|Ewalt, Darla - USDA/APHIS|
Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 11, 2003
Publication Date: July 11, 2003
Citation: Bricker, B.J., Alt, D.P., Ewalt, D.R., Halling, S.M. 2003. Brucella 'hoof-prints': strain typing by multi-locus analysis of variable number tandem repeats (vntrs). Journal of Clinical Microbiology. Interpretive Summary: Brucellosis is a bacterial disease that causes abortions in cattle, swine, sheep, bison, elk, dogs and many other animals. The disease, found in the USA and many other countries, can also infect and cause disease in humans. One important aspect of controlling the spread of diseases is finding the source of the infection, a process known as trace-back. It is important to find and eliminate the original source of an infection so that the source can't continue to spread the disease in the future. Currently, it is very difficult to be certain which strain was the original source for a brucellosis outbreak. This is because most of the strains are too much alike. We have developed a new technique for DNA-fingerprinting the bacteria that cause brucellosis. It is very similar to the technology used for DNA fingerprinting humans to find out if they are related (such as in paternity cases). Similarly, this technology can show whether two strains of bacteria are directly related to each other. Therefore, it will finally be possible to say with certainty whether a disease outbreak came from a particular source.
Technical Abstract: Currently, there are very few tools available for subtyping Brucella isolates for epidemiological trace-back. To a large extent, subtyping is difficult because of the genetic homogeneity within the genus, and the apparently slow genetic drift over time. In this paper, we have described a new method for subtyping Brucella isolates based on microsatellite fingerprinting. This technique exploits and octameric sequence that is tandemly repeated a variable number of times in different strains. To add to the discriminatory power of this approach, the same tandem repeat sequence was found in nine independent loci in the Brucella genome, of which eight loci showed hypervariability in the number of repeat units. Each locus appeared to mutate at a different rate, allowing for multiple levels of discrimination among isolates. A PCR-based method was developed for comparing the differential numbers of repeat units (alleles) at each of the eight loci. The technique was used to discriminate among Brucella species and biovars, among unrelated isolates of B. abortus biovar 1 field isolates in cattle, and among a small number of B. abortus strains isolated from bison and elk. The data showed that multiple isolates derived from a single infected herd exhibited little or no variability in fingerprint pattern, however, the patterns from unrelated isolates were distinct. This technique will be a helpful new tool in the world-wide effort to eliminate brucellosis.