Genetic analysis of Pasteurella organisms has resulted in a new classification for several strains of the organism commonly involved in respiratory tract disease in cattle. Mannheimia haemolytica (formerly Pasteurella haemolytica) is the new taxonomic classification, as suggested on the basis of results from a study published in 1999 (Angen O, Mutters R, Caugant DA, et al. Int J Syst Bacteriol 1999;49:67-86).

According to Kim Alan Brogden, PhD, of the USDA-ARS National Animal Disease Center, historically, two biotypes have been recognized for the taxon Pasteurella haemolytica: biotype A isolates that ferment l-arabinose, and biotype T isolates that ferment trehalose. The trehalose-positive isolates were found to represent a distinct species (P trehalosi, which currently contains serovars 3, 4, 10, and 15). The trehalose-negative organisms were found to represent a distinct genus (Mannheimia) with five species (M glucosida, M granulomatis, M haemolytica, M ruminalis, and M varigena). The trehalose-negative organisms are now classified as M haemolytica and contain serovars 1, 2, 5-9, 12-14, 16, and 17. The trehalose-negative organisms of P haemolytica serovar 11 are now M glucosida.

These new classifications should assist researchers, clinicians, and pathologists as they attempt to corral the organism and elucidate its role in the bovine respiratory disease complex.