Fluoroquinolone heteroresistance, antimicrobial tolerance, and lethality enhancement

The role of Mycobacterium tuberculosis acetyltransferase and protein acetylation modifications in tuberculosis

Tuberculosis (TB) is a widespread infectious disease caused by Mycobacterium tuberculosis (M. tb), which has been a significant burden for a long time. Post-translational modifications (PTMs) are essential for protein function in both eukaryotic and prokaryotic cells. This review focuses on the contribution of protein acetylation to the function of M. tb and its infected macrophages. The acetylation of M. tb proteins plays a critical role in virulence, drug resistance, regulation of metabolism, and host anti-TB immune response. Similarly, the PTMs of host proteins induced by M. tb are crucial for the development, treatment, and prevention of diseases. Host protein acetylation induced by M. tb is significant in regulating host immunity against TB, which substantially affects the disease's development. The review summarizes the functions and mechanisms of M. tb acetyltransferase in virulence and drug resistance. It also discusses the role and mechanism of M. tb in regulating host protein acetylation and immune response regulation. Furthermore, the current scenario of isoniazid usage in M. tb therapy treatment is examined. Overall, this review provides valuable information that can serve as a preliminary basis for studying pathogenic research, developing new drugs, exploring in-depth drug resistance mechanisms, and providing precise treatment for TB.

Pattern and characteristics of mutations conferring resistance to second line drugs in Mycobacterium tuberculosis isolates of pulmonary and extrapulmonary TB samples

BACKGROUND & OBJECTIVES

The purpose of present study is to analyse the distribution and pattern of genetic mutations in PRE-XDR-TB and extensive drug resistant Mycobacterium tuberculosis (XDR-TB) using second-line line probe assay and to compare them with different parameters.

METHOD

Sputum, Lymph node aspirate and cold accesses from patients with rifampicin resistant Tuberculosis were subjected to first line and second line Probe Assay (Genotype MTBDRsl by Hain Life Science, Germany) to assess additional drug resistance to fluroquinolones (Levofloxacin & Moxifloxacin) and Aminoglycosides (Amikacin, Ofloxacin and Kanamycin). The genetic mutation pattern was analysed and compared with demographic, clinical and other parameters.

RESULTS

The final study population included 123 fluoroquinolone resistant isolates including 14 isolates with additional second line aminoglycosides drug resistance. The most frequent mutation observed among Gyr A drug resistance mutation was D94G (Gyr A MUT3C, 50/123,40%) corresponding to high level resistance to levofloxacin and moxifloxacin. The most frequent wild type mutant among Gyr A gene locus was WT 3 (85/123,69%). The most common mutation among second line aminoglycoside resistant isolates was at eis WT2 (7/14,50%) followed by rrs MUT 2 (4/14,29%).

CONCLUSIONS

GyrA MUT3C (Asp94Gly) was the most common mutation in Gyr A gene locus in M. tuberculosis causing high level levofloxacin and moxifloxacin resistance. Patients with Asp94Gly mutation was significantly associated with underweight body mass index (p = 0.026). This study also observed that history of anti-tuberculosis therapy is a risk factor for FQ drug resistance mutations (p < 0.001).

Quantification of Isoniazid-Heteroresistant Mycobacterium tuberculosis Using Droplet Digital PCR

The quantitative detection of drug-resistance mutations in Mycobacterium tuberculosis (MTB) is critical for determining the drug resistance status of a sample. We developed a drop-off droplet digital PCR (ddPCR) assay targeting all major isoniazid (INH)-resistant mutations. The ddPCR assay consisted of three reactions: reaction A detects mutations at katG S315; reaction B detects inhA promoter mutations; and reaction C detects ahpC promoter mutations. All reactions could quantify 1%-50% of mutants in the presence of the wild-type, ranging from 100 to 50,000 copies/reaction. Clinical evaluation with 338 clinical isolates yielded clinical sensitivity of 94.5% (95% confidence interval [CI] = 89.1%-97.3%) and clinical specificity of 97.6% (95% CI = 94.6%-99.0%) compared with the traditional drug susceptibility testing (DST). Further clinical evaluation using 194 nucleic acid-positive MTB sputum samples revealed clinical sensitivity of 87.8% (95% CI = 75.8%-94.3%) and clinical specificity of 96.5% (95% CI = 92.2%-98.5%) in comparison with DST. All the mutant and heteroresistant samples detected by the ddPCR assay but susceptible by DST were confirmed by combined molecular assays, including Sanger sequencing, mutant-enriched Sanger sequencing and a commercial melting curve analysis-based assay. Finally, the ddPCR assay was used to monitor longitudinally the INH-resistance status and the bacterial load in nine patients undergoing treatment. Overall, the developed ddPCR assay could be an indispensable tool for quantification of INH-resistant mutations in MTB and bacterial loads in patients.

