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Ophthalmology > Day 3 (3): Ocular Microbiology > Flashcards

Day 3 (3): Ocular Microbiology Flashcards

1
Q

Normal flora of the outer eye (conjunctiva and lid margin).

A
  1. Staphylococcus epidermidis
  2. Staphylococcus aureus
  3. Corynebacterium
  4. Micrococcus
  5. Propionibacterium acnes
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2
Q

Most common infectious cause of blepharitis?

A
  1. Staphylococcus
  2. Moraxella
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3
Q

Most common infectious cause of conjunctivitis?

A
  1. Staphylococcus aureus
  2. Streptococcus
  3. Chlamydia trachomatis
  4. Neisseria gonorrhoeae
  5. Haemophilus influenzae
  6. Moraxella
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4
Q

Most common infectious cause of keratitis?

A
  1. Staphylococcus (aureus and epidermidis)
  2. Streptococcus pneumoniae
  3. Pseudomonas aeruginosa
  4. Moraxella
  5. Fungal (Fusarium, Aspergillus, Candida albicans)
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5
Q

Most common infectious cause of canaliculitis?

A

Actinomycetes

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6
Q

Hordeolum vs Chalazion

A

Hordeolum:
- location: at or near an eyelash follicle
- cause: ACUTE BACTERIAL INFECTION of the glands of Zeis or Moll (EXTERNAL/Stye) or Meibomian Gland (INTERNAL)
- presentation: acute redness, swelling and tenderness; pimple-like
- treatment: warm compress, antibiotics

Chalazion:
- location: above or extending beyond eyelashes on upper lid
- cause: CHRONIC, STERILE INFLAMMATION due to a blocked Meibomian or Zeis gland
- may develop from an INTERNAL hordeolum
- presentation: chronic, firm, nontender nodule; larger
- treatment: warm compress, surgery

Mnemonics:

No! Stay back! It HURTS - HORDEOLUM
Dude! Take a CHILL pill - CHALAZION

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7
Q

Bacterial classification according to GRAM STAIN and SHAPE

A

Coccus = sphere
Bacillus = rod

Gram (+) Cocci:
1. Staphylococcus
2. Streptococcus
3. Enterococcus

Gram (+) Bacilli:
1. Bacillus: (+) spores
2. Corynebacterium: (-) spores

Gram (+) Pleomorphic:
1. Propionibacterium

Gram (+) Filaments:
1. Actinomyces israelli
2. Nocardia asteroides

Gram (-) Cocci:
1. Neisseria

Gram (-) Bacillus:
1. Moraxella
2. Haemophilus
3. Pseudomonas
4. Enterobacter

Gram (-) Spirochetes (spiral, comma):
1. Treponema pallidum
2. Borrelia burgdorferi

Gram (-) Pleomorphic
1. Chlamydia

OTHERS:

AFB: Mycobacteria

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8
Q

Rationale behind Gram staining

A

Gram Stain
- separates bacteria based on CELL WALL COMPOSITION

Gram POSITIVE (PURPLE)
- 90% peptidoglycan which acts like a mesh that traps crystal violet in between layers

Gram NEGATIVE (RED)
- 10% peptidoglycan BUT high lipid content

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9
Q

What are the steps of Gram Staining?

A
  1. Primary Stain: Crystal Violet
  2. Mordant/Fixant: Iodine
    - binds to crystal violet and traps and fixes it in the cell wall
  3. Decolorizing Agent: Acetone/Ethanol
    - Gram (+): THICK peptidoglycan layer traps the dye
    - Gram (-): outer lipid layer of cell wall is partially dissolved thus crystal violet is washed out from the THIN peptidoglycan layer
  4. Counterstain: Safranin
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10
Q

Culture media classification by function.

A
  1. Basic: simple media that supports growth of most NON-FASTIDIOUS bacteria
    - okay for most bacteria but cannot isolate
  2. Enriched: extra nutrients added for growth of FASTIDIOUS bacteria (choosy)
    - for bacteria with special needs
  3. Selective/Differential: inhibitory agents added to suppress growth of some microorganisms while allowing some to thrive
    - antibiotics, dyes, chemicals, pH alteration
    - for bacterial isolation
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11
Q

Most basic culture medium

A

Nutrient Agar

  • (+) Growth: NON-FASTIDIOUS bacteria –> mixed colonies
  • Contains needs of most bacteria to grow BUT LACKS nutrients needed by FASTIDIOUS bacteria
  • FASTIDIOUS bacteria DOES NOT grow:
    1. Neisseria
    2. Moraxella
    3. H. influenzae
    4. Streptococcus
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12
Q

What is Blood agar for?

A

Blood Agar

  • Enriched: Nutrient agar (basic) + 5-10% Sheep’s blood
  • Differential: (+) Growth and differentiation based on hemolytic activity by HEMOLYSINS
    1. Staphylococcus
    2. Streptococcus
  • Hemolysins: lipids and proteins that cause lysis of RBCs by disrupting the cell membrane
  • Selective: (-) Growth because of inhibitors in fresh blood
    1. Neisseria
    2. Haemophilus
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13
Q

Classification of bacteria based on hemolysis of RBCs on blood agar.

