Jackson: Eye Infections Flashcards by Andrew Kumar

Staphylococcus Aureus

Relevant Virulence Factors:

Alpha toxin (primary)
Teichoic acid (aids in colonization)
Antiphagocytic compounds

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Staphylococcus Aureus

Basics:

Infections

Blepharitis:
Dacrocystitis:
Conjunctivitis:
Keratoconjunctivitis:
Endophthalmitis:

Basics: principle cause of eye infections due to high carriage rates in humans

Infections:

Blepharitis: infection of eyelid margin or sebaceous gland (also called a sty)

Dacrocystitis: inflammation of lacrimal sac

Conjunctivitis: inflammation of conjunctiva (can spread to cornea, eyelids and sclera)

Keratoconjunctivitis: conjunctiva and cornea

Endophthalmitis: infection of the aqueous or vitreous humor; requires ulceration/penetrating injury to compromise cornea and sclera

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Staphylococcus Aureus

ID
Shape/Staining:
Biochemical Tests:

Shape/Staining: Gram positive cocci in clusters

Biochemical Tests:
o Catalase positive
o Coagulase positive
o Antimicrobial susceptibility testing

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Streptococcus Pneumoniae

Relevant Virulence Factors (3):

Polysaccharide capsule: interferes with complement pathway (84 different serotypes); primary virulence factor

Pneumolysin: membrane damaging cytolysin related to SLO

Cell wall: techoic acid and peptidoglycan contribute to inflammatory response

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Streptococcus Pneumoniae

Etiology/Pathogenesis

Basics:
Infections (3):

Basics: common in upper respiratory tract; may cause infection due to close proximity of eyes to this area

Infections:
o Dacrocystitis
o Conjunctivitis
o Keratoconjunctivitis

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Streptococcus Pneumoniae

ID
Shape/staining
Classification:
Biochemical Tests:

Shape/Staining: Gram positive diplococcus (pneumococcus; lancet shaped)

Classification: not part of Lancefield grouping

Biochemical Tests:
o Capsular serotyping
o Quelling reaction (capsular swelling due to adding anti-capsule Abs)
o Optochin (P disk) susceptibility test
o Bile solubility (differentiate from S. viridians)

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Haemophilus Influenzae

Relevant Virulence Factor:
What is the most virulent serotype?

Polysaccharide Capsule: antiphagocytic and antigenic change; most important VF

6 different serotypes (a-f)
Serotype b (Hib): most virulent; composed of polyribitol phosphate (now vaccine for children to prevent associated meningitis)

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Haemophilus Influenzae

Etiology/Pathogenesis
Basics:
Infections:

Exclusively found in humans, and we have a high carriage rate in upper respiratory tract (normal flora typically has no capsule)

Infections:
o Conjunctivitis
o Keratoconjunctivitis

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Haemophilus Influenzae

ID
Shape/Staining:

Satellite Growth Phenomenon:

Capsular serotyping:

Shape/Staining: Gram negative rod (pleiomorphic)

Satellite Growth Phenomenon: require blood products (hematin/X factor and NAD/V factor) for growth; will grow only when supplied with these; on chocolate agar but not on blood agar

Capsular serotyping: with anti-capsule Abs

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Pseudomonas Aeruginosa

Relevant Virulence Factors (4):

Exotoxin A

Exotoxin S

Elastase

Adhesin for colonization

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Pseudomonas Aeruginosa

Exotoxin A:

Cytotoxin that causes ADP-ribosylation of elongation factor 2, stopping protein synthesis and leading to cell death
o Same mechanism as diphtheria toxin
o Promotes tissue invasion and evasion of immune system

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Pseudomonas Aeruginosa

Exotoxin S:

ADP-ribsoylation of other proteins

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Pseudomonas Aeruginosa

Elastase:

A cytolysin that acts as a protease for elastin, human IgA, IgG, complement and collagen
o Primary cause of corneal perforation during eye infection

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Pseudomonas Aeruginosa

Adhesin for colonization:

Adhesion to cornea requires trauma to expose receptors.

