B-199. Sequence Analysis of Bordetella avium Strains Lacking Potential Virulence Factors
Bordetella avium causes a respiratory disease in turkeys that is similar to whooping cough in humans, caused by Bordetella pertussis. The bordetellae are pathogenic bacteria that are known to have a genome that changes rapidly over time as well as a property that allows them to grow in specific environments and evade the immune systems of their host. We hypothesized that genetic variation in potential virulence factor genes would be evident among isolates from commercially grown turkeys and wild birds. A diverse collection of B. avium strains isolated from wild and commercial birds was analyzed by comparative genomic hybridization (CGH) using a DNA microarray representing the B. avium 197N genome. Many regions of difference were found among the 36 strains compared, most which represent bacterial virus sequences. The results indicated changes in regions expected to code for virulence factors, including fimbrial genes. Strains shown to have variation in these genes were further analyzed to determine the nature of their differences. Polymerase chain reaction was used to amplify, clone, and sequence a region of the genome containing a cluster of four fimbrial subunit genes (BAV0313-6). Sequences were aligned and compared using BLAST and BioEdit. Results revealed the absence of one or more fimbrial subunits in the cluster when compared to the sequenced strain (197N). In addition to the apparent missing subunits, extensive variations among the subunits themselves were discovered. Short direct repeated sequences (ATTGCGG) within the 5’ end of each gene were conserved, although the number of repeats varied. The presence of these repeats strongly indicates a potential mechanism for recombination of subunits that would explain the noted variation in this locus. The BAV0313-6 locus warrants further investigation as a potentially important source of antigenic diversity in B. avium. Understanding the variations in genes coding for virulence factors is the first step in the creation of an avirulent vaccine strain for B. avium.