Lsr2 in mycobacteria.

Tuberculous meningitis in adults: a review of a decade of developments focusing on prognostic factors for outcome

Tuberculous meningitis (TBM) is the most severe form of TB. Despite treatment, mortality and long-term disability remain unacceptably high. Prevention, early recognition, diagnosis and treatment are fundamental to improving outcomes. However, an effective vaccine remains elusive, initial symptoms are nonspecific, and sensitive diagnostic tests are not available. There has been progress in our understanding of the immunopathology of TBM, and several factors have been found to be associated with susceptibility to infection, disease progression and clinical outcome. However, these have not yet impacted on treatment. Early treatment initiation and uninterrupted continuation, severity on presentation, seizures, stroke, cranial nerve involvement, cerebrospinal fluid cell count and lactate levels, hyponatreamia and coinfection with HIV are all found to be important prognostic factors for outcome. Pathogen lineage (Beijing genotype) and host genetics (polymorphisms in TLR2, TIRAP and LTA4H genes) can influence susceptibility to TBM. However, these findings have not yet impacted on treatment. Progress in vaccine development, opportunities for better diagnostic tests, novel insights into pathogenesis and an increasing evidence base for improving treatment should impact the current high mortality and morbidity, if translated to global and local guidelines.

Inferred spoligoforest topology unravels spatially bimodal distribution of mutations in the DR region

Biomarkers of Mycobacterium tuberculosis complex (MTBC) mutate over time. Among the biomarkers of MTBC, spacer oligonucleotide type (spoligotype) and mycobacterium interspersed repetitive unit (MIRU) patterns are commonly used to genotype clinical MTBC strains. In this study, we present an evolution model of spoligotype rearrangements using MIRU patterns to disambiguate the ancestors of spoligotypes. We use a large patient dataset from the United States Centers for Disease Control and Prevention (CDC) to generate this model. Based on the contiguous deletion assumption and rare observation of convergent evolution, we first generate the most parsimonious forest of spoligotypes, called a spoligoforest, using three genetic distance measures. An analysis of topological attributes of the spoligoforest and number of variations at the direct repeat (DR) locus of each strain reveals interesting properties of deletions in the DR region. First, we compare our mutation model to existing mutation models of spoligotypes and find that our mutation model produces as many within-lineage mutation events as other models, with slightly higher segregation accuracy. Second, based on our mutation model, the number of descendant spoligotypes follows a power law distribution. Third, contrary to prior studies, the power law distribution does not plausibly fit to the mutation length frequency. Moreover, we find that the total number of mutation events at consecutive spacers follows a spatially bimodal distribution. The two modes are spacers 13 and 40, which are hotspots for chromosomal rearrangements, and the change point is spacer 34, which is absent in most MTBC strains. Based on this observation, we built two alternative models for mutation length frequency: the Starting Point Model (SPM) and the Longest Block Model (LBM). Both models are plausibly good fits to the mutation length frequency distribution, as verified by the goodness-of-fit test. We also apply SPM and LBM to a dataset from Institut Pasteur de Guadeloupe and verify that these models hold for different strain datasets.

Combined species identification, genotyping, and drug resistance detection of Mycobacterium tuberculosis cultures by MLPA on a bead-based array

The population structure of Mycobacterium tuberculosis is typically clonal therefore genotypic lineages can be unequivocally identified by characteristic markers such as mutations or genomic deletions. In addition, drug resistance is mainly mediated by mutations. These issues make multiplexed detection of selected mutations potentially a very powerful tool to characterise Mycobacterium tuberculosis. We used Multiplex Ligation-dependent Probe Amplification (MLPA) to screen for dispersed mutations, which can be successfully applied to Mycobacterium tuberculosis as was previously shown. Here we selected 47 discriminative and informative markers and designed MLPA probes accordingly to allow analysis with a liquid bead array and robust reader (Luminex MAGPIX technology). To validate the bead-based MLPA, we screened a panel of 88 selected strains, previously characterised by other methods with the developed multiplex assay using automated positive and negative calling. In total 3059 characteristics were screened and 3034 (99.2%) were consistent with previous molecular characterizations, of which 2056 (67.2%) were directly supported by other molecular methods, and 978 (32.0%) were consistent with but not directly supported by previous molecular characterizations. Results directly conflicting or inconsistent with previous methods, were obtained for 25 (0.8%) of the characteristics tested. Here we report the validation of the bead-based MLPA and demonstrate its potential to simultaneously identify a range of drug resistance markers, discriminate the species within the Mycobacterium tuberculosis complex, determine the genetic lineage and detect and identify the clinically most relevant non-tuberculous mycobacterial species. The detection of multiple genetic markers in clinically derived Mycobacterium tuberculosis strains with a multiplex assay could reduce the number of TB-dedicated screening methods needed for full characterization. Additionally, as a proportion of the markers screened are specific to certain Mycobacterium tuberculosis lineages each profile can be checked for internal consistency. Strain characterization can allow selection of appropriate treatment and thereby improve treatment outcome and patient management.

