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OD2 S1 > M: Bacteria causing ocular infections 1 - Week 2 (lec 5) > Flashcards

M: Bacteria causing ocular infections 1 - Week 2 (lec 5) Flashcards

1
Q

Describe the presence of microbiota in the mucosa? How much microbiota is there? Does it vary? Provide an example.

A

Mucosa can have anywhere from no microbiota to large amounts, depending on where

e..g large amounts of microbiota found in the mucosa in the mouth

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2
Q

Name 6 factors that can influence the composition of normal microbiota

A
  1. climate/geography
  2. age
  3. shared living: family, institutions, aged care
  4. personal hygeine
  5. diet
  6. medical tx/interventions/hospitalisation
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3
Q

How does normal microbiota function to minimise colonisation by potential pathogens? (3 ways)

A

by:
1. preventing adhesion
2. out-competing for nutrients
3. producing toxic/inhibitory substances (antibiosis)

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4
Q

Name the 3 types of microbiota? (note: these are just generic terms obviously, it’s in terms of their danger level I guess)

A
  1. harmless organisms
  2. opportunistic pathogens
  3. pathogens
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5
Q

What is the most common microbiota that you’ll find on the skin?

A

Staphyloccocus Epidermidis (85-100%)

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6
Q

Even though some microbiota still live there, why is the skin considered to be inhospitable for microbiota generally?

A

Because it is dry, acidic and salty
- and protected by lysozyme and antimicrobial compounds from sweat glands

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7
Q

How is the mucus in our nose beneficial?

A
  • it traps foreign particles (and bacteria)
  • it contains antimicrobial compunds such as lysozyme, lactoferrin, immunoglobulins and defensins
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8
Q

What is used to sweep away the mucus in the nose?

A

Cilia

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9
Q

What are the 2 most common microbial inhabitants in the nose?

A
  • Staphyloccocus epidermidis (90%)
  • Staphylococcus aureus (20-85%)
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10
Q

Describe the effect that blinking has on bacteria

A

Blinking is a sheer force across the eye that pushes against any bacteria on the eye surface. If the bacteria are not firmly adhered, they will be washed away by the blink

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11
Q

Name 6 ways that the normal microbiota of the eye can vary

A

varies with:
- mode of delivery at birth (regular vs c-section)
- age (strep. pneu = young, gram -ve = old)
- location
- sleep (action of neutrophils overnight)
- contact lens wear
- antibiotic use

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12
Q

Why is there less microbiota in the eye? List the 3 reasons for this

A
  1. mechanical removal (via cilia, blinking)
  2. IgA in tears stops adhesion
  3. lactoferrin binds iron needed by bacteria
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13
Q

is the eye a mainly aerobic or anaerobic site?

A

aerobic

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14
Q

Name 4 areas of the eye (that can be subject to ocular infection)

A
  1. eyelids and tissues surrounding the eye
  2. conjunctiva
  3. cornea
  4. intraocular area
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15
Q

Name 3 infections that affect the eyelids and tissue surrounding the eye

A
  1. Blepharitis
  2. Hordeolum (stye)
  3. Chalazion (meibomian cyst)
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16
Q

What is Blepharitis?

A

infection of the eyelash follicles along the edges of the eyelid

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17
Q

List 4-9 symptoms of blepharitis

A

burning, flaking, crusting, tearing, irritation, itching, redness in the eyelid margins, foreign body sensation, scales similar to dandruff at base of eyelashes

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18
Q

Is blepharitis associated with age? Also, is it bilateral, unilateral or both?

A

Blepharitis is common in all age groups. Can be either bilateral or unilateral

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19
Q

Name 2-3 causes for anterior blepharitis?

A
  1. mite infection or seborrhoeic dermatitis (dandruff)
  2. Staphylococcus aureus or a mixed infection of S.aureus and staphylococcus epidermidis and propionibacterium acnes
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20
Q

What could be the potential outcome if blepharitis goes without treatment?