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Pseudomonas Aeruginosa

Etiology/Pathogenesis

Basics:
Infections (3):

Basics: found free-living in most environments, and is an oppotunisitc pathogen; causes eye infections by contaminating water and contact lens solution, or via iatrogenic means (contaminated ophthalmologic equipment)

Infections:

Conjunctivitis
Keratitis: infection of the cornea; requires trauma to expose receptors
- Associated with extended wear contacts
- Can rapidly destroy cornea in 1-2 days
Endophthalmitis

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Pseudomonas Aeruginosa

ID
Shape/staining:
Growth Characteristics:
Biochemical Tests:

Shape/Staining: Gram negative rod (motile in wet mount)

Growth Characteristics:
o Classified as aerobic because it never uses fermentation pathway, but without O2 it can use NO3
o Tolerates lots of temperatures and high salt content
o Fruity odor on solid media
o Blue-green fluorescence under UV light (pyoverdin)

Biochemical Tests:
o Oxidase positive*: Produces high levels of cytochrome oxidase
- Oxidation-fermintation (OF) Dextrose tubes demonstrate aerobic growth

Chlamydia Trachomatis

Relevant Virulence Factors (2):

Life cycle

Infectious elementary body
Intracellular replicative reticulate body

Endocytosis

Elementary body carries adhesins for attachment to epithelial cell receptors
Endocytosed elementary bodies do not stimulate lysosomal fusion
Organism may remain in dormant state but elicit inflammatory response

(Natalia’s notes: Life Cycle: replicates in reticulate body and the lyses out to release infectious elementary bodies; organism can remain in dormant state while still eliciting inflammatory response)

Chlamydia Trachomatis

Transmission:

Transmission: primarily STI, but also role in eye infections

Vertical: mother to newborn (inclusion conjunctivitis)

Horizontal: person to person (trachoma)

Chlamydia Trachomatis

Trachoma:

Chronic follicular conjunctivitis causing trachiasis (inward growth of eyelashes that scrape cornea)

Recurrent infections due to fingers and contaminated objects

Chronic inflammation of eyelids lead to corneal scarring and blindness

Chlamydia Trachomatis

Inclusion Conjunctivitis (Opthalmia Neonatorum):

Associated with genital serotypes (passed from mother to child during birth via contact with cervical secretions)

Eye discharge 2-25 days after delivery

Chlamydia Trachomatis

ID
Shape/staining:
Detection:
Diagnosis by conjunctival scrapings:

Shape/Staining: Gram negative outer membrane with no peptidoglycan (does not gram stain); coccobacilli
- Note: no peptidoglycan also means you cannot treat with b-lactams

Detection: intracellular parasite (several methods to detect)

Diagnosis by conjunctival scrapings

C.trachomatis isolated by cell culture for 3-7 days
a. Cytoplasmic inclusions detected by iodine staining of glycogen
b. Immunofluorescent staining of outer membrane proteins
Methods not requiring cell culture
a. Direct fluorescent antibody staining & enzyme assays
b. DNA or RNA detected using probes and PCR

Candida Albicans

Relevant Virulence Factors:

Adhesins and invasive hyphae (bind fibronectin, collagen and laminin)

Proteases and elastases (invasion process)

Candida Albicans

Basics:
Infections (2):

Basics: Commensal of oral cavity and urogenital tract

Infections:
Endophthalmitis: white cotton ball expanding on retina/floating in vitreous humor

Chorioretinitis: in immunocompromised patients; manifestation of systemic diseases that can lead to blindness

Candida Albicans

ID (2):

ID:

Blood culture (detection of disseminated disease)
KOH/Gram stain reveals budding round/oval yeast with hyphae

Histoplasma Capsulatum | Relevant Virulence Factors:

Dimorphic growth phases (pathogenic form in tissue at body temperature) Evasion of immune system (can be dormant; can grow in phagocytes)

Histoplasma Capsulatum | Basics:

