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OD2 (S1&2) > MIIM - Bacteria Causing Ocular Infections I & II - Week 2 > Flashcards

MIIM - Bacteria Causing Ocular Infections I & II - Week 2 Flashcards

1
Q

Describe the protective function of the normal microbiota, and describe three mechanisms by which this occurs.

A

Minimises colonisation by harmful pathogens by:

  • preventing adhesion of invading pathogens
  • out-competing for nutrients
  • producing toxic/inhibitory substances
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2
Q

Define antibiosis.

A

Preventing competition by producing toxic/inhibitory substances

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3
Q

Name 4 reasons why skin is a generally inhospitable environment for bacteria.

A

Dry

Acidic

Salty

Protected by lysozyme and antimicrobial compounds from sweat glands

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4
Q

What is the nose layered by, and what structure sweeps it away?

A

Has a layer of mucus that is swept away by cilia

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5
Q

True or false

Mucus doesnt contain antimicrobial compounds

A

False, it does contain them

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6
Q

Is the normal ocular microbiota dense or sparse? Why is this so (3)?

A

Sparse due to innate defences:

  • mechanical removal (cilia and blinking)
  • IgA in tears stop adhesion
  • lactoferrin binds iron needed by bacteria
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7
Q

What metabolic type of bacteria are the ocular microbiota mainly?

A

They are mainly aerobic

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8
Q

Name 6 factors that the normal ocular microbiota can vary with.

A

Mode of delivery at birth

Age

Location of the eye

Sleep

Contact lens wear (especially extended wear)

Antibiotic use

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9
Q

How does age affect the ocular microbiota?

A

In younger individuals, streptococcus pneumoniae In older individuals, mostly gram negatives

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10
Q

What is blepharitis?

A

Infection of the eyelash follicles along the edge of the eyelid.

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11
Q

Name 9 symptoms of blepharitis.

A

Burning

Flaking

Crusting

Tearing

Irritation

Itching

Redness

Foreign body sensation

Dandruff-like scales at the base of the eyelash

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12
Q

Consider anterior blepharitis. Name 2 conditions it may be associated. Name a bacteria, or combination of bacteria that can cause it.

A

Associated with:

Mite infection

Seborrhoeic dermatitis

May caused by:

Staphylococcus aureus, or a mix of S. aureus, S epidermidis, and Proprionibacterium acnes

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13
Q

What 3 things can occur with untreated, severe anterior blepharitis?

A

Ectropion - eversion of the eyelid edge

Entropion - inversion of the eyelid edge

Trichiasis - inturning eyelashes

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14
Q

Distinguish between anterior and posterior blepharitis.

A

Anterior - along the eyelashes, on the anterior eyelid

Posterior - along the bottom border of the eyelashes, more posteriorly on the eyelid

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15
Q

Name two conditions associated with posterior blepharitis.

A

Meibomianitis

Meibonian seborrhoea

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16
Q

Define meinbomianitis.

A

Inflammation of the meibomian glands, with excess oil production

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17
Q

Define two ways of managing staphylococcal blepharitis.

A
  • Good eyelid hygiene to remove debris (baby shampoo, NaHCO3, artificial tears
  • Antibiotic treatment until clinically resolved
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18
Q

What is an external hordeolum?

A

Also known as a stye, it is an acute, localised swelling of the eyelid, typically due to an obstructed or infected eyelash follicle.

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19
Q

What is an external hordeolum associated with, and in what two ways can it be treated? What is its localisation, and is it painful?

A

Associated with a staphylococcal infection.

Treated with a hot compress, or drainage.

Is painful and remains localised to the eyelid margin.

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20
Q

Are external hordeolums pyogenic?

A

Yes

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21
Q

What is an internal hordeolum, and what is it usually caused by?

A

It is an infection of the meibomian gland, typically by staphyococci

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22
Q

Name two ways to treat an internal hordeolum.

A

Hot compresses, and oral anti-stphylococcal antibiotics

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23
Q

What intervention is prompted by persistent or recurrent internal hordeolums?

A

Surgery

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24
Q

What is a chalazion?

A

It is the inflammation of the meibomian gland, and not an infection.

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25
Q

Which eyelid are chalazions usually on?

A

Upper

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26
Q

Differentiate between a chalazion (3) and hordeola (2).

A

Chalazion are painless, subacute, and sits inside the lid, not the margin.

