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Neisseria: Overview

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Neisseria bacteria are gram-negative diplococci; the genus includes Neisseria gonorrhoeae and Neisseria meningitidis. Neisseria gonorrhoeae can metabolize glucose, while Neisseria meningitidis is capable of metabolizing glucose and maltose. Both Neisseria species exhibit a positive oxidase reaction. Although Neisseria bacteria do not thrive in sheep's blood agar, they can be successfully cultivated on chocolate agar and Thayer-Martin agar, which contains vancomycin, polymyxin, nystatin, and trimethoprim. The host defense against Neisseria infections involves the membrane attack complex (MAC), an essential mechanism that ruptures bacterial cell membranes. Terminal complement factors (C5 to C9) deficiencies can result in heightened susceptibility to Neisseria infections.

The key virulence factor of Neisseria species is their, pili, which allow attachment to mucosal surfaces and antigenic variation to evade the immune system. Another factor is production of an IgA protease, which enables Neisseria to colonize mucosal surfaces more easily. Additional virulence factors are lipooligosaccharides (LOS), a highly-inflammatory compound similar to endotoxins produced by other gram-negative bacteria, and OPA (opacity proteins) found on Neisseria's outer surfaces, which help form tight bonds with each other and host cells, aiding in bacterial colonization.

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What is Neisseria and what are the main species of clinical importance?

Neisseria is a genus of gram-negative, oxidase-positive, aerobic diplococci that reside in the mucous membranes of humans. The two primary species of clinical significance are Neisseria gonorrhoeae, which causes the sexually transmitted infection gonorrhea, and Neisseria meningitidis, which causes meningitis and septicemia.

What are chocolate agar and Thayer-Martin agar, and why are they used in the cultivation of Neisseria species?

Chocolate agar and Thayer-Martin agar are both culture media used for the isolation and growth of Neisseria species. Chocolate agar is a non-selective medium made from lysed red blood cells that provides essential nutrients for bacterial growth. Thayer-Martin agar is a modified version of chocolate agar that contains antibiotics, which inhibit the growth of other bacteria and allow the selective growth of Neisseria species. These media are used due to the fastidious nature of Neisseria, which requires specific growth factors and conditions for successful cultivation.

What are the roles of membrane attack complex (MAC) and terminal complement deficiency in Neisseria infections?

The membrane attack complex (MAC) is an important component of the complement system that is responsible for creating pores in the cell membranes of bacterial pathogens, eventually leading to cell lysis and destruction. Neisseria species, especially Neisseria meningitidis, can evade the host immune system by inhibiting MAC formation. Terminal complement deficiency, wherein components of the MAC are lacking or non-functional, predisposes individuals to recurrent and severe Neisseria infections due to an impaired ability to eliminate these pathogens.

Why is IgA protease significant in Neisseria pathogenesis?

IgA protease is an enzyme produced by Neisseria species, specifically Neisseria meningitidis and Neisseria gonorrhoeae. It cleaves immunoglobulin A (IgA), an important antibody found in mucosal secretions that protects the host against invading pathogens. By breaking down IgA, Neisseria bacteria can evade host defenses and colonize the mucosa, promoting infection and allowing spread to other tissues.

How do lipooligosaccharides (LOS) and opacity proteins contribute to Neisseria virulence?

Lipooligosaccharides (LOS) are components of the outer membrane in Neisseria species that can trigger a potent inflammatory response in the host during infection. LOS can also enhance bacterial survival by contributing to resistance against complement-mediated killing. Opacity proteins are surface proteins in Neisseria, specifically in Neisseria gonorrhoeae, that play a critical role in host immune evasion. They undergo antigenic variation, allowing the bacteria to escape immune recognition and facilitate attachment to host cells. These factors collectively contribute to Neisseria virulence and pathogenesis.