SNP/RD typing of Mycobacterium tuberculosis Beijing strains reveals local and worldwide disseminated clonal complexes

Genetic profiling of Mycobacterium tuberculosis revealed "modern" Beijing strains linked to MDR-TB from Southwestern Colombia

Beijing strains of Mycobacterium tuberculosis (lineage 2) have been associated with drug-resistance and transmission of tuberculosis worldwide. Most of the Beijing strains identified in the Colombian Pacific coast have exhibited a multidrug resistant (MDR) phenotype. We sought to evaluate the clonality and sublineage of Beijing strains circulating in Southwestern Colombia. Thirty-seven Beijing strains were identified through spoligotyping out of 311 clinical isolates collected in 9 years from 2002-2010. Further analysis by MIRU-VNTR 24 loci was conducted for the Beijing strains. For sublineage classification, deletions of RD105, RD207, and RD131 and point mutations at fbpB, mutT2, and acs were evaluated. Drug-resistance associated mutations to first- and second-line anti-TB drugs were also evaluated. Additionally, two Beijing strains were Illumina-whole genome sequenced (one MDR and one drug-susceptible). Among the 37 Beijing strains characterized, 36 belonged to the SIT190 type from which 28 were MDR, four pre-extensively drug resistant (XDR) TB, and four XDR-TB. The remaining strain was SIT1 and drug susceptible. MIRU-VNTR analysis allowed the identification of three Beijing clusters and two unique strains. Beijing strains were confirmed as "modern" sublineage. The mutations rpoB S531L and katG S315T were the most common among MDR strains. Moreover, the two strains evaluated by whole genome sequencing (WGS) shared most of the genetic features with the sublineage 2.2.1 "modern" Beijing previously characterized from Asian strains. WGS analysis of the MDR strain revealed the presence of eight SNPs previously reported in other MDR "Beijing-like" strains from Colombia. The presence of "modern" Beijing strains in Southwestern Colombia, most of them with MDR phenotype, suggests a different origin of this M. tuberculosis sublineage compared to other Beijing strains found in neighboring South American countries. This work may serve as a genetic baseline to study the evolution and spread of M. tuberculosis Beijing strains in Colombia, which play an important role in the propagation of MDR-TB.

Evaluation of a gene-by-gene approach for prospective whole-genome sequencing-based surveillance of multidrug resistant Mycobacterium tuberculosis

Whole-genome sequencing (WGS) offers unprecedented resolution for tracking Mycobacterium tuberculosis transmission and antibiotic-resistance spread. Still, the establishment of standardized WGS-based pipelines and the definition of epidemiological clusters based on genetic relatedness are under discussion. We aimed to implement a dynamic gene-by-gene approach, fully relying on freely available software, for prospective WGS-based tuberculosis surveillance, demonstrating its application for detecting transmission chains by retrospectively analysing all M/XDR strains isolated in 2013-2017 in Portugal. We observed a good correlation between genetic relatedness and epidemiological links, with strongly epilinked clusters displaying mean pairwise allele differences (AD) always below 0.3% (ratio of mean AD over the total number of shared loci between same-cluster strains). This data parallels the genetic distances acquired by the core-SNV analysis, while providing higher resolution and epidemiological concordance than MIRU-VNTR genotyping. The dynamic analysis of strain sub-sets (i.e., increasing the number of shared loci within each sub-set) also strengthens the confidence in detecting epilinked clusters. This gene-by-gene strategy also offers several practical benefits (e.g., reliance on freely-available software, scalability and low computational requirements) that further consolidated its suitability for a timely and robust prospective WGS-based laboratory surveillance of M/XDR-TB cases.

Structure and variation of CRISPR and CRISPR-flanking regions in deleted-direct repeat region Mycobacterium tuberculosis complex strains

Background

CRISPR and CRISPR-flanking genomic regions are important for molecular epidemiology of Mycobacterium tuberculosis complex (MTBC) strains, and potentially for adaptive immunity to phage and plasmid DNA, and endogenous roles in the bacterium. Genotyping in the Israel National Mycobacterium Reference Center Tel-Aviv of over 1500 MTBC strains from 2008–2013 showed three strains with validated negative 43-spacer spoligotypes, that is, with putatively deleted direct repeat regions (deleted-DR/CRISPR regions). Two isolates of each of three negative spoligotype MTBC (a total of 6 isolates) were subjected to Next Generation Sequencing (NGS). As positive controls, NGS was performed for three intact-DR isolates belonging to T3_Eth, the largest multiple-drug-resistant (MDR)-containing African-origin cluster in Israel. Other controls consisted of NGS reads and complete whole genome sequences from GenBank for 20 intact-DR MTBC and for 1 deleted-DR MTBC strain recognized as CAS by its defining RD deletion.