A
  1. BETA-Hemolytic: CLEAR zone with clear edge around colony = COMPLETE hemolysis

Mnemonic: CLEAR Py (Pie) BAG

  • Streptococcus PYogenes (Group A Streptococcus/GAS)
  • Beta
  • Staphylococcus Aureus
  • Streptococcus aGalactiae (Group B Streptococcus/GBS)
  1. ALPHA-Hemolytic: GREEN (Biliverdin) cloudy zone around = PARTIAL hemolysis

Mnemonic: GREEN VAN

  • Viridans streptococcus group
  • Alpha
  • Streptococcus pNeumoniae

GAMMA-Hemolytic: NO COLOR CHANGE (still red) around =
NO HEMOLYSIS

  • Staphylococcus epidermidis and saprophyticus
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14
Q

What is Chocolate agar?

A

Chocolate Agar

  • Blood agar heated to 80 degrees Celsius to:
    1. Inactivate inhibitors in fresh blood
    2. Release growth factors
  • Heating causes lysis of RBCs
  • (+) Growth: Haemophilus influenzae Type B
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15
Q

What is Thayer-Martin VPN agar?

A

Thayer-Martin VPN Agar

  • Chocolate agar + antibiotics
    1. Vancomycin: (-) Gram positive
    2. Polymyxin/Colistin: (-) Gram negative
    3. Nystatin: (-) fungi
  • (+) Growth: Neisseria gonorrhoeae and meningitidis

Modified VPN Agar
- (+) Trimethoprim: (-) Proteus

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16
Q

What is the MacConkey and EMB agar?

A

Similarities:
1. BOTH selective and differential media (only different additives)
2. BOTH allow growth of Gram (-) bacteria ONLY
3. BOTH utilize lactose and dyes to differentiate Gram (-) bacteria
4. BOTH work by the same principle: strength of lactose fermentation to lactic acid causing an increase pH

MacConkey Agar

  • Inhibitors: Bile Salts + Crystal Violet –> inhibit Gram (+)
  • pH Indicator: Neutral Red –> differentiate lactose vs non-lactose fermenters
  1. Weak - Strong fermenters: pink to dark red
  2. Non-fermenters: colorless

EMB Agar

  • Inhibitors: Methylene Blue –> inhibit Gram (+)
  • pH Indicator: Eosin Y –> differentiate lactose vs non-lactose fermenters
  1. Weak - Strong fermenters: brown-pink to deep purple to black
  2. Non-fermenters: colorless

Fermenters: Enterobacteriaceae, E. coli (with green metallic sheen)
Non-fermenters: P. aeruginosa, Salmonella, Shigella

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17
Q

What is the Thioglycolate Broth?

A

Thioglycolate Broth

  • Differentiates bacteria based on oxygen requirements
  • Enriched: Sodium thioglycolate –> absorbs oxygen –> anaerobic environment
  • Differential: Resazurin –> dye that turns pink if (+) oxygen
  • Agar: prevent diffusion of oxygen to lower layers
  1. Obligate aerobes: NEED oxygen
    - topmost layer
  2. Microaerophiles: anaerobes that can tolerate oxygen IN MODERATION
    - upper part but not at top because too much oxygen is poison
  3. Facultative anaerobe: aerobes that PREFER OXYGEN but can grow with no oxygen
    - mostly at top but can be found everywhere
  4. Aerotolerant: can tolerate any condition thus NO PREFERENCE
    - everywhere
  5. Obligate anaerobes: HATE oxygen
    - bottommost layer
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18
Q

What is Brain Heart Infusion agar?

A

BHI Agar

  • Enhanced: (+) boiled bovine/porcine heart and brain
  • Non-selective
  • Growth of FASTIDIOUS organisms
    1. Streptococcus
    2. Meningococcus/Neisseria meningitides
    3. Fungi
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19
Q

What are the other culture media used and organisms that grow on them?

A
  1. Potassium Tellurite Agar: Corynebacterium
  2. Lowenstein-Jansen Agar: Mycobacterium
  3. Non-Nutrient Agar with E. coli overlay: Acanthamoeba
    - alternative to corneal biopsy in keratitis
  4. Saboraud Agar: Fungi
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20
Q

Common stains used.

A
  1. Gram Stain
    - Gram (+): purple/blue
    - Gram (-): red/pink
  2. Giemsa/Wright-Giemsa Stain
    - Nucleic acid stain: phosphate group of DNA
    - Human cells: purple/blue
    - Bacterial cells: red/pink
  3. Acid Fast (Ziehl-Neelsen/Kinyoun) Stains
    - Mycobacteria: red/pink
    - Others: blue (ZN) or green (K)
  4. Potassium Hydroxide (KOH) Stain
    - Fungi (Dermatophytes, Candida)
  5. Calcofluor-White Stain
    - Acanthamoeba keratitis
  6. Gomori-Methenamine Silver Stain
    - Fungi (BOTH dead and alive)
    - Cell wall: brown to black
    - Background: green
  7. Periodic Acid Schiff
    - Fungi (ALIVE only)
    - Cell wall: magenta
    - Background: blue
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21
Q

When presented with a Gram (+) cocci, what test is used to determine if its Staphylococcus or Streptococcus?

