Significance of ahpC promoter mutations for the prediction of isoniazid resistance in Mycobacterium tuberculosis

Immunometabolism during Mycobacterium tuberculosis Infection

Over a quarter of the world's population is infected with Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB). Approximately 3.4% of new and 18% of recurrent cases of TB are multidrug-resistant (MDR) or rifampicin-resistant. Recent evidence has shown that certain drug-resistant strains of Mtb modulate host metabolic reprogramming, and therefore immune responses, during infection. However, it remains unclear how widespread these mechanisms are among circulating MDR Mtb strains and what impact drug-resistance-conferring mutations have on immunometabolism during TB. While few studies have directly addressed metabolic reprogramming in the context of drug-resistant Mtb infection, previous literature examining how drug-resistance mutations alter Mtb physiology and differences in the immune response to drug-resistant Mtb provides significant insights into how drug-resistant strains of Mtb differentially impact immunometabolism.

Prevalence, risk and genetic characteristics of drug-resistant tuberculosis in a tertiary care tuberculosis hospital in China

Objectives

To explore the prevalence, risk and genetic characteristics of drug-resistant tuberculosis (TB) from a tertiary care TB hospital in China.

Patients and methods

We carried out a retrospective study including isolates from 189 patients with pulmonary TB at Fuzhou Pulmonary Hospital. All isolates from these patients were subjected to drug susceptibility testing and genotyping. For drug-resistant isolates, DNA sequencing was used to investigate mutations in 12 loci, including katG, inhA, oxyR–ahpC, rpoB, rpsL, rrs₁ (nucleotides 388–1084 of rrs), embB, tlyA, eis, rrs₂ (nucleotides 1158–1674 of rrs), gyrA and gyrB.

Results

Among 189 isolates, 28.6% were resistant to at least one of the seven anti-TB drugs, including isoniazid (INH), rifampin (RIF), streptomycin (STR), ethambutol (EMB), capreomycin (CAP), kanzmycin (KAN) and ofloxacin (OFX). The proportion of multidrug-resistant TB and extensively drug-resistant TB isolates was 9.5% and 1.1%, respectively. Patients in rural areas as well as previously treated patients showed a significantly increased risk of developing drug resistance. In addition, among these isolates, 111 (58.7%) were Beijing genotype strains, 84 (75.7%) of which belonged to modern Beijing sublineage. There was no association between genotype and drug resistance. The most common mutations were katG315, rpoB531 rpsL43, embB306, rrs1401 and gyrA94.

Conclusion

These findings provided additional information of drug-resistant TB in China. Previously treated patients and patients in rural areas should receive greater attention owing to their higher risk of developing drug resistance.

Effects of a previously selected antibiotic resistance on mutations acquired during development of a second resistance in Escherichia coli

Background

The effect of mutations conferring antibiotic resistance can depend on the genetic background. To determine if a previously de novo acquired antibiotic resistance influences the adaptation to a second antibiotic, antibiotic resistance was selected for by exposure to stepwise increasing sublethal levels of amoxicillin, enrofloxacin, kanamycin, or tetracycline. E. coli populations adapted to either a single or two antibiotics sequentially were characterized using whole genome population sequencing and MIC measurements.

Results

In a wild-type background, adaptation to any of the antibiotics resulted in the appearance of well-known mutations, as well as a number of mutated genes not known to be associated with antibiotic resistance. Development of a second resistance in a strain with an earlier acquired resistance to a different antibiotic did not always result in the appearance of all mutations associated with resistance in a wild-type background. In general, a more varied set of mutations was acquired during secondary adaptation. The ability of E. coli to maintain the first resistance during this process depended on the combination of antibiotics used. The maintenance of mutations associated with resistance to the first antibiotic did not always predict the residual MIC for that compound.

Conclusions

In general, the data presented here indicate that adaptation to each antibiotic is unique and independent. The mutational trajectories available in already resistant cells appear more varied than in wild-type cells, indicating that the genetic background of E. coli influences resistance development. The observed mutations cannot always fully explain the resistance pattern observed, indicating a crucial role for adaptation on the gene expression level in de novo acquisition of antibiotic resistance.

Evolution of drug resistance in Mycobacterium tuberculosis: a review on the molecular determinants of resistance and implications for personalized care

Drug-resistant TB (DR-TB) remains a significant challenge in TB treatment and control programmes worldwide. Advances in sequencing technology have significantly increased our understanding of the mechanisms of resistance to anti-TB drugs. This review provides an update on advances in our understanding of drug resistance mechanisms to new, existing drugs and repurposed agents. Recent advances in WGS technology hold promise as a tool for rapid diagnosis and clinical management of TB. Although the standard approach to WGS of Mycobacterium tuberculosis is slow due to the requirement for organism culture, recent attempts to sequence directly from clinical specimens have improved the potential to diagnose and detect resistance within days. The introduction of new databases may be helpful, such as the Relational Sequencing TB Data Platform, which contains a collection of whole-genome sequences highlighting key drug resistance mutations and clinical outcomes. Taken together, these advances will help devise better molecular diagnostics for more effective DR-TB management enabling personalized treatment, and will facilitate the development of new drugs aimed at improving outcomes of patients with this disease.