Results

NGS reads from negative spoligotype MTBC mapped to reference H37Rv NC_000962.3 suggested that the DR/CRISPR regions were completely deleted except for retention of the middle IS6110 mobile element. Clonally specific deletion of CRISPR-flanking genes also was observed, including deletion of at least cas2 and cas1 genes. Genomic RD deletions defined lineages corresponding to the major spoligotype families Beijing, EAI, and Haarlem, consistent with 24 loci MIRU-VNTR profiles. Analysis of NGS reads, and analysis of contigs obtained by manual PCR confirmed that all 43 gold standard DR/CRISPR spacers were missing in the deleted-DR genomes.

Conclusions

Although many negative spoligotype strains are recorded as spoligotype-international-type (SIT) 2669 in the SITVIT international database, this is the first time to our knowledge that it has been shown that negative spoligotype strains are found in at least 4 different 24 loci MIRU-VNTR and RD deletion families. We report for the first time negative spoligotype-associated total loss of CRISPR region spacers and repeats, with accompanying clonally specific loss of flanking genes, including at least CRISPR-associated genes cas2 and cas1. Since cas1 deleted E.coli shows increased sensitivity to DNA damage and impaired chromosomal segregation, we discussed the possibility of a similar phenotype in the deleted-DR strains and Beijing family strains as both lack the cas1 gene.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3560-6) contains supplementary material, which is available to authorized users.

Mechanisms of Phenotypic Rifampicin Tolerance in Mycobacterium tuberculosis Beijing Genotype Strain B0/W148 Revealed by Proteomics

The "successful" Russian clone B0/W148 of Mycobacterium tuberculosis Beijing is well-known for its capacity to develop antibiotic resistance. During treatment, resistant mutants can occur that have inheritable resistance to specific antibiotics. Next to mutations, M. tuberculosis has several mechanisms that increase their tolerance to a variety of antibiotics. Insights in the phenotypic mechanisms that contribute to drug tolerance will increase our understanding of how antibiotic resistance develops in M. tuberculosis. In this study, we examined the (phospho)proteome dynamics in M. tuberculosis Beijing strain B0/W148 when exposed to a high dose of rifampicin; one of the most potent first-line antibiotics. A total of 2,534 proteins and 191 phosphorylation sites were identified, and revealed the differential regulation of DosR regulon proteins, which are necessary for the development of a dormant phenotype that is less susceptible to antibiotics. By examining independent phenotypic markers of dormancy, we show that persisters of in vitro rifampicin exposure entered a metabolically hypoactive state, which yields rifampicin and other antibiotics largely ineffective. These new insights in the role of protein regulation and post-translational modifications during the initial phase of rifampicin treatment reveal a shortcoming in the antituberculosis regimen that is administered to 8-9 million individuals annually.

Genetic diversity of the Mycobacterium tuberculosis Beijing family based on multiple genotyping profiles

Among the most prevalent Mycobacterium tuberculosis (Mtb) strains worldwide is the Beijing genotype, which has caused large outbreaks of tuberculosis (TB). Characteristics facilitating the dissemination of Beijing family strains remain unknown, but they are presumed to have been acquired through evolution of the lineage. To explore the genetic diversity of the Beijing family Mtb and explore the discriminatory ability of mycobacterial interspersed repetitive units-variable number of tandem repeats (MIRU-VNTR) loci in several regions of East Asia, a cross-sectional study was conducted with a total of 163 Beijing strains collected from registered TB patients between 1 June 2009 and 31 November 2010 in Funing County, China. The isolated strains were analysed by 15-MIRU-VNTR loci typing and compared with published MIRU-VNTR profiles of Beijing strains. Synonymous single nucleotide polymorphisms at 10 chromosomal positions were also analysed. The combination of SNP and MIRU-VNTR typing may be used to assess Mtb genotypes in areas dominated by Beijing strains. The modern subfamily in Shanghai overlapped with strains from other countries, whereas the ancient subfamily was genetically differentiated across several countries. Modern subfamilies, especially ST10, were prevalent. Qub11b and four other loci (MIRU 26, Mtub21, Qub26, Mtub04) could be used to discriminate Beijing strains.

