Matthew Silcocks

Background: Tuberculosis (TB) continues to be a leading cause of morbidity and mortality worldwide. Although numerous genome-wide association studies (GWAS) have explored TB susceptibility across various ethnic groups, multi-population replication of findings has been very limited, particularly outside the HLA region, and a significant portion of TB heritability remains unexplained. Methods: We conducted GWAS in the Singapore Chinese and Vietnamese, followed by a comprehensive meta-analysis incorporating 4 independent East Asian datasets ( N = 11,841 cases; N = 197,373 controls). The transferability of any identified association was assessed using summary statistics from independent European populations. Potential candidate genes were prioritized using gene-based association testing and integrative bioinformatic database mining, followed by functional validation through assessment of Mycobacterium marinum ( M.marinum ) infection burden in CRISPR-Cas9-edited zebrafish embryos. Results: We identified a novel susceptibility locus for pulmonary TB (PTB) at 22q12.2 in East Asians [rs6006426, OR (95%Cl) = 1.097(1.066, 1.130), P _meta =3.31 × 10 ^− 10 ]. The association was further validated in Europeans [OR (95%Cl) = 1.101(1.002, 1.211), P = 0.046] and was strengthened in the combined meta-analysis including a total of 12,736 PTB cases and 673,864 controls [OR (95%Cl) = 1.098 (1.068, 1.129); P _meta =4.33 × 10 ^− 11 ]. Gene-based association test identified Oncostatin M ( OSM ) to be significantly associated with PTB (ZSTAT = 5.013; P = 2.68 × 10 ^− 7 ; P _adj =0.005). The lead SNP rs6006426 affected Splicing factor 3a subunit 1 ( SF3A1 ) expression in various immune cells ( P from 0.003 to 6.17 × 10 ^− 18 ) and OSM expression in monocytes post lipopolysaccharide stimulation ( P = 5.57 × 10 ^− 4 ) as reported in the eQTL Catalogue. CRISPR-Cas9 edited zebrafish embryos with osm depletion resulted in decreased burden of M.marinum in infected embryos ( P = 0.047). Conclusions: Our findings offer novel insights into the genetic factors underlying TB and reveals new avenues for understanding its etiology.

The rapid emergence of multidrug-resistant Mycobacterium tuberculosis (Mtb) threatens global tuberculosis (TB) control, yet the mechanisms enabling rapid evolution of resistance in Mtb remain poorly understood. Here, we show that pre-existing mutations in oxidative stress response genes create permissive genomic backgrounds that accelerate high-level isoniazid resistance (INH ^R ), challenging the paradigm that resistance mutations must precede compensatory adaptation. Using Mycobacterium smegmatis mc ² 155 (Msm) as a model, we demonstrate that brief exposure to sublethal isoniazid (INH) enriches for “low-level resistance and tolerance” (LLRT) mutants in a single step. LLRT mutants, particularly those with ohrR loss-of-function mutations, acquire high-level resistance (>500× IC ₅₀ ) at ~6-fold higher rates than wildtype, primarily through otherwise deleterious mycothiol biosynthesis mutations that become tolerable in an oxidative stress-buffered background. Crucially, sublethal oxidative stress alone, mimicking host immune pressure, nearly tripled the rate of INH ^R evolution. Analysis of 1578 clinical Mtb isolates revealed significant enrichment of oxidative stress-related loci among those associated with INH ^R . Reanalysis of genome-wide CRISPRi data further linked oxidative stress response pathways to survival under multiple antibiotics. Together, these findings suggest that host-imposed oxidative stress and suboptimal drug exposure may prime Mtb populations for rapid resistance evolution, highlighting oxidative stress defenses as potential targets to limit resistance emergence.

