This document discusses ocular (eye) infections, including the microorganisms that commonly cause infections. It focuses on bacterial infections, describing characteristics of gram-positive bacteria like staphylococci and streptococci. Staphylococcus aureus is highlighted as a major pathogen in various eye infections like blepharitis and keratitis. Staphylococcus epidermidis is discussed as an opportunistic pathogen associated with infections after eye surgeries or implants. Streptococcus pneumoniae is also mentioned as a cause of conjunctivitis.

1. OCULAR INFECTIONSOPTOM FASLU MUHAMMED

2. Infection is the invasion of a host organism's body
tissues by disease-causing agents.
 Microbiology is important in aetiologicl diagnosis.
 Bacterias occupy human eye at the time of birth are
Staph.epidermidis , Staph.aureus ,Neisseria sps
,viruses ,chlamydia etc
 Normal flora may lead to infection only at the time of
physical injury or immunosuppression

3. Defense mechanisms of eye
 Lysozyme
 Lactoferrin
 IgA
 Phagocytic cells etc

4. Types of ocular infections based on the
nature of infective agents
 Bacterial
 Fungal
 Viral
 Parasitic

5. Bacterial infections
Gram positive bacteria
Gram negative bacteria
Mycobacteria
Spirochetes

6. Gram positive bacteria
• Staphylococci
• Streptococci
• Corynebacteria
• Listeria monocytogenes
• Aerobic spore forming bacilli
• Nocardia

7. Staphylococci
The genus staphylococci play a major part in ocular
infections. They are classified into two main groups based
on the ability to clot blood plasma.
Coagulase – Positive
Coagulase - Negative
Coagulase – Positive (Staph.aureus) are potential
pathogens . Coagulase - Negative are coming under
normal flora but can cause opportunistic infections
(Staph.epidermidis, Staph.saprophyticus)

9. Morphology
• Spherical (cocci) arranged in grape like clusters, may
be tetrads or in groups.
• Non sporing ,non motile , non capsulated
• Aerobic or facultative anaerobes
Cultural characters
Nutrient agar- Circular ,opaque, smooth, shiny colonies.
Staph . aureus produces a golden yellow pigment

10. Blood agar – Staph aureus produces hemolysis
MacConkey agar – Pink colonies due to lactose
fermentation
Biochemical characters
S.aureus S.epidermidis
• Produce golden yellow pigment
• Coagulase positive
• Ferment lactose
• Grey to white pigment
• Coagulase negative
• Do not ferment lactose

11. Pathogenesis
Staph.aureus: Most pathogenic and common bacteria in
ocular infections because it posses many virulent factors
like coagulase ,hemolysis , lipases , proteases etc . It is
commonly isolated in the case of
• Blepheritis
• Orbital cellulitis
• Corneal ulcers
• Socket infection
• Chronic bacterial conjunctivitis Etc

12. Staphylococcal blepharitis
Staphylococcal blepharitis is caused by infection of
the anterior portion of the eyelid ,which is primary
invader in ulcerative type and secondary in squamous
type
Keratitis
The eye's cornea, the front part of the eye,
becomes inflamed. Staphylococcus keratitis is
frequently marginal .

13. Staph.epidermidis
Though epidermidis does not possess virulence factors
like aureus they have the ability to form adherent
biofilms on the surface of polymers which is used for
implants like intra ocular lenses because of specific
surface proteins.
It is commonly isolated in the case of
• Post cataract surgery
• Endophthalmitis (inflammation of the internal coats of
the eye)

14. Diagnosis:
Gram’s staining
Culture on blood agar
Biochemical tests
Phage typing
Treatment:
Most of them are resistant to penicillin and sensitive to
methicillin ,cephalosporin etc Coagulase negatives are
sensitive to vancomycin

15. STREPTOCOCCI
Streptococci are gram positive cocci appear in chains.
They are part of normal flora of humans and animals. The
virulent species posses capsule , consist of hyaluronic
acid and M protein.
Based on the pattern of hemolysis on horse blood
agar they are classified into three groups.
1.Alpha hemolytic streptococci
2.Beta hemolytic streptococci
3.Gamma hemolytic streptococci

16. Morphology
 Oval or spherical in shape.
 They are non sporing and non motile.
Cultural characteristics:
 It is an aerobic or facultative anaerobe.
 It is an exacting organism grow only in media
containing fermentable carbohydrate or enriched with
blood or serum.
 In blood agar colonies are small, circular ,
semitransparent with a clear hemolytic area around
the colony.

17. Pathogenesis
The pathogenicity is caused by various
substances (toxins and enzymes )such as
Streptokinase ,streptodornase , hyaluronidase ,
leucocidine , erythrogenic toxins etc

18. Streptococcus pneumonia:
(pneumococcus)
It is common inhabitant of the normal conjunctiva
and nasolacrimal system.
Pneumococci are gram positive lancet shaped
diplococci,posses a polysaccharide capsule.

19. • An ocular injury may lead to purulent infection ,
hypopyon keratitis.
• Epidemics of acute pneumococcal conjunctivitis
happens in children. It is contagious and usually
associated with respiratory infection.