Drug Resistance Mechanisms in Mycobacterium tuberculosis

Tuberculosis (TB) is a serious public health problem worldwide. Its situation is worsened by the presence of multidrug resistant (MDR) strains of Mycobacterium tuberculosis, the causative agent of the disease. In recent years, even more serious forms of drug resistance have been reported. A better knowledge of the mechanisms of drug resistance of M. tuberculosis and the relevant molecular mechanisms involved will improve the available techniques for rapid drug resistance detection and will help to explore new targets for drug activity and development. This review article discusses the mechanisms of action of anti-tuberculosis drugs and the molecular basis of drug resistance in M. tuberculosis.

Selection of mutations to detect multidrug-resistant Mycobacterium tuberculosis strains in Shanghai, China

Novel tools are urgently needed for the rapid, reliable detection of multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains of Mycobacterium tuberculosis. To develop such tools, we need information about the frequency and distribution of the mycobacterial mutations and genotypes that are associated with phenotypic drug resistance. In a population-based study, we sequenced specific genes of M. tuberculosis that were associated with resistance to rifampin and isoniazid in 242 phenotypically MDR isolates and 50 phenotypically pan-susceptible isolates from tuberculosis (TB) cases in Shanghai, China. We estimated the sensitivity and specificity of the mutations, using the results of conventional, culture-based phenotypic drug susceptibility testing as the standard. We detected mutations within the 81-bp core region of rpoB in 96.3% of phenotypically MDR isolates. Mutations in two structural genes (katG and inhA) and two regulatory regions (the promoter of mabA-inhA and the intergenic region of oxyR-ahpC) were found in 89.3% of the MDR isolates. In total, 88.0% (213/242 strains) of the phenotypic MDR strains were confirmed by mutations in the sequenced regions. Mutations in embB306 were also considered a marker for MDR and significantly increased the sensitivity of the approach. Based on our findings, an approach that prospectively screens for mutations in 11 sites of the M. tuberculosis genome (rpoB531, rpoB526, rpoB516, rpoB533, and rpoB513, katG315, inhA-15, ahpC-10, ahpC-6, and ahpC-12, and embB306) could detect 86.8% of MDR strains in Shanghai. This study lays the foundation for the development of a rapid, reliable molecular genetic test to detect MDR strains of M. tuberculosis in China.

HIV evades RNA interference directed at TAR by an indirect compensatory mechanism

HIV can rapidly evolve when placed under selective pressure, including immune surveillance or the administration of antiretroviral drugs. Typically, a variant protein allows HIV to directly evade the selective pressure. Similarly, HIV has escaped suppression by RNA interference (RNAi) directed against viral RNAs by acquiring mutations at the target region that circumvent RNAi-mediated inhibition while conserving necessary viral functions. However, when we directed RNAi against the viral TAR hairpin, which plays an indispensable role in viral transcription, resistant strains were recovered, but none carried a mutation at the target site. Instead, we isolated several strains carrying promoter mutations that indirectly compensated for the RNAi by upregulating viral transcription. Combining RNAi with the application of an antiviral drug blocked replication of such mutants. Evolutionary tuning of viral transcriptional regulation may serve as a general evasion mechanism that may be targeted to improve the efficacy of antiviral therapy.

Molecular analysis of isoniazid-resistant Mycobacterium tuberculosis isolates from England and Wales reveals the phylogenetic significance of the ahpC -46A polymorphism

The present study investigated the prevalence and diagnostic potential of the most commonly reported mutations associated with isoniazid resistance, katG 315Thr, katG 315Asn, inhA -15T, inhA -8A, and the oxyR-ahpC intergenic region, in a population sample of 202 isoniazid-resistant Mycobacterium tuberculosis isolates and 176 randomly selected fully sensitive isolates from England and Wales identified by using a directed oligonucleotide array and limited DNA sequencing. The strains were recovered from patients originating from 29 countries; 41 isolates were multidrug resistant. Mutations affecting katG 315, the inhA promoter, and the oxyR-ahpC intergenic region were found in 62.7, 21.9, and 30% of 169 genotypically distinct isoniazid-resistant isolates, respectively, whereas they were found in 0, 0, and 8% of susceptible strains, respectively. The frequency of mutation at each locus was unrelated to the resistance profile or previous antituberculous drug therapy. The commonest mutation in the oxyR-ahpC intergenic region, ahpC -46A, was present in 23.7% of isoniazid-resistant isolates and 7.5% of susceptible isolates. This proved to be a phylogenetic marker for a subgroup of M. tuberculosis strains originating on the Indian subcontinent, which shared IS6110-based restriction fragment length polymorphism and spoligotype features with the Delhi strain and Central Asian strain CAS1; and this marker is strongly associated with isoniazid resistance and the katG 315Thr mutation. In total, 82.8% of unrelated isoniazid-resistant isolates could be identified by analysis of just two loci: katG 315 and the inhA promoter. Analysis of the oxyR-ahpC intergenic region, although phylogenetically interesting, does not contribute significantly to further identification of isoniazid-resistant isolates.

Mutations in katG, inhA, and ahpC genes of Brazilian isoniazid-resistant isolates of Mycobacterium tuberculosis

The presence of mutations in specific regions of the katG, inhA, and ahpC genes was analyzed with 69 Mycobacterium tuberculosis isoniazid-resistant isolates from three Brazilian states. Point mutations in codon 315 of the katG gene were observed in 87.1, 60.9, and 60% of the isolates from Rio Grande do Sul, Rio de Janeiro, and São Paulo, respectively. Mutations in the inhA gene were identified only in one isolate from RJ State, and the ahpC promoter region revealed mutations in distinct positions in 12.9, 21.7, and 6.7% of the isolates from RS, RJ and SP, respectively.