GeneXpert on patients with human immunodeficiency virus and smear-negative pulmonary tuberculosis

Rapid Phenotypic and Genotypic Antimicrobial Susceptibility Testing Approaches for Use in the Clinical Laboratory

The rapid rise in increasingly resistant bacteria has become a major threat to public health. Antimicrobial susceptibility testing (AST) is crucial in guiding appropriate therapeutic decisions and infection prevention practices for patient care. However, conventional culture-based AST methods are time-consuming and labor-intensive. Therefore, rapid AST approaches exist to address the delayed gap in time to actionable results. There are two main types of rapid AST technologies- phenotypic and genotypic approaches. In this review, we provide a summary of all commercially available rapid AST platforms for use in clinical microbiology laboratories. We describe the technologies utilized, performance characteristics, acceptable specimen types, types of resistance detected, turnaround times, limitations, and clinical outcomes driven by these rapid tests. We also discuss crucial factors to consider for the implementation of rapid AST technologies in a clinical laboratory and what the future of rapid AST holds.

A Comparative Analysis of Microscopy, Culture, and the Xpert Mycobacterium tuberculosis/Rifampicin Assay in Diagnosing Pulmonary Tuberculosis in Human Immunodeficiency-Positive Individuals

INTRODUCTION

Individuals with human immunodeficiency virus (HIV) infection have an increased likelihood of developing tuberculosis (TB). The primary objective of this study was to compare the diagnostic accuracy of microscopy, culture, and the Xpert Mycobacterium tuberculosis/Rifampicin (MTB/RIF) assay in the diagnosis of pulmonary TB in sputum samples of HIV-infected patients. The secondary objectives were to evaluate the sensitivity and specificity of these three methods along with a comparison of diagnostic approaches for detecting drug-resistant strains.

MATERIAL AND METHODS

This prospective, laboratory-based study was done in the Microbiology Department of IGIMS, Patna. The study included sputum samples of 102 individuals who were HIV-positive and exhibited symptoms indicative of tuberculosis.

RESULTS

Out of 102 individuals suspected of having tuberculosis, 18 tested positive for M. tuberculosis. Male individuals between the ages of 31 and 40 were more affected by both HIV and tuberculosis, and in most of these cases, their CD4 cell count was below 200 cells/µl. Among the 102 sputum samples collected, 18% (18 samples) were found to be positive using the Mycobacterium Growth Indicator Tube (MGIT) 960 liquid culture method. Two samples were contaminated, and 14.7% (15 cases) tested positive using the cartridge-based nucleic acid amplification test (CBNAAT) method. Additionally, 3.92% (four samples) were positive using the ZN staining method.

CONCLUSION

The study found that Xpert MTB/RIF outperformed other methods in identifying resistance to RIF, showed better agreement with gene sequencing results for RIF resistance, and had higher accuracy in detecting tuberculosis cases, including both smear-positive and smear-negative cases.

Targeted Chromosomal Barcoding Establishes Direct Genotype-Phenotype Associations for Antibiotic Resistance in Mycobacterium abscessus

A bedaquiline-resistant Mycobacterium abscessus isolate was sequenced, and a candidate mutation in the atpE gene was identified as responsible for the antibiotic resistance phenotype. To establish a direct genotype-phenotype relationship of this mutation which results in a Asp-to-Ala change at position 29 (D29A), we developed a recombineering-based method consisting of the specific replacement of the desired mutation in the bacterial chromosome. As surrogate bacteria, we used two M. abscessus bedaquiline-susceptible strains: ATCC 19977 and the SL541 clinical isolate. The allelic exchange substrates used in recombineering carried either the sole D29A mutation or a genetic barcode of silent mutations in codons flanking the D29A mutation. After selection of bedaquiline-resistant M. abscessus colonies transformed with both substrates, we obtained equivalent numbers of recombinants. These resistant colonies were analyzed by allele-specific PCR and Sanger sequencing, and we demonstrated that the presence of the genetic barcode was linked to the targeted incorporation of the desired mutation in its chromosomal location. All recombinants displayed the same MIC to bedaquiline as the original isolate, from which the D29A mutation was identified. Finally, to demonstrate the broad applicability of this method, we confirmed the association of bedaquiline resistance with the atpE A64P mutation in analysis performed in independent M. abscessus strains and by independent researchers. IMPORTANCE Antimicrobial resistance (AMR) threatens the effective prevention and treatment of an ever-increasing range of infections caused by microorganisms. On the other hand, infections caused by Mycobacterium abscessus affect people with chronic lung diseases, and their incidence has grown alarmingly in recent years. Further, these bacteria are known to easily develop AMR to the few therapeutic options available, making their treatment long-lasting and challenging. The recent introduction of new antibiotics against M. abscessus, such as bedaquiline, makes us anticipate a future when a plethora of antibiotic-resistant strains will be isolated and sequenced. However, in the era of whole-genome sequencing, one of the challenges is to unequivocally assign a biological function to each identified polymorphism. Thus, in this study, we developed a fast, robust, and reliable method to assign genotype-phenotype associations for putative antibiotic-resistant polymorphisms in M. abscessus.

The Value of GeneXpert MTB/RIF for Detection in Tuberculosis: A Bibliometrics-Based Analysis and Review

With the continuous development of medical science and technology, especially with the advent of the era of precision diagnosis and treatment, molecular biology detection technology is widely valued and applied as an aid to early diagnosis of tuberculosis. The GeneXpert Mycobacterium tuberculosis Branching (MTB) technology is a suite of semi-nested real-time fluorescent quantitative PCR in vitro diagnostic technologies developed by Cepheid Inc. It targets the rifampicin resistance gene, rpoB, and can detect both MTB and resistance to rifampicin within 2 h. This review analyzed the papers related to GeneXpert using bibliometric software CiteSpace and Bibliometrix. A total of 151 articles were analyzed, spanning from 2011 to 2021. This bibliometrics-based review summarizes the history of the development of GeneXpert in tuberculosis diagnosis and its current status. Contributions of different countries to the topic, journal analysis, key paper analysis, and clustering of keywords were used to analyze this topic.