Investigation of putative invasion determinants of Actinobacillus species using comparative genomics.

Actinobacillus spp. are Gram-negative bacteria associated with mucosal membranes. While some are commensals, others can cause important human and animal diseases. A. pleuropneumoniae causes severe fibrinous hemorrhagic pneumonia in swine but not systemic disease whereas other species invade resulting in septicemia and death. To understand the invasive phenotype of Actinobacillus spp., complete genomes of eight isolates were obtained and pseudogenomes of five isolates were assembled and annotated. Phylogenetically, A. suis isolates clustered by surface antigen type and were more closely related to the invasive A. ureae, A. equuli equuli, and A. capsulatus than to the other swine pathogen, A. pleuropneumoniae. Using the LS-BSR pipeline, 251 putative virulence genes associated with serum resistance and invasion were detected. To our knowledge, this is the first genome-wide study of the genus Actinobacillus and should contribute to a better understanding of host tropism and mechanisms of invasion of pathogenic Actinobacillus and related genera.