Neisseria

Gram-negative cocci Neisseria are paired; they tend to look like coffee beans. Catalase and oxidase positive – Catalase is an enzyme that protects bacteria from oxidative damage. Pathogenic Neisseria with Type IV pili have twitching motility (be aware of intertextual variation regarding the motility of Neisseria). Invade host cells; in the image of a fluid sample, we see the tiny Neisseria gonorrhoeae inside the larger neutrophils. Neisseria meningitidis Aka, meningococcus. Pathogenic serogroups include A, B, C, Y, and W-135. – Different serotypes are responsible for geographically distinct epidemics. Neisseria meningitidis can be grown on both chocolate agar and blood agar; under some conditions, it can be grown on nutrient agar. Neisseria gonorrhoeae Aka, gonococcus. Require highly specific growth conditions, and can only be grown on chocolate agar. – Selective Thayer-Martin chocolate agar has antibiotics to exclude other bacterial types present in the sample. Many virulence factors are part of the cell wall. Neisseria endotoxin comprises Lipooligosaccharide (LOS), with toxic lipid A region. – During infection, Neisseria can release "blebs" of their cell membranes with the endotoxin. Pili have multiple effects: – Attach to host cells, which is a key step in colonization. – Resist neutrophil bactericidal activities. – Type IV pili facilitate twitching motility. IgA1 protease degrades Immunoglobulin A, which enables the bacteria to reach the mucous membranes of the respiratory and genital tracts. Neisseria have special receptors that bind to host transferrin, lactoferrin, and hemoglobin to acquire iron, which is crucial for bacterial metabolism. – Notice that this mechanism is different from the siderophores of other bacteria. Opacity proteins (aka, Opa), which bind epithelial and phagocytic cells; they also engage in cell to cell signaling. – Strains with these proteins appear opaque in culture, hence their name. Reduction-modifiable proteins (Rmp) protect porin and lipooligosaccharide from bactericidal antibodies. Porin proteins (aka, Por) insert pores into the bacterial cells to allow for movement of nutrients and wastes; they also prevent phagolysosome fusion within neutrophils, which allows the bacteria to survive intracellularly and aid in the invasion of epithelial cells. There are two porin genes: PorA is only active in Neisseria meningitidis PorB is active in both N. meningitidis and N. gonorrhoeae. Opa, Por, and Rmp proteins are also referred to as outer membrane protein classes I-V, particularly in Neisseria meningitidis. Specific Virulence Factors: Neisseria meningitidis Outer polysaccharide capsule that allows it to resist phagocytosis. Several vaccines use the capsule as immunogen, however, this is not effective for Group B meningococcus because its capsule is not immunogenic. Factor H binding protein (FHBP) binds Factor H to inhibit complement factor C3b; thus, this protein inhibits opsonization and membrane attack complex formation. And, because it is present on Group B meningococci, it is used as a vaccine immunogen. Specific Virulence Factors: Neisseria gonorrhoeae Some strains produce beta-lactamase (aka, penicillinase), which promotes penicillin resistance.