M: Bacteria causing ocular infections 5 - Week 3 Flashcards
1
Q
What sexuality and age group is more likely to have contracted an STI, and by how much?
A
Men who have sex wiht men (aged 20-39) are 5 times more likely to have contracted an STI
2
Q
What microorganism causes Syphilis?
A
spirochaete Treponema Pallidum
3
Q
Who is Mr Syph and Mrs Illis?
A
Mr Syph is Davud Akgun. Mrs Illis is Nguyen Ho
:D
4
Q
If untreated, what are the 3 stages of Syphilis?
A
Stage 1/Primary: painless chancre (fluid-filled ulcer) at inoculation site – lasts 3-4 weeks
Stage 2/Secondary: skin rash, other organ involvement (after 6-12 weeks)
Stage 3/Tertiary: cardiovascular involvement and neurosyphilis
5
Q
In what stage of syphilis do ocular complications first occur? What proportion of syphilis sufferers get ocular complications? Which ocular complication is most common in this case?
A
Secondary Stage. less than 10%. Most commonly uveitis (iritis) = inflammation inside the eye
6
Q
How can a definitive diagnosis of syphilis be made?
A
only through laboratory testing (serology)
7
Q
What ocular symptoms can syphilis present with? (in those who get them) (4)
A
- redness
- pain
- light sensitivity
- loss of vision
8
Q
What proportion of people who have ocular symptoms of syphilis DON’T have any other symptoms?
A
25%. Therefore, these people won’t even know they have syphilis
9
Q
What drug is used for the treatment of syphilis
A
Penicillin (b/c no resistance) (however reinfection can occur)
10
Q
Name 2 ocular infections that affect the cornea
A
- keratitis
- keratoconjunctivitis
11
Q
Name 3 ocular infections that affect the intraorbital area
A
- orbital cellulitis
- endophthalmitis
- uveitis
12
Q
Define keratitis
A
inflammation of the cornea (may or may not be associated with infection)
13
Q
What’s the difference between non-infectious and infectious keratitis?
A
non-infectious: from a relatively minor injury; wearing CLs too long; or other diseases
infectious: is a SIGHT-THREATENING emergency (urgent referral = essential) caused by bacteria, viruses, parasites, fungi
14
Q
List the symptoms of keratitis (5)
A
- red eye
- discomfort
- photophobia
- blurred or decreased vision
- may rapidly progress
15
Q
List 3 symptoms from a more serious infection of keratitis
A
- pain
- vision loss
- pus
16
Q
If left untreated, what can severe keratitis lead to? (3)
A
- perforation of the cornea
- endophthalmitis
- eye loss
17
Q
List 4 risk factors for keratitis
A
- CL wear: too long, poor disinfection, wearing while swimming
- Reduced immunity, including use of topical steroids
- Warm climate, esp. if plant material gets in eyes
- Previous eye injury or recent corneal disease
18
Q
Name 5 bacteria that cause keratitis
A
- staph. aureus
- strep. pneumoniae
- pseudomonas aeruginosa
- enterobacteriae
- moraxella
19
Q
How might fungi cause keratitis?
A
via contamination of CL solution
20
Q
Provide an example of a parasitic cause of keratitis. How serious is this?
A
Acanthamoeba. Very serious
21
Q
Provide 2 examples of a viral cause of keratitis
A
HSV and VSV
22
Q
Describe the following features of Pseudomonas: A: Gram stain B: Response to oxygen env C: Growth requirements D: Type of pathogen
A
A: Gram negative rods, moderately large
B: Aerobic (but can adapt to low oxygen levels)
C: Minimal growth requirements (grows in moist environments)
D: Opportunistic pathogen
23
Q
How many pigments does pseudomonas produce? What are they?
A
- Pyocyanin and Fluorescein
24
Q
What is pseudomonas resistant to?
A
Resistant to many disinfectants and antimicrobials
25
How common is pseudomonas in the environment?
