Mycobacterium tuberculosis rrs A1401G mutation correlates with high-level resistance to kanamycin, amikacin, and capreomycin in clinical isolates from mainland China

Evaluation of AAICare®-TB sequence analysis tool for accurate diagnosis of drug-resistant tuberculosis: A comparative study with TB-Profiler and Mykrobe

A rapid and comprehensive drug susceptibility test is essential for eliminating drug resistant tuberculosis. Next generation sequencing (NGS) based susceptibility testing is being explored as a potential substitute for the conventional phenotypic and genotypic testing methods. However, the adoption of NGS based genotypic susceptibility testing depends on the availability of simple, accurate and efficient analysis tools. This preliminary study aimed to evaluate the performance of a Mycobacterium tuberculosis (Mtb) genome analysis pipeline, AAICare®-TB, for susceptibility prediction, in comparison to two widely used gDST prediction tools, TB-Profiler and Mykrobe. This study was performed in a National Reference Laboratory in India on presumptive drug-resistant tuberculosis (DR-TB) isolates. Whole genome sequences of the 120 cultured isolates were obtained through Illumina sequencing on a MiSeq platform. Raw sequences were simultaneously analysed using the three tools. Susceptibility prediction reports thus generated, were compared to estimate the total concordance and discordance. WHO mutation catalogue (1st edition, 2021) was used as the reference standard for categorizing the mutations. In this study, AAICare®-TB was able to predict drug resistance status for First Line (Streptomycin, Isoniazid, Rifampicin, Ethambutol and Pyrazinamide) and Second Line drugs (Fluoroquinolones, Second Line Injectables and Ethionamide) in 93 samples along with lineage and hetero-resistance as per the WHO guidelines.

Increased expression of Mycobacterium tuberculosis Rv3737 gene associated with low-level amikacin resistance

INTRODUCTION

As an infectious disease, tuberculosis (TB) poses a serious threat to public health. Although amikacin (AMK) is an important antibiotic for the treatment of drug-resistant TB, its resistance mechanisms are not fully understood.

METHODS

To investigate the role of Rv3737 gene on AMK drug susceptibility, a Mycobacterium tuberculosis (M.tb) Rv3737 knockout strain (H37Rv△Rv3737) and a Mycobacterium smegmatis (M.sm) Rv3737 overexpressing strain (Msm/pMV261-Rv3737) were used to detect their minimal inhibitory concentrations (MICs) in this study.

RESULTS

The AMK MICs of Rv3737 knockout and overexpressing strains were 4-fold lower and 2-fold higher than those of the wild-type and empty plasmid strains, respectively. The results of clinical isolates showed that no Rv3737 gene mutation was found to be associated with AMK susceptibility, while the rrs A1401G mutation remained the main mechanism of high level of AMK resistance (MIC>32 μg/ml). There was a positive correlation between Rv3737 mRNA expression level and AMK MIC. In the isolates with low-level AMK resistance (MIC = 4 μg/ml) without rrs A1401G mutation, the expression level of Rv3737 gene was significantly higher than those of susceptible isolates.

CONCLUSIONS

In this study, the Rv3737 gene was reported for the first time for its effect on AMK susceptibility in M.tb. Although the rrs A1401G mutation remains the main reason of high-level AMK resistance, high expression of the Rv3737 gene was associated with low-level AMK resistance in clinical isolates.

Deciphering the emerging role of phytocompounds: Implications in the management of drug-resistant tuberculosis and ATDs-induced hepatic damage

Tuberculosis is a disease of poverty, discrimination, and socioeconomic burden. Epidemiological studies suggest that the mortality and incidence of tuberculosis are unacceptably higher worldwide. Genomic mutations in embCAB, embR, katG, inhA, ahpC, rpoB, pncA, rrs, rpsL, gyrA, gyrB, and ethR contribute to drug resistance reducing the susceptibility of Mycobacterium tuberculosis to many antibiotics. Additionally, treating tuberculosis with antibiotics also poses a serious risk of hepatotoxicity in the patient's body. Emerging data on drug-induced liver injury showed that anti-tuberculosis drugs remarkably altered levels of hepatotoxicity biomarkers. The review is an attempt to explore the anti-mycobacterial potential of selected, commonly available, and well-known phytocompounds and extracts of medicinal plants against strains of Mycobacterium tuberculosis. Many studies have demonstrated that phytocompounds such as flavonoids, alkaloids, terpenoids, and phenolic compounds have antibacterial action against Mycobacterium species, inhibiting the bacteria's growth and replication, and sometimes, causing cell death. Phytocompounds act by disrupting bacterial cell walls and membranes, reducing enzyme activity, and interfering with essential metabolic processes. The combination of these processes reduces the overall survivability of the bacteria. Moreover, several phytochemicals have synergistic effects with antibiotics routinely used to treat TB, improving their efficacy and decreasing the risk of resistance development. Interestingly, phytocompounds have been presented to reduce isoniazid- and ethambutol-induced hepatotoxicity by reversing serum levels of AST, ALP, ALT, bilirubin, MDA, urea, creatinine, and albumin to their normal range, leading to attenuation of inflammation and hepatic necrosis. As a result, phytochemicals represent a promising field of research for the development of new TB medicines.

Whole-genome sequencing and transcriptome-characterized in vitro evolution of aminoglycoside resistance in Mycobacterium tuberculosis

Antibiotic resistance of Mycobacterium tuberculosis (Mtb) is a major public health concern worldwide. Therefore, it is of great significance to characterize the mutational pathways by which susceptible Mtb evolves into drug resistance. In this study, we used laboratory evolution to explore the mutational pathways of aminoglycoside resistance. The level of resistance in amikacin inducing Mtb was also associated with changes in susceptibility to other anti-tuberculosis drugs such as isoniazid, levofloxacin and capreomycin. Whole-genome sequencing (WGS) revealed that the induced resistant Mtb strains had accumulated diverse mutations. We found that rrs A1401G was the predominant mutation in aminoglycoside-resistant clinical Mtb isolates from Guangdong. In addition, this study provided global insight into the characteristics of the transcriptome in four representative induced strains and revealed that rrs mutated and unmutated aminoglycoside-resistant Mtb strains have different transcriptional profiles. WGS analysis and transcriptional profiling of Mtb strains during evolution revealed that Mtb strains harbouring rrs A1401G have an evolutionary advantage over other drug-resistant strains under the pressure of aminoglycosides because of their ultra-high resistance level and low physiological impact on the strain. The results of this study should advance our understanding of aminoglycoside resistance mechanisms.

