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OD2 S1 > M: Bacteria causing ocular infections 4 - Week 3 > Flashcards

M: Bacteria causing ocular infections 4 - Week 3 Flashcards

1
Q

What gram stain and structure is Moraxella?

A

Gram negative diplococci

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2
Q

Moraxella is similar to neisseria. At what level do the two bacteria become distinct?

A

at the DNA level

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3
Q

How does moraxella present on the oxidase and catalase test?

A

Both positive

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4
Q

How does moraxella respond to an oxygen environment?

A

strict aerobe (only grows in air)

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5
Q

Name the 2 major pathogens for moraxella, and state what they can cause

A
  1. moraxella lacunata - ay cause epidemics; may lead to chronic muco-purulent conjucntvitis, keratitis
  2. moraxella catarrhalis - normal ocular microbiota but also causes acute conjunctivitis and opportunistic infections
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6
Q

What type of opportunistic infections can moraxella catarrhalis be responsible for? (2)

A
  • endophthalmitis
  • CL assoc infections
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7
Q

Describe 2 features of moraxella that contribute to its ability to cause disease?

A
  1. the fimbriae can mediate attachment
  2. LPS is present in the gram negative cell wall and induces inflammation
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8
Q

Describe how the lipid portion of LPS. What is it and when is it released, and what does this cause (2)?

A

is an endotoxin. Is released when the bacterial cells dies, and it causes a generic septic or toxic schock

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9
Q

Where is moraxella typically found? (6)

A

As normal respiratory and ocular flora: in the oropharynx, mucous membrane, skin and genital tract

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10
Q

On what media do moraxella grow (2)?

A

Growth on both Horse Blood Agar and Chocolate Agar

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11
Q

Describe the following features of nesseria:
- Microscopy appearance and gram stain
- response to oxygen environment
- growth on media (culture)

A

Gram negative diplococci that is aerobic and fastidious

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12
Q

Name the 2 neisseria pathogens and the condition they each cause

A
  1. Neisseria meningitidis: cause meningococcal disease
  2. Neisseria gonorrhoeae: cause gonorrhoeae (STI)
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13
Q

What is ophthalmia neonatorum and what causes it?

A

It is a mucopurulent conjunctivitis in infants born to mothers infected with either nesseria gonorhoeae or chlamydia trachomatis serovars D-K

(mucopurulent = containing mucus or pus)

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14
Q

How can you prevent Neisseria infection? Name 2 methods/drugs

A
  1. Silver nitrate drops at birth: to prevent gonococcal eye infection (however can result in chemical conjunctivitis)
  2. Erythromycin ophthalmic ointment:
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15
Q

Which drug used for prevention of neisseria infection causes less chemical conjunctivitis?

A

Erythroymycin ointment

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16
Q

Which drug used for prevention of neisseria infection is more effective as a prophylaxis for penicillinase-producing neisseria gonorrheoea?

A

Silver Nitrate

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17
Q

Name 6 features of neisseria gonorrhoeae that contribute to its pathogenesis

A
  1. can penetrate corneal epithelium without pre-existing defect
  2. fimbriae mediate attachment
  3. variation in fimbrial proteins counteracts immune response (can change proteins expressed)
  4. outer membrane proteins mediate invasion
  5. cell wall components, especially Lipo-oligosaccharide, cause inflammation
  6. IgA protease
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18
Q

Where do Neisseria come from?

A

People, endogenously or exogenously
- N. gonorrhoeae = spread from contacts with gonorrhoea (sexual or poor hygeine)

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19
Q

In what community is neisseria an ongiong problem?

A

indigenous communities, particularly in central and northern australia

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20
Q

Does Neisseria survive well outside the body?

A

No

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21
Q

How do we transport Neisseria specimens for laboratory diagnosis?

A

After specimen is obtained, it is put into a transport medium that keeps the organism alive until it reaches the laboratory (transport quickly) and placed onto a medium where it can grow

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22
Q

On what type of media does Neisseria grow?

