Ocular Microbiology (Bacteriology, Virology, Mycology, and ...



Ocular Microbiology

(Bacteriology, Virology, Mycology, and Parasitology)

Description: Review of the viral, bacterial, mycotic, and parasitic pathogens of the eye. The disease characteristics, transmission, pathogenesis, laboratory diagnosis, treatment, management and prevention of the previously mentioned pathogens will be discussed.

Content: Microbiology related to disease/disorder:

Ocular adnexa

Lacrimal system

Conjunctiva

Cornea

Anterior uvea

Clinical application: Selection of treatment/management, including systemic considerations

General Objective: To develop an understanding of the organisms that cause the more common ocular infections. As well as the prevention, treatment and management of these infections.

Specific Objectives:

I. Virology

A. Discuss the following characteristics of viruses

1. Composition of viruses

2. Morphology of viruses

3. Life cycle of viruses

4. Classification of viruses

5. Pathogenesis of viral infections

6. Therapy for viral infections

7. Immunization against viral infections

B. Describe the infectious etiology, pathogenesis, transmission, management and prevention of the following viral eye infections.

C. Discuss the following characteristics of representative viral infections:

1. Medically important viruses

2. Ocular infections

3. Transmission

4. Pathogenesis

5. Therapy/management

6. Prevention and control

II. Bacteriology

A. Discuss the relationship between bacteria and host

1. Normal flora

2. The infective process

B. Describe the basic laboratory methods utilized in the identification of clinically important bacteria

1. Gram stain

2. Culture

3. Antibiotic susceptability testing

C. Recall the following characteristics of representative genera of bacteria

1. Medically important species

2. Ocular infections

3. Pathogenesis

4. Unique morphological or biochemical properties

5. Therapy

6. Prevention and control

III. Mycology

A. Describe the following characteristics of representative fungal infections

1. Medically important species

2. Ocular infections

3. Pathogenesis

4. Therapy

5. Prevention and control

IV. Parasitology

A. Discuss the following characteristics of representative parasitic infections

1. Medically important species

2. Ocular infections

3. Pathogenesis

4. Therapy

5. Prevention and control

INTRODUCTION TO MICROBIOLOGY

I. Microbiology

Biology and study of organisms that are not directly visible to the naked eye.

II. Traditional Taxonomy

“Where microorganisms fit into the scheme of living things."

A. Animal Kingdom

B. Plant Kingdom

C. Kingdom Monera

D. Kingdom Fungi

E. Kingdom Protista

F. Virus – separate entity

Virology

I. Introduction to viruses (The term viruses is derived from Latin word meaning "poison")

A. General characteristics of viruses

1. Smallest infections agents (20-300 nm)

2. Contain only one kind of nucleic acid

a. RNA or DNA

3. Virion—entire infectious unit

4. Incapable of metabolic activity outside living cells

5. Replicate only in living cells

6. Parasites at the genetic level

7. Host for a given virus may be broad or extremely limited

8. Virus replication is initiated when virus penetrates host cell

9. Intracellular synthesis of viral gene products often results with death or damage to host cell

10. Cells that are damaged or destroyed cause the manifestations of viral disease

11. Viruses infect virtually all living organisms

12. Several hundred infect man; many of these infect the eye

B. Properties of viruses

1. Virion

a. Capsid: The protein shell, or coat, that encloses the nucleic acid genome (protective coat); proteins on coat have affinity for receptor sites on host

b. Nucleocapsid: The capsid together with the enclosed nucleic acid

c. Capsomers: Morphological units seen in electron microscope on the surface of icosahedral virus particles

d. Envelope: A lipid-containing membrane that surrounds some virus particles; virus-encoded glycoproteins are exposed on the surface of the envelope

2. Classification of viruses (in descending order of importance)

a. Nucleic acid type: RNA or DNA—single or double stranded

b. Size and morphology; type of symmetry of nucleocapsid (helical or cubic); number of capsomers; existence of envelope

c. Presence of specific enzymes: DNA or RNA polymerases (used in replication)

d. Susceptibility to physical or chemical agents

e. Immunologic properties

f. Natural methods of transmission

g. Host, tissue, and cell tropisms

h. Pathology

i. Symptomatology

C. Pathogenesis of viral diseases

1. To produce disease a virus must enter a host; come into contact with susceptible cells; replicate; produce cell injury

2. Entry and primary replication

a. Means of entry

1) Breaks in skin

2) Mucosa of respiratory or gastrointestinal tracts

b. Replication at primary site of entry

c. Modes of transmission

1) Fecal-oral route

2) Respiratory route

3) Venereal route

4) Direct contact

5) Epidermal route

6) Arthropod vector

3. Viral spread and cell tropism

a. After primary replication at site of entry

b. Viral spread via (varies depending on type of virus):

1) Period of virus spread is known as viremic phase of infection

2) Bloodstream

3) Lymphatics

4) Neuronal spread

c. Cell tropism (what cells viruses attach to); receptor sites on host cell

Lifecycle of H.I.V.

[pic]

4. Cell injury and clinical illness

a. Typical life cycle of virus (replication)

b. Clinical Illness > depends on what host cells arer affected (i.e., HIV affects T4 helper cells—immunosuppression)

c. When are virus-infected patients most infectious?