A

Catalase Test: catalase breaks down peroxide into oxygen and water
- (+) if with bubbles or oxygen production

Positive: STAPHYLOcoccus (+ grape-like cluster)
Negative: STREPTOcoccus (+ pairs/chains/strips)

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22
Q

How to differentiate Staphylococcus species?

A
  1. Coagulase Test: coagulase activates prothrombin and causes fibrin in plasma to clot
    - (+) if with clumps = clotting

Positive: S. aureus
Negative: Others

  1. Novobiocin Test: test for antibiotic resistance

Sensitive/(+) Zone of Inhibition: S. epidermidis
Resistant/(-) Inhibition: S. saprophyticus

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23
Q

How to differentiate Streptococcus species?

A

Growth pattern on BLOOD AGAR

  1. Beta-hemolytic: complete hemolysis = clear zone

–> Bacitracin Test
Sensitive/(+) Zone of Inhibition: S. pyogenes (Group A)
Resistant/(-) Zone: S. agalactiae (Group B)

Mnemonic: Clear Py (pie) BAG

PYogenes - Beta - Aureus - aGalactiae

  1. Alpha-hemolytic: partial hemolysis = green zone (biliverdin)

–> Optochin Test
Sensitive/(+) Zone of Inhibition: S. pneumoniae
Resistant/(-) Zone: Viridans group

Mnemonic: Green VAN

Viridans - Alpha - pNeumoniae

  1. Gamma-hemolytic: no hemolysis = no change
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24
Q

Antibiotic resistance tests to determine Staphylococcus or Streptococcus species

A

Novobiocin: Staphylococcus (epidermis vs saprophyticus)
Bacitracin: Beta-hemolytic Streptococcus (pyogenes vs agalactiae)
Optochin: Alpha-hemolytic Streptococcus (pneumoniae vs viridans)

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25
Q

Describe Staphylococcus spp.

A

Mnemonic: CLUSTER of people posing for a group photo with a CAT wearing GOLD (aureus) medals

Gram POSITIVE cocci - purple/blue
In grape-like CLUSTERS
Facultative anaerobe: aerobe with faculty to become anaerobe
CATalase POSITIVE: (+) bubble formation

  • Common infectious agent in EXTERNAL eye infections (especially BLEPHARITIS)

Treatment:
Penicillins, Cephalosporins, Clindamycin, Tobramycin, Erythromycin, Vancomycin, Fluoroquinolones (Levo, Gati, Moxi)

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26
Q

Describe Staphylococcus aureus.

A

Gram POSITIVE cocci - purple/blue
Grape-like CLUSTERS
Facultative anaerobe
Catalase POSITIVE: (+) bubble formation

Coagulase POSITIVE: (+) clumping or clots
BETA-hemolytic: (+) GOLD pigments

Virulence factors:
1. Coagulase: activates prothrombin and causes fibrin to clot
- fibrin formation around the bacteria protective from phagocytosis

  1. Hemolysin: destroys RBCs, WBCs, platelets
    - tested with blood agar
  2. Leukocidin: destroys WBC
    - Panton-Valentine-Leukocidin: in CA-MRSA, (+) recurrent abscess
  3. Penicillinase: destroys B-lactam ring on penicillins
  4. Exfoliatin: causes skin to slough off (Scalded Skin Syndrome)
  5. Toxic Shock Syndrome Toxin (TSST-1): cytokine storm
  6. Enterotoxin: gastroenteritis
  7. Staphylokinase: thrombolytic to break up blood clots and spread from the initial site of infection
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27
Q

Describe Staphylococcus epidermidis.

A

Gram POSITIVE cocci - purple/blue
Grape-like CLUSTERS
Facultative anaerobe
Catalase POSITIVE: (+) bubble formation

Coagulase NEGATIVE: (-) clumping
GAMMA-hemolytic

Novobiocin SENSITIVE: (+) zone of inhibition

  • Part of normal skin flora
  • Problematic in immunocompromised and nosocomial
  • (+) Biofilm formation in catheters and prosthetic devices
  • Multiple antibiotic resistance
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28
Q

Describe Staphylococcus saprophyticus.

A

Gram POSITIVE cocci - purple/blue
Grape-like CLUSTERS
Facultative anaerobe
Catalase POSITIVE: (+) bubble formation

Coagulase NEGATIVE: (-) clumping
GAMMA-hemolytic

Novobiocin RESISTANT: (-) zone of inhibition

  • UTI in females
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29
Q

Describe Streptococcus spp.

A

Mnemonic: STRIPtococcus

Gram POSITIVE cocci - purple/blue
In PAIRS/CHAINS/STRIPS
Facultative anaerobe: aerobe with faculty to become anaerobe
CATalase NEGATIVE: (-) bubble formation

Classification based on:

  1. Hemolytic activity in blood agar

Beta = CLEAR zone = complete hemolysis = pyogenes, agalactiae
Alpha = GREEN zone = partial hemolysis = viridans, pneumoniae
Gamma = NO zone = non-hemolytic

  1. Lancefield antigen: antigenicity of C carbohydrate on cell wall

Group A: Pyogenes
Group B: Agalactiae
No antigen: Viridans and Pneumoniae

  • Common cause of CONJUNCTIVITIS and KERATITIS

Treatment:
Penicillins, Cephalosporins, Clindamycin, Erythromycin, Vancomycin, Fluoroquinolones (Levo, Gati, Moxi)

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30
Q

Describe Streptococcus pyogenes.

