L15 Gonorrhoea Flashcards
(34 cards)
What bacterium causes Gonorrhoea and how does it cause it?
Neisseria gonorrhoeae, evasion by antigenic variation
There are many species of Neisseria. Name 2 clinically important ones
N. gonorrhoeae and N. meningitidis (6 different serotypes)
What is a commensal strain of Neisseria?
N. lactamica
What is the main difference between N. meningitidis and N. gonorrhoeae?
Lack of a capsule in the gonococcus
whereas disease-causing meningococci in immunocompetent individuals are nearly always encapsulated
What does the capsule allow for?
A vaccine
N. gonorrhoeae does not produce a capsule, therefore we cannot be vaccinated against gonorrhoea
Features of N. gonorrhoeae?
- Gram neg
- (diplo)coccus
- Requires CO2
- Does not survive well outside human host
- LOS (lipo-oligosaccharide) rather than LPS
How is Gonorrhoea spread?
Transmitted person to person, a leading cause of STDs
True or False: Many people who are infected with Gonorrhoea are asymptomatic
True - 30% of females, 10% of males
What is a result of women frequently being asymptomatic?
Under-reporting
Symptoms of Gonorrhoea?
- Localised inflammatory response with a characteristic purulent discharge (esp. in males)
- Can lead to scarring of Fallopian tubes → infertility or ectopic pregnancy
- Can colonise columnar epithelial cells of cervix & urethra, & mucosal surfaces of throat & rectum
Where does Gonorrhoea infection initially occur?
In the urethra in males and cervix in females
Can gonorrhoea also be transmitted to neonates during birth?
Yes - it leads to eye infection & blindness
Why is vaccination against gonorrhoea extremely difficult?
Because N. gonorrhoeae changes surface antigens regularly (and no capsule)
Gonorrhoea virulence factors:
- Adherence/invasion: colonises columnar epithelial cells (mucosal surface), can be taken up by PMNs
- Attachment: initially involves pili (type 4 pilus only), second stage involves a tighter attachment mediated by Opa/PII
- PI, membrane porin: allows diffusion of low MW compounds through the vacuolar membrane, prevents phagosomal maturation
Why are they called Opa proteins?
because PII positive strains produce opaque colonies, while PII negative strains produce transparent colonies (phase variation)
How can disseminated gonococcal or meningococcal infections occur?
If the bacterium penetrates across the endothelium and spreads through the bloodstream
Most obvious surface antigens in gonorrhoea?
the pili (type 4 pilus), PI, Opa proteins
What makes vaccination difficult and reinfection common?
Hypervariability of the surface antigens
this hypervariability is a consequence of several different genetic strategies employed by Neisseria
What is the name of the process in phase variation of Opa?
Slipped strand synthesis
Briefly describe phase variation of Opa
Phase variation depends on whether the stop codons are in or out of frame.
Stop codons out of frame - protein is made
Phase variation = on/off - gene is either expressed and protein is produced, or it’s not expressed and therefore, protein is not produced.
No. of repeats → stop codon in frame → Opa -
No. of repeats → stop codon not in frame → Opa +
Antigenic variation is caused by?
Changing which gene is expressed
Further variation is possible through?
Exchange of homologous fragments (recombination)
Opa variation influences __ __ of N. gonorrhoeae.
cell tropism
Around how many different Opa genes are in the chromosome?
11
