Histophilus somni

Histophilus somni is a non-motile, gram-negative, rod or coccobacillus shaped, facultative anaerobe bacterial species belonging to the family Pasteurellaceae.^[2] Prior to 2003, it was thought Haemophilus somnus, Histophilus ovis, and Histophilus agni were three different species, but now are all classified as Histophilus somni. Histophilus somni is a commensal bacteria of mucous membranes of the upper respiratory tract and reproductive tract^[3][4][5][6] with a global prevalence^[6] and is found in cattle and other small ruminants.^[4] Histophilus somni is also a known causative agent that is a part of the Bovine Respiratory Disease (BRD) complex,^[4] which typically involves multiple pathogens residing together in biofilm environments. Histophilus somni may also cause Histophilosus symptoms and clinical presentation will depend on the tissue affected.^[5] When disease does occur, it can be difficult to catch in time and is often diagnosed post mortem.^[7] This means that treatment often involves metaphylactic mass treatment or no treatment at all. This organism is more fastidious than others and requires knowledge for sample collection, storage and culture. Genomic studies related to this bacteria have enabled scientists to pinpoint antibiotic resistance genes.