1) During prodromal viremia

2) During active infection

a) Primary infection

b) Secondary infection after latency

d. Consequences of viral infection

1) Elimination of virus and subsequent immunity

2) Latency: virus not eliminated; virus persists as a subclinical infection;inaccessible to circulating antiviral antibodies; infection can reactivate, e.g., herpesvirus

D. Control of virus infections

1. Antiviral therapy

a. Inhibit viral functions without damaging host

b. Affect viral replicative cycle; inhibition of enzymes for RNA or DNA replication: i.e., reverse transcriptase in HIV infection

2. Virus vaccines

a. Passive immunization

Injection of specific protective antibodies

Short-acting

TABLE OF VACCINES

|Immunization |Disease |Source of Vaccine |Condition |Route of |

|Recommendation | | |of Virus |Administration |

|For General Public |Poliomyelitis |Tissue culture |Live attenuated |Oral |

| | |(human diploid) |Killed |Subcutaneous |

| | |(monkey kidney) | | |

| |Measles |Tissue culture |Live attenuated |Subcutaneous |

| | |(chick embryo) | | |

| |Mumps |Tissue culture |Live attenuated |Subcutaneous |

| | |(chick embryo) | | |

| |Rubella |Tissue culture |Live attenuated |Subcutaneous |

| | |(duck embryo) | | |

| | |rabbit or | | |

| | |human diploid | | |

|Only Under Certain Conditions|Hepatitis B |Purified HBsAG from “Healthy” |Subunit |Subcutaneous |

| |(Health Care Workers) |carriers HBsAG from recombinant | | |

| | |DNA in yeast | | |

| |Infuenza |Highly purified or subunits forms|Killed |Subcutaneous |

| |(Elderly, HCW) |of or intradermal chick embryo | | |

| | |allantoic fluid | | |

| |Rabies |Tiiue culture duck embryo or |Killed |Subcutaneous |

| | |human diploid | | |

| |Adenovirus |Tiisue culture human diploid cell|Live attenuated |Oral, by Enteric- |

| |(military) |cultures | |coated capsule |

| |Varicella Zoster | |Live attenuated | |

b. Active immunization:

Stimulation of host's own immune defenses by injection of live attenuated virus strains, killed viruses, recombinant viruses, or purified viral antigens

E. Laboratory approaches to ocular viral infections

1. Direct examination of clinical materials for virus or virus antigen

a. Examine ocular materials with light or electron microscopy

Look for morphology of cytopathic effect

Look for inclusion bodies and multinucleate giant cells

b. Treat specimens with specific viral antibody

1) Immunofluorescence

2) Immunoperoxidase enhances observation or virus inclusions, virus-infected cells

2. Isolation and identification of viruses from clinical specimens

6. Swabb conjunctiva

Viral collection and transport kits available; viral Culturette

a. Culturing of viruses

b. Specimen from acute stage of illness

c. Inoculation into susceptible cells

d. Isolate and identify virus

3. Serologic diagnosis

a. Commonly used

b. Identification of unknown virus isolates with known specific antisera

c. Determination of specific antibody against a virus

d. Neutralization test

e. Complement fixation test

f. Hemagglutination inhibition test

g. Radioimmunoassays (RIAs)

h. Enzyme linked immunosorbent assay (ELISA)

II. Adenovirus

Serotypes Hemagglutination Property

Group 1 3, 7, 11, 14, 21

Group 11 8, 9, 10, 13, 19, 30

Group III 1, 2, 4, 5, 6

97% of Human eye infections are caused by serotypes 3, 4, 7, 8 10, 15 & 19

A. General characteristics

1. In man cause mainly ocular, respiratory, and gastrointestinal disease

2. “Naked" Virion; nonenveloped

3. Icosahedral nucleocapsid

4. Double-stranded DNA

5. Immunologically distinct serotypes

7. Use hemagglutination properties to classify twelve that cause eye infections

B. Disease/eye infections

1. Probably most common cause of acute viral infections of ocular adnexa and cornea

2. Acute, self-limiting, follicular keratoconjunctivitis; patient may not seek care

3. Three adenoviral eye syndromes

a. Epidemic keratoconjunctivitis (EKC)

b. Pharyngoconjunctival fever

c. Acute nonspecific follicular conjunctivitis

4. Epidemic keratoconjunctivitis

a. Adenovirus types 8 and 19 most common; also 2-4, 7-11, 14, 16, 29, 37

b. Epidemiology

1) Iatrogenic outbreaks

2) Children and young adults commonly infected

3) Both sexes equally

C. Transmission

1. Primarily iatrogenic

a. Tonometer tips

b. Schiotz tonometers

2. Respiratory droplets

3. Fecal-oral route

4. Children in schools

5. Swimming pools

6. Close personal contact: sexual transmission

D. Pathogenesis

1. Virus prefers intact epithelium of eyes (conjunctiva and cornea) and respiratory tract

2. Incubation period: 2-14 days

3. Acute active infection: Cornea and conjunctival epithelial cells are infected with the virus; virus replication occurs within epithelial cells and provides antigens for later delayed hypersensitivity

a. Clinical presentation

1) Sudden onset

2) Acute watery discharge

3) Tenderness of preauricular lymph nodes

4) Follicular and papillary conjunctival response with or without conjunctival hemorrhage

5) Punctate keradtis

4. Delayed hypersensivity response

a. 3rd to 4th week of infection

b. Corneal infiltrates

c. Immune response to infection

d. Infiltrates can persist for months

E. Lab diagnosis (not commonly done clinically)

1. Culture from conjunctival swabs (expensive); (2-28 days) takes too long

2. Examine conjunctival swab: Intranuclear basophilic inclusion bodies

3. Immunoperoxidase and immunofluorescence techniques

4. Serologic diagnosis

a. Complement fixation

b. Hemagglutination

c. Antibody titer rise in convalescent phase is diagnostic

F Treatment: No established antivirals for adnenoviruses

G. Prevention

1. Infection control procedures

2. Live vaccines against types: 3, 4, and 7

3. Used in military

III. Herpesviruses

A. Herpesvirus of humans

1. Herpes simplex virus types 1 and 2

2. Varicella-zoster virus

3. Cytomegalovirus

4. Epstein-Barr virus

B. Important properties of herpesviruses

1. Large spherical virion: 120-200 nm

2. Double-stranded DNA

3. Possesses an envelope

4. Icosahedral nucleocapsid

5. Establish latent infections

6. Persist indefinitely in infected hosts

7. Frequently reactivated in immunocompromised hosts

C. Herpes simplex virus

8. HSV-1 (causes infection “above the waist" and most commonly affects the eye)

9. HSV-2 (causes genital infections—can also cause eye infections)

1. Pathogenesis of HSV infection

a. Virus enters the host through mucous membranes or breaks in the skin, usually direct contact

b. Causes primary infection after a 1-12-day incubation

c. Infects tissues of ectodermal origin, such as skin and nervous tissue

d. After resolution of 1° infection, the virus migrates up neuron to remain latent in ganglia (sensory and automatic)

e. Length of remissions is variable; stresses such as sunlight, fever, or immunosuppression trigger recurrences

f. Virus then migrates down the nerve ending and causes labial and/or corneal infection

