Serum Cell-Free DNA-based Detection of Mycobacterium avium Complex Infection.

Rationale: Mycobacterium avium complex (MAC) is the most common cause of nontuberculous mycobacterial (NTM) pulmonary disease (PD), which exhibits increasing global incidence. Current microbiologic methods routinely used in clinical practice lack sensitivity and have long latencies, leading to delays in diagnosis and treatment initiation and evaluation. A clustered regularly interspaced short palindromic repeats (CRISPR)-based assay that measures MAC cell-free DNA (cfDNA) concentrations in serum could provide a rapid means to detect MAC infection and monitor response to antimicrobial treatment. Objectives: To develop and optimize a CRISPR MAC assay for MAC infection detection and to evaluate its diagnostic and prognostic performance in two MAC disease cohorts. Methods: MAC cfDNA serum concentrations were measured in individuals with diagnoses of MAC disease or who had bronchiectasis or chronic obstructive pulmonary disease diagnoses without histories of NTM PD or NTM-positive sputum cultures. Diagnostic performance was analyzed using pretreatment serum from two cohorts. Serum MAC cfDNA changes during MAC PD treatment were evaluated in a subset of patients with MAC PD who received macrolide-based multidrug regimens. Measurements and Main Results: The CRISPR MAC assay detected MAC cfDNA in MAC PD with 97.6% (91.6-99.7%) sensitivity and 97.6% (91.5-99.7%) specificity overall. Serum MAC cfDNA concentrations markedly decreased after MAC-directed treatment initiation in patients with MAC PD who demonstrated MAC culture conversion. Conclusions: This study provides preliminary evidence for the utility of a serum-based CRISPR MAC assay to rapidly detect MAC infection and monitor the response to treatment.

Evolution towards extremely high ß-lactam resistance in Mycobacterium abscessus outbreak strains.

Treatment of Mycobacterium abscessus pulmonary disease requires multiple antibiotics including intravenous ß-lactams (e.g., imipenem, meropenem). M. abscessus produces a ß-lactamase (BlaMab) that inactivates ß-lactam drugs but less efficiently carbapenems. Due to intrinsic and acquired resistance in M. abscessus and poor clinical outcomes, it is critical to understand the development of antibiotic resistance both within the host and in the setting of outbreaks. We compared serial longitudinally collected M. abscessus subsp. massiliense isolates from the index case of a CF center outbreak and four outbreak-related strains. We found strikingly high imipenem resistance in the later patient isolates, including the outbreak strain (MIC >512 µg/ml). The phenomenon was recapitulated upon exposure of intracellular bacteria to imipenem. Addition of the ß-lactamase inhibitor avibactam abrogated the resistant phenotype. Imipenem resistance was caused by an increase in ß-lactamase activity and increased bla Mab mRNA level. Concurrent increase in transcription of preceding ppiA gene indicated upregulation of the entire operon in the resistant strains. Deletion of the porin mspA coincided with the first increase in MIC (from 8 to 32 µg/ml). A frameshift mutation in msp2 responsible for the rough colony morphology, and a SNP in ATP-dependent helicase hrpA co-occurred with the second increase in MIC (from 32 to 256 µg/ml). Increased BlaMab expression and enzymatic activity may have been due to altered regulation of the ppiA-bla Mab operon by the mutated HrpA alone, or in combination with other genes described above. This work supports using carbapenem/ß-lactamase inhibitor combinations for treating M. abscessus, particularly imipenem resistant strains.

Whole-genome sequence of Mucor velutinosus NIH1002, a strain associated with disseminated disease.

The draft genome of Mucor velutinosus NIH1002, a 2011 isolate from a case of disseminated disease, was sequenced using PacBio long-read and HiSeq short-read technologies. The genome has 43 contigs, an N50 of 2.65 Mb, and 13,295 protein-coding genes. It is the most complete M. velutinosus genome to date.