The allelic identities of Single Nucleotide Repeat (SNR) markers in Bacillus anthracis are typically ascertained by DNA sequencing through the direct repeat. Here we describe a reproducible method for genotyping closely related isolates by using four SNR loci in a multiplex-PCR capillary electrophoresis system amenable to high-throughput analysis.

AIMS:Bacillus anthracis is a genetically monomorphic bacterium with little diversity to be expected during an outbreak. This study used more rapidly evolving genetic markers on outbreak samples to ascertain genetic diversity.METHODS AND RESULTS:Forty-seven isolates from a B. anthracis outbreak during the summer of 2005 in South Dakota were analysed using single nucleotide polymorphisms (SNP) and multi-locus VNTR analysis (MLVA). Results indicated that all of the outbreak strains belonged to a single clonal lineage. However, analysis of four single nucleotide repeat (SNR) markers resolved these isolates into six distinct genotypes providing insights into disease transmission.CONCLUSIONS:Strain determination of unknown B. anthracis samples can be ascertained by SNP and MLVA markers. However, comparison of many samples obtained during an outbreak will require markers with higher rates of mutation to ascertain genetic diversity.SIGNIFICANCE AND IMPACT OF THE STUDY:SNR4 analysis allowed discrimination of closely related B. anthracis isolates and epidemiological tracking of the outbreak. When used in conjunction with other genotyping schemes that allow broad genetic relationships to be determined, SNR markers are powerful tools for detailed tracking of natural B. anthracis outbreaks and could also prove useful in forensic investigations.

ABSTRACTA TaqMan-minor groove binding assay designed around a nonsense mutation in theplcRgene was used to genotypeBacillus anthracis,B. cereus, andB. thuringiensisisolates. The assay differentiatedB. anthracisfrom these genetic near-neighbors and determined that the nonsense mutation is ubiquitous across 89 globally and genetically diverseB. anthracisstrains.