Resistance and tolerance of Mycobacterium tuberculosis to antimicrobial agents-How M. tuberculosis can escape antibiotics

Tuberculosis (TB) poses a serious threat to public health worldwide since it was discovered. Until now, TB has been one of the top 10 causes of death from a single infectious disease globally. The treatment of active TB cases majorly relies on various anti-tuberculosis drugs. However, under the selection pressure by drugs, the continuous evolution of Mycobacterium tuberculosis (Mtb) facilitates the emergence of drug-resistant strains, further resulting in the accumulation of tubercle bacilli with multiple drug resistance, especially deadly multidrug-resistant TB and extensively drug-resistant TB. Researches on the mechanism of drug action and drug resistance of Mtb provide a new scheme for clinical management of TB patients, and prevention of drug resistance. In this review, we summarized the molecular mechanisms of drug resistance of existing anti-TB drugs to better understand the evolution of drug resistance of Mtb, which will provide more effective strategies against drug-resistant TB, and accelerate the achievement of the EndTB Strategy by 2035. This article is categorized under: Infectious Diseases > Molecular and Cellular Physiology.

Rapid Identification of Drug-Resistant Tuberculosis Genes Using Direct PCR Amplification and Oxford Nanopore Technology Sequencing

Mycobacterium tuberculosis antimicrobial resistance has been continually reported and is a major public health issue worldwide. Rapid prediction of drug resistance is important for selecting appropriate antibiotic treatments, which significantly increases cure rates. Gene sequencing technology has proven to be a powerful strategy for identifying relevant drug resistance information. This study established a sequencing method and bioinformatics pipeline for resistance gene analysis using an Oxford Nanopore Technologies sequencer. The pipeline was validated by Sanger sequencing and exhibited 100% concordance with the identified variants. Turnaround time for the nanopore sequencing workflow was approximately 12 h, facilitating drug resistance prediction several weeks earlier than that of traditional phenotype drug susceptibility testing. This study produced a customized gene panel assay for rapid bacterial identification via nanopore sequencing, which improves the timeliness of tuberculosis diagnoses and provides a reliable method that may have clinical application.

Molecular Epidemiology and Polymorphism Analysis in Drug-Resistant Genes in M. tuberculosis Clinical Isolates from Western and Northern India

Introduction

The mechanistic details of first line drug (FLD) resistance have been thoroughly explored but the genetic resistance mechanisms of second line injectables, which form the backbone of the combinatorial drug resistant tuberculosis therapy, are partially identified. This study aims to highlight the genetic and spoligotypic differences in the second line drug (SLD) resistant and sensitive Mycobacterium tuberculosis (Mtb) clinical isolates from Mumbai (Western India) and Lucknow (Northern India).

Methods

The rrs, eis, whiB7, tlyA, gyrA and gyrB target loci were screened in 126 isolates and spoligotyped.

Results

The novel mutations were observed in whiB7 loci (A43T, C44A, C47A, G48T, G59A and T152G in 5’-UTR; A42C, C253T and T270G in gene), tlyA (+CG200, G165A, C415G, and +G543) and gyrB (+G1359 and +A1429). Altogether, the rrs, eis, and whiB7 loci harbored mutations in ~86% and ~47% kanamycin resistant isolates from Mumbai and Lucknow, respectively. Mumbai strains displayed higher prevalence of mutations in gyrA (~85%) and gyrB loci (~13%) as compared to those from Lucknow (~69% and ~3.0%, respectively). Further, spoligotyping revealed that Beijing lineage is distributed equally amongst the drug resistant strains of Mumbai and Lucknow, but EAI-5 is existed at a higher level only in Mumbai. The lineages Manu2, CAS1-Delhi and T1 are more prevalent in Lucknow.

Conclusion

Besides identifying novel mutations in whiB7, tlyA and gyrB target loci, our analyses unveiled a potential polymorphic and phylogeographical demarcation among two distinct regions.

Molecular characterization of mutations associated with resistance to second line drugs in Mycobacterium tuberculosis patients from Casablanca, Morocco

The emergence and spread of extensively drug-resistant tuberculosis (XDR-TB) is a serious threat to global health. Therefore, its rapid diagnosis is crucial. The present study aimed to characterize mutations conferring resistance to second line drugs (SLDs) within multidrug Mycobacterium tuberculosis (MDR-MTB) isolates and to estimate the occurrence of XDR-TB in Casablanca, Morocco. A panel of 200 MDR-TB isolates was collected at the Pasteur Institute between 2015-2018. Samples were subjected to drug susceptibility testing to Ofloxacin (OFX), Kanamycin (KAN) and Amikacin (AMK). The mutational status of gyrA, gyrB, rrs, tlyA and eis was assessed by sequencing these target genes. Drug susceptibility testing for SLDs showed that among the 200 MDR strains, 20% were resistant to OFX, 2.5% to KAN and 1.5% to AMK. Overall, 14.5% of MDR strains harbored mutations in gyrA, gyrB, rrs and tlyA genes. From the 40 OFX^R isolates, 67.5% had mutations in QRDR of gyrA and gyrB genes, the most frequent one being Ala90Val in gyrA gene. Of note, none of the isolates harbored simultaneously mutations in gyrA and gyrB genes. In eight out of the 200 MDR-TB isolates resistant either to KAN or AMK, only 25% had A1401G or Lys89Glu change in rrs and tlyA genes respectively. This study is very informative and provides data on the alarming rate of fluoroquinolone resistance which warrants the need to implement appropriate drug regimens to prevent the emergence and spread of more severe forms of Mycobacterium tuberculosis drug resistance.

Detection of Resistance to Fluoroquinolones and Second-Line Injectable Drugs Among Mycobacterium tuberculosis by a Reverse Dot Blot Hybridization Assay

Background

Reliable and timely determination of second-line drug resistance is essential for early initiation effective anti-tubercular treatment among multi-drug resistant (MDR) patients and blocking the spread of MDR and extensively drug-resistant tuberculosis. Molecular methods have the potency to provide accurate and rapid drug susceptibility results. We aimed to establish and evaluate the accuracy of a reverse dot blot hybridization (RDBH) assay to simultaneously detect the resistance of fluoroquinolones (FQs), kanamycin (KN), amikacin (AMK), capreomycin (CPM) and second-line injectable drugs (SLIDs) in Mycobacterium tuberculosis.

Methods

We established and evaluated the accuracy of the RDBH assay by comparing to the phenotypic drug susceptibility testing (DST) and sequencing in 170 M. tuberculosis, of which 94 and 27 were respectively resistant to ofloxacin (OFX) and SLIDs.

Results

The results show that, compared to phenotypic DST, the sensitivity and specificity of the RDBH assay for resistance detection were 63.8% and 100.0% for OFX, 60.0% and 100.0% for KN, 61.5% and 98.1% for AMK, 50.0% and 99.3% for CPM, and 55.6% and 100% for SLIDs, respectively; compared to sequencing, the sensitivity and specificity of the RDBH assay were 95.2% and 100.0% for OFX, 93.8% and 100.0% for SLIDs or KN (both based on mutations in rrs 1400 region and eis promoter), and 91.6% and 100.0% for AMK or CPM (both based on mutations in rrs 1400 region), respectively. The turnaround time of the RDBH assay was 7 h for testing 42 samples.

Conclusion

Our data suggested that compared to sequencing, the RDBH assay could serve as a rapid and reliable method for testing the resistance of M. tuberculosis against OFX and SLIDs, enabling early administration of appropriate treatment regimens among MDR tuberculosis patients.

