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Shared Mycobacterium avium genotypes observed among unlinked clinical and environmental isolates*
Ashworth Dirac, M., K. Weigel, M. Yakrus, A. Becker, H. Chen, G. Fridley, A. Sikora, C. Speake, E Hilborn, S. Pfaller, AND G. Cangelosi. Shared Mycobacterium avium genotypes observed among unlinked clinical and environmental isolates*. APPLIED AND ENVIRONMENTAL MICROBIOLOGY. American Society for Microbiology, Washington, DC, 79(18):5601-7, (2013).
Please note- this report is a revision of the 2009 paper that underwent technical clearance, entitled: "Pathogen genotypic analysis reveals strains of Mycobacterium avium subspecies hominissuis that appear in human disease at diverse geographic locations, suggesting a global genotypic structure within this emerging environmental pathogen". This version now incorporates author and reviewer comments. Note - EPA disclaimer is included with acknowledgements. Mycobacterium avium is listed as a microbial contaminant on Candidate Contaminant Lists 1 -3. Molecular methods such as genotyping can greatly improve the specificity of the exposure effect relationship in infectious disease research. This is particularly important for environmental pathogens such as M. avium where analysis of human contact patterns is useless in ascertaining the ultimate source of illness. Among pathogens such as M avium where broadly dispersed environmental sources of potential illness may occur, it is important to characterize occurrence of genotypes among human and environmental isolates in order to better interpret microbial isolates collected during epidemiologic investigations. This report describes the occurrence of related genotypes among apparently unrelated sources, suggesting that the M avium genome may be less heterogeneous than currently understood.
Our understanding of the sources of Mycobacterium avium infection is partially based on genotypic matching of pathogen isolates from cases and environmental sources. These approaches assume that genotypic identity is rare in isolates from unlinked cases or sources. To test this assumption, a high-resolution PCR-based genotyping approach, LSP-MVR, was selected and used to analyze clinical and environmental isolates of M. avium from geographically diverse sources. Among 127 clinical isolates from seven locations in North America, South America, and Europe, 42 genotypes were observed. Twelve of these genotypes were seen in isolates from apparently unlinked patients in two or more geographic locations. Six of the twelve were also observed in environmental isolates. A subset of these isolates was further analyzed by alternative strain genotyping methods, PFGE and MIRU-VNTR, which confirmed the existence of geographically dispersed strain genotypes. These results suggest that caution should be exercised in interpreting high-resolution genotypic matches as evidence for an acquisition event.