Common. It is considered a "water bug"
26
Which psuedomonas microorganism is an ocular pathogen?
pseudomonas aeruginosa
27
Which bacteria is the most common bacterium in CL-assoc. keratitis?
pseudomonas aeruginosa (60-70%)
28
What 2 conditions is pseudomonas aeruginosa known for causing?
1. CL assoc. keratitis
| 2. exogenous endophthalmitis (following penetrating eye injury)
29
How would you describe the outcome of a Pseudomonas eye infection?
Very poor.
30
What features of Pseudomonas contribute to its pathogenesis? (7)
1. adhesion structures (both fimbrial and non-fimbrial)
2. nutritionally resourceful
3. opportunistic pathogen
4. induces inflammatory response (ocular damage due to inflammatory cytokines)
5. produces exotoxins (necrotic central corneal ulceration)
6. pyocyanin = a toxin (targets many pathways).
7. has cytotoxic and invasive strains
31
Where do pseudomonas come from?
Environment, as exogenous infections:
- survives on any moist surface e.g. soil, plants, water, biofilm on CL, CL cases, in pipes, showerheads, sinks
- is very difficult to eradicate
32
```
For the laboratory diagnosis of pseudomonas, describe the following:
A: Specimen
B: Microscopy
C: Culture
D: Confirmation
```
A: conjunctival swab, corneal scraping
B: Gram negative rods (and many inflammatory cells)
C: On basal media (NA) produces large colonies with blue-green water soluble pigment; characteristic odour (ammonia)
D: i. selected biochemical tests (oxidase positive)
ii. pigment production (pyocyanin and fluorescein)
33
How do you manage pseudomonas? (4)
- often difficult to treat ocular pseudomonas infections
- is resistant to many antibiotics: perform antimicrobial susceptibility test
- usually susceptible to quinolones
- more serious infections treated with combination of tobramycin and ticarcillin (synergism)
34
How do you prevent psueomonas infection? (3) (CLs)
- Prevent CL assoc infection by: compliance to wearing and cleaning instructions
- note: that home-made cleaning salines are a source of contamination, therefore CL cleanse with approved, sterile, commercial solutions
- CL storage must also be sterile
35
Define orbital cellulitis. What distinguishes it from periorbital cellulitis?
infection of the soft tissues behind the orbital septum (can affect the eyelid, eyebrow and cheek)
Unlike periorbital cellulitis, it infects the eye socket as well as the skin closest to it
36
What happens if orbital cellulitis infection spreads through thin bones?
There's a possibility that periorbital cellulitis spreads through thin bones (especially from abscesses), along optic nerve or via blood to the brain.
-- this leads to MENINGITIS
37
What symptoms can we see in orbital cellulitis?
- proptosis of eye
- pain
- fever
- difficulty moving the eye
- infection
38
What is orbital cellulitis usually caused by? List some other causes (3 others)
Usually caused by infection of the sinuses (more than 90%)
Also by: insect bites, injuries or dental infections
39
Is orbital cellulitis a medical emergency? When would surgery be required?
Yes. Urgent IV antimicrobial therapy and hospitalization is needed.
Surgery is needed in case of abscesses
40
Name the 4 common bacterial causes of orbital cellulitis
- strep pneumoniae (sinus infection)
- haemophilus influenzae type b (less due to vaccine)
- staph aureus
- strep pyogenes (trauma)
41
What ocular infection presents with sterile pus (hypopyon) in the anterior chamber?