Burden of baseline resistance of Mycobacterium tuberculosis to fluoroquinolones and second-line injectables in central India

Background

Drug-resistant TB is a serious public health problem in India. Pre-existing resistance to fluoroquinolones (FQs) and second-line injectable drugs (SLIDs) in strains of Mycobacterium tuberculosis (MTB) resistant to rifampicin (RIF) and/or isoniazid (INH) contributes to treatment failures and consequent transmission of drug-resistant TB. A baseline assessment of resistance of MTB to FQs and SLIDs may help guide policies to further improve management of drug-resistant TB in India. This study aims to determine the prevalence of resistance to FQs and SLIDs among MTB strains having RIF and/or INH resistance in central India.

Method

A total of 1032 smear positive sputum samples were subjected to line probe assay (GenoType MTBDRsl version 2) to test for resistance to FQs and SLIDs, according to the integrated diagnostic algorithm of the revised national TB control programme.

Results

Of 1032 samples, 92 (8.91%) were not interpretable and hence excluded, 295 (31.38%) were resistant to FQs alone, 13 (1.38%) were resistant to SLIDs alone, 15 (1.59%) were resistant to both FQs as well as SLIDs and 617 (65.63%) were sensitive to both FQs and SLIDs. The most common mutations in gyrA and gyrB genes were observed at codons D94G and E540V, respectively. Mutations at codon A1401G in rrs genes and in the C-14 T region of eis genes were most frequently observed.

Conclusion

High levels of FQ resistance points towards indiscriminate use of this class of drugs. Regulation for judicial use of FQs is an urgent requirement.

Comparisons of whole-genome sequencing and phenotypic drug susceptibility testing for Mycobacterium tuberculosis causing MDR-TB and XDR-TB in Thailand

Drug-resistant tuberculosis (TB) is a major public health problem. There is little information regarding the genotypic-phenotypic association of anti-TB drugs, especially for second-line drugs. This study compared phenotypic drug susceptibility testing (DST) with predictions based on whole-genome sequencing (WGS) data for 266 Mycobacterium tuberculosis isolates. Phenotypic DST used the standard proportional method. Clinical isolates of M. tuberculosis collected in Thailand between 1998 and 2013 comprised 51 drug-sensitive strains, six mono-resistant strains, two multiple-resistant strains, 88 multi-drug-resistant strains, 95 pre-extensively drug-resistant strains and 24 extensively drug-resistant strains. WGS analysis was performed using the computer programs PhyResSE and TB-Profiler. TB-Profiler had higher average concordance with phenotypic DST than PhyResSE for both first-line (91.96% vs. 91.4%) and second-line (79.67% vs. 78.20%) anti-TB drugs. The average sensitivity for all anti-TB drugs was also higher (83.13% vs. 72.08%) with slightly lower specificity (83.50% vs. 86.68%). Regardless of the program used, isoniazid, rifampicin and amikacin had the highest concordance with phenotypic DST (96.2%, 93.5% and 95.6%, respectively). Ethambutol, ethionamide and fluoroquinolones had the lowest concordance (87.34%, 81.44% and 73.85%, respectively). Concordance rates of ofloxacin (a second-generation fluoroquinolone), levofloxacin, moxifloxacin and gatifloxacin (third- and fourth-generation fluoroquinolones) were 91.79%, 76.62%, 72.64% and 57.35%, respectively. Discordance between phenotypic and WGS-based DSTs may be due, in part, to the choice of critical concentration and variable reproducibility of the phenotypic tests. It may also be due to limitations of the mutation databases (especially for the second-line drugs) and the analysis program used. Mutations related to fluoroquinolone resistance, especially the later generations, need to be identified.

Genetics and roadblocks of drug resistant tuberculosis

Considering the extensive evolutionary history of Mycobacterium tuberculosis, anti-Tuberculosis (TB) drug therapy exerts a recent selective pressure. However, in a microorganism devoid of horizontal gene transfer and with a strictly clonal populational structure such as M. tuberculosis the usual, but not sole, path to overcome drug susceptibility is through de novo mutations on a relatively strict set of genes. The possible allelic diversity that can be associated with drug resistance through several mechanisms such as target alteration or target overexpression, will dictate how these genes can become associated with drug resistance. The success demonstrated by this pathogenic microbe in this latter process and its ability to spread is currently one of the major obstacles to an effective TB elimination. This article reviews the action mechanism of the more important anti-TB drugs, including bedaquiline and delamanid, along with new findings on specific resistance mechanisms. With the development, validation and endorsement of new in vitro molecular tests for drug resistance, knowledge on these resistance mechanisms and microevolutionary dynamics leading to the emergence and fixation of drug resistance mutations within the host is highly important. Additionally, the fitness toll imposed by resistance development is also herein discussed together with known compensatory mechanisms. By elucidating the possible mechanisms that enable one strain to reacquire the original fitness levels, it will be theoretically possible to make more informed decisions and develop novel strategies that can force M. tuberculosis microevolutionary trajectory down through a path of decreasing fitness levels.

A Chip for Detecting Tuberculosis Drug Resistance Based on Polymerase Chain Reaction (PCR)-Magnetic Bead Molecule Platform

Objective: A Tag Array chip was used to detect plasmids of different template concentration, and then analyzed for sensitivity and specificity. Drug resistance genes from tuberculosis clinical specimens were detected, giving comparative phenotypic resistance results to explore the feasibility and value of clinical applications.

Methods: Twenty-four strains of Mycobacterium Tuberculosis (MTB) having sequence differences in extracted plasmids of mutant strains. The plasmid was diluted into different concentrations, and then was performed to analyze the sensitivity and specificity of the chip system. A total of 427 clinical specimens (including spinal tuberculosis and pulmonary tuberculosis) were collected from patients who came from seven hospitals. Design, optimization and preparation of the chip detection system, sequencing and phenotypic drug susceptibility results were analyzed to evaluate the sensitivity and specificity of the gene chip.

Results: In the template, concentrations of 1 × 10³ copies/μL and above were consistent with sequencing results in the mutant. The sensitivity and specificity in spine Tuberculosis specimen of rifampicin (RFP) were 94.40 and 92.86%; isoniazide (INH) were 92.37 and 87.50%; ethambutol (EMB) were 61.36 and 89.29%; fluoroquinolones (FQS) were 79.41 and 92.86%; streptomycin (SM) were 90.18 and 89.29%; second line drugs (SLD) were 77.61 and 83.93%. In Pulmonary Tuberculosis specimen, the sensitivity and specificity respectively were RFP: 92.74%; 93.75%; INH: 91.26%; 87.50%; EMB: 54.17%; 89.58%; FQS: 84.87%; 93.75%; SM: 86.73%; 85.42%; SLD: 80.9%; 91.67%. The RFP, INH, FQs and SM resistance genes was highly sensitive and specific: however, for detection of amikacin (AMK), capreomycin (CPM), kanamycin (KM), specificity was higher, but sensitivity was lower. Sensitivity for the detection of a mutation in the eis promoter region could be improved.