Mycobacterium tuberculosis complex lipid virulence factors preserved in the 17,000-year-old skeleton of an extinct bison, Bison antiquus

Tracing the evolution of ancient diseases depends on the availability and accessibility of suitable biomarkers in archaeological specimens. DNA is potentially information-rich but it depends on a favourable environment for preservation. In the case of the major mycobacterial pathogens, Mycobacterium tuberculosis and Mycobacterium leprae, robust lipid biomarkers are established as alternatives or complements to DNA analyses. A DNA report, a decade ago, suggested that a 17,000-year-old skeleton of extinct Bison antiquus, from Natural Trap Cave, Wyoming, was the oldest known case of tuberculosis. In the current study, key mycobacterial lipid virulence factor biomarkers were detected in the same two samples from this bison. Fluorescence high-performance liquid chromatography (HPLC) indicated the presence of mycolic acids of the mycobacterial type, but they were degraded and could not be precisely correlated with tuberculosis. However, pristine profiles of C₂₉, C₃₀ and C₃₂ mycocerosates and C₂₇ mycolipenates, typical of the Mycobacterium tuberculosis complex, were recorded by negative ion chemical ionization gas chromatography mass spectrometry of pentafluorobenzyl ester derivatives. These findings were supported by the detection of C₃₄ and C₃₆ phthiocerols, which are usually esterified to the mycocerosates. The existence of Pleistocene tuberculosis in the Americas is confirmed and there are many even older animal bones with well-characterised tuberculous lesions similar to those on the analysed sample. In the absence of any evidence of tuberculosis in human skeletons older than 9,000 years BP, the hypothesis that this disease evolved as a zoonosis, before transfer to humans, is given detailed consideration and discussion.

Two new rapid SNP-typing methods for classifying Mycobacterium tuberculosis complex into the main phylogenetic lineages

There is increasing evidence that strain variation in Mycobacterium tuberculosis complex (MTBC) might influence the outcome of tuberculosis infection and disease. To assess genotype-phenotype associations, phylogenetically robust molecular markers and appropriate genotyping tools are required. Most current genotyping methods for MTBC are based on mobile or repetitive DNA elements. Because these elements are prone to convergent evolution, the corresponding genotyping techniques are suboptimal for phylogenetic studies and strain classification. By contrast, single nucleotide polymorphisms (SNP) are ideal markers for classifying MTBC into phylogenetic lineages, as they exhibit very low degrees of homoplasy. In this study, we developed two complementary SNP-based genotyping methods to classify strains into the six main human-associated lineages of MTBC, the "Beijing" sublineage, and the clade comprising Mycobacterium bovis and Mycobacterium caprae. Phylogenetically informative SNPs were obtained from 22 MTBC whole-genome sequences. The first assay, referred to as MOL-PCR, is a ligation-dependent PCR with signal detection by fluorescent microspheres and a Luminex flow cytometer, which simultaneously interrogates eight SNPs. The second assay is based on six individual TaqMan real-time PCR assays for singleplex SNP-typing. We compared MOL-PCR and TaqMan results in two panels of clinical MTBC isolates. Both methods agreed fully when assigning 36 well-characterized strains into the main phylogenetic lineages. The sensitivity in allele-calling was 98.6% and 98.8% for MOL-PCR and TaqMan, respectively. Typing of an additional panel of 78 unknown clinical isolates revealed 99.2% and 100% sensitivity in allele-calling, respectively, and 100% agreement in lineage assignment between both methods. While MOL-PCR and TaqMan are both highly sensitive and specific, MOL-PCR is ideal for classification of isolates with no previous information, whereas TaqMan is faster for confirmation. Furthermore, both methods are rapid, flexible and comparably inexpensive.