Hordeola are painful and tender

27
Q

Name three ways a chalazion can be treated. What should one not do to a chalazion?

A

Warm compresses

Larger ones may beed surgery, or corticosteroid injections

Often disappear without treatment

28
Q

What colour do staphylococci have on a gram stain? What shape and arrangement do they have on a smear? Are they pyogenic bacteria? What metabolic type are they?

A

Gram stain - positive

Round and in clusters in a smear

Are pyogenic, and facultative anaerobes

29
Q

On what media do staphylococci bacteria grow?

Can they tolerate bile salts, and what colour do they appear on a McConkey agar plate?

Are they catalase positive or negative?

A

They can grow on simple media - nutrient agar

They can tolerate bile salts, and appear pink on a MC agar

Is catalase positive

30
Q

Name the major staphylococcus pathogen. Give an example of an opportunistic pathogen (a staphylococcus). Note whether they care coagulase positive or negative.

A

Major pathogen - staphylococcus aureus, coagulase positive

Opportunistic - staphylococcus epidermidis, coagulase negative

31
Q

What colour are staphylococcus aureus colonies, and what is the common name for it?

A

It is yellow, and is sometimes referred to as golden staph

32
Q

Name 7 ocular conditions that can be caused by staphylococcus aureus.

A

Blepharitis

Meibonianitis/stye

Preseptal cellulitis

Conjunctivitis

Keratitis

Endophthalmitis

Sterile corneal ulcer

33
Q

Name a bacteria that is a major cause of endophthalmitis, especially post-op.

A

Staphylococcus epidermidis

34
Q

Staphylococci are responsible for many diseases. How do they cause disease (3)?

A

They are hardy, can survive drying, and survive well in the environment

35
Q

In what two ways do staphylococci cause damage?

A

Production of toxins (haemolysins, enterotoxins, etc)

Production of enzymes (hyaluronidase, lipases, proteases, DNases, etc)

36
Q

In addition to producing virulence factors, in what two ways do staphylococci achieve pathogenesis?

A

Inducing acute inflammatory reactions (complement cascade)

Evading phagocyte action (catalase, leucocidin)

37
Q

What bacteria is the most common cause of infections of indwelling medical devices? Give two reasons why this is so. Are these life-threatening?

A

Staphylococcus epidermidis, due to:

  • permanent and prevalent coloniser of skin of patients, providing a source of infection
  • colonising factors of skin help with device colonisation

These are rarely life-threatening, but difficult and expensive to treat

38
Q

Name the 5 components of a laboratory diagnosis for bacteria. Explain them, and give an example for each.

A
  • Specimen: discharge (like pus), corneal scraping
  • Microscopy: Gram stain, shape, arrangement, evidence of pus cells (indicating infection)
  • Culture: the culture it grows on, such as nutrient or horse blood agar
  • Identification: Gram stain of a suspicious colony, followed by catalase and coagulase tests (or MALDI-TOF)
  • Antimicrobial susceptibility: strain typing
39
Q

What is a catalase test, and what is the expected outcome in a positive result? What is the significance of this?

A

It assays for the ability of an organism to produce catalase. A positive result would therefore result in the production of O2 and H20 when added to H2O2. This enables the organism to evade some of the killing pathways of phagocytes.

40
Q

What is a catalase test, and what is the expected outcome in a positive result? Give an example of a coagulase positive and negative bacteria.

A

It assays whether an organism produces the enzyme coagulase, responsible for degrading fibrinogen into insoluble fibrin. Blood plasma containing fibrinogen added to coagulase positive bacteria will result in the formation of aggregates.

Coagulase positive - S. aureus

Coagulase negative - S epidermidis

41
Q

What is S. epidermidis colonisation mediated by (3)?

A

By receptors for fibronectin, vitronectin, collagen

42
Q

Name 3 people more likely to be infected by S. epidermidis.

A

Healthcare workers

Diabetics

IV drug users

43
Q

How can superficial staph infections be managed?

A

Topical antibiotics (polymycin, neomycin, gramicidin, chloramphenicol)

44
Q

How can deep infections be managed?

A

Antimicrobial susceptibility is variable, so testing must be carried out first, followed by oral antibiotics.

The site may need surgical drainage.

45
Q

Is healthcare-associated golden staph very resistant or susceptible to antibiotics?