Conclusion: Tag Array chip can achieve rapid, accurate detection of tuberculosis resistance, which has important clinical significance and feasibility.

A rapid identification technique for drug-resistant Mycobacterium tuberculosis isolates using mismatch specific cleavage enzyme

The emergence of multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB) strains is a major health problem for high Tuberculosis (TB) incidence countries. Therefore, it is of interest to identify antibiotic resistant bacteria by mismatch detection using DNA hybridization. We generated PCR products for five genes (rpoB, inhA, katG, gyrA and rrs) associated with drug resistance TB from MDR and XDR Mycobacterium tuberculosis (MTB) DNA samples. These were hybridized to PCR products from MTB H37Rv (pansusceptible laboratory strain) to generate DNA hetero-duplex products, which was digested by Detection Enzyme (GeneArt Genomic Cleavage Detection Kit) and visualized by agarose gel electrophoresis. Results show different bands with sizes of 400 bp and 288 bp (rpoB), 280 bp (inhA), 310 bp (katG), 461 bp (gyrA) and 427 bp (rrs) suggesting mutations in DNA heteroduplex for each gene. Detection Enzyme specifically cleaves DNA hetero-duplex with mismatch. The technique helps in the improved detection of MDR (mutations in rpoB, inhA and katG) and XDR (mutations in rpoB, inhA katG, gyrA and rrs) MTB strains. Moreover, the technique is customized without expensive specialized equipment to detect mutations. It is also fast, efficient and easy to implement in standard molecular biology laboratories.

Multi- and Extensively Drug Resistant Mycobacterium tuberculosis in South Africa: a Molecular Analysis of Historical Isolates

Modern advances in genomics provide an opportunity to reinterpret historical bacterial culture collections. In this study, genotypic antibiotic resistance profiles of Mycobacterium tuberculosis isolates from a historical 20-year-old multidrug-resistant tuberculosis (MDR-TB) culture collection in South Africa are described. DNA samples extracted from the phenotypically MDR-TB isolates (n = 240) were assayed by Hain line probe assay (LPA) for the confirmation of MDR-TB and by Illumina Miseq whole-genome sequencing (WGS) for the characterization of mutations in eight genes (rpoB, katG, inhA, rpsL, pncA, embB, gyrA, and rrs) that are known to code for resistance to commonly used anti-TB agents. LPA identified 71.3% of the TB isolates as MDR-TB, 18.3% as rifampin (RIF) monoresistant, 2% as isoniazid (INH) monoresistant, and 8.3% as susceptible to both RIF and INH (RIF+INH). In a subset of 42 randomly selected isolates designated as RIF+INH resistant by Löwenstein-Jensen (LJ) culture in 1993, LPA and WGS results confirmed MDR-TB. In all five INH-monoresistant isolates by LPA and in all but one (the wild type) of the 34 successfully sequenced RIF-monoresistant isolates, WGS revealed matching mutations. Only 26% of isolates designated as susceptible by LPA, however, were found to be wild type by WGS. Novel mutations were found in the rpoB (Thr480Ala, Gln253Arg, Val249Met, Val251Tyr, Val251Phe), katG (Trp477STOP, Gln88STOP, Trp198STOP, Trp412STOP), embB (Thr11Xaa, Gln59Pro), and pncA (Thr100Ile, Thr159Ala, Ala134Arg, Val163Ala, Thr153Ile, DelGpos7, Phe106Ser) genes. Three MDR-TB isolates showed mutations in both the gyrA and rrs genes, suggesting that extensively drug-resistant tuberculosis existed in South Africa well before its formal recognition in 2006.

Molecular Targets Related Drug Resistance Mechanisms in MDR-, XDR-, and TDR-Mycobacterium tuberculosis Strains

Tuberculosis (TB) is a formidable infectious disease that remains a major cause of death worldwide today. Escalating application of genomic techniques has expedited the identification of increasing number of mutations associated with drug resistance in Mycobacterium tuberculosis. Unfortunately the prevalence of bacillary resistance becomes alarming in many parts of the world, with the daunting scenarios of multidrug-resistant tuberculosis (MDR-TB), extensively drug-resistant tuberculosis (XDR-TB) and total drug-resistant tuberculosis (TDR-TB), due to number of resistance pathways, alongside some apparently obscure ones. Recent advances in the understanding of the molecular/ genetic basis of drug targets and drug resistance mechanisms have been steadily made. Intriguing findings through whole genome sequencing and other molecular approaches facilitate the further understanding of biology and pathology of M. tuberculosis for the development of new therapeutics to meet the immense challenge of global health.

Amikacin: Uses, Resistance, and Prospects for Inhibition

Aminoglycosides are a group of antibiotics used since the 1940s to primarily treat a broad spectrum of bacterial infections. The primary resistance mechanism against these antibiotics is enzymatic modification by aminoglycoside-modifying enzymes that are divided into acetyl-transferases, phosphotransferases, and nucleotidyltransferases. To overcome this problem, new semisynthetic aminoglycosides were developed in the 70s. The most widely used semisynthetic aminoglycoside is amikacin, which is refractory to most aminoglycoside modifying enzymes. Amikacin was synthesized by acylation with the l-(-)-γ-amino-α-hydroxybutyryl side chain at the C-1 amino group of the deoxystreptamine moiety of kanamycin A. The main amikacin resistance mechanism found in the clinics is acetylation by the aminoglycoside 6'-N-acetyltransferase type Ib [AAC(6')-Ib], an enzyme coded for by a gene found in integrons, transposons, plasmids, and chromosomes of Gram-negative bacteria. Numerous efforts are focused on finding strategies to neutralize the action of AAC(6')-Ib and extend the useful life of amikacin. Small molecules as well as complexes ionophore-Zn⁺² or Cu⁺² were found to inhibit the acetylation reaction and induced phenotypic conversion to susceptibility in bacteria harboring the aac(6')-Ib gene. A new semisynthetic aminoglycoside, plazomicin, is in advance stage of development and will contribute to renewed interest in this kind of antibiotics.

A comparative study of phenotypic and genotypic first- and second-line drug resistance testing of Mycobacterium tuberculosis

This study aimed to evaluate the frequency of resistance to first- and second-line drugs using phenotypic and genotypic methods and its correlation with resistance-linked mutations in Mycobacterium tuberculosis (M. tb) isolated in Iran. Three different methods, including the indirect proportion method(PM), direct and indirect nitrate reductase assay(NRA), and direct sequencing were used to assess drug resistance. In this study, sensitivity, specificity, agreement, costs, and turnaround time of these methods were compared in 395 smear positive isolates. Compared to the PM, the NRA and the direct sequencing methods demonstrated higher specificity, sensitivity, and agreement for detection of all anti-tuberculosis drugs. The NRA had a short turnaround time and was more cost-effective than the other methods. Mutations in codon 531 in rpoB, 315 in katG, 18 in rpsL, and 306 in embB were associated with high-level resistance to the first-line drugs, and mutations in codon 94 in gyrA, and A1401G in rrs were correlated with resistance to the second-line drugs. We found that the NRA is a highly sensitive, specific, inexpensive, and rapid test with strong potential to be a useful and interesting alternative tool, particularly in low-income countries. In addition, these molecular data will be helpful for developing new molecular methods for detecting first- and second-line drug-resistant M. tb.

