M: Bacteria causing ocular infections 2 - Week 2 Flashcards
Define periorbital (preseptal) cellulitis
Inflammation and infection of the eyelid and portions of the skinDes around the eye anterior to the orbital septum
In what age group is periorbital cellulitis typically found?
Primarily seen in children (typically less than 10 years, mostly under 5 years)
Describe the onset of periorbital cellulitis. Does this condition affect one or both eyes?
Acute onset. Is unilateral
Why is it important to exclude potential orbital involvement when examining periorbital cellulitis?
Because there is a condition called ‘orbital cellulitis’, which is considered an EMERGENCY
Describe orbital cellulitis, where is the infection? and what can this lead to?
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)
What criteria is used to exclude orbital involvement when examining periorbital cellulitis?
To exclude orbital involvement: there should be no disturbance in visual acuity or ocular motility, and no proptosis
Why does periorbital cellulitis need to be quickly treated with antimicrobial agents?
Because there is a (rare) possibility that the infection can spread to cause a ‘meningitis’, which is a very serious infection of the brain
How seriously should you consider sending a child to the emergency if they come in with a swollen eye?
very seriously. Don’t just send them home with a warm compress, because that could lead to very severe problems for the patientw
Name a scenario that can mimic periorbital cellultis, and state a differentiating feature to this scenario
Insect bites. However the eyelid is not as sore
What is erysipelas and how might it occur?
is a superficial form of cellulitis resulting from an infection of the skin from streptococcus pyogene
Name 5 conditions/events that can predispose to periorbital cellulitis
- Upper respiratory tract infection (2/3rd of periorbital cellulitis cases)
- Otitis media (middle ear infection)
- Insect bites/trauma related lesions (incl. dog bites)
- Skin infections (e.g. erysipelas)
- Ruptured dacryocoele (protrusion of the lacrimal sac) in infants
What bacteria might be involved in periorbital cellulitis resulting from upper respiratory tract infection or otitis media?
strep. pneumoniae, haemophilus influenzae type b (if unvaccinated), s. aureus
What bacteria might be involved in periorbital cellulitis resulting from insect bites/trauma related lesions?
staph. aureus, strep. pyogenes, maybe anaerboic bacteria like peptostreptococcus
What bacteria might be involved in periorbital cellulitis resulting from skin infections?
strep. pyogenes, s. aureus
What bacteria might be involved in periorbital cellulitis resulting from ruptured dacryocoele?
staph. aureus, strep. pyogenes
If you are concerned that a child is severely ill with periorbital cellulitis, what responses can you make to help manage? (3)
- use IV antimicrobials (treatment)
- take blood cultures (b/c of the possibility of microoganism spreading and multiplying in the blood)
- do a CT scan of sinus (to check where the infection actually is)
In periorbital cellulitis, what 2 regions is it essential that we prevent the spreading of the microorganism to?
post-septal area (orbital cellulitis) and meninges (meningitis)
If the child is otherwise well, what treatment can we provide for the management of periorbital cellulitis?
Oral therapy prescribed by doctor
What is meant for an organism to be “pyogenic”? Are streptococci pyogenic?
pus producing. Yes
Can herpes simplex virus cause periorbital cellulitis?
yes. HSV 1 and 2. Also VZV as well (whatever that is)
How do streptococci look under microscopy? are they gram positive or negative? Describe their structure
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
Do streptococci require oxygen or no oxygen to grow?
They are facultative anaerobes. So either is fine
What type of media to streptococci grow on?
They require enriched media for growth (e.g. HBA)
What type of colonies do streptococci often produce on HBA?
haemolytic colonies (alpha and beta) (alpha-haemolysis is responsible for “greening”)
Colonies of streptococcus bacteria produce haemolysins. What is their role and how do they spread?
They spread out radially from the colonies. They break down the medium and allow us to see straight through the horse blood agar
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
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
Name 2 conditions that can be caused by ocular infection with viridans streptococci
- conjunctivitis
- endophthalmitis
Name 2 scenarios in which viridans streptococci can infect the eye and cause endophthalmitis
- post-surgical: surgery opens up eye allowing microorganism to enter
- post-injection - microorganisms can inadvertently be placed in eye with contaminated medication
How does endophthalmitis present itself?
sterile pus collection inside the eye, that has a meniscus which will move as you move your head
what type of pathogen is viridans streptococci?
opportunistic pathogen
Explain the pathogenesis of viridans streptococci?
viridans streptococci produce adhesins which allow colonisation, they then bind to fibrin, platelets and fibronectin
Name 3 conditions that ocular infection with strep. pyogenes can lead to
- preseptal cellulitis
- endophthalmitis
- conjunctivitis (in less than 5% of cases)
List and briefly describe 5 features of streptococcus pyogenes that contribute to its pathogenesis
- adhesins (M protein, Protein F, LTA)
- capsule (hyaluronic acid)
- M protein: blocks complement cascade; inhibits opsonisation
- causes damage (streptolysin, DNA-ases)
- produces exotoxins/invasins (streptokinase, proteases, etc.)
Name 4 conditions that can result from ocular infection with streptococcus pneumoniae
- preseptal cellulitis
- conjunctivitis
- acute keratitis (most common cause in children) and corneal ulcer
- endophthalmitis
List and briefly describe 3 features of streptococcus pneumoniae that contribute to its pathogenesis
- Capsule (90 serotypes) - adhesion; evasion of innate immune response
- IgA protease: breaks down IgA in tears and on mucosal surfaces
- Pneumolysin (toxin) - kills cilia, binds Fc portion of antibodies
In laboratory diagnosis of streptococci, list the following items that would be used/found for the following categories:
a) specimen
b) microscopy
c) culture
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
How would you confirm the specific bacteria identity when looking at a streptococci (3)
- bacteria from colonies do not produce catalase
- beta haemolytic colonies - bacitracin sensitive: Group A Strep (GAS) = strep. pyogenes
- alpha haemolytic: optochin sensitive = s. pneumoniae while optochin resistant = viridans streps
Between the following, which is optochin resistant and which is optochin sensitive:
Viridans streptococci vs Streptococcus pneumoniae
Optochin resistant = Viridans
Optochin sensitive = Pneumoniae
Is Streptococcus pyogenes bacitracin resistant or sensitive?
bacitracin sensitive
How would you manage a superficial streptococci infection?
Topical antimicrobials e.g. polymyxin/neomycin, chloramphenicol
How would you manage a deep streptococci infection?
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
How would you manage endophthalmitis?
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
