Background Information

The genus Brucella is a member of family Brucellaceae and includes ten species which are small, non-motile, non-sporing, aerobic, gram-negative intracellular coccobacilli. They are catalase, oxidase and urea positive bacteria. Members of the genus can grow on enriched media like blood agar or chocolate agar. Brucellosis is a well-known zoonosis, present in all the continents, but with greatly varying prevalence and incidence, in the animal and human populations. Brucellae, as facultative intracellular parasites, colonize many species of social animals in a chronic, possibly permanent way, perhaps for their whole lifetime. 

Brucella colony appearance 

Transmission

Brucella species are usually transmitted between animals by contact with the placenta, fetus, fetal fluids and vaginal discharges of an infected animal.  Most or all Brucella species are also found in semen. Male can shed these organisms for long periods or lifelong.  Some Brucella species have also been detected in other sctretions and excretions including urine, feces, hygroma fluid, salvia, milk and nasal and ocular secretions 

Ecology of zoonotic Brucella infections