Analysis of rrs gene mutations in amikacin resistant clinical isolates of Mycobacterium tuberculosis from Khyber Pakhtunkhwa, Pakistan

Tuberculosis is a major infectious disease caused by Mycobacterium tuberculosis complex. Antimicrobial drugs are used to control TB infections. Molecular mechanisms controlling resistance to second-line drugs are not completely understood and no endogenous information is available regarding these mechanisms. The present study reports mutational analysis of rrs gene in Mycobacterium tuberculosis isolates collected from Khyber Pakhtunkhwa province of Pakistan. A total of 499 Mycobacterium tuberculosis isolates were analyzed for resistance against amikacin. Thirty resistant isolates were selected for mutational analysis in rrs gene. Among the 30 amikacin resistant isolates of Mycobacterium tuberculosis, 9 (30%) had mutation in the hotspot region of rrs gene. The predominant mutation was 1401A > G which was observed in 5 isolates. Maximum number of mutations was observed in isolate 6 and isolate 16 with six different mutations each. Mutations in isolate 6 included 1260G > A, 1278A > T, 1278_1279insT, 1300C > T, 1321G > A and 1445C > T. Mutation in isolate 16 included 1255_1256insA, 1364_1365insG, 1384_1385insA, 1880_1881insT, 1487G > A, and 1493delA. The mutation 1263G > A was observed in isolate 1. Isolate 2 had the 1484G > T mutation. The findings could be used as reference for future endures. It was evident from the results that mutations in rrs gene do not always contribute to amikacin resistance; hence, traditional drug susceptibility testing is still helpful for evaluation of such samples.

Interplay between Mutations and Efflux in Drug Resistant Clinical Isolates of Mycobacterium tuberculosis

Numerous studies show efflux as a universal bacterial mechanism contributing to antibiotic resistance and also that the activity of the antibiotics subject to efflux can be enhanced by the combined use of efflux inhibitors. Nevertheless, the contribution of efflux to the overall drug resistance levels of clinical isolates of Mycobacterium tuberculosis is poorly understood and still is ignored by many. Here, we evaluated the contribution of drug efflux plus target-gene mutations to the drug resistance levels in clinical isolates of M. tuberculosis. A panel of 17 M. tuberculosis clinical strains were characterized for drug resistance associated mutations and antibiotic profiles in the presence and absence of efflux inhibitors. The correlation between the effect of the efflux inhibitors and the resistance levels was assessed by quantitative drug susceptibility testing. The bacterial growth/survival vs. growth inhibition was analyzed through the comparison between the time of growth in the presence and absence of an inhibitor. For the same mutation conferring antibiotic resistance, different MICs were observed and the different resistance levels found could be reduced by efflux inhibitors. Although susceptibility was not restored, the results demonstrate the existence of a broad-spectrum synergistic interaction between antibiotics and efflux inhibitors. The existence of efflux activity was confirmed by real-time fluorometry. Moreover, the efflux pump genes mmr, mmpL7, Rv1258c, p55, and efpA were shown to be overexpressed in the presence of antibiotics, demonstrating the contribution of these efflux pumps to the overall resistance phenotype of the M. tuberculosis clinical isolates studied, independently of the genotype of the strains. These results showed that the drug resistance levels of multi- and extensively-drug resistant M. tuberculosis clinical strains are a combination between drug efflux and the presence of target-gene mutations, a reality that is often disregarded by the tuberculosis specialists in favor of the almost undisputed importance of antibiotic target-gene mutations for the resistance in M. tuberculosis.

Molecular Investigation of Resistance to Second-Line Injectable Drugs in Multidrug-Resistant Clinical Isolates of Mycobacterium tuberculosis in France

The second-line injectable drugs (SLID, i.e., amikacin, kanamycin, capreomycin) are key drugs for the treatment of multidrug-resistant tuberculosis. Mutations in rrs region 1400, tlyA, and eis promoter are associated with resistance to SLID, to capreomycin, and to kanamycin, respectively. In this study, the sequencing data of SLID resistance-associated genes were compared to the results of phenotypic drug susceptibility testing by the proportion method for the SLID in 206 multidrug-resistant clinical isolates of Mycobacterium tuberculosis collected in France. Among the 153 isolates susceptible to the 3 SLID, 145 showed no mutation, 1 harbored T1404C and G1473A mutations in rrs, and 7 had an eis promoter mutation. Among the 53 strains resistant to at least 1 of the SLID, mutations in rrs accounted for resistance to amikacin, capreomycin, and kanamycin for 81%, 75%, and 44% of the isolates, respectively, while mutations in eis promoter were detected in 44% of the isolates resistant to kanamycin. In contrast, no mutations in tlyA were observed in the isolates resistant to capreomycin. The discrepancies observed between the genotypic (on the primary culture) and phenotypic drug susceptibility testing were explained by (i) resistance to SLID with MICs close to the critical concentration used for routine DST and not detected by phenotypic testing (n = 8, 15% of SLID-resistant strains), (ii) low-frequency heteroresistance not detected by sequencing of drug resistance-associated genes on the primary culture (n = 8, 15% of SLID-resistant strains), and (iii) other resistance mechanisms not yet characterized (n = 7, 13% of SLID-resistant strains).

Methodological and Clinical Aspects of the Molecular Epidemiology of Mycobacterium tuberculosis and Other Mycobacteria

Molecular typing has revolutionized epidemiological studies of infectious diseases, including those of a mycobacterial etiology. With the advent of fingerprinting techniques, many traditional concepts regarding transmission, infectivity, or pathogenicity of mycobacterial bacilli have been revisited, and their conventional interpretations have been challenged. Since the mid-1990s, when the first typing methods were introduced, a plethora of other modalities have been proposed. So-called molecular epidemiology has become an essential subdiscipline of modern mycobacteriology. It serves as a resource for understanding the key issues in the epidemiology of tuberculosis and other mycobacterial diseases. Among these issues are disclosing sources of infection, quantifying recent transmission, identifying transmission links, discerning reinfection from relapse, tracking the geographic distribution and clonal expansion of specific strains, and exploring the genetic mechanisms underlying specific phenotypic traits, including virulence, organ tropism, transmissibility, or drug resistance. Since genotyping continues to unravel the biology of mycobacteria, it offers enormous promise in the fight against and prevention of the diseases caused by these pathogens. In this review, molecular typing methods for Mycobacterium tuberculosis and nontuberculous mycobacteria elaborated over the last 2 decades are summarized. The relevance of these methods to the epidemiological investigation, diagnosis, evolution, and control of mycobacterial diseases is discussed.

