Ocular pathogens

1. Dr. Munir Hussain

2.  The eye is sterile in utero and only acquires
normal flora during birth.
 The normal flora of eye consists of;
 Bacteria
 Staphylococcus. epidermidis (40–45%)
 Corynebacterim. diphtheriae ( 25–40%)
 Staphylococcus. aureus (25%)

3.  Streptococcus viridans and streptococcus
pneumoniae (2–3%).
 Propioni-bacterium acnes.
 Viruses: No virus forms flora of the eye.
 Protozoa: Demodex follicularum
 It is a type of mite.
 Common in old age (˃ 70 years)
 Not in children
 Found on eye lashes

4.  Ocular pathogens:
A. Gram positive cocci:
1. Staphylococcus aureus
2. Staphylococcus epidermidis
3. Streptococcus pneumoniae
4. Streptococcus pyogenes

5. B. Gram positive bacilli
1. Propionibacterium acnes
2. Actinomyces israelli (Branching)
3. Nocardia (Branching) (Corneal abscess and
endophthalmitis)
4. Corynebacterium diphtheriae ( Non branching)

6. C. Gram negative Cocci
1. Neisseria. gonorrhoeae
2. Neisseria meningitidis
D. Gram negative bacilli
1. Haemophilus influenzae
2. Moraxella catarrhalis
3. Pseudomonas aeruginosa
4. Proteus species (esp. Proteus mirabilis)

7. 5. Escherichia coli
6. Klebsiella species
E. Others
1. Chlamydia
2. Rickettsiae
F. Viruses
1. DNA viruses
a. Herpes (simplex and zoster)
b. Varicella
c. Cytomegalo virus
d. Adeno virus

8. 2. RNA viruses
a. Measles
b. Mumps
c. Rubella
G. Fungi
a. Candida
b. Aspergillus

10.  Two medically important genera of gram-positive
cocci.
1. Staphylococcus
2. Streptococcus
 They are distinguished by two main criteria.
 Microscopically, staphylococci appear in grapelike
clusters, whereas streptococci are in chains.
 Biochemically, staphylococci produce catalase
while streptococci do not.

12.  Three main organisms
1. Staph.aureus
2. Staph.saprophyticus
3. Stap.epidermidis

13.  PROPERTIES:
 All staphylococci including s. aureus are spherical
gram-positive cocci arranged in irregular grapelike
clusters.
 Catalase positive
 Coagulase positive

14. NEUTROPHIL

15. COAGULUM

16.  S. aureus produces golden color colonies on manitol salt
agar.
 S. aureus ferments mannitol and hemolyzes red blood
cells.
 More than 90% are resistant to beta lactam antibiotics.
 Some are resistant to beta-lactamase-resistant penicillins,
such as methicillin, Oxacillin, Amoxiclav and nafcillin.
 These are called methicillin-resistant S. aureus (MRSA)
or nafcillin-resistant S. aureus (NRSA).

19.  S. aureus has several important cell wall
components and antigens.
1.Protein A is an important virulence factor.
 It prevents the activation of complement.
2. Teichoic acids. They mediate adherence of the
staphylococci to mucosa.
3.Polysaccharide capsule is also an important
virulence factor (12 serotypes)
4.The peptidoglycan of S. aureus has endotoxin-like
properties.

20.  TRANSMISSION:
 Humans are reservoir.
 The nose is the main site of colonization of S.
aureus.
 The skin, especially of hospital personnel and
patients, is also a common site of S. aureus
colonization.
 Hand contact is an important mode of transmission
and hand washing decreases transmission.

21.  S. aureus is found in the vagina of approximately
5% of women, which predisposes them to toxic
shock syndrome.
 Diabetes and intravenous drug use predispose to
infections by S. aureus.

22.  PATHOGENESIS:
 S. aureus causes disease both by producing toxins
and by inducing pyogenic inflammation.
 Produces several toxins and enzymes.
 Toxins:
1.Enterotoxin
2.Exfoliatin
3.Toxic shock syndrome toxin (TSST)
4. Leukocidins

23. 1.ENTEROTOXIN:
 Causes food poisoning
2.EXFOLIATIN:
 It causes "scalded skin" syndrome in young children.
3.TOXIC SHOCK SYNDROME TOXIN (TSST):
 Causes toxic shock, especially in women or in
individuals with wound infections.