High resolution discrimination of clinical Mycobacterium tuberculosis complex strains based on single nucleotide polymorphisms

Recently, the diversity of the Mycobacterium tuberculosis complex (MTBC) population structure has been described in detail. Based on geographical separation and specific host pathogen co-evolution shaping MTBC virulence traits, at least 20 major lineages/genotypes have evolved finally leading to a clear influence of strain genetic background on transmissibility, clinical presentation/outcome, and resistance development. Therefore, high resolution genotyping for characterization of strains in larger studies is mandatory for understanding mechanisms of host-pathogen-interaction and to improve tuberculosis (TB) control. Single nucleotide polymorphisms (SNPs) represent the most reliable markers for lineage classification of clinical isolates due to the low levels of homoplasy, however their use is hampered either by low discriminatory power or by the need to analyze a large number of genes to achieve higher resolution. Therefore, we carried out de novo sequencing of 26 genes (approx. 20000 bp per strain) in a reference collection of MTBC strains including all major genotypes to define a highly discriminatory gene set. Overall, 161 polymorphisms were detected of which 59 are genotype-specific, while 13 define deeper branches such as the Euro-American lineage. Unbiased investigation of the most variable set of 11 genes in a population based strain collection (one year, city of Hamburg, Germany) confirmed the validity of SNP analysis as all strains were classified with high accuracy. Taken together, we defined a diagnostic algorithm which allows the identification of 17 MTBC phylogenetic lineages with high confidence for the first time by sequencing analysis of just five genes. In conclusion, the diagnostic algorithm developed in our study is likely to open the door for a low cost high resolution sequence/SNP based differentiation of the MTBC with a very high specificity. High throughput assays can be established which will be needed for large association studies that are mandatory for detailed investigation of host-pathogen-interaction during TB infection.

Sequence analysis for detection of first-line drug resistance in Mycobacterium tuberculosis strains from a high-incidence setting

BACKGROUND

Drug resistance displays a problem for the therapy of Mycobacterium tuberculosis infections. For molecular resistance testing, it is essential to have precise knowledge on genomic variations involved in resistance development. However, data from high-incidence settings are only sparely available. Therefore we performed a systematic approach and analyzed a total of 97 M. tuberculosis strains from previously treated patients in Sierra Leone for mutations in katG, rpoB, rrs, rpsL, gidB, embB, pncA and where applicable in inhA and ahpC. Of the strains investigated 50 were either mono- or poly-resistant to isoniazid, rifampin, streptomycin, ethambutol and pyrazinamide or MDR and 47 fully susceptible strains served as controls.

RESULTS

The majority of isoniazid and rifampin resistant strains had mutations in katG315 (71.9%) and rpoB531 (50%). However, rpoB mutations in codons 511, 516 and 533 were also detected in five rifampin susceptible strains. MIC determinations revealed low-level rifampin resistance for those strains. Thus, the sensitivity and specificity of sequencing of katG for detection of drug resistance were 86.7% and 100% and for sequencing of rpoB 100% and 93.8%, respectively.Strikingly, none of the streptomycin resistant strains had mutations in rrs, but 47.5% harboured mutations in rpsL. Further changes were detected in gidB. Among ethambutol resistant strains 46.7% had mutations at embB306. Pyrazinamide resistant strains displayed a variety of mutations throughout pncA. The specificities of sequencing of rpsL, embB and pncA for resistance detection were high (96-100%), whereas sensitivities were lower (48.8%, 73.3%, 70%).

CONCLUSIONS

Our study reveals a good correlation between data from molecular and phenotypic resistance testing in this high-incidence setting. However, the fact that particular mutations in rpoB are not linked to high-level resistance is challenging and demonstrates that careful interpretation of molecular resistance assays is mandatory. In addition, certain variations, especially in gidB, appear to be phylogenetically informative polymorphisms rather than markers for drug resistance.