Clinical value of whole-genome sequencing of Mycobacterium tuberculosis

Whole-genome sequencing (WGS) is now common as a result of new technologies that can rapidly sequence a complete bacterial genome for US$500 or less. Many studies have addressed questions about tuberculosis with WGS, and knowing the sequence of the entire genome, rather than only a few fragments, has greatly increased the precision of molecular epidemiology and contact tracing. Additionally, topics such as the mutation rate, drug resistance, the target of new drugs, and the phylogeny and evolution of the Mycobacterium tuberculosis complex bacteria have been elucidated by WGS. Nonetheless, WGS has not explained differences in transmissibility between strains, or why some strains are more virulent than others or more prone to development of multidrug resistance. With advances in technology, WGS of clinical specimens could become routine in high-income countries; however, its relevance will probably depend on easy to use software to efficiently process the sequences produced and accessible genomic databases that can be mined in future studies.

Marked microevolution of a unique Mycobacterium tuberculosis strain in 17 years of ongoing transmission in a high risk population

The transmission and persistence of Mycobacterium tuberculosis within high risk populations is a threat to tuberculosis (TB) control. In the current study, we used whole genome sequencing (WGS) to decipher the transmission dynamics and microevolution of M. tuberculosis ON-A, an endemic strain responsible for an ongoing outbreak of TB in an urban homeless/under-housed population. Sixty-one M. tuberculosis isolates representing 57 TB cases from 1997 to 2013 were subjected to WGS. Sequencing data was integrated with available epidemiological information and analyzed to determine how the M. tuberculosis ON-A strain has evolved during almost two decades of active transmission. WGS offers higher discriminatory power than traditional genotyping techniques, dividing the M. tuberculosis ON-A strain into 6 sub-clusters, each defined by unique single nucleotide polymorphism profiles. One sub-cluster, designated ON-A^NM (Natural Mutant; 26 isolates from 24 cases) was also defined by a large, 15 kb genomic deletion. WGS analysis reveals the existence of multiple transmission chains within the same population/setting. Our results help validate the utility of WGS as a powerful tool for identifying genomic changes and adaptation of M. tuberculosis.

Beijing lineage of MDR Mycobacterium tuberculosis in Bulgaria, 2007-2011

To assess the spread of the Mycobacterium tuberculosis Beijing genotype among patients with multidrug-resistant and extensively resistant tuberculosis in Bulgaria, we genotyped 188 (72%) of 261 microbiologically confirmed resistant isolates obtained during 2007–2011. The estimated prevalence of the Beijing genotype among these patients was 3.2%.

Whole-genome sequencing of the Mycobacterium tuberculosis Manila sublineage results in less clustering and better resolution than mycobacterial interspersed repetitive-unit-variable-number tandem-repeat (MIRU-VNTR) typing and spoligotyping

Mycobacterium tuberculosis isolates of the Manila sublineage are genetically homogeneous. In this study, we used whole-genome sequencing (WGS) to type a collection of 36 M. tuberculosis isolates of the Manila family. WGS enabled the subtyping of these 36 isolates into at least 10 distinct clusters. Our results indicate that WGS is a powerful approach to determining the relatedness of Manila family M. tuberculosis isolates.