A

If severe, possible long term effects incl. ectropion (eyelid edge eversion), entropion (inversion), and trichiasis (abnormally positioned eyelashes)

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21
Q

What could cause posterior blepharitis? (2)

A
  • meibomianitis: excess production of oil by the gland
  • meibomian seborrhoea (dandruff like situation)
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22
Q

How can you manage blepharitis?

A
  • good eyelid hygeine (to remove debris)
  • antibiotic oitment can also be used
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23
Q

How can dilute sodium bicarbonate be useful in the management of blepharitis?

A

Used to wash the crusted material at the base of the eyelashes

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24
Q

Is blepharitis always cured with treatment?

A

The condition might never be cured. But we can keep it under control

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25
Q

Describe the gram stain of staphylococci: positive or negative? appearance?

A

Gram positive cocci, typically in clusters

26
Q

Staphylococci is considered ‘pyogenic’ bacteria, what does pyogenic mean?

A

pus producting (pyo = pus, genic = producing)

27
Q

What type of oxygen situation is required for staphylococci to grow?

A

They are facultative anaerobes, so they can grow both aerobically and anaerobically

28
Q

What type of media do Staphylococci grow on?

A

Can grow on simple media and can also grow on MacConkey agar (as creamy pink colonies on this agar)

29
Q

What is unique about MacConkey agar?

A

Contains bile salts, this agar is used to select for organisms that can survive in the gut
- so anything that can tolerate the bile salts will survive in the gut

30
Q

True or False: staphylococci may produce pigmented colonies

A

True

31
Q

What is catalase? is staphyloccic catalase positive or negative?

A

Catalase positive.

  • is an enzyme that allows the organism to break down hydrogen peroxide (H2O2), this helps the organism be more resistant to death by phagocyte.
32
Q

Are staphyloccocus coagulase positive or negative?

A

The major pathogen staph. aureus is coagulase positive. The rest are coagulase negative (e.g. s. epidermidis, an opportunistic pathogen)

33
Q

When put on agar, what determines if an organism will turn pink, yellow or colourless?

A

Lactose. If an organism uses lactose (lactose fermentis), then they produce an acid = bright pink in colour

If an organism doesn’t use lactose, then they’ll have an alkaline bi-product as they grow = yellow or colourless colonies

34
Q

How fast do staph. aureus and epidermidis grow on basic media?

A

rapidly

35
Q

Name 4-7 conditions that can be caused by infection with staph. aureus?

A
  1. preseptal cellulitis
  2. meiomianitis/stye
  3. blepharitis
  4. conjunctivitis
  5. keratitis
  6. endophthalmitis
  7. ‘sterile’ corneal ulcer (aka CNPU)
36
Q

Which disease is staph. epidermidis a major cause of? Can this microbe cause anything else?

A

Endopthalmitis. Can also cause similar diseases to S. aureus but far less frequently

37
Q

What features of staphylococci help it to cause disease? (pathogenesis) (2)

A
  1. hardy, survive drying, survive well in environment
  2. produce adhesins allowing colonisation
38
Q

Staphylococcus aureus induces acute inflammatory reactions. What does these consist of? and what can this often lead to?

A

consists of: complement cascade triggered by cell wall components
- often leads to abscess formation (aided by coagulase production)

39
Q

Name 3 things that help staphylococcus aureus evade phagoyctic action (like enzymes, compounds etc.)

A
  1. catalase - breaks down H2O2
  2. leucocidin - produces agents that kill WBCs
  3. protein A - binds Ig
40
Q

Describe the interaction between the IgG antibody and staphyloccous epidermidis

A

IgG antibody recognises something on surface of staph. epi. - antibody binds, - Fc portion will bind to Fc receptor on the phagocyte
- the staph. epi will then be phatocytosed

41
Q

Define Epitopes

A

the part of an antigen molecule to which an antibody attaches itself.