2. Primary ocular herpes

a. Vessicular lid lesions

b. Follicular conjunctivitis

c. Lymphadenopathy, mild malaise, fever

d. Epithelial punctate keratitis

3. Recurrent herpes simplex

a. Epithelial infections; ulceration;virus-laden epithelial cells

b. Stromal disease

4. Transmission

a. HSV-1: Saliva or direct contact with virus from vessicle.

b. HSV-2: Sexual contact

5. Laboratory diagnosis

a. Infected tissue scrapings

b. Serology—antibodies

c. Virus isolation

6. Management

a. Topical antivirals

10. 1% Trifluridine q2h

11. 3% Vidarabine qhs

b. Oral acyclovir

7. Prevention: No vaccine

D. Herpes zoster (varicella-zoster virus)

12. Varicella (chicken pox)—children

13. Zoster (shingles)—adults

l. Pathogenesis

a. Virus enters host via mucosa of upper respiratory tract or contact with infected skin

b. Virus circulates in blood and localizes in skin

c. Virus becomes latent in sensory and dorsal root ganglia; produces infection in a similar manner to herpes simplex; latency in dorsal root ganglia

d. Reactivation of virus results in skin lesions in the skin (vessicles) that corresponds to area of innervation from an individual dorsal root ganglion

2. Ocular herpes zoster

a. Prodromal flu-like illness

b. Pain over distribution of ophthalmic nerve (cranial nerve V)

c. Rash with even distribution

d. Papule ( vessicle ( pustules corresponding to skin supplied by all or just one of cutaneous branches of ophthalmic nerve

e. Lasts 7 days

f. Usually respects midline

g. Nasociliary nerve involvement of rash on tip of nose usually is a sign of ocular complications (Hutchinson’s sign)

h. Lesion resolution—postherpetic neuralgia

i. Other ocular involvement: conjunctivitis, episcleritis, keratitis, uveitis

3. Laboratory diagnosis (not commonly done clinically)

a. Viral culturing

b. Serology—antibodies

4. Management

a. Topical steroids

b. Topical antivirals

c. Oral antivirals

14. 3% Acyclovir ointment for skin lesions

15. Oral Acyclovir 600-800 mg 5x per day for 10 days

5. Prevention and control—live attenuated vaccine

E. Cytomegalovirus (CMV)

1. Pathogenesis and pathology

a. Ubiquitous human virus

b. Congenital infection in infants—acquired from primary infection of mother during pregnancy or during delivery process

c. Acquired infection of CMV is common and often inapparent

d. Ninety to 100% of adults in developed countries show past exposure to CMV (usually acquired during first 5 years of life)

e. Port of entry via contact with infected saliva or urine

f. Location of latency is not fully understood

g. Immunosuppression (severe) causes reactivation of virus

2. Eye disease

a. Cytomegalovirus retinitis in AIDS patients

3. Transmission—contact with infected body fluids, across placenta

4. Laboratory diagnosis

a. Virus recovery from mouth swabs, urine, liver, adenoids, kidneys, and peripheral blood leukocytes by inoculation of human fibroblastic cell cultures

b. Serology—antibodies

5. Treatment

a. Ganciclovir

b. Foscarnet

6. Prevention—no vaccine

IV. Poxvirus family (poxviridae)

A. General characteristics

1. Large—seen with light microscope

2. Double-stranded DNA

3. Contain envelope

B. Eye diseases

1. Smallpox eradicated by vaccine

2. Molluscum virus

16. Wart-like (Benign epithelial tumor)

17. Confined to skin and margin of eye

18. Spread by direct contact; sexually transmitted among young adults

V. Human papilloma virus

A. General characteristics

1. Double-stranded DNA

2. No envelope

3. Papillovirus family

B. Eye diseases

1. Tropic for epithelial cells of the skin and mucous membranes

2. Wart-like lesions along eyelid margin and conjunctiva

3. Neurologic damage

a. Deafness

b. Retardation

4. Treatment—none

5. Prevention—immunization of women of child-bearing age

VI. Hepatitis

A. General characteristics

1. Hepadnavirus

2. Double-stranded DNA

3. Envelope

4. Causes hepatitis A and B infection

B. Hepatitis B infection—liver infection

C. Transmission

1. Contact with infected body fluids

D. Prevention

1. Recombinant vaccines

2. Recommended for health-care workers

VII. Human immunodeficiency virus

A. General characteristics

1. Lentivirus family (very long latency)

2. RNA virus

3. Envelope

4. Causes acquired immune deficiency syndrome

5. Infects T4 helper lymphocytes (severe immunosuppression)

B. Eye infections

1. Retina

2. Blood vessels—cotton-wool spots

3. Opportunistic infections

C. Transmission

1. Contact with infected body fluids

2. Sexual contact

3. Patients most infectious during initial viremic stage and after latency

D. Laboratory diagnosis

1. ELISA

2. Western blot

E. Treatment

1. Reverse Transcriptase Inhibitors

2. Protease inhibitors

3. Highly Active Antiretroviral Therapy

F. Prevention – No Vaccine

Bacteriology

I. Introduction to Bacteria

A. General structure of bacteria

1. Gross forms can be detected by light microscope

a. Spherical, cocci

b. Rod-shaped, bacilli

c. Curved spirochetes, vibrios, spirilla

2. Cell structure

a. Cytoplasm: nuclear body, ribosomes, mesosomes, granules of reserve material tglycogen)

b. Cell envelope surrounds cytoplasm

1) Cytoplasmic membrane

2) Rigid cell wall: responsible for shape of bacterium and protection against osmotic Lysis

c. Nuclear body (nucleoid)