Induction of mycobacterial resistance to quinolone class antimicrobials

An agar plate assay was developed for detecting the induction of drug-resistant mycobacterial mutants during exposure to inhibitors of DNA gyrase. When Mycobacterium smegmatis on drug-containing agar, resistant colonies arose over a period of 2 weeks. A recA deficiency reduced mutant recovery, consistent with involvement of the SOS response in mutant induction. The C-8-methoxy compounds gatifloxacin and moxifloxacin allowed the recovery of fewer resistant mutants than either ciprofloxacin or levofloxacin when present at the same multiple of the MIC; a quinolone-like 8-methoxy-quinazoline-2,4-dione was more effective at restricting the emergence of resistant mutants than its cognate fluoroquinolone. Thus, the structure of fluoroquinolone-like compounds affects mutant recovery. A spontaneous mutator mutant of M. smegmatis, obtained by growth in medium containing both isoniazid and rifampin, increased mutant induction during exposure to ciprofloxacin. Moreover, the mutator increased the size of spontaneous resistant mutant subpopulations, as detected by population analysis. Induction of ciprofloxacin resistance was also observed with Mycobacterium tuberculosis H37Rv. When measured with clinical isolates, no difference in mutant recovery was observed between multidrug-resistant (MDR) and pansusceptible isolates. This finding is consistent with at least some MDR isolates of M. tuberculosis lacking mutators detectable by the agar plate assay. Collectively, the data indicate that the use of fluoroquinolones against tuberculosis may induce resistance and that the choice of quinolone may be important for restricting the recovery of induced mutants.

Variations in the occurrence of specific rpoB mutations in rifampicin-resistant Mycobacterium tuberculosis isolates from patients of different ethnic groups in Kuwait

BACKGROUND & OBJECTIVES

Frequency of resistance-conferring mutations vary among isoniazid- and ethambutol-resistant Mycobacterium tuberculosis isolates obtained from patients of various ethnic groups. This study was aimed to determine the occurrence of specific rpoB mutations in rifampicin-resistant M. tuberculosis isolates from tuberculosis patients of various ethnic groups in Kuwait.

METHODS

Rifampicin-resistant M. tuberculosis isolates (n=119) from South Asian (n=55), Southeast Asian (n=23), Middle Eastern (n=39) and other (n=2) patients and 107 rifampicin-susceptible isolates were tested. Mutations in rpoB were detected by DNA sequencing. Polymorphisms at katG463 and gyrA95 were detected by PCR-RFLP for genetic group assignment.

RESULTS

None of rifampicin-susceptible but 116 of 119 rifampicin-resistant isolates showed rpoB mutation(s). Mutations among isolates from South Asian patients were distributed at rpoB516 (20%), rpoB526 (24%) and rpoB531 (27%) while 78 and 51 per cent of isolates from Southeast Asian and Middle Eastern patients, respectively, contained a mutated rpoB531. All isolates with rpoB N-terminal and cluster II mutations were obtained from Middle Eastern and South Asian patients. Most isolates from South Asian (84%) and Southeast Asian (70%) patients belonged to genetic group I while nearly all remaining isolates belonged to genetic group II. Isolates from Middle Eastern patients were distributed among genetic group I (46%), genetic group II (33%) and genetic group III (21%).

INTERPRETATION & CONCLUSIONS

The occurrence of specific rpoB mutations varied considerably in rifampicin-resistant M. tuberculosis isolates obtained from patients of different ethnic groups within the same country. The present data have important implications for designing region-specific rapid methods for detecting majority of rifampicin-resistant strains.

Comparative analysis of Mycobacterium tuberculosis pe and ppe genes reveals high sequence variation and an apparent absence of selective constraints

Mycobacterium tuberculosis complex (MTBC) genomes contain 2 large gene families termed pe and ppe. The function of pe/ppe proteins remains enigmatic but studies suggest that they are secreted or cell surface associated and are involved in bacterial virulence. Previous studies have also shown that some pe/ppe genes are polymorphic, a finding that suggests involvement in antigenic variation. Using comparative sequence analysis of 18 publicly available MTBC whole genome sequences, we have performed alignments of 33 pe (excluding pe_pgrs) and 66 ppe genes in order to detect the frequency and nature of genetic variation. This work has been supplemented by whole gene sequencing of 14 pe/ppe (including 5 pe_pgrs) genes in a cohort of 40 diverse and well defined clinical isolates covering all the main lineages of the M. tuberculosis phylogenetic tree. We show that nsSNP's in pe (excluding pgrs) and ppe genes are 3.0 and 3.3 times higher than in non-pe/ppe genes respectively and that numerous other mutation types are also present at a high frequency. It has previously been shown that non-pe/ppe M. tuberculosis genes display a remarkably low level of purifying selection. Here, we also show that compared to these genes those of the pe/ppe families show a further reduction of selection pressure that suggests neutral evolution. This is inconsistent with the positive selection pressure of "classical" antigenic variation. Finally, by analyzing such a large number of genes we were able to detect large differences in mutation type and frequency between both individual genes and gene sub-families. The high variation rates and absence of selective constraints provides valuable insights into potential pe/ppe function. Since pe/ppe proteins are highly antigenic and have been studied as potential vaccine components these results should also prove informative for aspects of M. tuberculosis vaccine design.