Disclosure of selective advantages in the "modern" sublineage of the Mycobacterium tuberculosis Beijing genotype family by quantitative proteomics

The Mycobacterium tuberculosis Beijing genotype, consisting of the more ancient (atypical) and modern (typical) emerging sublineage, is one of the most prevalent and genetically conserved genotype families and has often been associated with multidrug resistance. In this study, we employed a 2D-LC-FTICR MS approach, combined with dimethylation of tryptic peptides, to systematically compare protein abundance levels of ancient and modern Beijing strains and identify differences that could be associated with successful spread of the modern sublineage. The data is available via ProteomeXchange using the identifier PXD000931. Despite the highly uniform protein abundance ratios in both sublineages, we identified four proteins as differentially regulated between both sublineages, which could explain the apparent increased adaptation of the modern Beijing strains. These proteins are; Rv0450c/MmpL4, Rv1269c, Rv3137, and Rv3283/sseA. Transcriptional and functional analysis of these proteins in a large cohort of 29 Beijing strains showed that the mRNA levels of Rv0450c/MmpL4 are significantly higher in modern Beijing strains, whereas we also provide evidence that Rv3283/sseA is less abundant in the modern Beijing sublineage. Our findings provide a possible explanation for the increased virulence and success of the modern Beijing sublineage. In addition, in the established dataset of 1817 proteins, we demonstrate the pre-existence of several, possibly unique, antibiotic efflux pumps in the proteome of the Beijing strains. This may reflect an increased ability of Beijing strains to escape exposure to antituberculosis drugs.

Optimizing multiplex SNP-based data analysis for genotyping of Mycobacterium tuberculosis isolates

Background

Multiplex ligation-dependent probe amplification (MLPA) is a powerful tool to identify genomic polymorphisms. We have previously developed a single nucleotide polymorphism (SNP) and large sequence polymorphisms (LSP)-based MLPA assay using a read out on a liquid bead array to screen for 47 genetic markers in the Mycobacterium tuberculosis genome. In our assay we obtain information regarding the Mycobacterium tuberculosis lineage and drug resistance simultaneously. Previously we called the presence or absence of a genotypic marker based on a threshold signal level. Here we present a more elaborate data analysis method to standardize and streamline the interpretation of data generated by MLPA. The new data analysis method also identifies intermediate signals in addition to classification of signals as positive and negative. Intermediate calls can be informative with respect to identifying the simultaneous presence of sensitive and resistant alleles or infection with multiple different Mycobacterium tuberculosis strains.

Results

To validate our analysis method 100 DNA isolates of Mycobacterium tuberculosis extracted from cultured patient material collected at the National TB Reference Laboratory of the National Center for Tuberculosis and Lung Diseases in Tbilisi, Republic of Georgia were tested by MLPA. The data generated were interpreted blindly and then compared to results obtained by reference methods. MLPA profiles containing intermediate calls are flagged for expert review whereas the majority of profiles, not containing intermediate calls, were called automatically. No intermediate signals were identified in 74/100 isolates and in the remaining 26 isolates at least one genetic marker produced an intermediate signal.

Conclusion

Based on excellent agreement with the reference methods we conclude that the new data analysis method performed well. The streamlined data processing and standardized data interpretation allows the comparison of the Mycobacterium tuberculosis MLPA results between different experiments. All together this will facilitate the implementation of the MLPA assay in different settings.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-572) contains supplementary material, which is available to authorized users.

Phylogenetic and population genetic analysis of Salmonella enterica subsp. enterica serovar Infantis strains isolated in Japan using whole genome sequence data

Salmonella enterica subsp. enterica serovar Infantis has been reported to be carried asymptomatically in chickens and isolated from some human patients with diarrhea. The aim of this study was to investigate the phylogeny of S. Infantis strains isolated in Japan from chicken meat, chicken egg shells, environmental samples from a grading and packing center for chicken eggs (GP center), diarrhea patients, and asymptomatic carriers based on whole genome sequence data. The S. Infantis strains were in five clusters in a phylogenetic tree reconstructed by the maximum likelihood method. The five clusters were confirmed by neighbor-net and Bayesian cluster analyses. Two of the five clusters formed a group containing all of the strains isolated from chicken meat and some of the strains isolated from diarrhea patients and asymptomatic carriers. The median-joining network reconstructed in this study showed that strains in one of these two clusters diverged from one node with similar relatively short branches, suggesting clonal dissemination of these strains. The other three clusters formed a group containing all of the strains isolated from chicken egg shells and the GP center, and the remaining strains from diarrhea patients and asymptomatic carriers. Interestingly, strains isolated from patients did not cluster in only one group, indicating that none of the S. Infantis strains in this study had significantly higher human pathogenicity. The population genetic analyses in this study showed the separation of the five clusters into two groups was concordant with the sources where the strains in the clusters were isolated. These results suggested that evolutionary groups with higher hierarchy than the clusters identified in this study may be present, although such groups could not be determined by phylogenetic, neighbor-net, and Bayesian analyses in this study. Determination of higher level S. Infantis evolutionary groups should be investigated using other types of genetic markers.