Phenotypically agnostic screens for positive selection in pathogen populations provide a means of pinpointing genes and regulatory regions involved in adaptation to the local environment or host population. We screened a large ( n = 2506) collection of Vietnamese Mycobacterium tuberculosis ( Mtb ) isolates, finding targets of selection to be lineage-specific, and encompass diverse functions, including dormancy ( Rv0080 ), zinc homeostasis ( zur ), and virulence (ESX-1 structure). Extending our screen to the wider Mtb complex (MTBC) phylogeny demonstrated Rv0080 to display an extraordinarily dynamic evolutionary history, acquiring premature stop codons or putative functional mutations on branches upstream of 8 of the 10 human-adapted lineages, and undergoing positive selection in the remaining 2. Lineage 1, which is one of two such lineages retaining the ancestral Rv0080 sequence, displays a rate of selection for this gene (dN/dS=9.37) exceeding any other in the Mtb genome, save a transcription factor linked to its expression ( Rv0042c ; dN/dS=11.02). Deletion of Rv0080 ’s M. smegmatis orthologue confers a survival advantage in hypoxic conditions, as does the evolution of nonsense or missense mutations on an ancestral Rv0080 background. We show the dormancy survival regulon experienced recurrent episodes of reductive evolution across the MTBC phylogeny, illuminating a novel mechanism via which it adapted to human populations.

The rapid emergence of multidrug-resistant Mycobacterium tuberculosis (Mtb) threatens global TB control, yet the mechanisms enabling rapid evolution of drug resistance in Mtb remain poorly understood. Here we reveal that pre-existing mutations in oxidative stress response genes create permissive genomic backgrounds that accelerate high-level isoniazid resistance (INH ^R ) without fitness costs, challenging the paradigm that resistance mutations always precede their fitness compensatory adaptations. Using M. smegmatis mc ² 155 (Msm) as a model, we show that brief exposure to sublethal INH (2× IC ₅₀ ) enriches for "low-level resistance and tolerance" (LLRT) mutants in a single step. These LLRT mutants, particularly those with ohrR loss-of-function mutations, acquire high-level resistance (> 500× IC ₅₀ ) at 6-fold higher rates than wildtype, primarily through otherwise-deleterious mycothiol biosynthesis mutations that become tolerable in the oxidative stress-buffered background. Crucially, we demonstrate that sublethal oxidative stress alone, mimicking host immune pressure, nearly tripled the rate of INH resistance evolution in Msm. Bayesian analysis of 1,578 clinical Mtb isolates from Vietnam confirmed that mutations in oxidative stress response genes were significantly associated with the emergence of INH ^R strains ( p-value = 1.09×10 ^-7 ). Independently, reanalysis of genome-wide CRISPRi screens revealed that the OSR network and high Bayes probability genes are functionally associated with treatment escape and survival with multiple antibiotics, including isoniazid, rifampicin, ethambutol, bedaquiline, vancomycin, clarithromycin, linezolid, and streptomycin. Our findings that host-imposed oxidative stress and inadequate drug penetration may synergistically prime Mtb populations for rapid resistance evolution suggest that targeting pre-resistance mechanisms, such as oxidative stress defenses, could help slow the emergence of antibiotic resistance in tuberculosis.

Structural variants (SVs) are increasingly recognized as key drivers of bacterial evolution, yet their role has not been explored thoroughly. This is due to limitations in traditional short-read sequencing and linear reference-based analyses, which can miss complex structural changes. Tuberculosis (TB), a disease caused by Mycobacterium tuberculosis ( Mtb ), remains a major global health concern. In this study, we harness long-read sequencing technologies and genome graph tools to construct a Mtb pangenome reference graph (PRG) from 859 high-quality, diverse, long-read assemblies. To enable accurate genotyping of SVs leveraging the PRG, we developed miniwalk, a tool that outperforms a traditional linear genome-based approach in precision for SV detection. We characterize patterns of structural variation genome-wide, revealing a virulence-associated ESX-5 deletion to be recurrent across the phylogeny, and fixed in a sub-lineage of L4. Systematic screens for additional genes that are recurrently affected by SVs implicated those related to metal homeostasis, including a copper exporter fixed in the widely distributed L1.2.1 sub-lineage. Lastly, we genotyped 41,134 isolates and found SVs putatively associated with resistance to various first and second-line drugs. These findings underscore the broader role of SVs in shaping Mtb diversity, highlighting their importance in both understanding evolution and designing strategies to combat drug-resistant TB.

