Eye Infections and Microbiota

Eye Infections

Normal Ocular Microbiota

• The normal resident conjunctival and lid microbiota changes with age
• The intact epithelia of the lid, conjunctiva, and cornea provide a protective barrier against invasion by most microorganisms
• Tears contain high concentrations of IgA, lysozyme, and lactoferrin, which have antimicrobial properties
• Lysozyme attacks bacterial cell walls by splitting bonds in the peptidoglycan layer
• Lactoferrin inhibits the growth of bacteria by competing for and binding to iron
• The flow of tears protects the eye from infection by removing bacteria and debris from the ocular surface

Risk Factors for Ocular Infections

• Age
• Sex
• Race
• Socioeconomic status
• Behavior
• Geographic location
• Occupation
• Underlying disease

Conjunctivitis

• Acute bacterial and viral conjunctivitis occurs more frequently in childhood, whereas chronic conjunctivitis and varicella-zoster virus (VZV) conjunctivitis occurs most frequently in the elderly
• Women are more likely than men to be associated with Trachoma, a disease caused by Chlamydia (C.trachomatis)
• Several pathogens can penetrate the intact epithelium of the conjunctiva or cornea, including Neisseria gonorrhoeae, Neisseria meningitidis, S.pneumoniae, Listeria monocytogenes, and Corynebacterium diphtheriae

Microorganisms Associated with Conjunctivitis

• Gram-negative: Acinetobacter spp., Borrelia burgdorferi, Enterobacteriaceae, Haemophilus influenza, Moraxella catarrhalis, Neisseria gonorrhoeae, Neisseria meningitidis, Pseudomonas aeruginosa
• Gram-positive: B-Hemolytic streptococci, Corynebacterium diphtheriae, Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pneumoniae, Viridans Streptococci
• Viruses: Human coronavirus, Herpesviruses, Chlamydia and related spp.
• Fungi (rare): Candida spp.
• Parasites (rare): Ascaris lumbricoides

Laboratory Diagnosis

• Laboratory tests can be of assistance in differentiating acute, allergic, and chronic conjunctivitis
• Conjunctival scrapings are collected using a spatula, blade, or sterile swabs
• Plated directly onto slides and culture media

Infections of the Lacrimal Apparatus

• The lacrimal glands, accessory glands, puncta, canaliculi, tear sac, and nasolacrimal duct together are known as the lacrimal apparatus
• Disorders and infections of the lacrimal apparatus are caused by blockage, underproduction, or overproduction of tears
• Inflammation of the main lacrimal gland, known as dacryoadenitis, may be infectious or noninfectious

Microorganisms Associated with Lacrimal Apparatus Infections

• Bacteria: Staphylococcus aureus, Streptococcus pneumonia, Streptococcus pyogenes, Haemophilus influenzae, Pseudomonas aeruginosa, Proteus mirabilis, Chlamydia trachomatis, Treponema pallidum
• Viruses: Coxsackie A virus, Cytomegalovirus, Echovirus, Epstein-Barr virus, Herpes simplex virus types 1 and 2, Influenza, Measles, Varicella-zoster virus
• Fungi: Aspergillus spp., Candida albicans, Rhizopus spp., Mucor
• Parasites: Cysticercus cellulosae, Onchocerca volvulus, Schistosoma haematobium

Discriminating Between Indigenous Microbiota and Pathogens

• The distinction between indigenous microbiota and ocular pathogens is blurred
• Coagulase-negative staphylococci, Propionibacterium acnes, and S.aureus are responsible for a majority of intraocular and corneal infections
• The presence of biomaterials, use of steroids, and antimicrobials can predispose ocular tissues to infection with indigenous flora

Infections of the Conjunctiva

• Viral Conjunctivitis
• Bacteria Conjunctivitis

Anatomy of the Eye

• Sclera
• Vitreous
• Iris
• Choroid
• Cornea
• Optic nerve
• Pupil
• Macula
• Lens
• Retina
• Conjunctiva

Culture and Identification

• Most of the bacterial and fungal ocular isolates may be recovered on chocolate and blood agar when they are incubated under the proper conditions of temperature and atmosphere
• The addition of thioglycollate broth, Thayer-Martin agar, Sabouraud agar with gentamicin, viral and chlamydial transport media, Löwenstein-Jensen slants allows for the recovery of most pathogens involved in ocular disease

Molecular Techniques

• DNA probes and PCR help in confirming clinical diagnosis for difficult or unusual ocular pathogens
• This method may be ideal for detecting microbes in ocular samples because of the small volume

Lab Diagnosis of Eye Infection

• Specimen: Eye swab (2), and scraping in case of keratitis
• Transportation: Stuart or Amies transport media
• Microexamination: Gram stain, Direct immunofluorescence stain, Geimsa stain, Iodine preparation
• Culture: Routine, Additive media, and Liquid media

Infections of the Lids (Blepharitis)

• Blepharitis (inflammation of the lid margins) and inflammation of the conjunctivae are not mutually exclusive
• Any organism that causes conjunctivitis can affect the lids
• Staphylococcus aureus and members of the coagulase-negative staphylococcal family are the most frequently isolated bacteria from the lid margins
• Blepharitis involving these organisms is a low-grade inflammation associated with functional diseases of the seborrheic glands (seborrheic blepharitis)

Microorganisms Associated with Blepharitis

• Bacteria: Staphylococcus aureus, Staphylococcus epidermidis, Group A and other β-streptococci, Moraxella lacunata, Moraxella spp.
• Fungi (rare): Candida spp., Cryptococcus neoformans
• Viruses: Herpes simplex virus types 1 and 2