M: Bacteria causing ocular infections 2 - Week 2

Question 1

Define periorbital (preseptal) cellulitis

Answer 1

Inflammation and infection of the eyelid and portions of the skinDes around the eye anterior to the orbital septum

Question 2

In what age group is periorbital cellulitis typically found?

Answer 2

Primarily seen in children (typically less than 10 years, mostly under 5 years)

Question 3

Describe the onset of periorbital cellulitis. Does this condition affect one or both eyes?

Answer 3

Acute onset. Is unilateral

Question 4

Why is it important to exclude potential orbital involvement when examining periorbital cellulitis?

Answer 4

Because there is a condition called ‘orbital cellulitis’, which is considered an EMERGENCY

Question 5

Describe orbital cellulitis, where is the infection? and what can this lead to?

Answer 5

Is where the tissues BEHIND the eye are infected, and there can be proptosis (b/c the swelling behind the eye will push the eye forward)

Question 6

What criteria is used to exclude orbital involvement when examining periorbital cellulitis?

Answer 6

To exclude orbital involvement: there should be no disturbance in visual acuity or ocular motility, and no proptosis

Question 7

Why does periorbital cellulitis need to be quickly treated with antimicrobial agents?

Answer 7

Because there is a (rare) possibility that the infection can spread to cause a ‘meningitis’, which is a very serious infection of the brain

Question 8

How seriously should you consider sending a child to the emergency if they come in with a swollen eye?

Answer 8

very seriously. Don’t just send them home with a warm compress, because that could lead to very severe problems for the patientw

Question 9

Name a scenario that can mimic periorbital cellultis, and state a differentiating feature to this scenario

Answer 9

Insect bites. However the eyelid is not as sore

Question 10

What is erysipelas and how might it occur?

Answer 10

is a superficial form of cellulitis resulting from an infection of the skin from streptococcus pyogene

Question 11

Name 5 conditions/events that can predispose to periorbital cellulitis

Answer 11

1. Upper respiratory tract infection (2/3rd of periorbital cellulitis cases)
2. Otitis media (middle ear infection)
3. Insect bites/trauma related lesions (incl. dog bites)
4. Skin infections (e.g. erysipelas)
5. Ruptured dacryocoele (protrusion of the lacrimal sac) in infants

Question 12

What bacteria might be involved in periorbital cellulitis resulting from upper respiratory tract infection or otitis media?

Answer 12

strep. pneumoniae, haemophilus influenzae type b (if unvaccinated), s. aureus

Question 13

What bacteria might be involved in periorbital cellulitis resulting from insect bites/trauma related lesions?

Answer 13

staph. aureus, strep. pyogenes, maybe anaerboic bacteria like peptostreptococcus

Question 14

What bacteria might be involved in periorbital cellulitis resulting from skin infections?

Answer 14

strep. pyogenes, s. aureus

Question 15

What bacteria might be involved in periorbital cellulitis resulting from ruptured dacryocoele?

Answer 15

staph. aureus, strep. pyogenes

Question 16

If you are concerned that a child is severely ill with periorbital cellulitis, what responses can you make to help manage? (3)

Answer 16

1. use IV antimicrobials (treatment)
2. take blood cultures (b/c of the possibility of microoganism spreading and multiplying in the blood)
3. do a CT scan of sinus (to check where the infection actually is)

Question 17

In periorbital cellulitis, what 2 regions is it essential that we prevent the spreading of the microorganism to?

Answer 17

post-septal area (orbital cellulitis) and meninges (meningitis)

Question 18

If the child is otherwise well, what treatment can we provide for the management of periorbital cellulitis?

Answer 18

Oral therapy prescribed by doctor

Question 19

What is meant for an organism to be “pyogenic”? Are streptococci pyogenic?

Answer 19

pus producing. Yes

Question 20

Can herpes simplex virus cause periorbital cellulitis?

Answer 20

yes. HSV 1 and 2. Also VZV as well (whatever that is)

Question 21

How do streptococci look under microscopy? are they gram positive or negative? Describe their structure

Answer 21

They are gram positive cocci found in chains or pairs

(these chains or pairs can be distinctive in terms of diagnosing when looking under the microscope)

Question 22

Do streptococci require oxygen or no oxygen to grow?

Answer 22

They are facultative anaerobes. So either is fine

Question 23

What type of media to streptococci grow on?

Answer 23

They require enriched media for growth (e.g. HBA)

Question 24

What type of colonies do streptococci often produce on HBA?

