also cross the blood–brain barrier and cause meningitis. Virulence, culturing, and metabolism P. multocida expresses a range of virulence factors including a polysaccharide capsule and the variable carbohydrate surface molecule, lipopolysaccharide (LPS). The capsule has been shown in strains of serogroups A and B to help resist phagocytosis by host immune cells and capsule type A has also been shown to help resist complement-mediated lysis. The LPS produced by P. multocida consists of a hydrophobic lipid A molecule (that anchors the LPS to the outer membrane), an inner core, and an outer core, both consisting of a series of sugars linked in a specific way. There is no O-antigen on the LPS and the molecule is similar to LPS produced by Haemophilus influenzae and the lipooligosaccharide of Neisseria meningitidis. A study in a serovar 1 strain showed that a full-length LPS molecule was essential for the bacteria to be fully virulent in chickens. Strains that cause atrophic rhinitis in pigs are unique as they also have P. multocida toxin (PMT) residing on a bacteriophage. PMT is responsible for the twisted snouts observed in pigs infected with the bacteria. 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 has been observed invading and replicating inside host amoebae, causing lysis in the host. P. multocida will grow at on blood or chocolate agar, HS 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-positive and catalase-positive, and can also ferment a large number of carbohydrates in anaerobic conditions. The survival of P. multocida bacteria has also been shown to be increased by the addition of salt into their environments. Levels of sucrose and pH also have been shown to have minor effects on bacterial survival. Diagnosis and treatment Diagnosis of the bacterium in humans was traditionally based on clinical findings, and culture and serological testing, but false negatives have been a problem due to easy death of P. multocida, and serology cannot differentiate between current infection and previous exposure. The quickest and most accurate method for confirming an active P. multocida infection is molecular