Drug resistance mechanisms and novel drug targets for tuberculosis therapy

Drug-resistant tuberculosis (TB) poses a significant challenge to the successful treatment and control of TB worldwide. Resistance to anti-TB drugs has existed since the beginning of the chemotherapy era. New insights into the resistant mechanisms of anti-TB drugs have been provided. Better understanding of drug resistance mechanisms helps in the development of new tools for the rapid diagnosis of drug-resistant TB. There is also a pressing need in the development of new drugs with novel targets to improve the current treatment of TB and to prevent the emergence of drug resistance in Mycobacterium tuberculosis. This review summarizes the anti-TB drug resistance mechanisms, furnishes some possible novel drug targets in the development of new agents for TB therapy and discusses the usefulness using known targets to develop new anti-TB drugs. Whole genome sequencing is currently an advanced technology to uncover drug resistance mechanisms in M. tuberculosis. However, further research is required to unravel the significance of some newly discovered gene mutations in their contribution to drug resistance.

Molecular characterization of multidrug-resistant Mycobacterium tuberculosis isolates from high prevalence tuberculosis states in Mexico

Mexico is one of the most important contributors of multidrug resistance tuberculosis (MDR-TB) in Latin-America, however little is known about the molecular characteristics of these strains. For this reason, the objective of this work was to determine the genotype and characterize polymorphisms in genes associated with resistance to rifampicin, isoniazid, and second-line drugs in isolates from two regions of Mexico with high prevalence of drug resistant tuberculosis. Clinical isolates from individuals with confirmed MDR-TB were genotyped using MIRU-VNTR 12 loci. To characterize the polymorphisms in genes associated with resistance to rifampicin, isoniazid and second-line drugs; rpoB, katG, inhA, rrs, eis, gyrA, gyrB and tlyA were sequenced. 22 (41%) of the 54 MDR-TB isolates recovered were from the state of Baja California, while 32 (59%) were from Veracruz. The results show the katGS315T mutation was observed in 20% (11/54) of the isolates, while rpoBS315L was present in 33% (18/54). rrs had three polymorphisms (T1239C, ntA1401C and ntA1401G), gyrB presented no modifications, whereas gyrA showed five (S95T, F60Y, A90V, S91P and P124A), eis two (G-10A and A431G) and tlyA one (insertion at codon 67). Only 20% (11/54) of isolates were confirmed as MDR-TB by sequencing, and no mutations at any of the genes sequenced were observed in 43% (23/54) of the strains. Two isolates were recognized with the proper set of mutations like pre-XDR and one was XDR-TB. Eighteen isolates were classified as orphans and the remaining thirty-six were distributed in fourteen lineages, the most frequent were S (11%), Haarlem (9%), Ghana (9%) and LAM (7%). Out of the fourteen clusters identified, seven included unknown genotypes and nine had lineages. This is one of the most detailed analyses of genotypic characteristics and mutations associated with drug resistance to first and second-line drugs in MDR-TB isolates from Mexico. An important genetic variability and significant discrepancy between phenotypic tests and polymorphisms was observed. Our results set the need to screen additional loci as well as implement a molecular epidemiological surveillance system of MDR-TB in the country.

Molecular analysis of genetic mutations among cross-resistant second-line injectable drugs reveals a new resistant mutation in Mycobacterium tuberculosis

Mutations causing mono and cross-resistance among amikacin, kanamycin and capreomycin of second-line injectable drugs (SLIDs) namely are not well understood. We investigated 124 isolates of Mycobacterium tuberculosis for mutations within rrs, eis, tlyA and efflux pump (Rv1258c and Rv0194) genes involved in resistance towards SLIDs. The distribution of mutations across these genes were significantly different in strains with mono-resistance or cross-resistance. A new mutation G878A was found in rrs gene, among strains with capreomycin mono-resistant, or in strains with cross-resistance of capreomycin, kanamycin and amikacin. This mutation was associated with the Euro-American X3 lineage (P < 0.0001). Mutations in the two efflux genes Rv1258c and Rv0194 were confined to strains with only capreomycin/amikacin/kanamycin cross-resistance. We further investigated the minimum inhibitory concentration of capreomycin on isolates with new G878A mutation ranging from 8 μg/mL to 64 μg/mL. Inclusion of G878A on new molecular assays could increase the sensitivity of capreomycin resistance detection.

Performance of the New Version (v2.0) of the GenoType MTBDRsl Test for Detection of Resistance to Second-Line Drugs in Multidrug-Resistant Mycobacterium tuberculosis Complex Strains

Detecting resistance to fluoroquinolones (FQ) and second-line injectable drugs (amikacin [AMK], kanamycin [KAN], and capreomycin [CAP]) is crucial given the worldwide increase in the incidence of extensively drug-resistant tuberculosis (XDR-TB). A new version of the GenoType MTBDRsl test (v2.0) has been developed to improve the detection of resistance to FQ (involving gyrA and gyrB mutations) and to second-line injectable drugs (involving rrs and eis promoter mutations) in Mycobacterium tuberculosis A collection of 127 multidrug-resistant (MDR) M. tuberculosis complex strains was tested using the first (v1) and second (v2.0) versions of the MTBDRsl test, as well as DNA sequencing. The specificities in resistance detection of v1 and v2.0 were similar throughout, whereas the levels of sensitivity of v2.0 were superior for FQ (94.8% versus 89.6%) and KAN (90.5% versus 59.5%) but similar for AMK (91.3%) and CAP (83.0%). The sensitivity and specificity of v2.0 were superior to those of v1 for the detection of pre-XDR strains (83.3% versus 75.0% and 88.6% versus 67.1%, respectively), whereas the sensitivity of v2.0 was superior to that of v1 only for the detection of XDR strains (83.0% versus 49.1%). In conclusion, MTBDRsl v2.0 is superior to MTBDRsl v1 and efficiently detects the most common mutations involved in resistance to FQ and aminoglycosides/CAP. However, due to mutations not recognized by v2.0 or to the presence of resistance mechanisms not yet characterized (particularly mechanisms related to monoresistance to aminoglycosides or CAP), the results for wild-type strains obtained with MTBDRsl v2.0 should be confirmed by further DNA sequencing and phenotypic drug susceptibility testing.