A

Lancefield antigen: Group A

Gram POSITIVE cocci - purple/blue
In CHAINS/STRIPS
Facultative anaerobe/Microaerophile
CATalase NEGATIVE: (-) bubble formation

BETA-hemolytic
Bacitracin SENSITIVE: (+) zone of inhibition

Virulence factors:

  1. Pyogenes = Pus-producing = microaerophile = skin infections
  2. Streptolysin O: similar to hemolysin of S. aureus
    - destroys RBCs, WBCs, and platelets
    - test: Anti-Streptolysin O antibodies
  3. Erythrogenic Toxin: similar to TSST-1 of S. aureus
    - cytokine storm
  4. Streptokinase: thrombolytic to break up blood clots and spread from the initial site of infection
  5. M protein: adherence, antigenicity and anti-phagocytic
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31
Q

Similarities in virulence factors of S. pyogenes and S. aureus

A

Thrombolytic: Staphylokinase :: Streptokinase
Cytokine Storm: Toxic Shock Syndrome Toxin - 1 :: Erythrogenic Toxin
Hemolysis: Hemolysin :: Streptolysin O

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32
Q

Describe Streptococcus agalactiae.

A

Lancefield antigen: Group B

Gram POSITIVE cocci - purple/blue
In CHAINS/STRIPS
Facultative anaerobe
CATalase NEGATIVE: (-) bubble formation

BETA-hemolytic
Bacitracin RESISTANT: (-) zone of inhibition

Mnemonic: B for baby (found in vagina)

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33
Q

Describe Streptococcus pneumoniae/Pneumococcus.

A

Lancefield antigen: NONE

Gram POSITIVE - purple/blue
In PAIRS (diplococci), LANCET-shaped with tapered ends and surrounding CLEAR area
Facultative anaerobe
CATalase NEGATIVE: (-) bubble formation

ALPHA-hemolytic
Optochin SENSITIVE: (+) zone of inhibition
(+) Quellung Reaction: swelling when mixed with antibodies and methylene blue

Mnemonic: P for parents (pneumonia and meningitis in adults)
- vaccinate with Pneumococcal vaccines (PCV13 and PPSV23)

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34
Q

Describe Viridans streptococcus group.

A

Lancefield antigen: NONE

Gram POSITIVE cocci - purple/blue
In CHAINS/STRIPS
Facultative anaerobe
CATalase NEGATIVE: (-) bubble formation

ALPHA-hemolytic
Optochin RESISTANT: (-) zone of inhibition

Mnemonic: V as in verde/green = alpha-hemolytic

Found in GI tract, gums, teeth, tongue, saliva
- dental infections, endocarditis

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35
Q

Describe Bacillus spp.

A

Gram POSITIVE bacilli - purple/blue
Single cell, in clumps or in short chains (BOXCAR formation) SQUARED ends
Obligate aerobes
Ubiquitous SAPROPHYTES
SPORE-forming
Medium: (+) cotton or cloud-like with fringe-like edges
FULMINANT keratitis and endophthalmitis (POST-TRAUMA)
Food poisoning and gastroenteritis

Virulence Factors: inactivated by high temperature
1. Enterotoxins (Heat-labile and Heat-stable) - diarrhea
2. Emetic toxins - nausea and vomiting

Treatment: Resistant to beta-lactam antibiotics
Clindamycin, Erythromycin, Vancomycin, Fluoroquinolones (Levo, Gati, Moxi)
* Antibiotic tx will not alter course of s/sx because they’re caused by PREFORMED exotoxins.

36
Q

Describe Corynebacterium diphtheriae

A

Klebs-Loeffler Bacillus

Gram POSITIVE bacilli/rods - purple/blue
CLUB-shaped, or CHINESE CHARACTERS shape
Facultative anaerobe
NON-spore forming
DIPHTHERIA

  • colonizes pharynx, (+) pseudomembrane formation –> exotoxin release
  • attacks cardiac and neural tissues –> myocarditis and neuropathy
  • avoid scraping pseudomembrane or exudates in throat –> increases release of toxin
  • MEMBRANOUS conjunctivitis or ULCERATIVE keratitis

Virulence Factor:
Necrotizing Exotoxin
- “anti-human antibody” like an anti-ribosomal antibiotic
- blocks human protein synthesis

DX:
1. Potassium Tellurite Agar: brown colonies with black haloes
2. Loeffler’s Medium: club-shaped bacillus
- (+) Babes-Ernst/Volutin Granules: intracytoplasmic deposits of polymetaphosphate that appear red when stained with methylene blue

TX:
1. Antitoxin: only inactivates CIRCULATING exotoxin
2. Penicillins/Erythromycin/Vancomycin: kill the bacteria
3. TDaP: since infection does NOT always result to immunity

37
Q

Describe Propionibacterium/Cutibacterium acnes.

A

Gram POSITIVE bacilli - purple/blue
PLEOMORPHIC
Aerotolerant

Primary cause of acne
Primary cause of CHRONIC BLEPHARITIS and DELAYED-ONSET ENDOPHTHALMITIS (esp. post-intraocular or cataract surgery)
Normal part of flora feeding on fatty acids and sebum in follicles

Treatment:
Penicillins, Cephalosporins, Clindamycin, Erythromycin, Vancomycin, Fluoroquinolones (Levo, Gati, Moxi)

38
Q

Describe the Gram POSITIVE filamentous bacteria.

