Pasteurella multocida

Pasteurella multocida is a small, Gram-negative, non-motile coccobacillus that is penicillin-sensitive. It can cause a zoonotic infection in humans, which typically is a result of bites or scratches from pets (such as cats and dogs). Many mammals and fowl harbor it as part of their normal respiratory microbiota, displaying asyptomatic infections.

History
Pasteurella multocida was first found in 1878 in fowl cholera-infected birds. However, it was not isolated until 1880, by Louis Pasteur - the man whom Pasteurella is named in honor of.

Disease
P. multocida is the most common cause of infection from animal injuries. (Pneumonia in cattle and pigs, atrophic rhinitt in pigs and goats and wound infections, specially after dog/cat-bites.) A high leukocyte and neutrophil count is typically observed, leading to an inflammatory reaction at the infection site (generally a diffuse localized cellulitis). It can also infect other locales, such as the respiratory tract. In more serious cases, a bacteremia can result, causing an osteomyelitis or endocarditis. The bacteria may also cross the blood-brain barrier and cause a meningitis.

Virulence, Culturing, and Metabolism
A bacteriophage encodes the toxin responsible for most P. multocida virulence factors. This toxin activates Rho GTPases, which bind and hydrolyze GTP, and are important in actin stress fiber formation. Formation of stress fibers may aid in the endocytosis of P. multocida. The host cell cycle is also modulated by the toxin, which can act as an intracellular mitogen. P. multocida will grow at 37 degrees Celsius on blood or chocolate agar, but will not grow on MacConkey agar. Colony growth is accompanied by a characteristic "mousy" odor due to metabolic products. Being a facultative anaerobe, it is oxidase- and catalase-positive, and can also ferment a large number carbohydrates in anaerobic conditions.

Treatment
This bacterium is somewhat unusual in that it can be effectively treated with beta-lactam antibiotics, despite its Gram-negative structure. It is also often treated with fluoroquinolones or tetracyclines; fluoroquinolones inhibit bacterial DNA synthesis and tetracyclines interfere with protein synthesis by binding to the bacterial 30S ribosomal subunit.