Question

Neisseria gonorrhoeae has multiple different genes for fimbriae, and can change them so that the immune system no longer recognizes the bacteria. This is known as

1.   Parenteral infection

2.   Complement activation

3.   Neutralization

4.   Incomplete phagocytosis

5.   Antigenic variation

Answer 1

Neisseria gonorrhoeae has multiple different genes for fimbriae, and can change them so that the immune system no longer recognizes the bacteria. This is known as ANTIGENIC VARIATION.

Neisseria gonorrhoeae: Gram Negative cocci bacterium, exclusive human pathogen,disseminated disease, acute urethritis in males, dysuria in most patients,

Features: Kidney shaped, non capsulated, ferment glucose only

Virulence factor: Outer membrane protein, Pili, IgA protease

Mode of infection: Sexual contact

Incubation period: 2-8 days

Diagnosis : Pili agglutination Test

Antigenic Variation: This is the fundamental mechanism by which pathogens avoid immune clearance and lengthen the duration of persistence in the host. Variation can occur in epitopes recognised by Bcells and Tcells and is one in many mechanisms by which pathogens avoid antibody binding and the attentions of activated T cells. It is of

• Allelic variation: variation in single locus
• Simple switching: involving simple transcriptional control
• Antigenic variation: switching between members of a multigene family, involving complicated mechanism of activation and silencing.

In Neisseria gonorrhoeae the fimbriae or pili helps in adhering and extend from the cell surface of the host. This type IV pili apart from attachment also helps the bacteria to crawl over the surfaces. Neisseria gonorrhoeae changes the properties of its surface pili in a process called Pilin Antigenic Variation. It takes place by high frequency gene conversion reactions that transfer silent pilS sequences into expressed pilE locus and needs the formation of an upstream guanine quartet (G4) DNA structure to initiate the process. The bacterium alters the antigenicity of the pilus by directed recombination between partially homologous pilin copies in a process that require Guanine quartet structure.