24.  Enzymes:
 The enzymes include
1. Coagulase,
2. Hyaluronidase
3. Staphylokinase
4. Proteases, nucleases, lipases

25.  CLINICAL FINDINGS:
The important clinical manifestations can be
divided into two groups:
1. Pyogenic
2.Toxin-mediated
1.Pyogenic Diseases:
a. Skin infections. These include impetigo,
cellulitis, folliculitis, and postpartum breast
infections (mastitis).

26. b. Septicemia (sepsis) from any localized lesion.
c. Endocarditis (on normal or prosthetic heart valves) in
intravenous drug users.
d. Osteomyelitis and arthritis
e. Eye infections:
i. Hordeolum (stye):
 A stye is a localized infection or inflammation
of the eyelid margin.
 It can be external hordeolum involving hair
follicles of the eyelashes or internal hordeolum
involving meibomian glands .

27.  It is the cause in 90-95% cases.

28. ii. Acute and chronic
conjunctivitis.
 It is of milder intensity
than that caused by
gram negative bacteria
ii. Keratitis and
occasional ulceration

29. iv. Post-operative endophthalmitis
 Endophthalmitis is inflammation of the interior of
the eye.
 It is a possible complication of all intraocular
surgeries, particularly cataract surgery, with
possible loss of vision and the eye itself.

31. 2. Toxin-Mediated Diseases:
a. Food poisoning
b. Toxic shock syndrome
c. Scalded skin syndrome
a. Food poisoning (gastroenteritis) is caused by
ingestion of preformed enterotoxin.
 There is vomiting and watery, non bloody diarrhea.

32. b. Toxic shock syndrome:
 Fever; hypotension; a
diffuse, sunburn-like rash
and involvement of three
or more of the following
organs:
 Liver, kidney, GIT, CNS,
muscle, or blood.

33. c. Scalded-skin syndrome:
 Fever, large blisters, and an erythematous rash.
 Hair and nails can be lost.
 Recovery usually occurs within 7–10 days.

35.  LABORATORY DIAGNOSIS:
1. Smears from staphylococcal lesions reveal gram-
positive cocci in grape like clusters.
2. Cultures of S. aureus yield golden-yellow/Large,
beta hemolytic colonies on blood agar.
3. S. aureus is coagulase and catalase-positive.
4. Ferments Mannitol

38.  TREATMENT:
1. Amoxiclav as 90% of staphylococci produce
beta lactamases.
2. 20% are MRSA and treated by Vancomycin
 PREVENTION:
 No vaccine
 Improving personal hygiene helps in
prevention.

39.  Staphylococcus epidermidis & saprophyticus:
 Properties:
 Catalase positive
 Coagulase negative
 Both form white colonies on culture.
 Do not ferment manitol
 S. epidermidis forms normal flora of skin.
 Diseases:
1. S. epidermidis infections are almost always
hospital-acquired.

40.  S. epidermidis can enter the blood at the site of
intravenous catheters.
2. It commonly infects prosthetic implants.
3. It is also a major cause of sepsis in neonates.
4. S. saprophyticus infections are almost always
community-acquired.
5. S. saprophyticus is found on mucosa of the
genital tract in young women and from that site
can cause urinary tract infections.

41. 6. S. epidermidis can cause blepharoconjunctivitis.
7. It can also cause keratitis.

42.  LABORATORY DIAGNOSIS:
1. Smears from staphylococcal lesions reveal gram-
positive cocci in grape like clusters.
2. Other two are coagulase negative.
3. Do not ferment manitol.
4. Cultures of coagulase-negative staphylococci
yield white colonies.
5. They are non hemolytic.

45. The two coagulase-negative staphylococci are
distinguished by their reaction to the antibiotic
novobiocin: S. epidermidis is sensitive whereas
S. saprophyticus is resistant.

47. Species Frequency
of disease
Coagulase Color of
colonies
Mannitol
fermentatio
n
Novobiocin
resistance
S. aureus Common + Golden
yellow
+ –
S. epidermidis Common – White – –
S.
saprophyticus
Occasional – White – +

48. A 32-year-old woman
became ill 4 days after
the onset of her menstrual
period. She presented in
the emergency room with
fever (104°F), elevated
white blood cell count
(16,000/mm3), and an
erythematous, sunburn
like rash on her trunk and
extremities. The patient
described most likely has:

49. A. Staphylococcal food poisoning.
B. Scalded skin syndrome.
C. Infection with a Staph. saprophyticus.
D. Chickenpox.
E. Toxic shock syndrome.