M: Bacteria causing ocular infections 3 - Week 3 Flashcards
What is the main virulence mechanism for strep. pneumoniae?
its polysaccharide capsule
Name and explain the 2 vaccines available for strep. pneumoniae (i.e. what do the vaccines contain)
- polysaccharide vaccine: contains 23 capsular polysaccharide antigens most commonly found in serious infection in adults
- Conjugate paediatric vaccines: contain the 7 or 13 most common capsular antigens assoc. with childhood pneumococcal infection
Describe the efficacy of the polysaccharide vaccine in adults vs children for strep. pneumoniae
adults: limited efficacy
children: poor efficacy (b/c the b cells haven’t matured yet)
What age group are typically given polysaccharide vaccine for strep. pneumoniae? How often?
people over 65 years who are at risk for their age group. Generally given every 5 years (b/c long term memory is not developed)
Where do streptococci come from?
People. Both endogenous and exogenous
What age group most commonly have S. pneumonia as part of their normal conjunctival flora?
children under 5yrs (around 13%)
What proportion of our population carry viridans strep in the oropharynx?
100%. All of us
What proportion of our population carry viridans strep in the conjuctiva/eyelids
2% of us
Name 6 typical microbes that can be involved with preseptal cellulitis
- staph aureus
- strep pneumoniae
- strep pyogenes
- haemophilus influenza type b (if unvacc)
- peptostreptococcus
- HSV 1 and 2, VSV
Describe the following features of Haemophilus:
- Gram stain and shape
- Growth requirements relating to O2
- Growth requirements in general
Haemophilus:
- gram negative, pleomorphic cocco-bacillus
- aerobe and capnophilic (CO2 loving)
- “fastidious” (requires enriched medium like chocolate agar to grow. Doesn’t grow on horse blood agar)
Which type of Haemophilus influenzae is the most pathological/most likely to cause problems?
Type B. Fortunately we vaccinate against it
What can infection with Haemophilus influenzae lead to? (4)
- preseptal cellulitis following lower respiratory tract infection and/or otitis media, acute conjuctivitis
What type of haemophilus influenzae is always a pathogen out of the following? Capsular or un-encapsulated
capsular
Where is un-encapsulated haemophilus found as part of normal flora?
nasaopharynx
T/F: un-encapsulated haemophilus influenzae can someimes cause acute conjunctivitis?
True
What is Haemophilus influenzae biovar aegypticus
is a primary pathogen causing acute conjunctivitis
- some strains cause a virulent purpuric conjunctivitis and sepsis (brazillian purpuric fever, BPF)
Where does haemophilus come from?
People. Endogenous and Exogenous
Where does haemophilus influenzae typically colonize. Does this result in symptoms?
colonises upper respiratory tract. (usually asymptomatic)
How can haemophilus be spread?
person to person by:
- direct contact (to the conjunctiva)
- or through respiratory droplets (cough and sneeze)
How does haemophilus spread through the body in infection?
spreads through the tissues, lead to cellulitis
Describe 4 features of Haemophilus that contribute to its pathogenesis (How does haemophilus cause disease)?
- primary pathogens have polysacch. capsule: hides PAMPs from immune recognition
- fimbrial adhesions: allow attachment to conjunctival and corneal surfaces
- lipo-oligosaccharide (LOS) in cell wall: activates inflammatory response and aids immune evasion (mimics “self”)
- produces and IgA protease
Describe the laboratory diagnosis of Haemophilus.
Specimen:
Microscopy:
Culture:
Specimen: discharge (swab)
Microscopy: Gram negative pleomorphic rods (cocci-bacillus)
Culture: culture of pus on enriched media (choc agar, incubated in air and CO2) lead to tiny colourless colonies
Describe the laboratory diagnosis of Haemophilus
Confirmation:
Confirmation: organisms have specific requirements for “X” (haemin) and “V” (NAD) growth factors
– haemophilus needs BOTH for it to grow
(these growth factors can be found in lysed blood agar e.g. chocolate agar)
How do you manage Haemophilus?
- haemophilus may require resistance to commonly used antimicrobials (such as penicilin G and chloramphenicol): need to TEST ANTIMICROBIAL SUSCEPTIBILITY to ensure targeted therapy
- for orbital cellulitis use IV antimicrobials: 3rd generation cephalosporins (e.g.cefotaxime)
How do you prevent Haemophilus?
Vaccination with Hib vaccine (however infection with types other than type b still occur)
Define Dacryocystitis
Infection of the lacrimal sac/duct, usually associated with obstruction, leading to a stasis of lacrimal sac contents
List the symptoms for dacryocystitis
- excess tears
- pain
- redness
- swelling
What can an acute dacryocystitis infection lead to?
abscess formation requiring drainage
How common and severe is congenital dacryocystitis?
rare but potentially serious