Yersinia, Francisella, Brucella and Pasteurella (Gram-Negative)

These are gram-negative rods that cause disease in animals, and are transferred from animals to humans. They are facultative intracellular organisms (with the exception of Pasteurella multocida), meaning the bacteria can survive within macrophages, set up infection to regional lymph nodes of the site of contact, and infect organs via the bloodstream. Immune response is cell-mediated and exhibits delayed-type hypersensitivity.

Yersinia pestis
Causes bubonic plague. (Think rat and "pest"). This disease is still contractible in southwestern US. 

• Virulence factors: 
• Fraction 1 (F1), antiphagocytic capsular antigen.
• V and W antigens, unknown function.

Francisella tularensis 
Causes tularemia, which closely resembles the bubonic plague. Infects many mammals, especially rabbits, and is carried by ticks and deerflies.

• Diseases: 
• Tularemia. Like the bubonic plague, symptoms include fever, swollen lymph nodes, and infection of multiple organs. Unlike the bubonic plague, there is no skin ulcer. 

Brucella
Usually contracted from handling meat, and is common worldwide in countries where animals are not immunized or where milk is not pasteurized.

Pasteurella multocida
Not a facultative intracellular organism. Lives in the mouths of cats, and infects humans from cat or dog bite.