A

Actinomyces israelli

Gram POSITIVE - purple/blue
Obligate ANaerobe
Branching/FILAMENTOUS
Part of the normal flora of the mouth and GIT

Disease:
1. Abscess formation following trauma to mouth
2. Dental infections
3. Canaliculitis
4. Chronic conjunctivitis

DX: Tissue/Discharge CS on Blood Agar with Vitamin K
- ANAEROBIC incubator
- (+) sulfur granules: microcolonies of Actinomyces

TX: Penicillin, TMP-SMX +/- incision and drainage

Nocardia asteroides

Gram POSITIVE - purple/blue
Partially ACID-FAST: (+) mycolic acid on cell wall
Obligate aerobe
Branching/FILAMENTOUS
NOT part of the normal flora
OPPORTUNISTIC: mistaken for TB

Disease:
1. Canaliculitis
2. Chronic conjunctivitis
3. Abscess formation
4. Pneumonia

DX: Modified Acid-Fast Stain
- decolorize with sulfuric acid instead of acid alcohol
- culture: (+) earthy odor

TX: Penicillin, TMP-SMX +/- incision and drainage

Mnemonics: SNAP

S - sulfamethoxazole/sulfur granules
N - nocardia
A - actinomyces
P - penicillin

39
Q

Describe Neisseria spp.

A

Gram NEGATIVE cocci - red/pink
Only pathogenic G (-) cocci
KIDNEY-BEAN shape DIPLOCOCCI and facing each other
DONUT-formation
Facultative anaerobe
Found INTRACELLULARLY (inside PMNs)
CAPNOphilic (HIGH carbon dioxide concentration)
Medium: Thayer-Martin VPN (chocolate agar + antibiotics)
- Vancomycin: inhibit G (+) bacteria
- Polymyxin/Colistin: inhibit G (-) bacteria
- Nystatin: inhibit fungi
- Trimethoprim: inhibit Proteus

Diseases:
1. Meningococcemia/Meningitis
2. Gonorrhea
3. Hyperacute, purulent conjunctivitis
4. Ophthalmia Neonatorum Conjunctivitis
5. Marginal Keratitis

40
Q

Describe Neisseria meningitidis/Meningococcus.

A

Gram NEGATIVE cocci - red/pink
KIDNEY-BEAN shape DIPLOCOCCI and facing each other
DONUT-formation
Facultative anaerobe
Found INTRACELLULARLY (inside PMNs)
Lives in nasopharynx of humans only
CAPNOphilic (HIGH carbon dioxide concentration)
Medium: Thayer-Martin VPN
Maltose- and Glucose-fermenter (MeninGitis)

Diseases:
1. Meningitis: most common cause in 6 mos - 2 yo
2. Meningococcemia

Virulence factors:
1. Pili and capsule: adherence and anti-phagocytic
2. Endotoxin: destroys blood vessels = (+) petechiae
3. IgA Protease

DX: Blood/CSF GS/CS or petechial biopsy

TX: Penicillin G, Ceftriaxone

41
Q

Describe Neisseria gonorrhoeae/Gonococcus.

A

Gram NEGATIVE cocci - red/pink
KIDNEY-BEAN shape DIPLOCOCCI and facing each other
DONUT-formation
Facultative anaerobe
Found INTRACELLULARLY (inside PMNs)
Medium: Thayer-Martin VPN + HIGH CO2
CAPNOphilic (HIGH carbon dioxide concentration)
Commonly occurs with CHLAMYDIA
Glucose-fermenter ONLY (Gonorrhea)

Diseases:
1. Gonorrhea: 2nd most common STI
- urethritis, rectal gonorrhea, pelvic inflammatory disease
2. Ophthalmia Neonatorum Conjunctivitis
- transmitted to infant during vaginal delivery
- manifest at the 1st or 2nd day of life
- may cause blindness
- Prophylaxis: Erythromycin Drops
- Treatment: Ceftriaxone injection and Erythromycin syrup

Virulence factor:
1. Pili: adherence
2. Endotoxin

DX: Discharge GS/CS from urethra

TX:
1. Ceftriaxone IM: N. gonorrhoeae
2. Azithromycin PO: C. trachomatis

42
Q

Describe Moraxella spp.

A

Gram NEGATIVE coccobacilli (short rods) - red/pink
DIPLOBACILLI in BOXCAR formation

Virulence factors:
1. Endotoxin
2. Proteases: canthal maceration

Moraxella lacunata:

ANGULAR BLEPHAROCONJUNCTIVITIS
- Chronic, mild blepharoconjunctivitis localized on outer canthus

Treatment:
Neomycin, Gentamycin, Tobramycin, Fluoroquinolones (Levo, Moxi, Gati)

  • Erythema of the edges of the lids
  • Canthal maceration especially the outer canthus
  • Superficial infiltration of the cornea (ULCERATIVE KERATITIS)
  • Grayish yellow discharge, (+) matting, mainly at the angles
43
Q

Describe Haemophilus influenzae.