Increased genetic diversity of the Mycobacterium tuberculosis W-Beijing genotype that predominates in eastern China

OBJECTIVES

To determine the genetic diversity of Mycobacterium tuberculosis (M. tuberculosis) strains in a Chinese population predominately infected with strains of the W-Beijing family.

METHODS

A cross-sectional study was conducted in three counties of eastern China. M. tuberculosis strains were collected at TB clinics, and patients were interviewed by trained physicians at the time of TB diagnosis. RD105 and RD181 were used to identify W-Beijing and modern W-Beijing strains, respectively, while seven-locus variable numbers of tandem repeat-mycobacterial interspersed repetitive unit (VNTR-MIRU) analysis was employed to differentiate the genotypes of these strains.

RESULTS

Of 441 strains studied, 394 (89.3%) were identified as W-Beijing family strains; of them, 299 were modern W-Beijing strains. VNTR-MIRU identified 409 genotypes from 426 strains, including 395 unique patterns and 14 clusters. Ancestral W-Beijing strains were more likely to be clustered (OR=1.32, 95%CI: 0.58-2.97) compared to modern W-Beijing strains. The proportions of clustered strains were 14.6%, 4.2% and 0% at sites Funing (FN), Deqing (DQ) and Yinzhou (YZ), respectively. Of the seven MIRU loci, VNTR3820 was found to have the highest discriminatory power and allelic diversity.

CONCLUSIONS

VNTR-MIRU typing appears to be a reliable method for analyzing M. tuberculosis transmission in relatively closed populations. The low clustering proportions indicate that endogenous relapse may be a main source of TB cases in eastern China. Furthermore, our results indicate that migration has played may play an important role in the recent transmission of the W-Beijing family of M. tuberculosis.

Epidemiological investigation of Pseudomonas aeruginosa isolates from a six-year-long hospital outbreak using high-throughput whole genome sequencing

Although previous bacterial typing methods have been informative about potential relatedness of isolates collected during outbreaks, next-generation sequencing has emerged as a powerful tool to not only look at similarity between isolates, but also put differences into biological context. In this study, we have investigated the whole genome sequence of five Pseudomonas aeruginosa isolates collected during a persistent six-year outbreak at Nottingham University Hospitals National Health Service (NHS) Trust – City Campus, United Kingdom. Sequencing, using both Roche 454 and Illumina, reveals that most of these isolates are closely related. Some regions of difference are noted between this cluster of isolates and previously published genome sequences. These include regions containing prophages and prophage remnants such as the serotype-converting bacteriophage D3 and the cytotoxin-converting phage phi CTX. Additionally, single nucleotide polymorphisms (SNPs) between the genomic sequence data reveal key single base differences that have accumulated during the course of this outbreak, giving insight into the evolution of the outbreak strain. Differentiating SNPs were found within a wide variety of genes, including lasR, nrdG, tadZ, and algB. These have been generated at a rate estimated to be one SNP every four to five months. In conclusion, we demonstrate that the single base resolution of whole genome sequencing is a powerful tool in analysis of outbreak isolates that can not only show strain similarity, but also evolution over time and potential adaptation through gene sequence changes.

The re-emergence of tuberculosis: what have we learnt from molecular epidemiology?

Tuberculosis (TB) has re-emerged over the past two decades: in industrialized countries in association with immigration, and in Africa owing to the human immunodeficiency virus epidemic. Drug-resistant TB is a major threat worldwide. The variable and uncertain impact of TB control necessitates not only better tools (diagnostics, drugs, and vaccines), but also better insights into the natural history and epidemiology of TB. Molecular epidemiological studies over the last two decades have contributed to such insights by answering long-standing questions, such as the proportion of cases attributable to recent transmission, risk factors for recent transmission, the occurrence of multiple Mycobacterium tuberculosis infection, and the proportion of recurrent TB cases attributable to re-infection. M. tuberculosis lineages have been identified and shown to be associated with geographical origin. The Beijing genotype is strongly associated with multidrug resistance, and may have escaped from bacille Calmette-Guérin-induced immunity. DNA fingerprinting has quantified the importance of institutional transmission and laboratory cross-contamination, and has helped to focus contact investigations. Questions to be answered in the near future with whole genome sequencing include identification of chains of transmission within clusters of patients, more precise quantification of mixed infection, and transmission probabilities and rates of progression from infection to disease of various M. tuberculosis lineages, as well as possible variations in vaccine efficacy by lineage. Perhaps most importantly, dynamics in the population structure of M. tuberculosis in response to control measures in high-prevalence areas should be better understood.