42
Q

How does protein A help prevent phagocytosis of staph. aureus?

A

When the IgG antibody becomes unable to bind using it’s Fc portion to the corresponding Fc receptor of the phagocyte, because the Fc portion is bound to protein A instead.

43
Q

What toxins are produced by staph. aureus?

A

haemolysins, exfoliative toxin, etc.

44
Q

When investigating Staphylococci in the laboratory, what would you use for the following:
1. Specimen
2. Culture

A
  1. discharge, corneal scraping
  2. culture of pus/scraping on Nutrient Agar (NA) or Horse Blood Agar (HBA) – expecting growth of small pigmented colonies on agar medium
45
Q

How would you identify staphylococci in the laboratory?

A

gram stain of “suspicious colony” followed by catalase test and caogulase test

Also, when required: antimicrobial susceptibility test; strain typing

46
Q

What is the catalase test?

A

this test assays for the ability of an organism to produce catalase, which is detected by the breakdown of H2O2

Catalase + organism added to H2O2 results in O2 gas and H2O (this enables the organism to evade some of the killing pathways of phagocytes). So if catalase is present, you’ll get bubbling trapped underneath cover slip

47
Q

What is the role of coagulase?

A

is an enzyme which degrades fibrinogen into insoluble fibrin

48
Q

What is the coagulase test?

A

tests for presence of coagulase. When plasma (containing fibrinogen) is added to emulsified S. aureus, the organism become trapped in the resultant fibrin clot, and aggregate

i.e. if coagulase is present, you’ll get this clumpy appearance (if not, you just get a blob)

49
Q

Where do staphylococci come from?

A

both exogenous and endogenous infections

50
Q

Describe the colonisation rates for endogenous s. aureus and s. epidermidis

A

s. aureus (around 30%)
s. epidermidis (60-70%)

51
Q

What helps colonisation for endogenous s. epidermidis?

A
  • colonisation mediated by receptor for fibronectin, vitronectin, collagen, etc.
  • some people are more susceptible to colonisation (health care workers, diabetics, I.V drug uses)
52
Q

How can we manage superficial staphylococci infections?

A

Topical antimicrobials (e.g. polymyxin/neomycin/gramicidin, chloramphenicol)

53
Q

How can we manage deep staphyloccoci infections?

A

Antimicrobial susceptibility is variable so antimicrobial susceptibility testing must be carried out (usually beta-lactam (penicillin) resistant)

The site of infection may need surgical drainage or debridement (good lid hygeine in blepharitis - difficult to eradicate)

54
Q

Describe the resistance of staph. aureus to antimicrobials

A

Around 30% of health care associated staph. aureus is resistant to all but a few antimicrobials (MRSA), e.g. sensitive to only vancomycin

55
Q

What is the most effective prevention method for staphylococci infection?

A

Strict adherence to good aseptic technique to reduce the spread of commensal bacteria, and prevent the transfer of transiently acquired organisms

56
Q

What is External Hordeolum (stye)?

A

An acute localised swelling of the eylid - typically due to obstruction or infection of eyelash folicle

  • is painful and localised to an eyelid margin. Is also pyogenic. And is associated with staphylococcal infection usually.
57
Q

How can you treat external hordeolum?

A

hot compress; sometimes drainage

58
Q

What is internal hordeolum?

A

infection of meibomian gland, usually caused by staphylococci

59
Q

How do you treat internal hordeolum?

A

warm compresses and oral anti-staphylococcal antibiotics such as flucloxacillin/cephalexin - particularly if there is cellulitis

60
Q

What is Chalazion?

A

inflammation of a blocked meibomian gland (not infection)
- usually on the upper eyelid and are usually painless

61
Q

How do you treat Chalazion?

A

warm compresses (to soften the hardened oil) - don’t squeese or “pop”; often disappear without trx; may need corticosteroid injection or surgical removal for larger ones

OD2 S1 (47 decks)

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