A

Gram NEGATIVE coccobacilli - red/pink
Short, slender rods
Facultative anaerobe
CAPNOphilic (HIGH carbon dioxide concentration)
BLOOD-loving: needs blood containing medium
OPPORTUNISTIC: attacks lungs after viral influenza
OBLIGATE human parasite
(+) Quellung Reaction; similar to S. pneumoniae
(+) SATELLITISM:
- most strains of Haemophilus don’t grow on blood agar (contains X factor but no V factor)
- S. aureus produces the V factor as a metabolic by-product when growing in a culture media containing blood.
- Haemophilus may grow on blood agar very close to the colonies of Staphylococcus aureus
6 mos - 2 yo: no antibodies to capsule because maternal Ab gone

Forms:
1. Encapsulated (Type B) = bad = invasive/systemic
2. Non-encapsulated/Non-typeable = non-invasive, local infection

Virulence factors:
1. Capsule: antiphagocytic
2. Hemolysin
3. Lipopolysaccharide Lipid A Endotoxin: heightened local inflammatory response

Diseases (non-encapsulated form):
1. Acute mucopurulent conjunctivitis
2. Dacryocystitis
3. Endophthalmitis

DX: Chocolate Agar with INCREASED CO2 at 37 degrees Celsius
- heating the blood agar releases:
1. Hemin (X factor)
2. NAD+ (V factor)

TX:
1. Steroids: 15-20 mins prior to antibiotics to limit local inflammatory response
2. Cephalosporins (2nd/3rd), Aminoglycosides, Fluoroquinolones
3. HiB Vaccine: children takes 3-5 years to produce own Ab to capsule

44
Q

What is the oxidase test?

A

Tests if organism used oxygen for energy production

45
Q

Describe Pseudomonas aeruginosa.

A

Gram NEGATIVE bacillus
Obligate aerobes
Ubiquitous
OPPORTUNISTIC: nosocomial or immunocompromised)
Oxidase POSITIVE
Lactose NEGATIVE: will NOT tolerate anaerobic respiration
Glucose NEGATIVE
Motile: (+) flagella

Virulence factors:
1. Hemolysin: beta-hemolytic
2. Exotoxin A: similar to diphtheria toxin which inhibits protein synthesis
3. Endotoxin: stromal ring infiltrate

Diseases:
1. Ulcerative Keratitis/Corneal melt
- especially in SOFT CONTACT LENS wearers
2. Scleritis/Scleral melt: due to exotoxin A
3. Dacryocystitis
4. Endophthalmitis

DX: CS in Blood Agar
- green metallic colonies with fruity GRAPE ODOR
- (+) Pyocyanin –> blue; (+) Pyoverdin –> green

TX:
Fluoroquinolones (moxi, gati, levo), 3rd Gen. Cephalosporins (anti-pseudomonal), Polymyxin B, Aminoglycosides (tobra, ami, genta), Polymyxin E/Colistin, Carbenicillin (penicillin for Gram negative)

46
Q

Describe the Enterobacteriaceae group.

A

Enterobacteriaceae (E.coli, Enterobacter, Proteus, Klebsiella)

Gram NEGATIVE coccobacilli to filamentous - pink/red
Opportunistic and ubiquitous
Facultative anaerobe
Oxidase NEGATIVE
Lactose POSITIVE
Glucose POSITIVE

Virulence factors:
1. Endotoxins/Lipopolysaccharide
2. Enterotoxins

Diseases:
1. Ulcerative keratitis
2. Endophthalmitis
3. Gastroenteritis

DX: MacConkey or EMB Agar
(+) Swarming: Proteus
(+) Mucoid/Moist colonies: Klebsiella

TX: Aminoglycosides, Fluoroquinolones, Cephalosporins (3rd Gen)

47
Q

What are the Spirochetes?

A

Gram NEGATIVE - red/pink
CORKSCREW-shaped, tightly coiled
Moves by spinning
TOO SMALL to be seen in light microscopy
CANNOT be cultured in ordinary media

DX:
1. Darkfield microscopy
2. Immunofluorescence tests
3. Silver stains
4. Serologic tests

Famous members:
1. Leptospira: Leptospirosis
2. Borrelia burgdorferi: Lyme disease
3. Treponema pallidum: Syphilis

48
Q

Describe Treponema pallidum.

A

Gram NEGATIVE - red/pink
Fine, helical, SPIROCHETE
Microaerophile
NO toxins or virulence factors
(+) Jarisch-Herxheimer Phenomenon: acute worsening of s/sx after antibiotic initiation due to release of pyrogen by dead spirochetes

Syphilis
- sexually transmitted illness found in humans ONLY
- transmission: contact with ulceration
- manifestations due to host’s immune response
- spectrum:
1. Primary Syphilis: PAINLESS ulcer
2. Secondary Syphilis: erythematous macular rash in palms, soles and mouth; condyloma latum; ANY organ can be affected
3. Latent Syphilis: ASYMPTOMATIC
4. Tertiary Syphilis: COMPLICATIONS (gummas of skin and bones; aneurysms; neurosyphilis: meningitis, stroke, tabes dorsalis, generalized paresis)

Ocular manifestations:
1. Loss of eyebrows - Secondary Syphilis
2. Conjunctivitis
3. Interstitial Keratitis
4. Episcleritis
5. Uveitis
6. Retinitis
7. Argyl-Robertson Pupil/Prostitute’s Pupil
- “accommodates but does not react”
- midbrain lesion causing light-near dissociation
8. Optic Neuritis

DX:
1. Darkfield microscopy
- helical organisms moving in corkscrew fashion
- only seen in lesions of PRIMARY and SECONDARY syphilis
2. VDRL/RPR: nonspecific
3. FTA-ABS/MHA-TP: specific and confirmatory
4. PCR Test

TX:
1. Penicillin G
2. Doxycycline
3. Erythromycin

49
Q

How is the Giemsa Stain performed?