A

Resistant to all but a few antimicrobials. Some are sensitive only to vancomycin.

46
Q

Is preseptal cellulitis typically chronic or acute? Does it occur uni- or bilaterally? Is pain felt? Does it cause VA or ocular motility changes? Is it associated with swelling or proptosis (or both)? Can it spread?

A

Chronic

Unilateral

Pain and mild fever

Periocular swelling (unable to open eye)

No VA or ocular motility changes

No proptosis

Rarely spreads (but still can)

47
Q

Is preseptal cellulitis a medical emergency?

A

It is in children. All cases require immediate treatment to prevent spread.

48
Q

Preseptal cellulitis may cause an orbital abcess. Name a possible condition that can occur secondary to this symptom.

A

Meningitis

49
Q

Name 8 predisposing conditions/events that can cause preseptal cellulitis.

A

Upper respiratory tract infection

Sinus infection

Otitis media

Insect bites

Trauma-related lesions

Skin infections

Ruptured dacryocoele

Herpetic disease

50
Q

Name 4 bacteria and 4 viruses that can cause preseptal cellulitis.

A

Bacteria

  • Strept. pneumoniae
  • Staph. aureus
  • Strept. pyogenes
  • Peptostreptococcus

Virus

  • HSV1
  • HSV2
  • VZV
  • Haemophilus influenzae type b (if unvaccinated)
51
Q

Are topical antibiotics adequate for preseptal cellulitis? Describe the management of this condition, including what is treated, and what is aimed to be prevented. What therapy can be given, in both cases where the patient is severely ill, or otherwise healthy.

A

Topical antibiotics are inadequate.

Management involves preventing spread elsewhere, causing meningitis.

The predisposing condition must be treated.

Oral therapy is prescribed by a doctor if the patient is well.

IV antimicrobials may be used if severely ill.

52
Q

Describe the gram stain of streptococci, their arrangement, thair metabolic state, media requirement, and whether they are haemolytic (mention how this can be known). Are they pyogenic?

A

Are gram positive cocci in chains or pairs.

Pyogenic

Facultative anaerobes

Requires enriched media (HBA)

Are haemolytic, can be seen as a clear halo around colonies when grown on HBA (due to haemolysis)

53
Q

Differentiate between α- and β-haemolysis.

A

α-haemolysis will result in a green halo around the bacteria colonies.

β-haemolysis will result in a clear halo around the bacteria colonies.

54
Q

Name two conditions that can be caused by viridans streptococci. What kind of pathogen is it?

A

Conjunctivitis and endophthalmitis. It is an opportunistic pathogen.

55
Q

What does preseptal cellulitis look like?

A
56
Q

Name two conditions caused by streptococcus pyogenes.

A

Preseptal cellulitis and endophthalmitis

57
Q

Name 5 diseases caused by streptococcus pneumoniae.

A

Preseptal cellulitis

Conjunctivitis

Acute keratitis

Corneal ulcer

Endophthalmitis

58
Q

Do strep. pyogenes and pmeumoniae have capsules?

A

Yes

59
Q

Are viridans streptococci haemolytic? If so, what kind? What gram stain and shape, and arrangement do they have? Does it have a capsule?

A

Is a-haemolytic. Gram positive cocci in chains. Unencapsulated.

60
Q

Are Strept. pyogenes haemolytic, and if so, what kind?

A

Yes, is B-haemolytic.

61
Q

Consider endophthalmitis. How is it managed? What about if an open globe injury is suspected?

A

It is managed with intra-vitreal antibiotics and immediate advice from an ophthalmologist.

If an open globe injury is suspected, topical antibiotics shouldnt be used because preservatives are toxic to intraocular contents.

62
Q

Name and describe the two vaccines for Strept. pneumoniae.

A

Polysaccharide vaccine - has 23 antigens found in the most common serious infections in adults. Poor efficacy in children, limited efficacy in older age groups.

Conjugate paediatric caccines - contains 13 of the most common antigens associated with childhood pneumococcal injections, and is conjugated to tetanus toxoid.

63
Q

Why are toxoids sometimes used in vaccines?

A

They are proteins which are bound to capsules (polysaccharides) in vaccines to allow greater activation of T cells (which in turn activate B cells, which make antibodies). There is a poor response to capsules alone.

64
Q
A

OD2 (S1&2) (174 decks)

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