Effect of mutation and genetic background on drug resistance in Mycobacterium tuberculosis

Bacterial factors may contribute to the global emergence and spread of drug-resistant tuberculosis (TB). Only a few studies have reported on the interactions between different bacterial factors. We studied drug-resistant Mycobacterium tuberculosis isolates from a nationwide study conducted from 2000 to 2008 in Switzerland. We determined quantitative drug resistance levels of first-line drugs by using Bactec MGIT-960 and drug resistance genotypes by sequencing the hot-spot regions of the relevant genes. We determined recent transmission by molecular methods and collected clinical data. Overall, we analyzed 158 isolates that were resistant to isoniazid, rifampin, or ethambutol, 48 (30.4%) of which were multidrug resistant. Among 154 isoniazid-resistant strains, katG mutations were associated with high-level and inhA promoter mutations with low-level drug resistance. Only katG(S315T) (65.6% of all isoniazid-resistant strains) and inhA promoter -15C/T (22.7%) were found in molecular clusters. M. tuberculosis lineage 2 (includes Beijing genotype) was associated with any drug resistance (adjusted odds ratio [OR], 3.0; 95% confidence interval [CI], 1.7 to 5.6; P < 0.0001). Lineage 1 was associated with inhA promoter -15C/T mutations (OR, 6.4; 95% CI, 2.0 to 20.7; P = 0.002). We found that the genetic strain background influences the level of isoniazid resistance conveyed by particular mutations (interaction tests of drug resistance mutations across all lineages; P < 0.0001). In conclusion, M. tuberculosis drug resistance mutations were associated with various levels of drug resistance and transmission, and M. tuberculosis lineages were associated with particular drug resistance-conferring mutations and phenotypic drug resistance. Our study also supports a role for epistatic interactions between different drug resistance mutations and strain genetic backgrounds in M. tuberculosis drug resistance.

Detection of first- and second-line drug resistance in Mycobacterium tuberculosis clinical isolates by pyrosequencing

Conventional phenotypic drug susceptibility testing (DST) methods for Mycobacterium tuberculosis are laborious and very time-consuming. Early detection of drug-resistant tuberculosis (TB) is essential for prevention and control of TB transmission. We have developed a pyrosequencing method for simultaneous detection of mutations associated with resistance to rifampin, isoniazid, ethambutol, amikacin, kanamycin, capreomycin, and ofloxacin. Seven pyrosequencing assays were optimized for following loci: rpoB, katG, embB, rrs, gyrA, and the promoter regions of inhA and eis. The molecular method was evaluated on a panel of 290 clinical isolates of M. tuberculosis. In comparison to phenotypic DST, the pyrosequencing method demonstrated high specificity (100%) and sensitivity (94.6%) for detection of multidrug-resistant M. tuberculosis as well as high specificity (99.3%) and sensitivity (86.9%) for detection of extensively drug-resistant M. tuberculosis. The short turnaround time combined with multilocus sequencing of several isolates in parallel makes pyrosequencing an attractive method for drug resistance screening in M. tuberculosis.

Genome sequencing of ovine isolates of Mycobacterium avium subspecies paratuberculosis offers insights into host association

Background

The genome of Mycobacterium avium subspecies paratuberculosis (MAP) is remarkably homogeneous among the genomes of bovine, human and wildlife isolates. However, previous work in our laboratories with the bovine K-10 strain has revealed substantial differences compared to sheep isolates. To systematically characterize all genomic differences that may be associated with the specific hosts, we sequenced the genomes of three U.S. sheep isolates and also obtained an optical map.

Results

Our analysis of one of the isolates, MAP S397, revealed a genome 4.8 Mb in size with 4,700 open reading frames (ORFs). Comparative analysis of the MAP S397 isolate showed it acquired approximately 10 large sequence regions that are shared with the human M. avium subsp. hominissuis strain 104 and lost 2 large regions that are present in the bovine strain. In addition, optical mapping defined the presence of 7 large inversions between the bovine and ovine genomes (~ 2.36 Mb). Whole-genome sequencing of 2 additional sheep strains of MAP (JTC1074 and JTC7565) further confirmed genomic homogeneity of the sheep isolates despite the presence of polymorphisms on the nucleotide level.

