A Rapid Screening Assay for Clarithromycin-Resistant Mycobacterium avium Complex Using Melting Curve Analysis with...

Area of Science:

• Microbiology
• Molecular Biology
• Antimicrobial Resistance

Background:

• Mycobacterium avium complex (MAC) causes lung disease, with macrolide resistance posing a significant treatment challenge.
• Over 95% of macrolide-resistant MAC strains harbor mutations in the 23S rRNA gene, specifically at positions 2058-2059.
• Accurate and rapid detection of these resistance mutations is crucial for effective patient management.

Purpose of the Study:

• To develop a novel, simple, and rapid melting curve assay for detecting macrolide resistance-associated mutations in the 23S rRNA gene of MAC.
• To differentiate between clarithromycin-susceptible (AA genotype) and resistant (TA, GA, AG, CA, AC, AT genotypes) MAC strains.
• To validate the assay's performance using genomic DNA from various M. avium and M. intracellulare strains.

Main Methods:

• Development of a melting curve assay utilizing nonfluorescently labeled probes.
• Design of specific probes to target the AA genotype (susceptible) and other genotypes (resistant) at positions 2058-2059 of the 23S rRNA gene.
• Testing the assay with characterized MAC strains and genomic DNA to confirm genotype identification based on melting temperatures (Tm).

Main Results:

• The assay successfully differentiated the AA genotype (Tm ~80°C) from resistant genotypes (Tm ~77°C) using an AA-specific probe.
• All six resistant genotypes (TA, GA, AG, CA, AC, AT) were correctly identified by their respective genotype-specific probes.
• Genomic DNA from M. avium and M. intracellulare strains was accurately identified by the assay, correlating highest Tm values with specific genotypes.

Conclusions:

• The developed melting curve assay is effective for determining MAC genotypes at positions 2058-2059 of the 23S rRNA gene.
• This simple, nonfluorescent probe-based method allows for the rapid detection of clarithromycin-resistant MAC strains.
• The assay facilitates timely and accurate drug therapy decisions for patients with MAC lung disease.