1) Lacks a nuclear membrane (not a true nucleus)

2) DNA—a single circular chromosome

d. Other appendages and layers

1) Flagella

2) Fimbriae (pili): protein rods that function as adhesions and have an important role in pathogenesis

3) Glycocalyx: extracellular polymer surrounding certain bacterial cells; allows for adherence of bacteria to surfaces

II. General Principles of Bacteriology

A. Normal flora

1. Most bacteria do not produce disease

2. Bacteria can inhabit the skin and mucous membranes of healthy normal persons

3. Role of resident flora

a. Synthesize vitamins

b. Aid in absorption of nutrients

c. Prevent colonization by pathogens

d. Have a capacity to produce disease when out of normal environment, if over abundant or with pre-existing tissue damage

4. Normal flora of the eye (conjunctiva)

a. Diptheroids (Corynebacterium xerosis)

b. Staphylococcus epidermidis

c. Nonhemolytic streptococci

d. Neisseria

e. Moraxella

5. Factors controlling flora

a. Mechanical: barrier effect of lid skin, conjunctiva, mucous membrane, action of the lids and flushing action of tears

b. Enzymatic: Lysozyme

c. Antibacterial agents: lactoferrin, Lysozyme, IgA, IgG

6. Overgrowth of normal flora can cause an inflammatory response or production of by-products that are toxic to the eye

7. Almost any strain of bacteria can cause infection if there is a breakdown in host defenses or if introduced in large numbers

B. The infectious process

1. Route of entry

a. Conjunctiva, cornea

1) Certain factors can predispose eye to infection: trichiasis, lagophthalmos, dry eye

b. Respiratory tract (mouth and nose)

c. Gastrointestinal tract

d. Genitourinary tract

e. Abnormal areas of mucous membranes and skin

2. Attach and adhere to host cells

a. Bacterial appendages (pili and fimbriae) can interact with host cell surfaces

b. Contact lenses provide a surface for bacterial adherence and multiplication

3. Multiply and spread

4. Production of virulence factors

a. Toxins

1) Exotoxins are excreted by living cell

2) Endotoxins are integral part of cell wall of gram negative bacteria

a) Released on bacterial death and in part during growth

b) May not need to be released to have biologic activity

b. Enzymes

1) Collagenase

2) Coagulase

3) Hyaluronidase

4) Streptokinase

5) Hemolysins

C. Methods of identification

1. Gram stain

a. Allows grouping of bacteria into two major categories

b. Based on structure of cell wall

c. Procedure

1) Crystal violet, a basic dye, is applied to bacterial smear

2) Iodine solution is applied; all bacteria will be stained blue at this point

3) Cells are treated with alcohol

a) Gram positive cells remain blue

b) Gram negative cells are decolorized

4) A counterstain (red dye safranin) is applied

d. Gram stain response

1) Gram positive bacteria stain purple

2) Gram negative bacteria stain red

e. Specimen collection

1) Cornea and conjunctival scrapings

a) Kimura platinum spatula

b) Calcium alginate swab

c) Topical anesthetics (preservative-free)

d) Slides and fixatives

2) Intraocular fluid

3) Tissue or biopsy

2. Culture

a. Specimen collection

b. Media (used by laboratory)

1) Soybean casein digest broth

2) Sheep blood agar

3) Chocolate blood agar, etc.

c. Interpretation (done by laboratory)

1) Knowledge of normal flora

2) Size and shape of colonies

3) Size and morphology and gram staining of organisms

4) Growth and nutritional requirements

3. Antibiotic susceptibility testing

a. Detection of antibiotic resistant bacteria

b. Methods

1) Serial broth dilution

a) Antibiotic + broth + test organism

b) Minimal inhibitory concentration (MIC)

2) Agar disc diffusion

a) Inoculated agar plates + antibiotic-impregnated disc

b) Use discs of different concentrations, establish MIC

3) Automated procedure

c. Interpretation

1) Reflects levels of drug achievable in serum, not tear film or ocular tissues

III. The Staphylococci

A. Medically important species

1. Staphylococcus aureus—colonizes anterior nares, skin

2. Staphylococcus epidermidis—normal skin flora

3. Staphylococcus saprophytcus—free-living, may colonize skin

B. Eye infections

1. Marginal blepharitis and meibomianitis

2. Conjunctivitis

3. Toxic epithelial keratitis

4. Marginal infiltrate

5. Ulcerative keratitis

6. Phlyctenular keratitis

7. Hordeola and chalazia

8. Dacryocystitis

9. Endophthalmitis

C. Other infections

1. Abscesses

2. Endocarditis

3. Food poisoning

D. Morphology

1. Gram positive cocci arranged in grape-like clusters, singly or in pairs

2. Ocular scraping usually in pairs

E. Pathogenesis

1. Members of normal flora of skin, respiratory, and gastrointestinal tracts

2. Toxins

a. Exotoxins

1) Probably account for clinical manifestations of blepharoconjunctivitis (ulcerative blepharitis, eczematoid scaling and weeping inflammation of lids)

2) Enterotoxins are produced by some strains of S. aureus while growing on certain foods contaminated by human carriers. Ingestion of this preformed toxin causes the symptoms of food poisoning

3) Toxic shock syndrome toxin

3. Enzymes

a. Catalase

b. Coagulase

c. Hyaluronidase

4. Antigens: cause sterile hypersensitivity reaction (marginal infiltrates) with blepharitis

F. Laboratory (laboratory would culture this for you) FYI

1. Culture = aerobic or facultative; catalase positive S. Ureas: coagulase (+), yellow pigment, hemolytic, ferments mannitol S. epidennidis: coagulase (-), nonhemolytic