Endophthalmitis
42
Define Endophthalmitis
inflammation of the interior of the eye (inside the globe)
43
What typically causes endophthalmitis?
infection from eye surgery or trauma
44
When is endophthalmitis considered a medical emergency?
always. Endophthalmitis is potentially devastating and not many patients maintain good visual acuity; may require enucleation of blind eye
45
List 5 symptoms of endophthalmitis
- progressive vision loss
- light sensitivity (photophobia)
- eye pain
- red/pink eye
- floaters
46
What are the sources of endophthalmitis infection? Where? Describe the proportion of incidence for these situtations
May be exogenous: direct inoculation due to surgery (60%), FBs and or blunt/penetrating ocular traumas (4-13%)
May be endogenous: haematogenous spread from a distant source e..g endocarditis (is rare)
47
How do you manage endophthalmitis? (2)
- medical emergency
- intravitreal injection of antibiotics. If no response, repeated injections may be necessary
- systemic antimicrobials used in cases of endogenous endophthalmitis and exogenous fungal endophthalmitis
48
How is the outcome of prompt and appropriate treatment of endophthalmitis?
Many eyes treated will recover useful vision (depends on severity, microbe, level of inflammation and scarring)
(severe cases: might lose sight or eye)
49
List 10 causitive microorganisms for endophthalmitis (note: this is not an exhaustive list)
- staph aureus (endogenous - endocarditis)
- staph epidermidis (most common cause of post cataract surgery endophthalmitis)
- viridans streptococci
- bacillus cereus (major cause of post traumatic endophthalmitis)
- clostridium sp
- cutibacterium sp
- pseudomonas aeruginosa
- enterobacteriaceae
- mycobacteria
- fungi
50
Which 2 microorganisms are associated with post intra-vitreal anti-VEGF injection?
- staph epidermidis
| - viridans (oral) streptococci
51
```
Describe the following features of Bacillus:
A: Gram stain and shape
B: response to oxgyen environment
C: Where they are found
D: Do they produce spores
E: How easily can we culture in lab
```
```
A: Gram positive rods
B: aerobic or facultative anaerobic
C: found in soil and dust (environmental organisms)
D: Yes they do produce spores
E: Easily
```
52
What type of pathogen is bacillus cereus?
Opportunistic pathogen
53
What types of endophthalmitis can bacillus cereus cause? How?
1. Exogenous endophthalmitis: directly during trauma
| 2. Endogenous endophthalmitis: inoculation by IV drug uses i.e. contaminated drugs/equipment -- blood -- eye
54
```
Describe the following features of Clostridia:
A: Gram stain and shape
B: response to oxygen environment
C: Where they are found in environment
D: Do they produce spores
E: How do we culture them in lab
```
A: Gram positive rods
B: Obligately anaerobic
C: soil and dust; and in gut of warm blooded animals including humans
D: Yes they produce spores
E: Culture under strict anaerobic conditions
55
What can clostridia infection cause?
keratitis or exogenous endophthalmitis (via trauma, or rarely, post corneal transplant)
56
Name 3 species of clostridia
1. tetani
2. botulinum
3. perfringens
Note: these are all toxins
57
```
Describe the following features of Family Enterobacteriacae:
A: Gram stain and shape
B: response to oxygen environment
C: How easy to culture them in lab
D: How many genera
```
A: Gram negative rods, relatively large
B: Facultative anaerobes
C: Easily cultured
D: More than 20 genera (incl. proteus, serratia, klebsiella, escherichia)
58
What type of pathogens are the enterobacteriacae serratia, proteus, E. coli and klebsiella? How do they infect?
Opportunistic pathogens, in:
- CL assoc. infections
- penetrating eye injuries (trauma)
59
Where do enterobacteriacae come from?
People and the environment, as endogenous and exogenous infections
- proteus, klebsiella and escherichia = found both in the env and as normal microbiota
- serratia sp. = common environmental organisms (assoc. with water)
60
How do we manage enterobacteriacae? (2)
- Can be very resistant to antimicrobials, therefore antimicrobial susceptibility testing essential
- appropriate CL use
61
Describe the following features of mycobacteria:
A: Gram stain
B: response to oxygen environment
C: speed of growth
A: "Acid fast" large rods (not seen on gram stain)
- cell wall has high lipid content; rendering the organism acid fast; also restricts entry of disinfectants and many antimicrobial agents
B: Aerobic
C: Generally slow growing (weeks) -- because restricted entry for nutrients through waxy cell wall
62
What are the 2 major pathogens of mycobacteria and what do they cause?
