MIIM - Bacteria Causing Ocular Infections I & II - Week 2 Flashcards
Describe the protective function of the normal microbiota, and describe three mechanisms by which this occurs.
Minimises colonisation by harmful pathogens by:
- preventing adhesion of invading pathogens
- out-competing for nutrients
- producing toxic/inhibitory substances
Define antibiosis.
Preventing competition by producing toxic/inhibitory substances
Name 4 reasons why skin is a generally inhospitable environment for bacteria.
Dry
Acidic
Salty
Protected by lysozyme and antimicrobial compounds from sweat glands
What is the nose layered by, and what structure sweeps it away?
Has a layer of mucus that is swept away by cilia
True or false
Mucus doesnt contain antimicrobial compounds
False, it does contain them
Is the normal ocular microbiota dense or sparse? Why is this so (3)?
Sparse due to innate defences:
- mechanical removal (cilia and blinking)
- IgA in tears stop adhesion
- lactoferrin binds iron needed by bacteria
What metabolic type of bacteria are the ocular microbiota mainly?
They are mainly aerobic
Name 6 factors that the normal ocular microbiota can vary with.
Mode of delivery at birth
Age
Location of the eye
Sleep
Contact lens wear (especially extended wear)
Antibiotic use
How does age affect the ocular microbiota?
In younger individuals, streptococcus pneumoniae In older individuals, mostly gram negatives
What is blepharitis?
Infection of the eyelash follicles along the edge of the eyelid.
Name 9 symptoms of blepharitis.
Burning
Flaking
Crusting
Tearing
Irritation
Itching
Redness
Foreign body sensation
Dandruff-like scales at the base of the eyelash
Consider anterior blepharitis. Name 2 conditions it may be associated. Name a bacteria, or combination of bacteria that can cause it.
Associated with:
Mite infection
Seborrhoeic dermatitis
May caused by:
Staphylococcus aureus, or a mix of S. aureus, S epidermidis, and Proprionibacterium acnes
What 3 things can occur with untreated, severe anterior blepharitis?
Ectropion - eversion of the eyelid edge
Entropion - inversion of the eyelid edge
Trichiasis - inturning eyelashes
Distinguish between anterior and posterior blepharitis.
Anterior - along the eyelashes, on the anterior eyelid
Posterior - along the bottom border of the eyelashes, more posteriorly on the eyelid
Name two conditions associated with posterior blepharitis.
Meibomianitis
Meibonian seborrhoea
Define meinbomianitis.
Inflammation of the meibomian glands, with excess oil production
Define two ways of managing staphylococcal blepharitis.
- Good eyelid hygiene to remove debris (baby shampoo, NaHCO3, artificial tears
- Antibiotic treatment until clinically resolved
What is an external hordeolum?
Also known as a stye, it is an acute, localised swelling of the eyelid, typically due to an obstructed or infected eyelash follicle.
What is an external hordeolum associated with, and in what two ways can it be treated? What is its localisation, and is it painful?
Associated with a staphylococcal infection.
Treated with a hot compress, or drainage.
Is painful and remains localised to the eyelid margin.
Are external hordeolums pyogenic?
Yes
What is an internal hordeolum, and what is it usually caused by?
It is an infection of the meibomian gland, typically by staphyococci
Name two ways to treat an internal hordeolum.
Hot compresses, and oral anti-stphylococcal antibiotics
What intervention is prompted by persistent or recurrent internal hordeolums?
Surgery
What is a chalazion?
It is the inflammation of the meibomian gland, and not an infection.
Which eyelid are chalazions usually on?
Upper
Differentiate between a chalazion (3) and hordeola (2).
Chalazion are painless, subacute, and sits inside the lid, not the margin.
Hordeola are painful and tender
Name three ways a chalazion can be treated. What should one not do to a chalazion?
Warm compresses
Larger ones may beed surgery, or corticosteroid injections
Often disappear without treatment
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?
Gram stain - positive
Round and in clusters in a smear
Are pyogenic, and facultative anaerobes
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?
They can grow on simple media - nutrient agar
They can tolerate bile salts, and appear pink on a MC agar
Is catalase positive
Name the major staphylococcus pathogen. Give an example of an opportunistic pathogen (a staphylococcus). Note whether they care coagulase positive or negative.