Analysis of mutations in streptomycin-resistant strains reveals a simple and reliable genetic marker for identification of the Mycobacterium tuberculosis Beijing genotype

The Mycobacterium tuberculosis pandemic is a major health problem, further complicated by an increasing incidence of drug-resistant isolates and the existence of highly transmissible strains, such as those in the Beijing family. Streptomycin (STR)-resistant M. tuberculosis clinical isolates have been analyzed to look for mutations in the rpsL, rrs, and gidB genes. In addition, the Rv1258c gene, which encodes Tap, an efflux pump that transports STR, has been sequenced. Mutations affecting codons 43 and 88 of the rpsL gene were found in 44.4% of the strains, and 16.7% of the strains carried mutations in the rrs gene, both of which probably contribute to STR resistance. Many strains presented with mutations in the gidB gene, but the implication of those mutations in STR resistance remains unclear. Interestingly, a cytosine nucleotide insertion between positions 580 and 581 (denominated Tap(580)) in the Rv1258c gene has been found in all Beijing isolates included in this study, suggesting that it might be a novel polymorphism specific to the Beijing family of M. tuberculosis. A simple and fast restriction fragment length polymorphism (RFLP)-PCR method for detecting the Tap(580) insertion has been developed and used to screen a collection of 220 DNA samples obtained from cultures of M. tuberculosis isolates and 30 respiratory specimens. In all cases, the Beijing and non-Beijing representative samples were identified correctly. Tap(580) is a novel polymorphism specific to the highly transmissible Beijing family, which allows for fast detection of these strains even at the very early stages of infection.

Mycobacterial genotypes are associated with clinical manifestation and progression of lung disease caused by Mycobacterium abscessus and Mycobacterium massiliense

BACKGROUND

Mycobacterium abscessus and Mycobacterium massiliense, which cause lung disease, are variable in their clinical manifestation and progression. We hypothesized that mycobacterial genotypes represent their pathogenic phenotypes, which would result in particular genotypes being associated with disease progression.

METHODS

Variable number tandem repeat (VNTR) loci were selected to establish a genotype assay that was capable of differentiating patients with heterogeneous prognoses in the development cohort (48 isolates). The analysis was reevaluated in the validation cohort (63 isolates).

RESULTS

A total of 53 M. abscessus and 58 M. massiliense isolates were assembled into 3 clusters based on their VNTR genotyping. The patients in cluster A were more likely to have stable disease of the nodular bronchiectatic form; 100% of M. abscessus patients and 96% of M. massiliense patients were followed without antibiotic treatment for >24 months after diagnosis. In contrast, the patients in cluster B were more likely to have progressive disease of the nodular bronchiectatic form; 96% of M. abscessus patients and 81% of M. massiliense patients started antibiotic treatment within 24 months after diagnosis. All patients in cluster C had fibrocavitary disease and started antibiotic treatment immediately after diagnosis. The genetic distance of each clinical isolate from the reference strain was associated with the highest likelihood of disease progression and a disease phenotype of the fibrocavitary form (P < .001).

CONCLUSIONS

Mycobacterial genotyping of M. abscessus and M. massiliense may provide valuable information for predicting disease phenotype and progression.

Whole genome sequencing versus traditional genotyping for investigation of a Mycobacterium tuberculosis outbreak: a longitudinal molecular epidemiological study

BACKGROUND

Understanding Mycobacterium tuberculosis (Mtb) transmission is essential to guide efficient tuberculosis control strategies. Traditional strain typing lacks sufficient discriminatory power to resolve large outbreaks. Here, we tested the potential of using next generation genome sequencing for identification of outbreak-related transmission chains.