A

Giemsa’s solution: methylene blue + eosin + Azure B

Steps:
1. FIXATION with METHANOL (30 seconds)
2. IMMERSION in 5% GIEMSA STAIN (20–30 minutes) or 10% (5–10 minutes) for emergencies
3. FLUSHING with tap water
4. AIR DRYING

50
Q

Discuss Chlamydia trachomatis.

A

Gram NEGATIVE but NO peptidoglycan layer
OBLIGATE INTRACELLULAR: uses host’s ATP as energy source
CANNOT be cultured on artificial media: only LIVING CELLS
Contains BOTH RNA and DNA
Prefers COLUMNAR epithelial cells lining mucous membranes
MOST COMMON sexually transmitted illness

Serotypes:
1. A to C: Trachoma
2. D to K: Inclusion Conjunctivitis
3. L: Lymphogranuloma Venereum

Life Cycle:
1. Elementary Body: metabolically inert infectious particle that attaches and enters columnar cells
2. Initial/Reticulate Body: after inhibition of phagosome-lysosome fusion
3. Inclusion Body: or liberated as more EB

Diseases:
1. Trachoma/Follicular Conjunctivitis/Adult Inclusion Conjunctivitis
- Serotypes A, B, C
- Chronic conjunctivitis that’s the LEADING CAUSE OF PREVENTABLE BLINDNESS
- Insidious course: over 10-15 years
- Inflammation + scarring –> cicatricial ENtropion –> corneal scarring
- (+) Artl’s Line: thick band of scar tissue running horizontally in the junction of the anterior 1/3 and posterior 2/3 of palpebral conjunctiva
- (+) Herbert’s Pits: depressions in the upper margin of cornea which are remnants of large conjunctival follicles
- TX: Azithromycin PO (topicals INEFFECTIVE)

  1. Neonatal Inclusion Conjunctivitis/Ophthalmia Neonatorum
    - Serotypes D to K
    - Purulent yellow discharge and lid edema
    - Acquired by neonate during vaginal delivery
    - DX: Scraping of palpebral conjunctival surface
    - TX: Doxycycline/Tetracycline (adults), Erythromycin/Azithromycin
    - Systemic treatment needed for eye infections because infants can develop pneumonia after conjunctivitis
    - Prophylaxis: Erythromycin drops
  2. Keratitis (punctate or marginal)
  3. Reiter Syndrome: triad of CONJUNCTIVITIS + URETHRITIS + ARTHRITIS
  4. Lymphogranuloma venereum: painless genital ulcer progressing to tender inguinal or femoral lymphadenopathy

DX:
1. Giemsa Stain: (+) BASOPHILIC INTRACYTOPLASMIC BODIES
- Collection of IB/RB in conjunctival cells
- Stains glycogen
2. PCR Test
3. Immunofluorescence Assay
4. Culture in live cell lines: not possible in artificial media

51
Q

What are the steps in Ziehl-Neelsen/Acid Fast Staining?

A
  1. Primary stain: CARBOLFUCHSIN (red)
  2. HEATING: for dye penetration
  3. Decolorizer: ACID ALCOHOL
    - cell wall lipids of mycobacteria do not dissolve thus remaining red
    - “hold FAST to the RED stain”
  4. Counterstain: METHYLENE BLUE
    - stains cell walls/membranes of non-mycobacteria

Remember:
Mycobacteria - lipid-rich walls that stain red/pink = ACID FAST

52
Q

Describe Mycobacterium tuberculosis.

A

ACID FAST bacilli - red/pink against a background of blue
Rod-shaped
Obligate aerobe
Slow-growing
Cell wall is 40% lipid (mycolic acid)
Hydrophobic = clumped colonies or floating blobs
FACULTATIVE INTRACELLULAR growth inside MACROPHAGES
- caseous necrosis –> MULTINUCLEATED GIANT CELLS

Ocular Manifestations:
1. Phlyctenulosis
- nodular inflammation of the cornea or conjunctiva that results from a hypersensitivity reaction to a foreign antigen
- (+) phlyctenules: subepithelial inflammatory nodules containing histiocytes, lymphocytes, plasma cells, and neutrophils
2. Granulomatous conjunctivitis
3. Interstitial/Ulcerative keratitis
4. Endo/Panophthalmitis
5. Orbital cellulitis
6. Osteomyelitis
7. Dacryocystitis/adenitis
8. Epi/scleritis
9. Granulomatous uveitis (iris, CB, choroid)
10. Retinal granuloma

DX:
1. AFB Smear/Ziehl-Neelsen Stain
2. Lowenstein-Jensen Culture
3. PPD Skin Test: delayed-type (Type 4) hypersensitivity
- tests for exposure and past infection = LATENT TB
4. Interferon Gamma Release Assay
5. CXR: for PTB
6. Gene Xpert MTB/RIF: nucleic acid amplification test

TX: HRZE +/- S (duration dependent on location of infection)

53
Q

Describe Mycobacterium leprae.