Major pathogen - staphylococcus aureus, coagulase positive
Opportunistic - staphylococcus epidermidis, coagulase negative
What colour are staphylococcus aureus colonies, and what is the common name for it?
It is yellow, and is sometimes referred to as golden staph
Name 7 ocular conditions that can be caused by staphylococcus aureus.
Blepharitis
Meibonianitis/stye
Preseptal cellulitis
Conjunctivitis
Keratitis
Endophthalmitis
Sterile corneal ulcer
Name a bacteria that is a major cause of endophthalmitis, especially post-op.
Staphylococcus epidermidis
Staphylococci are responsible for many diseases. How do they cause disease (3)?
They are hardy, can survive drying, and survive well in the environment
In what two ways do staphylococci cause damage?
Production of toxins (haemolysins, enterotoxins, etc)
Production of enzymes (hyaluronidase, lipases, proteases, DNases, etc)
In addition to producing virulence factors, in what two ways do staphylococci achieve pathogenesis?
Inducing acute inflammatory reactions (complement cascade)
Evading phagocyte action (catalase, leucocidin)
What bacteria is the most common cause of infections of indwelling medical devices? Give two reasons why this is so. Are these life-threatening?
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
Name the 5 components of a laboratory diagnosis for bacteria. Explain them, and give an example for each.
- 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
What is a catalase test, and what is the expected outcome in a positive result? What is the significance of this?
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.
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.
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
What is S. epidermidis colonisation mediated by (3)?
By receptors for fibronectin, vitronectin, collagen
Name 3 people more likely to be infected by S. epidermidis.
Healthcare workers
Diabetics
IV drug users
How can superficial staph infections be managed?
Topical antibiotics (polymycin, neomycin, gramicidin, chloramphenicol)
How can deep infections be managed?
Antimicrobial susceptibility is variable, so testing must be carried out first, followed by oral antibiotics.
The site may need surgical drainage.
Is healthcare-associated golden staph very resistant or susceptible to antibiotics?
Resistant to all but a few antimicrobials. Some are sensitive only to vancomycin.
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?
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)
Is preseptal cellulitis a medical emergency?
It is in children. All cases require immediate treatment to prevent spread.
Preseptal cellulitis may cause an orbital abcess. Name a possible condition that can occur secondary to this symptom.
Meningitis
Name 8 predisposing conditions/events that can cause preseptal cellulitis.
Upper respiratory tract infection
Sinus infection
Otitis media
Insect bites
Trauma-related lesions
Skin infections
Ruptured dacryocoele
Herpetic disease
Name 4 bacteria and 4 viruses that can cause preseptal cellulitis.
Bacteria
- Strept. pneumoniae
- Staph. aureus
- Strept. pyogenes
- Peptostreptococcus
Virus
- HSV1
- HSV2
- VZV
- Haemophilus influenzae type b (if unvaccinated)
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.
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.
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?
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)
Differentiate between α- and β-haemolysis.
α-haemolysis will result in a green halo around the bacteria colonies.
β-haemolysis will result in a clear halo around the bacteria colonies.
Name two conditions that can be caused by viridans streptococci. What kind of pathogen is it?
Conjunctivitis and endophthalmitis. It is an opportunistic pathogen.
What does preseptal cellulitis look like?
Name two conditions caused by streptococcus pyogenes.
Preseptal cellulitis and endophthalmitis
Name 5 diseases caused by streptococcus pneumoniae.
Preseptal cellulitis
Conjunctivitis
Acute keratitis
Corneal ulcer
Endophthalmitis
Do strep. pyogenes and pmeumoniae have capsules?
Yes
Are viridans streptococci haemolytic? If so, what kind? What gram stain and shape, and arrangement do they have? Does it have a capsule?
Is a-haemolytic. Gram positive cocci in chains. Unencapsulated.
Are Strept. pyogenes haemolytic, and if so, what kind?
Yes, is B-haemolytic.
Consider endophthalmitis. How is it managed? What about if an open globe injury is suspected?
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.
Name and describe the two vaccines for Strept. pneumoniae.
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.
Why are toxoids sometimes used in vaccines?
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.