Conclusions

Comparative sequence analysis employed here provided a better understanding of the host association, evolution of members of the M. avium complex and could help in deciphering the phenotypic differences observed among sheep and cattle strains of MAP. A similar approach based on whole-genome sequencing combined with optical mapping could be employed to examine closely related pathogens. We propose an evolutionary scenario for M. avium complex strains based on these genome sequences.

TB-Lineage: an online tool for classification and analysis of strains of Mycobacterium tuberculosis complex

This paper formulates a set of rules to classify genotypes of the Mycobacterium tuberculosis complex (MTBC) into major lineages using spoligotypes and MIRU-VNTR results. The rules synthesize prior literature that characterizes lineages by spacer deletions and variations in the number of repeats seen at locus MIRU24 (alias VNTR2687). A tool that efficiently and accurately implements this rule base is now freely available at http://tbinsight.cs.rpi.edu/run_tb_lineage.html. When MIRU24 data is not available, the system utilizes predictions made by a Naïve Bayes classifier based on spoligotype data. This website also provides a tool to generate spoligoforests in order to visualize the genetic diversity and relatedness of genotypes and their associated lineages. A detailed analysis of the application of these tools on a dataset collected by the CDC consisting of 3198 distinct spoligotypes and 5430 distinct MIRU-VNTR types from 37,066 clinical isolates is presented. The tools were also tested on four other independent datasets. The accuracy of automated classification using both spoligotypes and MIRU24 is >99%, and using spoligotypes alone is >95%. This online rule-based classification technique in conjunction with genotype visualization provides a practical tool that supports surveillance of TB transmission trends and molecular epidemiological studies.

After the bottleneck: Genome-wide diversification of the Mycobacterium tuberculosis complex by mutation, recombination, and natural selection

Many of the most virulent bacterial pathogens show low genetic diversity and sexual isolation. Accordingly, Mycobacterium tuberculosis, the deadliest human pathogen, is thought to be clonal and evolve by genetic drift. Yet, its genome shows few of the concomitant signs of genome degradation. We analyzed 24 genomes and found an excess of genetic diversity in regions encoding key adaptive functions including the type VII secretion system and the ancient horizontally transferred virulence-related regions. Four different approaches showed evident signs of recombination in M. tuberculosis. Recombination tracts add a high density of polymorphisms, and many are thus predicted to arise from outside the clade. Some of these tracts match Mycobacterium canettii sequences. Recombination introduced an excess of non-synonymous diversity in general and even more in genes expected to be under positive or diversifying selection, e.g., cell wall component genes. Mutations leading to non-synonymous SNPs are effectively purged in MTBC, which shows dominance of purifying selection. MTBC mutation bias toward AT nucleotides is not compensated by biased gene conversion, suggesting the action of natural selection also on synonymous changes. Together, all of these observations point to a strong imprint of recombination and selection in the genome affecting both non-synonymous and synonymous positions. Hence, contrary to some other pathogens and previous proposals concerning M. tuberculosis, this lineage may have come out of its ancestral bottleneck as a very successful pathogen that is rapidly diversifying by the action of mutation, recombination, and natural selection.

High-resolution melting analysis for the rapid detection of fluoroquinolone and streptomycin resistance in Mycobacterium tuberculosis

Background

Molecular methods for the detection of drug-resistant tuberculosis are potentially more rapid than conventional culture-based drug susceptibility testing, facilitating the commencement of appropriate treatment for patients with drug resistant tuberculosis. We aimed to develop and evaluate high-resolution melting (HRM) assays for the detection of mutations within gyrA, rpsL, and rrs, for the determination of fluoroquinolone and streptomycin resistance in Mycobacterium tuberculosis (MTB).

Methodology/Principal Findings

A blinded series of DNA samples extracted from a total of 92 clinical isolates of MTB were analyzed by HRM analysis, and the results were verified using DNA sequencing. The sensitivity and specificity of the HRM assays in comparison with drug susceptibility testing were 74.1% and 100.0% for the detection of fluoroquinolone resistance, and 87.5% and 100.0% for streptomycin resistance. Five isolates with low level resistance to ofloxacin had no mutations detected in gyrA, possibly due to the action of efflux pumps, or false negativity due to mixed infections. One fluoroquinolone-resistant isolate had a mutation in a region of gyrA not encompassed by our assay. Six streptomycin-resistant strains had undetectable mutations by HRM and DNA sequencing, which may be explained by the fact that not all streptomycin-resistant isolates have mutations within rpsL and rrs, and suggesting that other targets may be involved.

