Shared Mycobacterium avium genotypes observed among unlinked clinical and environmental isolates

Area of Science:

• Microbiology
• Genetics
• Epidemiology

Background:

• Mycobacterium avium infection source attribution relies on genotypic matching of clinical and environmental isolates.
• Current methods assume genotypic identity is rare between unlinked cases or sources.

Purpose of the Study:

• To evaluate the assumption of genotypic rarity in Mycobacterium avium isolates from diverse geographic locations.
• To assess the utility of high-resolution genotyping for tracing M. avium infection sources.

Main Methods:

• Utilized large-sequence polymorphism (LSP)-mycobacterial interspersed repetitive unit-variable-number tandem repeat (MIRU-VNTR) for high-resolution PCR-based genotyping.
• Analyzed 127 clinical and environmental M. avium isolates from North America, South America, and Europe.
• Confirmed findings with pulsed-field gel electrophoresis (PFGE) and standard MIRU-VNTR.

Main Results:

• Identified 42 distinct M. avium genotypes among 127 clinical isolates.
• Observed 12 genotypes shared among isolates from geographically dispersed, apparently unlinked patients.
• Found six of these shared genotypes also present in environmental isolates.

Conclusions:

• High-resolution genotypic matches are frequently observed between geographically dispersed M. avium isolates.
• The presence of identical genotypes in unlinked cases and environmental sources challenges direct source attribution assumptions.
• Caution is advised when interpreting high-resolution genotypic matches as definitive evidence of an acquisition event.