Eradication of Drug-Tolerant Mycobacterium tuberculosis 2022: Where We Stand

The lungs of tuberculosis (TB) patients contain a spectrum of granulomatous lesions, ranging from solid and well-vascularized cellular granulomas to avascular caseous granulomas. In solid granulomas, current therapy kills actively replicating (AR) intracellular bacilli, while in low-vascularized caseous granulomas the low-oxygen tension stimulates aerobic and microaerophilic AR bacilli to transit into non-replicating (NR), drug-tolerant and extracellular stages. These stages, which do not have genetic mutations and are often referred to as persisters, are difficult to eradicate due to low drug penetration inside the caseum and mycobacterial cell walls. The sputum of TB patients also contains viable bacilli called differentially detectable (DD) cells that, unlike persisters, grow in liquid, but not in solid media. This review provides a comprehensive update on drug combinations killing in vitro AR and drug-tolerant bacilli (persisters and DD cells), and sterilizing Mycobacterium tuberculosis-infected BALB/c and caseum-forming C3HeB/FeJ mice. These observations have been important for testing new drug combinations in noninferiority clinical trials, in order to shorten the duration of current regimens against TB. In 2022, the World Health Organization, following the results of one of these trials, supported the use of a 4-month regimen for the treatment of drug-susceptible TB as a possible alternative to the current 6-month regimen.

Identification of a Small Molecule Compound Active against Antibiotic-Tolerant Staphylococcus aureus by Boosting ATP Synthesis

Antibiotic tolerance poses a threat to current antimicrobial armamentarium. Bacteria at a tolerant state survive in the presence of antibiotic treatment and account for persistence, relapse and recalcitrance of infections. Antibiotic treatment failure may occur due to antibiotic tolerance. Persistent infections are difficult to treat and are often associated with poor prognosis, imposing an enormous burden on the healthcare system. Effective strategies targeting antibiotic-tolerant bacteria are therefore highly warranted. In this study, small molecule compound SA-558 was identified to be effective against Staphylococcus aureus that are tolerant to being killed by conventional antibiotics. SA-558 mediated electroneutral transport across the membrane and led to increased ATP and ROS generation, resulting in a reduction of the population of antibiotic-tolerant bacteria. In a murine chronic infection model, of which vancomycin treatment failed, we demonstrated that SA-558 alone and in combination with vancomycin caused significant reduction of MRSA abundance. Our results indicate that SA-558 monotherapy or combinatorial therapy with vancomycin is an option for managing persistent S. aureus bacteremia infection and corroborate that bacterial metabolism is an important target for counteracting antibiotic tolerance.

Heteroresistance to rifampicin & isoniazid in clinical samples of patients with presumptive drug-resistant tuberculosis in Central India

Background & objectives

A combination of resistant and susceptible Mycobacterium tuberculosis (MTB) isolated from clinical specimens is referred to as heteroresistance. Heteroresistance leads to difficulties in drug resistance testing and may adversely affect treatment outcomes. The present study estimated the proportion of heteroresistance among MTB in clinical samples of presumptive drug-resistant tuberculosis (TB) patients in Central India.

Methods

A retrospective analysis of data generated from line probe assay (LPA) at a tertiary care hospital in Central India between January 2013 and December 2018 was carried out. A heteroresistant MTB in a sample was indicated by the presence of both wild-type and mutant-type patterns on an LPA strip.

Results

Data analysis was carried out on interpretable 11,788 LPA results. Heteroresistance in MTB was detected in 637 (5.4%) samples. Of these, heteroresistance in MTB was detected in 413 (64.8%), 163 (25.5%) and 61 (9.5%) samples with respect to rpoB, katG and inhA genes, respectively.

Interpretation & conclusions

Heteroresistance is considered a preliminary step in the development of drug resistance. Delayed or suboptimal anti-tubercular therapy in patients with heteroresistance of MTB may elicit full clinical resistance and negatively impact the National TB Elimination Programme. Further studies are, however, needed to determine the impact of heteroresistance on treatment outcomes in individual patients.

Clinically encountered growth phenotypes of tuberculosis-causing bacilli and their in vitro study: A review

The clinical manifestations of tuberculosis (TB) vary widely in severity, site of infection, and outcomes of treatment-leading to simultaneous efforts to individualize therapy safely and to search for shorter regimens that can be successfully used across the clinical spectrum. In these endeavors, clinicians and researchers alike employ mycobacterial culture in rich media. However, even within the same patient, individual bacilli among the population can exhibit substantial variability in their culturability. Bacilli in vitro also demonstrate substantial heterogeneity in replication rate and cultivation requirements, as well as susceptibility to killing by antimicrobials. Understanding parallels in clinical, ex vivo and in vitro growth phenotype diversity may be key to identifying those phenotypes responsible for treatment failure, relapse, and the reactivation of bacilli that progresses TB infection to disease. This review briefly summarizes the current role of mycobacterial culture in the care of patients with TB and the ex vivo evidence of variability in TB culturability. We then discuss current advances in in vitro models that study heterogenous subpopulations within a genetically identical bulk culture, with an emphasis on the effect of oxidative stress on bacillary cultivation requirements. The review highlights the complexity that heterogeneity in mycobacterial growth brings to the interpretation of culture in clinical settings and research. It also underscores the intricacies present in the interplay between growth phenotypes and antimicrobial susceptibility. Better understanding of population dynamics and growth requirements over time and space promises to aid both the attempts to individualize TB treatment and to find uniformly effective therapies.