A

Neisseria is fastidious, so it needs enriched medium (e.g. chocolate agar) to grow

(i.e. will NOT grow on horse-blood agar/hba)

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23
Q

In the laboratory diagnosis of Neisseria, describe the following:
- specimen
- microscopy and Gram stain
- culture

A

Specimen: conjunctival swab or corneal scraping transported quickly to lab in transport medium
Microscopy and Gram Stain: numerous pus cells (neutrophils), small intra- and extracellular Gram -ve diploccoci
Culture: small colourless colonies after 24-48 hours on enriched media (chocolate agar)

24
Q

In the laboratory diagnosis of Neisseria, list the 3 ways we confirm identity of Neisseria

A

i. Oxidase positive
ii. selected biochemical tests
iii. immunofluorescence with specific anti-sera

25
Q

How do we manage Neisseria?(3)

A
  • antimicrobial susceptibility testing = essential
  • empirical (“best guess”) treatment: depends on source of infection
  • treatment of associated STI = essential (for neonatal conjunctivitis test and treat mother)
26
Q

List 5 factors involved in the prevention of Neisseria infection

A
  • Health education
  • Effective diagnosis and treatment
  • Contact tracing and treatment (of STI)
  • Barrier contraception
  • Vaccine containing fimbrial and other antigens (transferrin-binding proteins) – however this is a failed clinical trial, so research is still ongoing
27
Q

What is the most common STI? and what bacteria is involved? Is it always diagnosed?

A

Chlamydia (caused by chlamydia trachomatis). It can go undiagnosed.

28
Q

Describe the following features of chlamydia:
A: life cycle
B: how they exist extracellularly
C: how they exist intracellularly

A
  • unique dimorphic life cycle
  • exist extracellularly as infectious, hardy elementary bodies (EBs) (0.2 microns)
  • exist intracellularly as metabolically active replicating reticulate body (RB) (0.8 microns)
29
Q

What type of environment does chlamydia trachomatis prefer? intracellular or extracellular?

A

They are obliqate intracellular bacterium (“energy parasite”) – they require the ATP from the host cell to grow

30
Q

Describe the following features of chlamydia trachomatis:
- size
- cell wall

A
  • very small (0.2-0.8 microns)
  • no cell wall. Outer LPS membrane lacking peptidoglycan, therefore can’t see on gram stain
31
Q

Describe the life cycle of chlamidia in detail in terms of entry, mulplication and spread (6)

A
  1. EB attach by adhesins to columnar epithelial cells then enter into mucosal columnar epithelium by receptor mediated endocytosis (RME)
  2. EB incorporates into endosome
  3. EB-containing endosomes fuse to form inclusions
  4. EB transforms into metabolically active RB - these RBs multiply
  5. RB mature back into infectious EB (or persist in cell)
  6. Release of EB to infect other cells
32
Q

Which serovars of chlamydia trachomatis are responsible for causing trachoma?

A

Serovars A, B and C

33
Q

Which condition are serovars D-K of chlamydia trachomatis responsible for causing?

A

Inclusion conjunctvitis (and urethritis/cervicitis)

34
Q

What does chlamydia psittaci cause?

A

cause of psittacosis, which may be associated with a follicular conjunvtivitis

35
Q

What is psittacosis?

A

a contageous disease in birds. Can be transmissable to humans as a form of pneumonia

36
Q

Which disease is the most common preventable cause of blindness worldwide?

A

trachoma

37
Q

Where is trachoma most common?

A

hot, dry, dusty climates where water is scarce and sanitation is poor

38
Q

How does C.trachomitis infection lead to trachoma (describe progression)?

A

if left untreated (repeated infections):
eyelid scarring –> trichiasis and entropion –> conjunctival scarring –> trachoma

39
Q

Describe Follicular Conjunctivitis

A

is a condition where you can see follicles underneat the eyelids

40
Q

How can conjunctival infection cause lymphoid follicles and finlammatory infiltration?