Answer 24

haemolytic colonies (alpha and beta) (alpha-haemolysis is responsible for “greening”)

Question 25

Colonies of streptococcus bacteria produce haemolysins. What is their role and how do they spread?

Answer 25

They spread out radially from the colonies. They break down the medium and allow us to see straight through the horse blood agar

Question 26

Describe the pattern of haemolysis on blood agar for the following streptococci (useful for differenting)
a) viridans streptococci
b) streptococcus pneumoniae
c) streptococcus pyogenes

Also describe how much the different kinds of haemolysis break down red cells in the medium

Answer 26

a) greening
b) greening
c) beta-haemolytic

the greening ones (viridans and pneumoniae) partially break down red cells in medium of horse blood agar

the beta-haemolytic one (pyogenes) fully breads down red cells

Question 27

Name 2 conditions that can be caused by ocular infection with viridans streptococci

Answer 27

• conjunctivitis
• endophthalmitis

Question 28

Name 2 scenarios in which viridans streptococci can infect the eye and cause endophthalmitis

Answer 28

1. post-surgical: surgery opens up eye allowing microorganism to enter
2. post-injection - microorganisms can inadvertently be placed in eye with contaminated medication

Question 29

How does endophthalmitis present itself?

Answer 29

sterile pus collection inside the eye, that has a meniscus which will move as you move your head

Question 30

what type of pathogen is viridans streptococci?

Answer 30

opportunistic pathogen

Question 31

Explain the pathogenesis of viridans streptococci?

Answer 31

viridans streptococci produce adhesins which allow colonisation, they then bind to fibrin, platelets and fibronectin

Question 32

Name 3 conditions that ocular infection with strep. pyogenes can lead to

Answer 32

1. preseptal cellulitis
2. endophthalmitis
3. conjunctivitis (in less than 5% of cases)

Question 33

List and briefly describe 5 features of streptococcus pyogenes that contribute to its pathogenesis

Answer 33

1. adhesins (M protein, Protein F, LTA)
2. capsule (hyaluronic acid)
3. M protein: blocks complement cascade; inhibits opsonisation
4. causes damage (streptolysin, DNA-ases)
5. produces exotoxins/invasins (streptokinase, proteases, etc.)

Question 34

Name 4 conditions that can result from ocular infection with streptococcus pneumoniae

Answer 34

• preseptal cellulitis
• conjunctivitis
• acute keratitis (most common cause in children) and corneal ulcer
• endophthalmitis

Question 35

List and briefly describe 3 features of streptococcus pneumoniae that contribute to its pathogenesis

Answer 35

1. Capsule (90 serotypes) - adhesion; evasion of innate immune response
2. IgA protease: breaks down IgA in tears and on mucosal surfaces
3. Pneumolysin (toxin) - kills cilia, binds Fc portion of antibodies

Question 36

In laboratory diagnosis of streptococci, list the following items that would be used/found for the following categories:
a) specimen
b) microscopy
c) culture

Answer 36

a) discharge (pus), corneal scraping (as appropriate)
b) gram positive cocci in chains (pyogenes, viridans) or pairs (pneumoniae)
c) culture of pus/scrapings on HBA – lead to small haemolytic colonies

Question 37

How would you confirm the specific bacteria identity when looking at a streptococci (3)

Answer 37

1. bacteria from colonies do not produce catalase
2. beta haemolytic colonies - bacitracin sensitive: Group A Strep (GAS) = strep. pyogenes
3. alpha haemolytic: optochin sensitive = s. pneumoniae while optochin resistant = viridans streps

Question 38

Between the following, which is optochin resistant and which is optochin sensitive:

Viridans streptococci vs Streptococcus pneumoniae

Answer 38

Optochin resistant = Viridans

Optochin sensitive = Pneumoniae

Question 39

Is Streptococcus pyogenes bacitracin resistant or sensitive?

Answer 39

bacitracin sensitive

Question 40

How would you manage a superficial streptococci infection?

Answer 40

Topical antimicrobials e.g. polymyxin/neomycin, chloramphenicol

Question 41

How would you manage a deep streptococci infection?

Answer 41

Perform antimicrobial susceptibility test to determine optimum treatment, then:

Penicilin: pyogenes is always sensitive to this and viridans are usually highly sensitive, however pneumoniae is developing resistance

Question 42

How would you manage endophthalmitis?

Answer 42

intra-vitreal antibiotics and immediate advice from an ophthalmologist (treatment guided initially by gram stain of clinical material).

Do not use topical antibiotics if an open globe injury is suspected because preservatives are toxic to the intracellular contents