Leukotoxin of Contains a Unique Neutralizing Epitope, and a Non-Neutralizing Epitope Shared with Leukotoxin.

and , originally classified as biotype T and biotype A, respectively, under Genus has now been placed under two different Genera, and , based on DNA-DNA hybridization and 16S RNA studies. While has been the predominant pathogen of pneumonia in ruminants, is emerging as an important pathogen of ruminant pneumonia. Leukotoxin is the critical virulence factor of these two pathogens.