A

Occurs when you get repeated infections of conjunctiva

41
Q

How does trachoma affect:
- goblet cells
- lacrimal gland
- tear duct

A

Destruction of all of them

42
Q

Describe the life cycle of trachoma in 7 steps

A
  1. Infecting the eye: flies carrying the microorganism land on child’s eye, to feed on discharge
  2. Family contact: women who take care of the children also get infection
  3. Spreading out: flies that breed in human faeces spread the disease to others
  4. Dirty hands and face cloths also spread the disease
  5. The infections inflame and thicken the upper eyelid
  6. Scarred eyelids turn inwards
  7. The lashes scratch the cornea, leading to blindness
43
Q

Define Trichiasis

A

A common eyelid abnormality in which the eyelashes are misdirected and grow inwards towards the eye (and rub against cornea)

44
Q

Define Entropion

A

is the turning in of an edge of an eyelid, causing the lashes to rub against the eye (usually seen on lower eyelid)

45
Q

What proportion of acute conjunctivitis cases in adults are inclusion conjunctivitis?

A

2%

46
Q

What does inclusion conjunctivitis lead to if left untreated?

A

persistant follicular conjunctivitis

47
Q

What do most cases of adult inclusion conjunctivitis result from?

A

exposure to infected genital secretions

(and occasionally spread by water in pools, contaminated hot tubs, or by sharing makeup)

48
Q

When does neonatal inclusion conjunctivitis usually present?

A

5-19 days after birth (earlier if premature rupture of membranes and long exposure to genital organisms)

49
Q

What symptoms does neonatal inclusion conjunctivitis cause? (4)

A
  • swelling of lids
  • hyperaemia
  • conjunctival infiltration
  • discharge
50
Q

Describe the pathogenesis of chlamydiae? (6)

A
  • produce adhesins allowing colonisation of columnar epithelium
  • sequester in vacoules in infected host cells (invade immune response)
  • intracellular RB not susceptible to antibodies
  • T-cell response not effective
  • cross reactions between self and chlaymdial HSPs induces autoimmune disease
  • Reinfection or ongiong infection triggers chronic inflammatory processes
51
Q

How young are children typically infected with trachoma in endemic communities?

A

most children infected by 2 years

52
Q

In the laboratory diagnosis of chlamydiae, describe the following:
A: Specimen
B: Microscopy and gram stain
C: Detection methods for antigen
D: Detection methods for nucleic acid

A

A: conjunctival discharge, corneal scraping (transport quickly in special medium)
B: lymphocyte, macrophages, monocytes are not seen; chlamydia not seen
C: Direct immunofluorescence, and Enzyme Immunoassay (EIA)
D: PC3 for C. trachomatis

53
Q

How does antigen detection of chlamydiae via direct immunofluorescence work?

A

fix infected cells to a slide then permeabilize with acetone. Add an antibody to chlamydiae that’s been conjugated with a fluorescent dye - and allow it to interact
– if there’s any antigen in those cells, the antibody will attach
– we then do a washing step to wash away anything not bound, then we look under the microscope
– wherever we see fluorescence is where chlamydiae antigen was

54
Q

How do we manage chlamydiae infection?

A
  • RB form is the chemotherapuetically susceptible form; EB is not susceptible to antibodies
  • need long term treatment (due to life cycle)
  • personal hygiene important to avoid spread
  • contact racing for STIs important
55
Q

Name 3 drugs that could facilitate long term treatment of chlamydiae

A
  1. multi-dose tetracycline
  2. multi-dose erythromycin
  3. single dose azithromycin (long acting)
56
Q

Which country is the only developed country with endemic trachoma? Where in the country is this?

A

Australia. In indigenous communities

OD2 S1 (47 decks)

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