Phenotypic isoniazid resistance and associated mutations in pediatric tuberculosis

Revisiting the methods for detecting Mycobacterium tuberculosis: what has the new millennium brought thus far?

Tuberculosis (TB) affects around 10 million people worldwide in 2019. Approximately 3.4 % of new TB cases are multidrug-resistant. The gold standard method for detecting Mycobacterium tuberculosis, which is the aetiological agent of TB, is still based on microbiological culture procedures, followed by species identification and drug sensitivity testing. Sputum is the most commonly obtained clinical specimen from patients with pulmonary TB. Although smear microscopy is a low-cost and widely used method, its sensitivity is 50-60 %. Thus, owing to the need to improve the performance of current microbiological tests to provide prompt treatment, different methods with varied sensitivity and specificity for TB diagnosis have been developed. Here we discuss the existing methods developed over the past 20 years, including their strengths and weaknesses. In-house and commercial methods have been shown to be promising to achieve rapid diagnosis. Combining methods for mycobacterial detection systems demonstrates a correlation of 100 %. Other assays are useful for the simultaneous detection of M. tuberculosis species and drug-related mutations. Novel approaches have also been employed to rapidly identify and quantify total mycobacteria RNA, including assessments of global gene expression measured in whole blood to identify the risk of TB. Spoligotyping, mass spectrometry and next-generation sequencing are also promising technologies; however, their cost needs to be reduced so that low- and middle-income countries can access them. Because of the large impact of M. tuberculosis infection on public health, the development of new methods in the context of well-designed and -controlled clinical trials might contribute to the improvement of TB infection control.

A Mitocentric View of the Main Bacterial and Parasitic Infectious Diseases in the Pediatric Population

Infectious diseases occur worldwide with great frequency in both adults and children. Both infections and their treatments trigger mitochondrial interactions at multiple levels: (i) incorporation of damaged or mutated proteins to the complexes of the electron transport chain, (ii) mitochondrial genome (depletion, deletions, and point mutations) and mitochondrial dynamics (fusion and fission), (iii) membrane potential, (iv) apoptotic regulation, (v) generation of reactive oxygen species, among others. Such alterations may result in serious adverse clinical events with great impact on children's quality of life, even resulting in death. As such, bacterial agents are frequently associated with loss of mitochondrial membrane potential and cytochrome c release, ultimately leading to mitochondrial apoptosis by activation of caspases-3 and -9. Using Rayyan QCRI software for systematic reviews, we explore the association between mitochondrial alterations and pediatric infections including (i) bacterial: M. tuberculosis, E. cloacae, P. mirabilis, E. coli, S. enterica, S. aureus, S. pneumoniae, N. meningitidis and (ii) parasitic: P. falciparum. We analyze how these pediatric infections and their treatments may lead to mitochondrial deterioration in this especially vulnerable population, with the intention of improving both the understanding of these diseases and their management in clinical practice.

Variations in rifampicin and isoniazid resistance associated genetic mutations among drug naïve and recurrence cases of pulmonary tuberculosis

BACKGROUND

The resistance to first-line drugs can increase the risk of treatment failure and development of resistance to other anti-TB drugs. In TB endemic settings, a considerable rate of recurrence cases exhibited each, year which adds significant burden to the prevalence of disease worldwide.

METHODS

A total of 562 sputum samples were collected from presumptive positive clinical cases of MDR tuberculosis. Treatment history and demographic data of the patients were obtained after informed consent. Xpert MTB/RIF assay was performed for simultaneous detection of MTB and rifampicin resistance. The mutation patterns of isoniazid and rifampicin were observed after multiplex PCR and reverse hybridization by Genotype® MTBDRplus version 2.0 assay.

RESULTS

A total of 73 of 97 cases (75.2%) of treatment failure were found positive for MDR-TB, whereas 79.6% newly diagnosed and 72.9% default cases were MDR in our isolates. The mutation of rpoB S531L was slightly higher in new treatment cases (89.3%) as compared to the default (80.4%) and failure cases (84.8%), whereas rpoB D516V mutation was more prevalent in default cases (19.6%) with complete absence of rpoB 526 mutation, which was observed in the other two types of cases. The mutation pattern of katG resistance differed among drug naïve and recurrence cases. The resistance in newly diagnosed cases was mostly conferred by katG 315 (49.1%) whereas in default (70.8%) and failure cases (63.3%) isoniazid resistance was commonly associated with katG S315T1 mutation. Mutations in inhA promoter region occurred at nucleotide position -8 and -15. In new cases the rate of mutation of C-15T was 3.7% and T-8A was 1.5% while in treatment failure cases the frequency for C-15T and T-8C was 2.5 and 3.8% respectively. However, no inhA promoter region mediated mutations were detected in default treatment cases.

CONCLUSION

Retreated cases are at more risk of developing hot spot mutations. An unusual difference in mutation pattern was determined in naïve and recurrence cases. Some mutations were exclusively associated with the retreatment of 35anti-TB drugs which suggest the increased risk of resistance with poor treatment outcome.