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MB3001 > L15 Gonorrhoea > Flashcards

L15 Gonorrhoea Flashcards

1
Q

What bacterium causes Gonorrhoea and how does it cause it?

A

Neisseria gonorrhoeae, evasion by antigenic variation

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2
Q

There are many species of Neisseria. Name 2 clinically important ones

A

N. gonorrhoeae and N. meningitidis (6 different serotypes)

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3
Q

What is a commensal strain of Neisseria?

A

N. lactamica

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4
Q

What is the main difference between N. meningitidis and N. gonorrhoeae?

A

Lack of a capsule in the gonococcus

whereas disease-causing meningococci in immunocompetent individuals are nearly always encapsulated

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5
Q

What does the capsule allow for?

A

A vaccine

N. gonorrhoeae does not produce a capsule, therefore we cannot be vaccinated against gonorrhoea

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6
Q

Features of N. gonorrhoeae?

A
  • Gram neg
  • (diplo)coccus
  • Requires CO2
  • Does not survive well outside human host
  • LOS (lipo-oligosaccharide) rather than LPS
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7
Q

How is Gonorrhoea spread?

A

Transmitted person to person, a leading cause of STDs

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8
Q

True or False: Many people who are infected with Gonorrhoea are asymptomatic

A

True - 30% of females, 10% of males

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9
Q

What is a result of women frequently being asymptomatic?

A

Under-reporting

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10
Q

Symptoms of Gonorrhoea?

A
  • 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
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11
Q

Where does Gonorrhoea infection initially occur?

A

In the urethra in males and cervix in females

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12
Q

Can gonorrhoea also be transmitted to neonates during birth?

A

Yes - it leads to eye infection & blindness

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13
Q

Why is vaccination against gonorrhoea extremely difficult?

A

Because N. gonorrhoeae changes surface antigens regularly (and no capsule)

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14
Q

Gonorrhoea virulence factors:

A
  • 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
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15
Q

Why are they called Opa proteins?

A

because PII positive strains produce opaque colonies, while PII negative strains produce transparent colonies (phase variation)

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16
Q

How can disseminated gonococcal or meningococcal infections occur?

A

If the bacterium penetrates across the endothelium and spreads through the bloodstream

17
Q

Most obvious surface antigens in gonorrhoea?

A

the pili (type 4 pilus), PI, Opa proteins

18
Q

What makes vaccination difficult and reinfection common?

A

Hypervariability of the surface antigens

this hypervariability is a consequence of several different genetic strategies employed by Neisseria

19
Q

What is the name of the process in phase variation of Opa?

A

Slipped strand synthesis

20
Q

Briefly describe phase variation of Opa

A

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 +

21
Q

Antigenic variation is caused by?

A

Changing which gene is expressed

22
Q

Further variation is possible through?

A

Exchange of homologous fragments (recombination)

23
Q

Opa variation influences __ __ of N. gonorrhoeae.

A

cell tropism

24
Q

Around how many different Opa genes are in the chromosome?

A

11

25
Q

What is the main subunit of the pilus?

A

PilE

26
Q

What is PilC?

A

A minor component essential for pilus synthesis and involved in tropism

27
Q

What is another form of phase variation?

A

Poly G tract

28
Q

What is the first pilus protein produced?

A

PilC - cannot synthesise a pilus without PilC or PilE

29
Q

Phase variation is?

A

PilC - first protein produced

30
Q

Antigenic variation is in?

A

PilE - dominant protein

31
Q

True or False: There are up to 20 copies of the pilin gene, only one is expressed (PilE), 19 others are silent (PilS).

A

True

32
Q

Additional gonorrhoea virulence factors?

A
  • Evasion: can utilise host-derived sialic acid → serum-resistant → evades immune system
  • Strains of N. gonorrhoeae produce 2 distinct extracellular IgA1 proteases, which cleave antibodies
  • N. gonorrhoeae is highly efficient at utilising transferrin-bound iron for in vitro growth (some also utilise lactoferrin-bound iron)
33
Q

Acute stage of gonorrhoea involves?

A

Purulent discharge & inflammation

34
Q

Other Neisseria virulence factors?

A
  • ROS
  • Iron acquisition
  • Capsule (N. m)
  • Peptidoglycan modification

MB3001 (15 decks)

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