Conclusion

The HRM assays described here are potentially useful adjunct tests for the efficient determination of fluoroquinolone and streptomycin resistance in MTB, and could facilitate the timely administration of appropriate treatment for patients infected with drug-resistant TB.

SITVITWEB--a publicly available international multimarker database for studying Mycobacterium tuberculosis genetic diversity and molecular epidemiology

Among various genotyping methods to study Mycobacterium tuberculosis complex (MTC) genotypic polymorphism, spoligotyping and mycobacterial interspersed repetitive units-variable number of DNA tandem repeats (MIRU-VNTRs) have recently gained international approval as robust, fast, and reproducible typing methods generating data in a portable format. Spoligotyping constituted the backbone of a publicly available database SpolDB4 released in 2006; nonetheless this method possesses a low discriminatory power when used alone and should be ideally used in conjunction with a second typing method such as MIRU-VNTRs for high-resolution epidemiological studies. We hereby describe a publicly available international database named SITVITWEB which incorporates such multimarker data allowing to have a global vision of MTC genetic diversity worldwide based on 62,582 clinical isolates corresponding to 153 countries of patient origin (105 countries of isolation). We report a total of 7105 spoligotype patterns (corresponding to 58,180 clinical isolates) - grouped into 2740 shared-types or spoligotype international types (SIT) containing 53,816 clinical isolates and 4364 orphan patterns. Interestingly, only 7% of the MTC isolates worldwide were orphans whereas more than half of SITed isolates (n=27,059) were restricted to only 24 most prevalent SITs. The database also contains a total of 2379 MIRU patterns (from 8161 clinical isolates) from 87 countries of patient origin (35 countries of isolation); these were grouped in 847 shared-types or MIRU international types (MIT) containing 6626 isolates and 1533 orphan patterns. Lastly, data on 5-locus exact tandem repeats (ETRs) were available on 4626 isolates from 59 countries of patient origin (22 countries of isolation); a total of 458 different VNTR patterns were observed - split into 245 shared-types or VNTR International Types (VIT) containing 4413 isolates) and 213 orphan patterns. Datamining of SITVITWEB further allowed to update rules defining MTC genotypic lineages as well to have a new insight into MTC population structure and worldwide distribution at country, sub-regional and continental levels. At evolutionary level, the data compiled may be useful to distinguish the occasional convergent evolution of genotypes versus specific evolution of sublineages essentially influenced by adaptation to the host. This database is publicly available at: http://www.pasteur-guadeloupe.fr:8081/SITVIT_ONLINE.

Comparison of spoligotyping, mycobacterial interspersed repetitive units typing and IS6110-RFLP in a study of genotypic diversity of Mycobacterium tuberculosis in Delhi, North India

The aim of the present study was to compare polymerase chain reaction (PCR)-based methods--spoligotyping and mycobacterial interspersed repetitive units (MIRU) typing--with the gold-standard IS6110 restriction fragment length polymorphism (RFLP) analysis in 101 isolates of Mycobacterium tuberculosis to determine the genetic diversity of M. tuberculosis clinical isolates from Delhi, North India. Spoligotyping resulted in 49 patterns (14 clusters); the largest cluster was composed of Spoligotype International Types (SITs)26 [Central-Asian (CAS)1-Delhi lineage], followed by SIT11 [East-African-Indian (EAI) 3-Indian lineage]. A large number of isolates (75%) belonged to genotypic lineages, such as CAS, EAI and Manu, with a high specificity for the Indian subcontinent, emphasising the complex diversity of the phylogenetically coherent M. tuberculosis in North India. MIRU typing, using 11 discriminatory loci, was able to distinguish between all but two strains based on individual patterns. IS6110-RFLP analysis (n = 80 strains) resulted in 67 unique isolates and four clusters containing 13 strains. MIRUs discriminated all 13 strains, whereas spoligotyping discriminated 11 strains. Our results validate the use of PCR-based molecular typing of M. tuberculosis using repetitive elements in Indian isolates and demonstrate the usefulness of MIRUs for discriminating low-IS6110-copy isolates, which accounted for more than one-fifth of the strains in the present study.