G. Treatment - covered in detail in anti-infectives

1. Cephalosporins: cefazolin, cefepime

2. Nafcillin

3. Vancomycin

4. Many drug-resistant strains

a. Penicillin

b. Erythromycin

c. Tetracyclines

5. Topical Ocular Treatment

a. Bacitracin

b. Tobramycin

c. Trimethroprim

d. Erythromycin

e. Gentamicin

f. Norfloxacin (Chibroxin)

g. Ciprofloxacin (Ciloxan)

h. Ofloxacin (Ocuflox)

i. Levofloxacin (Quixin)

j. Moxifloxacin (Vigamox)

k. Gatifloxacin (Zymar)

H. Control

1. Susceptible to high temperatures, disinfectant, and antiseptic solutions

2. Careful hand washing (Standard Precautions)

IV. The Streptococci

A. Medically important species

1. Streptococcus pyogenes (group A)

2. Streptococcus pneumoniae (pneumococcus)

B. Eye infections

1. Membranous, purulent, or hemorrhagic conjunctivitis

2. Ulcerative keratitis

3. Dacryocystitis

4. Endophthalmitis

a. Most common cause of late-onset endophthalmitis in patients with filtering blebs

C. Morphology

1. Gram-positive cocci arranged typically in chains or pairs

2. S. pneumonias—gram.positive lancet- or bullet-shaped diplocci

D. Pathogenesis

1. Streptococci (in general)

a. Rapidly spreading infection

b. Produce a variety of toxins and enzymes

c. Antiphagocytic capsule

d. Strep infections can be associated with marked inflammation

E. Laboratory (FYI)

1. Culture: enriched media (fastidious)

a. Catalase negative

b. Hemolysis

c. A= incomplete (green)

d. B = complete (clear)

F. Treatment (covered in detail in anti-infective lecture)

1. Penicillin

2. Ceftriaxone

3. Clindamycin

4. Vancomycin

5. Response to aminoglycosides is unreliable

6. Ocular infections

a. Trimethroprim

b. Norfloxacin (Chibroxin)

c. Ciprofloxacin (Ciloxan)

d. Ofloxacin (Ocuflox)

e. Levofloxacin (Quixin)

f. Moxifloxacin (Vigamox)

g. Gatifloxacin (Zymar)

h. Bacitracin

i. Erythromycin ointment

V. The Neisseria

A. Medically important species

1. Neisseria meningitis (meningococcus)

2. Neisseria gonorrhoeae (gonococcus)

B. Eye infections

1. Both species can penetrate intact corneal epithelium

2. Hyperacute purulent conjunctivitis

a. Adults

b. Newborns (ophthalmia neonatorum) 3 to 5 days after delivery

3. Ulcerative keratitis (potential for perforation)

4. Endophthalmitis

C. Morphology

1. Gram-negative diplococci with kidney-bean shape

2. Ocular infections

a. Intracellular in polymorphonuclear leukocytes (PMNs/neutrophils)

D. Pathogenesis

1. N. gonorrhoeae

a. Invades surface of undamaged cornea

b. Attacks mucous membranes (eye, genitourinary tract)

c. Extracellular pathogenesis: can damage host cells without entering cytoplasm

1) Introduce pores into host cell

2) Cell leaks essential nutrients

d. Intracellular pathogenesis

1) Microvilli of comeal epithelium make initial contact with adhesive protein on surface of gonococci

2) Attachment of epithelial cells via pili

3) Engulfed by host cell membrane

4) Intracellular multiplication kills cell

e. Marked local inflammatory response

1) Symptomatic infection is caused by destnuction of mucosal surfaces, cell death,and accumulation of polymorphonuclear leukocytes (PMNs) and gonococci

E. Laboratory (FYI)

1. Specimen: conjunctival exudate; gram-stained smears reveal diplococci within PMNs

2. Culture: chocolate agar; COz atmosphere (5-10%); increased humidity 37°C; Thayer-Martin medium

19. Not as useful in ocular infections

20. Best for genitourinary specimens

F. Treatment (covered in detail in anti-infective lecture) - Cephalosporins

1. Azythromycin – Macrolide

2. Cephalosporins

a. Cefixime

b. Cefotaxime

c. Cefotetan

d. Cefoxitin

e. Ceftizoxime

f. Ceftriaxone

3. Topical Ocular Treatment

a. Bacitracin

b. Erythromycin

c. Neomycin

d. Tetracycline

e. Norfloxacin (Chibraxin)

f. Ciprofloxacin (Ciloxan)

g. Ofloxacin (Ocuflox)

h. Levofloxacin (Quixin)

i. Moxifloxacin (Vigamox)

j. Gatifloxacin (Zymar)

4. Ophthalmia neonatorum

a. Crede's prophylaxis

1) Topical 1% silver nitrate

2) Classic treatment

3) Not effective in preventing neonatal chlamydial ophthalmia

b. Topical 0.5% erythromycin ointment or 1% tetracycline ointment

1) Effective against Neisseria and Chlamydia

G. Prevention and control

1. Block direct mucosal contact (condoms)

2. Inhibit gonococcus (vaginal foams)

3. Treat infected pregnant women

VI. Pseudomonas aeruginosa

A. Eye infections

1. Ulcerative keratitis (can perforate within 72 h)

2. Contact lens wearers (soaking solutions)

3. Conjunctivitis

4. Dacryocystitis

5. Endophthalmitis

B. Morphology

1. Gram-negative slender rod, motile

C. Pathogenesis

1. Requires introduction into compromised tissue

a. Damaged skin or mucous membranes

2. Produces toxins and enzymes

D. Laboratory (FYI)

1. Culture

a. Obligate aerobe

b. Smooth, round colonies, blue-green pigment

c. Often sweet odor

E. Treatment (covered in detail in anti-infectives lecture)

1. Consistently resistant to antibiotics

2. Gentamycin, tobramycin, amikacin

3. Piperacillin and ticarcillin in high doses

4. Third and 4th generation cephalosporins

a. Cefotaxime

b. Cefepime

c. Cefoperazone

5. Ocular Treatment

a. Gentamycin

b. Polymyxin B

c. Tobramycin

d. Norfloxacin (Chibroxin)

e. Ciprofloxacin (Ciloxan)

f. Ofloxacin (Ocuflox)

g. Levofloxacin (Quixin)

h. Moxifloxacin (Vigamox)

i. Gatifloxacin (Zymar)

