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Journal of Clinical Microbiology, September 2001, p. 3186-3192, Vol. 39, No. 9
Department of Biological Sciences, Northern Arizona
University, Flagstaff, Arizona 86011-56401;
Microbial Diseases Laboratory, California Department of
Health Services, Berkeley, California 947042;
and Oklahoma State Department of Health, Oklahoma City,
Oklahoma 731173
Received 23 March 2001/Returned for modification 2 June
2001/Accepted 1 July 2001
Francisella tularensis, the etiological agent of
tularemia, is found throughout the Northern hemisphere. After analyzing
the F. tularensis genomic sequence for potential
variable-number tandem repeats (VNTRs), we developed a multilocus VNTR
analysis (MLVA) typing system for this pathogen. Variation was detected
at six VNTR loci in a set of 56 isolates from California, Oklahoma,
Arizona, and Oregon and the F. tularensis live vaccine
strain. PCR assays revealed diversity at these loci with total allele
numbers ranging from 2 to 20, and Nei's diversity index values ranging
from 0.36 to 0.93. Cluster analysis identified two genetically distinct groups consistent with the current biovar classification system of
F. tularensis. These findings suggest that these VNTR
markers are useful for identifying F. tularensis
isolates at this taxonomic level. In this study, biovar B isolates were
less diverse than those in biovar A, possibly reflecting the history of
tularemia in North America. Seven isolates from a recent epizootic in
Maricopa County, Ariz., were identical at all VNTR marker loci. Their
identity, even at a hypervariable VNTR locus, indicates a common source of infection. This demonstrates the applicability of MLVA for rapid
characterization and identification of outbreak isolates. Future
construction of reference databases will allow faster outbreak tracking
as well as providing a foundation for deciphering global genetic relationships.
0095-1137/01/$04.00+0 DOI: 10.1128/JCM.39.9.3186-3192.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Francisella tularensis Strain Typing
Using Multiple-Locus, Variable-Number Tandem Repeat Analysis
*
Corresponding author. Mailing address: Department of
Biological Sciences, Northern Arizona University, Flagstaff, AZ
86011-5640. Phone: (520) 523-1078. Fax: (520) 523-0639. E-mail:
Paul.Keim{at}nau.edu.
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