1. M. tuberculosis = tuberculosis
2. M. leprae = leprosy
- these 2 may infect the eye as part of a systemic infection
63
What do infections with M. chelonae and M. fortuitum cause?
may infect the cornea (keratitis) with trauma, or cause endophthalmitis post cataract or refractive surgery (environmental)
Also rare cause of scleritis
64
How do we manage mycobacteria infection?
- antimicrobial susceptibility testing
| - surgery for px's who don't respond to tx
65
Are fungi eukaryotic or prokaryotic? Describe their cell wall too
Eukaryotic. Rigid cell wall (chitin)
66
What is present in the cell membrane of fungi?
ergosterol
67
How do fungi propagate?
vegetatively or by (fungal) spores (specifically for conidia fungi)
68
How are fungi divided/classified?
Yeasts (unicellular) and moulds (filamentous)
| -- some are dimorphic (have both unicellular and filamentous forms)
69
How do fungi gain energy?
They are "saprophytic" - gain energy from the breakdown of dead organic matter
70
Do fungi commonly infect intact eyes? (i.e. intact surface epithelium)
No. Rarely. They are opportunistic and infect if trauma
71
How common are fungal ocular infections?
Rare - keratitis is the most common manifestation
72
Describe the onset of fungal ocular infections. What does this lead to?
Onset usually insidious. Leads to discomfort, photophobia, sometimes discharge, infiltrate -- later leads to stomach ulceration and corneal perforation
73
What type of fungal infection does a corneal injury via tree branches and vegetative material expose you to?
infection with filamentous fungi
74
What's another name for an ocular fungal infection?
Ocular Myoses
75
Can CL wear predispose to ocular myoses?/ocular fungal infection?
Yes. But rare compared to bacterial infections
76
What species of fungi are also involved with intraocular infections/fungal endophthalmitis?
- Candida species (especially C. albicans)
77
Name the 4 most common ocular fungal pathogens
1. Candida (yeast), especially candida albicans
2. Fusarium (filamentous)
3. Aspergillus (filamentous)
4. Scedosporium (filamentous)
78
What type of pathogens are fungi?
Opportunistic pathogens
79
Name 6 features of fungi that contribute to their pathogenesis
1. opportunistic pathogens
2. compromised immunosuppresed cornea susceptible to fungal infection
3. both yeasts and moulds produce adhesins
4. Candida produce (psuedo)hyphae; may be associated with invasion
5. Possible role of fungal toxins
6. Inflammation, and both cellular and humoral responses contribute to tissue damage
80
Where do fungi come from?
Endogenous or Exogenous
- People (candida) and environment (Fusarium, Aspergillus, Scedosporium)
- - Candida albicans found in around 50% of healthy people in most mucous membranes
- - trauma an important precipitating event
- - fungi can spread from the blood after fungaemia
81
```
In the laboratory diagnosis of fungi, describe the following:
A: Specimen
B: Microscopy
C: Culture
D: Identification
```
A: swab of discharge, corneal scraping
B: Direct examination of pus/corneal scrapings shows yeasts and/or hyphae or fungal spores
C: on HBA for yeasts, or appropriate fungal isolation medium (e.g. Sabouraud's Agar (SAB))
D: Microscopy of conidia produced by moulds in culture
82
How do we manage fungal infection?
- anti-fungal chemotherapy targeted principally at cell membrane
- difficult to achieve selective toxicity (ergosterol in fungi vs cholesterol in humans)
- often need long course; side effects are common
83
Name 3 examples of fungal management drugs:
1. Polyenes (e.g. nystatin) - bind fungal ergosterol altering membrane permeability
2. Azoles (e..g ketoconazole) - inhibit ergosterol synthesis
3. Fluorinated pyrimidines (e.g. 5-fluorocytosine) - fluorouracil in fungi; inhibit fungal thymidine synthesis