F. Prevention and control

1. Environmental: Water, soil, vegetation

2. Free-living in moist environment: humidifiers, contact lens case, eye drops

3. Opportunist—compromised host (widespread in hospital environment)

VII. Actinomyces israelii

A. Eye infections

1. Canaliculitis—most common cause

2. Chronic conjunctivitis

B. Morphology

1. Gram-positive branching filament

C. Pathogenesis

1. Found on teeth, mucous membranes of mouth

2. Typical lesion: abscess with sulfur granules

3. Pathogenic mechanism unknown

D. Laboratory

1. Sulfur granules on smear

2. Branching filaments

3. Culture

a. Obligate anaerobe

E. Treatment

1. Surgical evacuation of canaliculus

2. Irrigation with penicillin solution

3. Systemic penicillin G

a. Amoxicillin

b. Doxycycline

c. Erythromycin

d. Clindamycin

Vlll. Treponema palladium

A. Eye infectious/ocular conditions

1. Conjunctivitis

2. Uveitis

3. Argyll-Robertson pupils

4. Episcleritis

5. Optic neuritis

6. Retinitis

B. Other infections

1. Syphillis

a. Primary chancre

b. Secondary lesions

c. Cure, latency (host defenses)

d. Tertiary disease

1) Central nervous system, cardiovascular system, eyes (years after primary chancre)

e. Congenital disease

1) Spirochetes pass through placenta

2) Syphillitic mother transmits disease to infant

C. Pathogenesis

1. Sexual contact

2. Multiplies locally

3. Lymph nodes, bloodstream

D. Morphology

1. Fine, filamentous spirochete, motile

2. Darkheld microscopy and immunofluorescence

E. Laboratory (FYI)

1. Cannot be grown on lab media

2. Darkfield examination

3. Immunofluorescent staining

4. Serologic tests

F. Treatment (Systemic)

1. Benzathine Pencillin

2. Doxycylcine or Tetracycline

3. Ceftriaxone

4. Azythromycin

G. Prevention

1. Condoms

IX. Chlamydia trachomatis

A. Eye infections

1. Chronic keratoconjunctivitis (trachoma)

a. World's leading preventable cause of blindness

b. Endemic areas: developing countries

c. Associated with poverty, poor sanitation

d. Clinical course

1) Follicular keratoconjunctivitis with intense cellular infiltration and papillary hypertrophy

2) Comeal panni may result from response of local immune system to chlamydial antigens

3) Follicles necrose, resulting in conjunctival scarring; scars contract, causing entropion and trichiasis

2. Inclusion conjunctivitis

a. “Industrialized" countries

b. Clinical course—Newborns

1) Eye is inoculated during passage through birth canal

2) Acute onset 5-12 days after birth

3) Purulent conjunctivitis

4) Conjunctival hyperemia, lid edema

c. Clinical course—Adult

1) Typically young, sexually active adult

2) Bilateral follicular conjunctivitis with hyperemic bulbar conjunctivitis

3) Mucopurulent discharge

4) As disease progresses epithelial keratitis, subepithelial infiltrates and superior pannus formation

5) Painless swelling of regional lymph nodes

6) up to 60% of patients have concurrent genitourinary symptoms

B. Morphology

1. Gram-negative-type cell wall

2. Obligate intracellular parasites

3. Two morphological forms

a. Elementary body (EB) is adapted for extracellular survival; infectious

b. Reticulate body (RB) is adapted for intracellular multiplication; not infectious

C. Pathogenesis

1. Generalized natural history

a. Persistent infection and reinfection

b. Hypersensitivity reactions to organism

c. Superinfection with other bacterial species

D. Laboratory (FYI)

1. Cytoplasmic inclusions in smears of conjunctival scrapings (Giemsa stain)

2. Culture

a. Yolk sac of chick embryos

b. McCoy mouse cell line

E. Treatment (covered in detail in anti-infective lecture)

1. Topical erythromycin or tetracycline

2. Systemic tetracycline, doxycycline, minocycline, azythromycin. For pregnant women, use erythromycin

F. Epidemiology and control

1. Trachoma—improved sanitation

2. Inclusion conjunctivitis

a. Prevent sexual transmission of Chlamydia

b. Treatment of infected pregnant women

COMMON BACTERIAL OCULAR PATHOGENS

|ORGANISM |EYE INFECTIONS |MORPHOLOGY |EYE PATHOGENS |CONTROL |

|Pseudomonas |1) Ulcerative keratitis |1) Gm(-) |1) Route of entry: damage skin or |1) Found in water soil |

|aeruginosa |(perforate within 72 hrs) |2) Slender Rod |mucous membranes |vegetation |

| |2) Conjunctivitis |3) Motile |2) Attaches via pili |2) Immunocompentence |

| |3) Dacryocystitis | |3) Surface slime layer |3) Hygeine |

| |4) Endophthalmitis | |4) Toxins |4) Disinfectants |

| | | |5) Enzymes | |

|Actinomyces |1) Canaliculitis |1) GM (+) |1) Found on teeth, mucous membranes |1) Hygiene |

|Israeli |2) Conjunctivitis |2) Branching Filament |of mouth | |

|Treponema |1) Syphilis |1) Fine filamentous |1) Mucous membranes |1) Block mucous membranes |

|Palladum |a) Conjunctivitis |spirochete |2) Primary local replication at site |2) Hygiene |

| |b) Uveitis |2) Motile |of entry | |

| |c) Argyll-Robertson pupil |3) Dark field microscopy |3) Secondary lesions spread via | |

| |d) Episceritis | |lymph, blood stream | |

| |e) Optic neuritis | |4) Latency | |

| |f) Retinitis | | | |

|Staphylococci |1) Conjunctivitis |1) Gm (+) |1) Normal flora of skin, respiratory |1) Careful hygiene |

| |2) Toxic epithelial keratits |2) Cocci |and gastrointestinal tracts |handwashing |

