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Microbiology: Eye Infections (Jackson) BACTERIA CAUSING EYE INFECTIONS: Staphylococcus Aureus: Relevant Virulence Factors: Alpha toxin (primary) Teichoic acid (aids in colonization) Antiphagocytic compounds Etiology/Pathogenesis: Basics: principle cause of eye infections due to high carriage rates in humans Infections: o Blepharitis: infection of eyelid margin or sebaceous gland (also called a sty) o Dacrocystitis: inflammation of lacrimal sac o Conjunctivitis: inflammation of conjunctiva (can spread to cornea, eyelids and sclera) o Keratoconjunctivitis: conjunctiva and cornea o Endophthalmitis: infection of the aqueous or vitreous humor; requires ulceration/penetrating injury to compromise cornea and sclera ID: Shape/Staining: Gram positive cocci in clusters Biochemical Tests: o Catalase positive o Coagulase positive o Antimicrobial susceptibility testing Streptococcus Pneumoniae: Relevant Virulence Factors: 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 Etiology/Pathogenesis: 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 ID: 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) Haemophilus Influenzae: Relevant Virulence Factors: Polysaccharide Capsule: antiphagocytic and antigenic change; most important VF o 6 different serotypes (a-f) o Serotype b (Hib): most virulent; composed of polyribitol phosphate (now vaccine for children to prevent associated meningitis) Etiology/Pathogenesis: Basics: 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 ID: 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 Capsular serotyping: with anti-capsule Abs Pseudomonas Aeruginosa: Relevant Virulence Factors: Exotoxin A: o 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 Exotoxin S: o ADP-ribsoylation of other proteins Elastase: o A cytolysin that acts as a protease for elastin, human IgA, IgG, complement and collagen o Primary cause of corneal perforation during eye infection Adhesin for colonization: o Adhesion to cornea requires trauma expose receptors Etiology/Pathogenesis: 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: o Conjunctivitis o Keratitis: infection of the cornea; requires trauma to expose receptors Associated with extended wear contacts Can rapidly destroy cornea in 1-2 days o Endophthalmitis ID: 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* Chlamydia Trachomatis: Relevant Virulence Factors: 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 Etiology/Pathogenesis: Transmission: primarily STI, but also role in eye infections o Vertical: mother to newborn (inclusion conjunctivitis) o Horizontal: person to person (trachoma) Trachoma: o Chronic follicular conjunctivitis causing trachiasis (inward growth of eyelashes that scrape cornea) o Recurrent infections due to fingers and contaminated objects o Chronic inflammation of eyelids lead to corneal scarring and blindness Inclusion Conjunctivitis (Opthalmia Neonatorum): o Associated with genital serotypes (passed from mother to child during birth via contact with cervical secretions) o Eye discharge 2-25 days after delivery ID: Shape/Staining: Gram negative outer membrane with no peptidoglycan (does not gram stain); coccobacilli o Note: no peptidoglycan also means you cannot treat with b-lactams Detection: intracellular parasite (several methods to detect) FUNGI CAUSING EYE INFECTIONS: Candida Albicans: Relevant Virulence Factors: Adhesins and invasive hyphae (bind fibronectin, collagen and laminin) Proteases and elastases (invasion process) Etiology/Pathogenesis: Basics: commensal of oral cavity and urogenital tract Infections: o Endophthalmitis: white cotton ball expanding on retina/floating in vitreous humor o Chorioretinitis: in immunocompromised patients; manifestation of systemic diseases that can lead to blindness 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) Etiology/Pathogenesis: 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 Coccidiodes Immitis: 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 o More likely in immunocompromised Fusarium spp.: Abundant soil fungi Infections in humans: usually in immunocompromised Keratomycosis: infection of cornea Onychomycosis: infection of nails PARASITES CAUSING EYE INFECTIONS: Acnthamoeba spp: Etiology/Pathogenesis: Life Cycle: o Trophozoites (Ameba): are free living o Cysts: infectious stage; equivalent to spores Basics: inhabit soil, fresh or brackish water Infections: o 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 o Encephalitis: primarily in elderly and immunocompromised ID: Trophozoites and cysts can be seen in corneal biopsies 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 Etiology/Pathogenesis: Congenital Toxoplasmosis: o ~50% of the population has been infected o Can be passed in utero (“Don’t clean cat litter while pregnant”) Chorioretinitis: o Most common delayed manifestation of congenital toxoplasosis o Reactivation of dormant tissue cysts, especially in immunosuppression o Proliferates in the retina, leading to inflammation of the choroid Toxocara Canis: Round Worm in Dogs** Relevant Virulence Factors: Often carried by canines: eggs ingested, eventually travel to lung where they are coughed up and then reingested (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) Etiology/Pathogenesis: 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