Online tools for polyphasic analysis of Mycobacterium tuberculosis complex genotyping data: now and next

Molecular diagnostics and genotyping of pathogens have become indispensable tools in clinical microbiology and disease surveillance. For isolates of the Mycobacterium tuberculosis complex (MTBC, causative agents of tuberculosis), multilocus variable number tandem repeat analysis (MLVA) targeting mycobacterial interspersed repetitive units (MIRU) has been internationally adopted as the new standard, portable, reproducible, and discriminatory typing method. Here, we review new sets of specialized web based bioinformatics tools that have become available for analyzing MLVA data especially in combination with other, complementary genotyping markers (polyphasic analysis). Currently, there are only two databases available that are not restricted to store one kind of genotyping data only, namely SITVIT/SpolDB4 and MIRU-VNTRplus. SITVIT/SpolDB4 (http://www.pasteur-guadeloupe.fr:8081/SITVITDemo) contains spoligotyping data from a large number of strains of diverse origin. However, besides options to query the data, the actual version of SITVIT/SpolDB4 offers no functionality for more complex analysis e.g. tree-based analysis. In comparison, the MIRU-VNTRplus web application (http://www.miru-vntrplus.org), represents a freely accessible service that enables users to analyze genotyping data of their strains alone or in comparison with a currently limited but well characterized reference database of strains representing the major MTBC lineages. Data (MLVA-, spoligotype-, large sequence polymorphism, and single nucleotide polymorphism) can be visualized and analyzed using just one genotyping method or a weighted combination of several markers. A variety of analysis tools are available such as creation of phylogenetic and minimum spanning trees, semi-automated phylogenetic lineage identification based on comparison with the reference database and mapping of geographic information. To facilitate scientific communication, a universal, expanding genotype nomenclature (MLVA MtbC15-9 type) service that can be queried via a web- or a SOAP-interface has been implemented. An extensive documentation guides users through all application functions. Perspectives for future development, including generalization to other bacterial species, are presented.

Epidemiologic consequences of microvariation in Mycobacterium tuberculosis

BACKGROUND

Evidence from genotype-phenotype studies suggests that genetic diversity in pathogens have clinically relevant manifestations that can impact outcome of infection and epidemiologic success. We studied 5 closely related Mycobacterium tuberculosis strains that collectively caused extensive disease (n = 862), particularly among US-born tuberculosis patients.

METHODS

Representative isolates were selected using population-based genotyping data from New York City and New Jersey. Growth and cytokine/chemokine response were measured in infected human monocytes. Survival was determined in aerosol-infected guinea pigs.

RESULTS

Multiple genotyping methods and phylogenetically informative synonymous single nucleotide polymorphisms showed that all strains were related by descent. In axenic culture, all strains grew similarly. However, infection of monocytes revealed 2 growth phenotypes, slower (doubling ∼55 hours) and faster (∼25 hours). The faster growing strains elicited more tumor necrosis factor α and interleukin 1β than the slower growing strains, even after heat killing, and caused accelerated death of infected guinea pigs (∼9 weeks vs 24 weeks) associated with increased lung inflammation/pathology. Epidemiologically, the faster growing strains were associated with human immunodeficiency virus and more limited in spread, possibly related to their inherent ability to induce a strong protective innate immune response in immune competent hosts.

CONCLUSIONS

Natural variation, with detectable phenotypic changes, among closely related clinical isolates of M. tuberculosis may alter epidemiologic patterns in human populations.

Independent large scale duplications in multiple M. tuberculosis lineages overlapping the same genomic region

Mycobacterium tuberculosis, the causative agent of most human tuberculosis, infects one third of the world's population and kills an estimated 1.7 million people a year. With the world-wide emergence of drug resistance, and the finding of more functional genetic diversity than previously expected, there is a renewed interest in understanding the forces driving genome evolution of this important pathogen. Genetic diversity in M. tuberculosis is dominated by single nucleotide polymorphisms and small scale gene deletion, with little or no evidence for large scale genome rearrangements seen in other bacteria. Recently, a single report described a large scale genome duplication that was suggested to be specific to the Beijing lineage. We report here multiple independent large-scale duplications of the same genomic region of M. tuberculosis detected through whole-genome sequencing. The duplications occur in strains belonging to both M. tuberculosis lineage 2 and 4, and are thus not limited to Beijing strains. The duplications occur in both drug-resistant and drug susceptible strains. The duplicated regions also have substantially different boundaries in different strains, indicating different originating duplication events. We further identify a smaller segmental duplication of a different genomic region of a lab strain of H37Rv. The presence of multiple independent duplications of the same genomic region suggests either instability in this region, a selective advantage conferred by the duplication, or both. The identified duplications suggest that large-scale gene duplication may be more common in M. tuberculosis than previously considered.