A previous investigation has elucidated the landscape of Mtb genomic diversity and transmission dynamics in Ho Chi Minh City, Vietnam. Here, we expand the scope of this survey by adding a substantial number of additional genomes (total sample size: 2,542) and phenotypic drug susceptibility data for the majority of isolates. We aim to explore the prevalence and evolutionary dynamics of drug resistance and our ability to predict drug resistance from sequencing data. Among isolates tested phenotypically against first-line drugs, we observed high rates of streptomycin [STR, 37.7% ( N = 573/1,520)] and isoniazid resistance [INH, 25.7% ( N = 459/1,786)] and lower rates of resistance to rifampicin [RIF, 4.9% ( N = 87/1,786)] and ethambutol [EMB, 4.2% ( N = 75/1,785)]. Relative to global benchmarks, resistance to STR and INH was predicted accurately when applying the TB-Profiler algorithm to whole genome sequencing data (sensitivities of 0.81 and 0.87, respectively), while resistance to RIF and EMB was predicted relatively poorly (sensitivities of 0.70 and 0.44, respectively). Exploring the evolution of drug resistance revealed the main phylogenetic lineages to display differing dynamics and tendencies to evolve resistance via mutations in certain genes. The Beijing sublineage L2.2.1 was found to acquire de novo resistance mutations more frequently than isolates from other lineages and to suffer no apparent fitness cost acting to impede the transmission of resistance. Mutations conferring resistance to INH and STR arose earlier, on average, than those conferring resistance to RIF and are now more widespread across the phylogeny. The high prevalence of “background” INH resistance, combined with high rates of RIF mono-resistance (20.7%, N = 18/87), suggests that rapid assays for INH resistance will be valuable in this setting. These tests will allow the detection of INH mono-resistance and will allow multi-drug-resistant isolates to be distinguished from isolates with RIF mono-resistance. IMPORTANCE: Drug-resistant tuberculosis (TB) infection is a growing and potent concern, and combating it will be necessary to achieve the WHO’s goal of a 95% reduction in TB deaths by 2035. While prior studies have explored the evolution and spread of drug resistance, we still lack a clear understanding of the fitness costs (if any) imposed by resistance-conferring mutations and the role that Mtb genetic lineage plays in determining the likelihood of resistance evolution. This study offers insight into these questions by assessing the dynamics of resistance evolution in a high-burden Southeast Asian setting with a diverse lineage composition. It demonstrates that there are clear lineage-specific differences in the dynamics of resistance acquisition and transmission and shows that different lineages evolve resistance via characteristic mutational pathways.

The Two Layer hypothesis is fast becoming the favoured narrative describing East Asian population history. Under this model, hunter-gatherer groups who initially peopled East Asia via a route south of the Himalayas were assimilated by agriculturalist migrants who arrived via a northern route across Eurasia. A lack of ancient samples from tropical East Asia limits the resolution of this model. We consider insight afforded by patterns of variation within the human pathogen Mycobacterium tuberculosis (Mtb) by analysing its phylogeographic signatures jointly with the human Y-chromosome. We demonstrate the Y-chromosome lineages enriched in the traditionally hunter-gatherer groups associated with East Asia’s first layer of peopling to display deep roots, low long-term effective population size, and diversity patterns consistent with a southern entry route. These characteristics mirror those of the evolutionarily ancient Mtb lineage 1. The remaining East Asian Y-chromosome lineage is almost entirely absent from traditionally hunter-gatherer groups and displays spatial and temporal characteristics which are incompatible with a southern entry route, and which link it to the development of agriculture in modern-day China. These characteristics mirror those of the evolutionarily modern Mtb lineage 2. This model paves the way for novel host-pathogen coevolutionary research hypotheses in East Asia.