| |3) Marginal infiltrate |3) Singly or in pairs |2) Exotoxins |2) Disinfectants |

| |4) Ulcerative keratitis | |3) Enzymes | |

| |5) Phyctenular keratitis | | | |

| |6) Hordeola chalazia | |LABORATORY | |

| |7) Dacryocystitis | |Culture aerobic | |

| |8) Endopthalmitis | | | |

|Streptococci |1) Conjunctivitis |1) Gm (+) |1) Rapidily spreading infection |1) Careful hygiene |

| |2) Ulcerative keratitis |2) Cocci or lancet shape |2) Exotoxins |handwashing |

| |3) Dacryocystic |3) Chains or pairs |3) Enzymes |2) Disinfectants |

| |4) Endophthalmitis | |4) Antiphagocytic capsule | |

| | | |5) Marked inflammation | |

|Neisseria |1) Ulcerative keratitis |1) Gm (-) |1) Invades surface of undammaged |1) Block direct mucosal |

|meingitis |2) Conjunctivitis |2) Kidney bean shaped |cornea |contact |

|gonorrhoeae |3) Endophthalmitis |3) Diplococci |2) Attacks mucous membranes (eye and | |

| | | |GI) | |

| | | |3) Engulfed by host cell | |

| | | |4) Causes marked inflammation | |

| | | |5) Destroys mucosal surfaces | |

|Chlamydia |1) Conjunctivitis |1) Gm (-) |1) Attaches to & is injested by host |1) Inproved sanitation |

|trachomatis | |2) Obligate intracellular |cell |2) Mucous membrane barriers |

| | |parasite |2) Divides utilizing contents of host| |

| | | |by binary fission | |

| | | |3) Causes persitent infection and | |

| | | |reinfection | |

| | | |4) ATP parasite | |

Chart of common ocular bacterial pathogens.

Mycology

I. Ocular mycology

A. Filamentous

1. Aspergillus

B. Yeasts

1. Candida

C. Diphasic/dimorphic

1. Histoplasma

II. Candida: A yeast fungus that is the most common disease causing fungus in northern United States

A. Characteristics

1. Yeast fungus

2. Species

a. Candida albicans—most common disease-causing species

3. Morphology

a. Candida albicans is a gram-positive, oval yeast characterized by elongated budding cells (pseudohyphae) and submerged growths (pseudomycelia)

B. Diseases/eye infections the infections generally are present in certain persons with predisposing factors, e.g., diabetes mellitus, general disability, systemic immunodeficiency (chemotherapy, AIDS), indwelling urinary catheters, intravenous narcotic abuse, systemic antimicrobial therapy, and corticosteroid therapy

1. Other infections

a. Superficial infections—oral thrush, vaginal infection, diaper rash, chronic mucocutaneous candidiasis—T cell defect, esophagitis, intestinal, urinary tract, disseminated infection—immunocompromised host (kidneys, brain, heart, and eye)

2. Ocular infections

a. Endophthalmitis—a well-recognized complication of cataract surgery; characterized by a white cotton ball on the retina or floating free in the vitreous humor

b. Keratitis—usually filamentous form; both can be found in any of the above risk groups

C. Pathogenesis—Candida proliferates in GI tract after systemic antibiotic treatment; the organism can be disseminated throughout the body by way of the circulation

D. Transmission—Candida is not contagious because it is part of the normal body flora; however, large concentrations can enter the body parenterally

E. Laboratory diagnosis

1. KOH and Gram smears superficial

2. Culture and identification—germ tubes

3. Serodiagnosis—not perfected for routine use

F. Treatment

1. Amphotericin B (IV) with or without oral flucytosine for disseminated candidasis

2. Fluconazole

3. Itraconazole

4. Ketoconazole

a. Ocular Topical Treatment: Natamycin

G. Prevention—given its noncontagious nature, treatment is aimed at maintaining normal floral balance and monitoring of people at risk. Females should eat yogurt with active cultures to prevent secondary vaginal yeast infections following antibacterial treatment)

III. Histoplasma

A. Characteristics

1. Species

a. H. capsulatum

2. Morphology

a. Dimorphic fungus

b. Form tuberculate conidia

B. Eye infections/disease

1. Pulmonary disease

2. Disseminated disease

3. Presumed ocular histoplasmosis syndrome—triad; 50% bilateral

a. Punched-out chorioretinal lesions

b. Peripapillary scarring

c. Disciform maculopathy

C. Pathogenesis—inhalation of spores can result in a spectrum of disease; asymptomatic and pulmonary infection (acute and chronic) and disseminated disease, including eye disease.

D. Transmission—inhalation in areas of greatest concentration—Ohio and Mississippi River valleys; bird or bat excrement

E. Lab diagnosis

1. Direct examination difficult

2. Reticuloendothelial organ—intracellular yeasts

3. Culture

4. Serologic tests-Complement fixation (CF)

F. Treatment

1. Amphotericin B for acute systemic infection

2. Oral ketoconazole or IV amphotericin for chronic infection

3. Laser photocoagulation for subretinal neovascularization of maculopathy

G. Prevention—avoidance of infection sources

Parasitology

I. Parasitic infection of the eyes

II. Acanthamoeba—a protozoan in fresh waters, soil, sewage, water

A. Characteristics

1. Active form—trophozoite

2. Dormant-cystic form

3. Resistant to temperature, pH, and chemical conditions

B. Eye infections

1. Keratitis/ulceration that can persist for several months; can be mistaken for herpes simplex keratitis infection

C. Pathogenesis—chronological progression

1. Unilateral redness, foreign body sensation, irritation

2. Pseudodendrite, punctate stain, epithelial haze, microcysts, enlarging coalescing infiltrates, radial keratoneuritis

3. Ring of stromal corneal infiltrate—hypopyon

4. Recurrent comeal erosion

5. Blephrospasms, profuse serous discharge, low grade cell and flare, keratic precipitate, Descemet's folds

D. Transmission—direct contact with contaminated water—hot tubs, swimming pools, contact lens solutions, tapwater

E. Laboratory diagnosis

1. Corneal scraping

2. Corneal biopsy—indirect immunofluorescent antibody staining

3. Gram/Giemsa stains

4. Culture—non-nutrient agar, hint of gram-negative (E. coli) bacteria as food source

F. Treatment—difficult

Combination of multiple antibacterial, antifungal, antiamoebic agents:

1. Neomycin

2. Polyhexamethylene biguanide

3. Propamidine isethionate

4. Paromomycin

5. Miconazole

6. Clotrimazole

7. Ketoconazole (systemic)

8. Itraconazole (systemic)

9. Atropine

10. Topical Steroids

11. Penetrating keratoplasty

G. Prevention—avoid using contaminated sources for contact lens care

III. Toxoplasma gondii

A. Characteristics

1. Protozoan causing toxoplasmosis

2. Thirty-five to 40% of adults in United States have been infected by this organism—based on antibody titers

3. One percent diagnosed

4. Particularly threatening to immunocompromised patients (i.e., AIDS) and to the developing fetus

B. Eye diseases/eye infections

1. Infections of immunocompromised host—involves brain and heart

a. Chorioretinitis—lesions on retina caused by inactive cyst

b. Congenital—100% affect macula; posterior pole

C. Pathogenesis

1. Toxoplasma are found within macrophages

2. If macrophages are activated, the toxoplasma are killed

3. In absence of immune response, local inflammation, severe necrosis, and tissue damage occur

4. AIDS patients, if untreated, may die of toxoplasma infection of the brain

D. Acquired transmission

1. Acquired by eating undercooked meat or by ingesting food contaminated with infected cat feces

2. Cats are an important vector for disease because they harbor the sexual cycle of parasite and excrete oocysts in their stools

3. After ingestion parasites released in small intestine, penetrate gut wall; invade blood

4. Obligate intracellular parasites

5. Normal host mounts an immune response that controls infection and leads to formation of dormancy within tissue

6. If person becomes immunosuppressed at some time in the future, infection becomes active

E. Diagnosis

1. Immunologically competent host—rising antibody titer, IgG, IgM

2. Tissue cysts in biopsy material

F. Treatment

1. Healthy individuals do not require treatment

2. Congenital infections—too late to treat; damage has been done

3. Spiramycin

4. Pyrimethamine plus sulfadiaxine or trimethoprim plus sulfamethoxazole—in immunocompromised

5. Clindamycin

6. Steroids for anti-inflammatory treatment of the eye in combination with anti-infective

G. Prevention

1. Cook meat thoroughly

2. Avoid cat-box cleaning during pregnancy

3. Women should be screened for antitoxoplasma antibody at time of marriage

IV. Toxocara

A. Characteristics

1. Species

a. T. carus

2. Morphology

a. A larval nematode

B. Eye infections

1. Choroiditis

2. Iritis—iridocyclitis, pars planitis

3. Chorioretinitis

4. Keratitis

5. Retinal detachment

6. Endophthalmitis

C. Pathogenesis—creates a subretinal granuloma in posterior pole, resulting in a scar.

D. Transmission

1. Contaminated pets

2. Soil

3. Sand boxes

E. Lab diagnosis

1. ELISA—titer of 1.8

F. Treatment

1. Diethylcarbamazepine and thiabendazole

2. Corticosteroids in combination with anti-infective

3. Retinal detachment surgery

G. Prevention

1. Protect children against contact with infected dogs and cats, especially kittens and puppies

2. Animals should be dewormed—piperazine monthly

3. Cover sand boxes

V. Pediculosis/phthiriasis

A. Characteristics

1. Species: Phthirius pubis, corpans, capitis

2. Morphology—six-legged, ectoparasitic louse

B. Eye disease/infections

1. Pubic infestation

2. Eye infections

a. Chronic blepharoconjunctivitis

b. Infestation of eyelids

c. Follicular conjunctivitis

d. Marginal keratitis

e. Parasitophobia

C. Pathogenesis—saliva (from the parasite) when introduced into the host produces an immunologic and/or toxic reaction characterized by itching and/or burning

D. Transmission—oculogenital route, characterized as a sexually transmitted disease, can also be transmitted among household contacts

E. Lab diagnosis—none; diagnosis is made by identification of eggs in adult organism on lashes (biomicroscopy)

F. Treatment

1. Removal, smothering with bland ointment, physostigmine sulfate (eserine) ointment

2. Pubic—pyrethrin preparations that include gamma benzene hexachloride

3. Examine and treat sexual partners and household contacts

G. Prevention

Self-Assessment - Microbiology of the Eye Practice Questions

1. What parasitic infection of the eye is transmitted through eating undercooked meat?

a. Toxocara carus

b. Acanthomeoba

c. Phthirius pubis

d. Toxoplasma gondii

2. What mycologic species may cause an endophthalmitis after cataract surgery that looks like a “white cotton ball” on top of the retina floating free in the vitreous humor?

a. Aspergillus

b. Candida albicans

c. Histoplasmosis capsulatum

3. What group of bacteria is the most common cause of late-onset endophthalmitis in patients with filtering blebs?

a. Streptococci

b. Neisseria

c. Pseudomonas Aeruginosa

d. Actinomyces israelii

4. Why is it difficult to completely eliminate viruses?

a. Enzyme activity

2 Latency

b. Translation

c. Transcription

1. D 2. B 3. A 4. B

Literature Review: Ocular Microbiology

(Bacteriology, Virology, Mycology, and Parasitology)

Title: John Hopkins Division of Infectious Diseases Antibiotic Guide

Author:

Source: hopkins-

Title: Present Status of Contact Lens-Induced Corneal Infections

Author: Driebe, W.T.

Source: Ophthalmol Clin North Am 16(3):485-94, 2003.

Title: A Review of Bacterial Keratitis and Bacterial Conjunctivitis

Author: Limberg MB

Source: Am J Opthalmol 112:2S-9S, 1991

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download