METHODS AND FINDINGS

During long-term (1997 to 2010) prospective population-based molecular epidemiological surveillance comprising a total of 2,301 patients, we identified a large outbreak caused by an Mtb strain of the Haarlem lineage. The main performance outcome measure of whole genome sequencing (WGS) analyses was the degree of correlation of the WGS analyses with contact tracing data and the spatio-temporal distribution of the outbreak cases. WGS analyses of the 86 isolates revealed 85 single nucleotide polymorphisms (SNPs), subdividing the outbreak into seven genome clusters (two to 24 isolates each), plus 36 unique SNP profiles. WGS results showed that the first outbreak isolates detected in 1997 were falsely clustered by classical genotyping. In 1998, one clone (termed "Hamburg clone") started expanding, apparently independently from differences in the social environment of early cases. Genome-based clustering patterns were in better accordance with contact tracing data and the geographical distribution of the cases than clustering patterns based on classical genotyping. A maximum of three SNPs were identified in eight confirmed human-to-human transmission chains, involving 31 patients. We estimated the Mtb genome evolutionary rate at 0.4 mutations per genome per year. This rate suggests that Mtb grows in its natural host with a doubling time of approximately 22 h (400 generations per year). Based on the genome variation discovered, emergence of the Hamburg clone was dated back to a period between 1993 and 1997, hence shortly before the discovery of the outbreak through epidemiological surveillance.

CONCLUSIONS

Our findings suggest that WGS is superior to conventional genotyping for Mtb pathogen tracing and investigating micro-epidemics. WGS provides a measure of Mtb genome evolution over time in its natural host context.

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.

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.

Genetic diversity of the Mycobacterium tuberculosis Beijing family based on SNP and VNTR typing profiles in Asian countries

The Mycobacterium tuberculosis (MTB) Beijing strain is highly virulent, drug resistant, and endemic over Asia. To explore the genetic diversity of this family in several different regions of eastern Asia, 338 Beijing strains collected in Taiwan (Republic of China) were analyzed by mycobacterial interspersed repetitive unit-variable number tandem repeat (MIRU-VNTR) typing and compared with published MIRU-VNTR profiles and by the Hunter-Gaston diversity index (HGDI) of Beijing strains from Japan and South Korea. The results revealed that VNTR2163b (HGDI>0.6) and five other loci (VNTR424, VNTR4052, VNTR1955, VNTR4156 and VNTR 2996; HGDI>0.3) could be used to discriminate the Beijing strains in a given geographic region. Analysis based on the number of VNTR repeats showed three VNTRs (VNTR424, 3192, and 1955) to be phylogenetically informative loci. In addition, to determine the geographic variation of sequence types in MTB populations, we also compared sequence type (ST) data of our strains with published ST profiles of Beijing strains from Japan and Thailand. ST10, ST22, and ST19 were found to be prevalent in Taiwan (82%) and Thailand (92%). Furthermore, classification of Beijing sublineages as ancient or modern in Taiwan was found to depend on the repeat number of VNTR424. Finally, phylogenetic relationships of MTB isolates in Taiwan, South Korea, and Japan were revealed by a minimum spanning tree based on MIRU-VNTR genotyping. In this topology, the MIRU-VNTR genotypes of the respective clusters were tightly correlated to other genotypic characters. These results are consistent with the hypothesis that clonal evolution of these MTB lineages has occurred.

Scanning of genetic diversity of evolutionarily sequential Mycobacterium tuberculosis Beijing family strains based on genome wide analysis

The Beijing family is an endemic lineage of Mycobacterium tuberculosis in eastern Asia. In Japan, five evolutionarily sequential sublineages composing the lineage have predominated. Comparative genomic sequencing based on a microarray technique was conducted for five representative strains of those respective sublineages. Results revealed approximately 200 point mutations specific to each strain. Subsequently, to investigate the genetic diversity of each sublineage, we analysed the phylogenetic divergence of 103 domestic strains belonging to them using genetic markers derived from the mutation information. Results show that the five sublineages have comprised smaller lineages which had diverged at various points. The smaller sub-sublineages have emerged with respective bottlenecks, which are reflected in the excessive monophyletic evolution of the species. Our data provide necessary information to grasp a comprehensive picture of genetic diversity of the lineage constructed in its evolution.