pleuropneumoniae. Furthermore, the 11 differential sequences of the CVCC261 strain were found to show high similarities with the corresponding sequences of the A. pleuropneumoniae JL03 (serotype 3) genome, which has been completely sequenced. The 19 differential DNA sequences were registered in GenBank (accession nos, FJ773375–93),

and the summaries of the sequences analyses are listed in Tables 3 and 4. To further characterize the distribution of the 19 differential DNA sequences in the 15 A. pleuropneumoniae serotypes, the genomic DNA of the 16 reference strains BTK inhibitor were used as templates for PCR-based identification. The electrophoresis results showed that the 19 differential sequences showed JQ1 mouse variable distributions in the 15 serotypes (Table 5). Comparison of the genomes of two closely related strains and identification of functional genes are effective approaches for elucidating bacterial pathogenic mechanisms and developing multivalent vaccines (Lei et al., 2008; Sack & Baltes, 2009). Although the reference strains and selected Canadian field isolates have been compared with the A. pleuropneumoniae L20 strain (serotype 5b) by performing microarray analysis (Goure et al., 2009), the genomic differences between serotypes 1 and 3 have still not been elucidated. In this study, we identified eight DNA sequences in the genome of the CVCC259 strain

(serotype 1) that were absent in the genome of the CVCC261 strain (serotype 3), and 11 DNA sequences in the genome of the CVCC261 strain that were absent in the genome of the CVCC259 strain. These 19 DNA fragments represented 15 ORFs that encoded different proteins, including the transferrin-binding protein, autotransporters, glycosyltransferase, ATP-binding cassette (ABC) transporter systems, lipopolysaccharide-biosynthesis

proteins, various components of the Apx toxin, and other proteins of unknown function. Among these differential sequences, the genes for the autotransporter adhesion (a7), a hypothetical protein (a15), and the apxI operon (a1, a2, and a3) were common among serotypes 1, 5, 9, and 11, while the wzy (b12), rfaG (b13), glf (b15, b16), pst (b17), and apxIII operon (b1, b6) genes were common among serotypes 3, over 6, 8, and 15. Serological cross-reactivities between serotypes 1 and 9, serotypes 3, 6, and 8, and serotypes 1 and 5 have been reported (Mittal et al., 1987; Inzana et al., 1990; Mittal, 1990). Previous studies suggested that these cross-reactions can be primarily attributed to shared species-specific antigens such as lipopolysaccharide or membrane proteins (Perry et al., 1990). In our study, the distribution of the apxI and apxIII operon was in agreement with that presented in the previous report (Beck et al., 1994), and these operons have been shown to play the roles of immune-protective antigens (Du et al., 2008).