Effect of Mutations on the Binding of Kanamycin-B to RNA Hairpins Derived from the Mycobacterium tuberculosis Ribosomal A-Site

Kanamycin is an aminoglycoside antibiotic used in the treatment of drug-resistant tuberculosis. Mutations at the rRNA A-site have been associated with kanamycin resistance in Mycobacterium tuberculosis clinical isolates. Understanding the effect of these mutations on the conformation of the M. tuberculosis A-site is critical for understanding the mechanisms of antibiotic resistance in M. tuberculosis. In this work, we have studied RNA hairpins derived from the M. tuberculosis A-site, the wild type and three mutants at the following positions (M. tuberculosis/Escherichia coli numbering): A1400/1408 → G, C1401/1409 → U, and the double mutant G1483/1491 C1401/1409 → UA. Specifically, we used circular dichroism, ultraviolet spectroscopy, and fluorescence spectroscopy to characterize the conformation, stability, and binding affinity of kanamycin-B and other aminoglycoside antibiotics for these RNA hairpins. Our results show that the mutations affect the conformation of the decoding site, with the mutations at position 1401/1409 resulting in significant destabilizations. Interestingly, the mutants bind paromomycin with weaker affinity than the wild type, but they bind kanamycin-B with similar affinity than the wild type. The results suggest that the presence of mutations does not prevent kanamycin-B from binding. Instead, kanamycin may promote different interactions with a third partner in the mutants compared to the wild type. Furthermore, our results with longer and shorter hairpins suggest that the region of the A-site that varies among organisms may have modulating effects on the binding and interactions of the A-site.

Prevalence of mutations conferring resistance among multi- and extensively drug-resistant Mycobacterium tuberculosis isolates in China

To identify the mutations in multi- and extensively drug-resistant tuberculosis isolates and to evaluate the use of molecular markers of resistance, we analyzed 257 multi- and extensively drug-resistant isolates and 64 pan-sensitive isolates from 23 provinces in China. Seven loci associated with drug resistance, including rpoB for rifampin (RIF), katG, inhA and oxyR-ahpC for isoniazid (INH), gyrA and gyrB for ofloxacin (OFX), and rrs for kanmycin (KAN), were examined by DNA sequencing. Compared with the phenotypic data, the sensitivity and specificity for DNA sequencing were 91.1% and 98.4% for RIF, 80.2% and 98.4% for INH, 72.2% and 98.3% for OFX and 40% and 98.2% for KAN, respectively. The most common mutations found in RIF, INH, OFX and KAN resistance were Ser531Leu (48.2%) in rpoB, Ser315Thr (49.8%) in katG, C(-15)T (10.5%) in inhA, Asp94Gly (20.3%), Asp94Ala (12.7%) and Ala90Val (21.5%) in gyrA, and A1401G (40%) in rrs. This molecular information will be helpful to establish new molecular biology-based methods for diagnosing multi- and extensively drug-resistant tuberculosis in China.

Fighting an old disease with modern tools: characteristics and molecular detection methods of drug-resistant Mycobacterium tuberculosis

Tuberculosis (TB) is an ancient disease, but not a disease of the past. The increasing prevalence of drug-resistant strains of Mycobacterium tuberculosis, the causative agent of TB, demands new measures to combat the situation. Rapid and accurate detection of the pathogen, and its drug susceptibility pattern, is essential for timely initiation of treatment, and ultimately, control of the disease. Molecular-based methods offer a great chance to improve detection of drug-resistant TB; however, their development and usage should be accompanied with a profound understanding of drug resistance mechanisms and circulating M. tuberculosis strains in specific settings, as otherwise, the usefulness of such tests may be limited. This review gives an overview of the history of TB treatment and drug resistance, drug resistance mechanisms for the most commonly used drugs and molecular methods designed to detect drug-resistant strains.

Second-line anti-tuberculosis drug resistance and its genetic determinants in multidrug-resistant Mycobacterium tuberculosis clinical isolates

BACKGROUND

Mutations in several genetic loci have been implicated in the development of resistance to second-line anti-tuberculosis (TB) drugs (SLDs). The purpose of this study was to investigate the prevalence of resistance to SLDs and its association with specific mutations in multidrug-resistant (MDR) Mycobacterium tuberculosis clinical isolates.

MATERIALS AND METHODS

The study included 46 MDR-TB isolates. Mutation profiling was performed by amplifying and sequencing the following six genes: gyrA/gyrB, rrs, tlyA, and ethA/ethR, in which mutations are implicated in resistance of tubercle bacilli to ofloxacin (OFX), amikacin (AMK), capreomycin, and ethionamide (ETH), respectively.

RESULTS

Of the strains analyzed, 14 (30.4%) showed resistance to at least one of the four SLDs tested. Mutations in the gyrA gene occurred in 34 (73.9%) strains, with the most common amino acid change being Ser95Thr. The Asp94Asn and Ala90Val substitutions in the gyrA were present exclusively in OFX-resistant strains, yet represented only 40% of all OFX-resistant strains. The only mutation in the gyrB gene was substitution Ser447Phe, detected in one OFX-resistant isolate. None of the AMK-resistant strains carried a mutation in the rrs gene. Mutations in the ethA/ethR loci were found in one ETH-resistant and 11 ETH-susceptible strains.

CONCLUSIONS

The results of this study challenge the usefulness of sequence analyses of tested genes (except gyrA) for the prediction of SLD resistance patterns and highlight the need for searching other genetic loci for detection of mutations conferring resistance to SLDs in M. tuberculosis.

Genotypic susceptibility testing of Mycobacterium tuberculosis isolates for amikacin and kanamycin resistance by use of a rapid sloppy molecular beacon-based assay identifies more cases of low-level drug resistance than phenotypic Lowenstein-Jensen testing

Resistance to amikacin (AMK) and kanamycin (KAN) in clinical Mycobacterium tuberculosis strains is largely determined by specific mutations in the rrs gene and eis gene promoter. We developed a rapid, multiplexed sloppy molecular beacon (SMB) assay to identify these mutations and then evaluated assay performance on 603 clinical M. tuberculosis DNA samples collected in South Korea. Assay performance was compared to gold-standard phenotypic drug susceptibility tests, including Lowenstein-Jensen (LJ) absolute concentration, mycobacterial growth indicator tubes (MGIT), and TREK Sensititre MycoTB MIC plate (MycoTB) methods. Target amplicons were also tested for mutations by Sanger sequencing. The SMB assay correctly detected 115/116 mutant and mixed sequences and 487/487 wild-type sequences (sensitivity and specificity of 99.1 and 100%, respectively). Using the LJ method as the reference, sensitivity and specificity for AMK resistance were 92.2% and 100%, respectively, and sensitivity and specificity for KAN resistance were 87.7% and 95.6%, respectively. Mutations in the rrs gene were unequivocally associated with high-level cross-resistance to AMK and KAN in all three conventional drug susceptibility testing methods. However, eis promoter mutations were associated with KAN resistance using the MGIT or MycoTB methods but not the LJ method. No testing method associated eis promoter mutations with AMK resistance. Among the discordant samples with AMK and/or KAN resistance but wild-type sequence at the target genes, we discovered four new mutations in the whiB7 5' untranslated region (UTR) in 6/22 samples. All six samples were resistant only to KAN, suggesting the possible role of these whiB7 5' UTR mutations in KAN resistance.

