| Summary: | <p>Abstract</p> <p>Background</p> <p><it>Campylobacter jejuni </it>has been divided into two subspecies: <it>C. jejuni </it>subsp. <it>jejuni </it>(<it>Cjj</it>) and <it>C. jejuni </it>subsp. <it>doylei </it>(<it>Cjd</it>). Nearly all of the <it>C. jejuni </it>strains isolated are <it>Cjj</it>; nevertheless, although <it>Cjd </it>strains are isolated infrequently, they differ from <it>Cjj </it>in two key aspects: they are obtained primarily from human clinical samples and are associated often with bacteremia, in addition to gastroenteritis. In this study, we utilized multilocus sequence typing (MLST) and a DNA microarray-based comparative genomic indexing (CGI) approach to examine the genomic diversity and gene content of <it>Cjd </it>strains.</p> <p>Results</p> <p>A geographically diverse collection of eight <it>Cjd </it>strains was examined by MLST and determined to be phylogenetically distinct from <it>Cjj </it>strains. Microarray-based CGI approach also supported this. We were able to demonstrate that <it>Cjd </it>strains exhibited divergence from <it>Cjj </it>strains NCTC 11168 and RM1221 in many of the intraspecies hypervariable regions. Moreover, multiple metabolic, transport and virulence functions (e.g. cytolethal distending toxin) were shown to be absent in the <it>Cjd </it>strains examined.</p> <p>Conclusion</p> <p>Our data demonstrate that <it>Cjd </it>are phylogenetically distinct from <it>Cjj </it>strains. Using the CGI approach, we identified subsets of absent genes from amongst the <it>C. jejuni </it>genes that provide clues as to the potential evolutionary origin and unusual pathogenicity of <it>Cjd</it>.</p>
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