Mycobacterium chelonae Infection Identified by Metagenomic Next-Generation Sequencing as the Probable Cause of Acute Contained Rupture of a Biological Composite Graft—A Case Report

We present the case of a 72-year-old female patient with acute contained rupture of a biological composite graft, 21 months after replacement of the aortic valve and the ascending aorta due to an aortic dissection. Auramine-rhodamine staining of intraoperative biopsies showed acid-fast bacilli, but classical culture and molecular methods failed to identify any organism. Metagenomic analysis indicated infection with Mycobacterium chelonae, which was confirmed by target-specific qPCR. The complexity of the sample required a customized bioinformatics pipeline, including cleaning steps to remove sequences of human, bovine ad pig origin. Our study underlines the importance of multiple testing to increase the likelihood of pathogen identification in highly complex samples.

Development of a nucleic acid chromatography assay for the detection of commonly isolated rapidly growing mycobacteria

Introduction. Non-tuberculosis mycobacterium infections are increasing worldwide, including those caused by rapidly growing mycobacteria (RGM). Gap Statement. The identification of the aetiological agent in the context of infections is essential for the adoption of an adequate therapeutic approach. However, the methods for the rapid distinction of different RGM species are less than optimal. Aim. To develop a nucleic acid chromatography kit to identify clinically common RGM. Methodology. We tried to develop a nucleic acid chromatography kit designed to detect four RGM species (including three subspecies) i.e. Mycobacterium abscessus subsp. abscessus , Mycobacterium abscessus subsp. bolletii (detected as M. abscessus/bolletii) Mycobacterium abscessus subsp. massiliense , Mycobacterium fortuitum , Mycobacterium chelonae and Mycobacterium peregrinum . The amplified target genes for each species/subspecies using multiplex PCR were analysed using a nucleic acid chromatography assay. Results. Among the 159 mycobacterial type strains and 70 RGM clinical isolates tested, the developed assay correctly identified all relevant RGM without any cross-reactivity or false-negatives. The limits of detection for each species were approximately 0.2 pg µl-1. Conclusion. The rapid and simple nucleic acid chromatography method developed here, which does not involve heat denaturation, may contribute to the rapid identification and treatment of RGM infections.

Nontuberculous Mycobacteria under Scrutiny in the Geneva Area (2015–2020)

<b><i>Background:</i></b> Nontuberculous mycobacteria (NTM) are increasingly identified in industrialized countries, and their role as pathogens is more frequently recognized. The relative prevalence of NTM strains shows an important geographical variability. Thus, establishing the local relative prevalence of NTM strains is relevant and useful for clinicians. <b><i>Methods:</i></b> Retrospective analysis (2015–2020) of a comprehensive database was conducted including all results of cultures for mycobacteria in a University Hospital (Geneva, Switzerland), covering a population of approximately 500,000 inhabitants. All NTM culture-positive patients were included in the analyses. Patients’ characteristics, NTM strains, and time to culture positivity were reported. <b><i>Results:</i></b> Among 38,065 samples analyzed during the study period, 411 were culture-positive for NTM, representing 236 strains, and 231 episodes of care which occurred in 222 patients. Patients in whom NTM were identified were predominantly female (55%), with a median age of 62 years, and a low BMI (median: 22.6 kg/m²). The <i>Mycobacterium avium</i> complex (MAC) was the most frequently identified group (37% of strains) followed by <i>Mycobacterium gordonae</i> (25%) and <i>Mycobacterium xenopi</i> (12%) among the slowly growing mycobacteria (SGM), while the <i>Mycobacterium chelonae/abscessus</i> group (11%) were the most frequently identified rapidly growing mycobacteria (RGM). Only 19% of all patients were treated, mostly for pulmonary infections: the MAC was the most frequently treated NTM (<i>n</i> = 19, 43% of cases in patients treated) followed by RGM (<i>n</i> = 15, 34%) and <i>M. xenopi</i> (<i>n</i> = 6, 14%). Among those treated, 23% were immunosuppressed, 12% had pulmonary comorbidities, and 5% systemic comorbidities. Cultures became positive after a median of 41 days (IQR: 23; 68) for SGM and 28 days (14; 35) for RGM. <b><i>Conclusions:</i></b> In Western Switzerland, <i>M. avium</i> and <i>M. gordonae</i> were the most prevalent NTM identified. Positive cultures for NTM led to a specific treatment in 19% of subjects. Patients with a positive culture for NTM were mostly female, with a median age of 62 years, a low BMI, and a low prevalence of immunosuppression or associated severe comorbidities.

Mycobacterium chelonae Cutaneous Infection: A Challenge for an Internist

Cutaneous infections caused by the Mycobacterium chelonae complex show a heterogeneous clinical presentation, which varies according to the patient’s immune status. Most standard antimycobacterials have no effect against these species. Clarithromycin alone was shown to provide adequate treatment, although resistance has been reported. Consequently, the literature supports multi-drug therapy to combat resistant strains. Here, we describe the case of a 59-year-old man under systemic immunosuppressive therapy who developed cutaneous lesions whose evolution was highly suggestive of atypical infection.