Generation and screening of a comprehensive Mycobacterium avium subsp. paratuberculosis transposon mutant bank

Mycobacterium avium subsp. paratuberculosis (MAP) is the etiologic agent of Johne's Disease in ruminants. This enteritis has significant economic impact and worldwide distribution. Vaccination is one of the most cost effective infectious disease control measures. Unfortunately, current vaccines reduce clinical disease and shedding, but are of limited efficacy and do not provide long-term protective immunity. Several strategies have been followed to mine the MAP genome for virulence determinants that could be applied to vaccine and diagnostic assay development. In this study, a comprehensive mutant bank of 13,536 MAP K-10 Tn5367 mutants (P > 95%) was constructed and screened in vitro for phenotypes related to virulence. This strategy was designated to maximize identification of genes important to MAP pathogenesis without relying on studies of other mycobacterial species that may not translate into similar effects in MAP. This bank was screened for mutants with colony morphology alterations, susceptibility to D-cycloserine, impairment in siderophore production or secretion, reduced cell association, and decreased biofilm and clump formation. Mutants with interesting phenotypes were analyzed by PCR, Southern blotting and DNA sequencing to determine transposon insertion sites. These insertion sites mapped upstream from the MAP1152-MAP1156 cluster, internal to either the Mod operon gene MAP1566 or within the coding sequence of lsr2, and several intergenic regions. Growth curves in broth cultures, invasion assays and kinetics of survival and replication in primary bovine macrophages were also determined. The ability of vectors carrying Tn5370 to generate stable MAP mutants was also investigated.

Multidrug-resistant nontuberculous mycobacteria isolated from cystic fibrosis patients

Worldwide, nontuberculous mycobacteria (NTM) have become emergent pathogens of pulmonary infections in cystic fibrosis (CF) patients, with an estimated prevalence ranging from 5 to 20%. This work investigated the presence of NTM in sputum samples of 129 CF patients (2 to 18 years old) submitted to longitudinal clinical supervision at a regional reference center in Rio de Janeiro, Brazil. From June 2009 to March 2012, 36 NTM isolates recovered from 10 (7.75%) out of 129 children were obtained. Molecular identification of NTM was performed by using PCR restriction analysis targeting the hsp65 gene (PRA-hsp65) and sequencing of the rpoB gene, and susceptibility tests were performed that followed Clinical and Laboratory Standards Institute recommendations. For evaluating the genotypic diversity, pulsed-field gel electrophoresis (PFGE) and/or enterobacterial repetitive intergenic consensus sequence PCR (ERIC-PCR) was performed. The species identified were Mycobacterium abscessus subsp. bolletii (n = 24), M. abscessus subsp. abscessus (n = 6), Mycobacterium fortuitum (n = 3), Mycobacterium marseillense (n = 2), and Mycobacterium timonense (n = 1). Most of the isolates presented resistance to five or more of the antimicrobials tested. Typing profiles were mainly patient specific. The PFGE profiles indicated the presence of two clonal groups for M. abscessus subsp. abscessus and five clonal groups for M. abscesssus subsp. bolletii, with just one clone detected in two patients. Given the observed multidrug resistance patterns and the possibility of transmission between patients, we suggest the implementation of continuous and routine investigation of NTM infection or colonization in CF patients, including countries with a high burden of tuberculosis disease.

Characterization of a novel mutation in the overlap of tlyA and ppnK involved in capreomycin resistance in Mycobacterium

Capreomycin (CAP) is an important second-line drug for multidrug-resistant tuberculosis. To further define the drug resistance mechanism of CAP, a Mycobacterium smegmatis transposon mutant library was constructed using Tn5 transposon for screening isolates with enhanced CAP resistance. A mutant (named C4) with fourfold increased CAP resistance was isolated and characterized. Tn5 was found to be inserted into MSMEG_0841, an annotated pseudogene. However, knockout demonstrated that MSMEG_0841 was not responsible for CAP resistance. We further sequenced the whole genome of C4 and found an A to G substitution in the overlap region between tlyA and ppnK, which leads a stop codon mutation in upstream tlyA and a T2A mutation in downstream ppnK. Mutation in the overlap might confer the dysfuction of both genes. tlyA is a known gene involved in CAP action. Overexpression of ppnK in both Escherichia coli and M. smegmatis confer subtle susceptible to CAP. Taken together, our study found that a novel mutation involved in CAP resistance.

Prevalence and molecular characteristics of drug-resistant Mycobacterium tuberculosis in Hunan, China

To determine the prevalence and molecular characteristics of drug-resistant tuberculosis in Hunan province, drug susceptibility testing and spoligotyping methods were performed among 171 M. tuberculosis isolates. In addition, the mutated characteristics of 12 loci, including katG, inhA, rpoB, rpsL, nucleotides 388 to 1084 of the rrs gene [rrs(388-1084)], embB, pncA, tlyA, eis, nucleotides 1158 to 1674 of the rrs gene [rrs(1158-1674)], gyrA, and gyrB, among drug-resistant isolates were also analyzed by DNA sequencing. Our results indicated that the prevalences of isoniazid (INH), rifampin (RIF), streptomycin (SM), ethambutol (EMB), pyrazinamide (PZA), capreomycin (CAP), kanamycin (KAN), amikacin (AKM), and ofloxacin (OFX) resistance in Hunan province were 35.7%, 26.9%, 20.5%, 9.9% 15.2%, 2.3%, 1.8%, 1.2%, and 10.5%, respectively. The previously treated patients presented significantly increased risks for developing drug resistance. The majority of M. tuberculosis isolates belonged to the Beijing family. Almost all the drug resistance results demonstrated no association with genotype. The most frequent mutations of drug-resistant isolates were katG codon 315 (katG315), inhA15, rpoB531, rpoB526, rpoB516, rpsL43, rrs514, embB306, pncA96, rrs1401, gyrA94, and gyrA90. These results contribute to the knowledge of the prevalence of drug resistance in Hunan province and also expand the molecular characteristics of drug resistance in China.

Molecular characterization of multidrug-resistant Mycobacterium tuberculosis isolates from China

To investigate the molecular characterization of multidrug-resistant tuberculosis (MDR-TB) isolates from China and the association of specific mutations conferring drug resistance with strains of different genotypes, we performed spoligotyping and sequenced nine loci (katG, inhA, the oxyR-ahpC intergenic region, rpoB, tlyA, eis, rrs, gyrA, and gyrB) for 128 MDR-TB isolates. Our results showed that 108 isolates (84.4%) were Beijing family strains, 64 (59.3%) of which were identified as modern Beijing strains. Compared with the phenotypic data, the sensitivity and specificity of DNA sequencing were 89.1% and 100.0%, respectively, for isoniazid (INH) resistance, 93.8% and 100.0% for rifampin (RIF) resistance, 60.0% and 99.4% for capreomycin (CAP) resistance, 84.6% and 99.4% for kanamycin (KAN) resistance, and 90.0% and 100.0% for ofloxacin (OFX) resistance. The most prevalent mutations among the MDR-TB isolates were katG315, inhA15, rpoB531, -526, and -516, rrs1401, eis-10, and gyrA94, -90, and -91. Furthermore, there was no association between specific resistance-conferring mutations and the strain genotype. These findings will be helpful for the establishment of rapid molecular diagnostic methods to be implemented in China.