Basics: associated with bird and bat droppings; mold grows in soil when its humid, conidia inhaled by host and converts to pathogenic yeast form - Predominantly a pulmonary disease with possible dissemination --> chorioretinitis Infection elicits delayed type hypersensitivity

Histoplasma Capsulatum | POHS

Presumed ocular histoplasmosis syndrome (POHS) 1. Fungus causes small areas of inflammation and scarring of the retina 2. Peripheral scarring of the retina may have no impact on vision 3. Central scar affecting the macula may cause a prominent blind spot

Histoplasma Capsulatum Clinical identification of organism:

A. Examination of blood culture, biopsy, or bone marrow for yeast cells 1. Grows slowly (weeks) on blood and Sabouraud agar 2. Can be cultured for identification of dimorphic fungus B. Immunodiffusion test available to detect mycelial antigen

Coccidiodes Immitis: Relevant Virulence Factors: Etiology/Pathogenesis: More likely in:

Relevant Virulence Factors: - Mold form produces infectious arthroconidia - Dimorphic growth phases (spherule form, not yeast, invades tissue) Etiology/Pathogenesis: Basics: geographically limited to hot, dry regions of Southwestern US Primarily a pulmonary infection that can disseminate to the eye and CNS --> chorioretinitis - More likely in immunocompromised

Fusarium spp.: Keratomycosis: Onychomycosis

• Abundant soil fungi Produces T-2 mycotoxin toxic to humans Causes toxic aleukia (complete absence of leukocytes or platelets if consumed in contaminated grain over long period of time) • Infections in humans: usually in immunocompromised - Keratomycosis: infection of cornea - Onychomycosis: infection of nails No dimorphic growth phase

Acanthamoeba spp Etiology/Pathogenesis Life Cycle:

Life Cycle: o Trophozoites (Ameba): are free living o Cysts: infectious stage; equivalent to spores - Basics: inhabit soil, fresh or brackish water

Acanthamoeba spp | Infections (2):

Ulcerative Keratitis: - Amebas invade ocular tissue through break in corneal epithelium - Infection follows mild corneal trauma (ie. improperly sterilize hard contact lenses) - Granulomatous inflammation occurs as a result of trophozoite and cyst penetration - Normal immune defenses insufficient Encephalitis: primarily in elderly and immunocompromised (extremely rare)

Acanthamoeba spp | ID:

Trophozoites and cysts can be seen in corneal biopsies - Light and electron microscopy - Immunofluorescence Amoebas may be cultured using media containing G- bacteria (food)

Toxoplasma Gondii | Relevant Virulence Factors:

Often carried by cats: obligate, intracellular protozoan that requires warm-blooded mammal as host o Sexual stage occurs in intestinal tract of cats and oocysts passed in feces Humans accidentally ingest oocysts: after cleaning litter box or eating infected meat

Toxoplasma Gondii | Congenital Toxoplasmosis:

~50% of the population has been infected Can be passed in utero (“Don’t clean cat litter while pregnant”)

Toxoplasma Gondii | Chorioretinitis:

Most common delayed manifestation of congenital toxoplasosis Reactivation of dormant tissue cysts, especially in immunosuppression Proliferates in the retina, leading to inflammation of the choroid

Toxocara Canis: Round Worm in Dogs** | • Relevant Virulence Factors:

Relevant Virulence Factors: Often carried by canines: eggs ingested, eventually travel to lung where they are coughed up and then re-ingested (completes maturation in small bowel); larvae can enter pulmonary capillaries and go systemic o Tons of eggs released by the worm into the dog’s feces; can live in the soil for years Humans accidentally ingest eggs: larvae pass through pulmonary capillaries and enter systemic circulation; grow in capillaries (penetrate wall/enter tissue)

Toxocara Canis Etiology/Pathogenesis Visceral Larva Migrans: Chorioretinitis: Retinal Granulomas:

Visceral Larva Migrans: causes eosinophilic granulomas and tissue necrosis of liver, heart, lung, brain and skeletal muscle Chorioretinitis: due to ocular larva migrans (larva migrating to eye) Retinal Granulomas: cause unilateral strabismus and decreased visual acuity