A

ACID FAST bacilli - red/pink against a background of blue
Pleomorphic rod-shaped
Obligate aerobe
Cell wall is 40% lipid (mycolic acid)
OBLIGATE INTRACELLULAR
Grouped together like BUNDLES of CIGARS or PALISADING
Grows in cooler parts of the body close to skin surface:
skin, nerves, eyes, nose, testes

Hansen’s Disease spectrum
1. Lepromatous: most severe with NO cell mediated response
- entire body covered with lumps
- (+) Leonine facies: thickened facial skin
- (+) Saddle Nose Deformity: destroyed nasal cartilage
- damage to anterior segment of eye
- thickened peripheral nerves –> decreased sensation

  1. Intermediate
  2. Tuberculoid: least severe with SOME cell mediated response
    - mild and self-limiting
    - (+) localized, superficial, unilateral skin and nerve involvement

Ocular manifestations:
1. Lid thickening
2. Lash and brow loss
3. CN 3 and 7 palsy
4. Punctate or Avascular Interstitial Keratitis
5. Iridocyclitis
6. Nodular Epi/Scleritis

DX: Skin or Nerve biopsy
- Grown in footpads of mice, monkeys or armadillos
- Impossible to grow in artificial media

TX:
1. Rifampin
2. Dapsone
3. Clofazimine

54
Q

What are the DNA viruses?

A

HHAPPPy viruses

Herpesviridae: HSV, VZV, EBV, CMV
Hepadnaviridae: HBV
Adenoviridae:
Parvoviridae: Parvovirus B19
Papovaviridae: HPV
Poxviridae: Smallpox, Molluscum

Most are:
DOUBLE-stranded with
ICOSAHEDRAL symmetry and
Replicate in NUCLEUS (since DNA)

3 are ENVELOPED: Herpes, Hepadna, Pox
3 are NAKED: Parvo, Adeno, Papova (“naked for PAP”)

Exceptions:
1. PARVO: so simple that it’s SINGLE-stranded
2. POX: DOUBLE-stranded but so complex that it’s ASYMMETRIC and replicates in CYTOPLASM

55
Q

What are the RNA viruses?

A

RNA is a PROP

Picornaviridae
Retroviridae
Orthomyxoviridae
Paramyxoviridae

Most are:
SINGLE-stranded
HELICAL symmetry
ENVELOPED

2 replicate in CYTOPLASM: Picorna and Paramyxo
2 replicate in NUCLEUS: Retro and Orthomyxo

Exception:
Picorna: ICOSAHEDRAL symmetry and NON-enveloped

56
Q

What are the famous members of Herpesviridae?

A

Herpes simplex virus
Varicella zoster virus
Epstein-Barr virus
Cytomegalovirus

Note:
All herpesviridae cause MULTINUCLEATED GIANT CELLS with INTRANUCLEAR INCLUSION BODIES and can REACTIVATE during latent phase.

57
Q

Describe the Herpes Simplex Virus.

A

DNA virus
DOUBLE-stranded
ICOSAHEDRAL symmetry
Replicate in NUCLEUS
ENVELOPED

2 serotypes:
1: Head and Neck
2: Ocular and Genital

DX:
1. Fluorescent Antibody Technique
2. Pap Smear: (+) Lipschutz bodies (eosinophilic intraNUCLEAR IB)
3. Tzanck Smear with Giemsa Stain: (+) multinucleated giant cells with intraNUCLEAR IB (cannot distinguish between herpetic lesions)
4. Culture with live cells
5. PCR Test

Diseases:
1. Cold Sores: PAINFUL fluid-filled blisters that rupture
- transmitted by direct contact with mucous membranes and fluid inside the blister
- travels up via sensory nerve fibers –> may reactivate if IC
2. Genital Herpes: sexually-transmitted illness
3. Encephalitis

Ocular Manifestation:
1. Blepharodermatitis (vesiculo-pustular and ulcerative non-dermatomal)
2. Conjunctivitis (follicular or pseudomembranous)
3. Herpetic Keratitis: MC infectious cause of corneal blindness
(dendritic, epithelial, geographic, discoform stroma, metaherpetic)
4. Iridocyclitis
5. Necrotizing Herpetic Retinopathy (acute retinal necrosis, progressive outer retinal necrosis)
- may also be due to VZV

Treatment:
1. Trifluridine drops
2. Acyclovir/Valcyclovir/Famciclovir/Ganciclovir

58
Q

Describe the Varicella Zoster Virus.

A

DNA virus
DOUBLE-stranded
ICOSAHEDRAL symmetry
Replicate in NUCLEUS
ENVELOPED
MORPHOLOGICALLY-similar BUT SEROLOGICALLY-distinct to HSV
Highly contagious: spread via aerosol and contact with ruptured vesicles

DX
1. Fluorescent Antibody Technique
2. Pap Smear: (+) Lipschutz bodies (eosinophilic intraNUCLEAR IB)
3. Tzanck Smear with Giemsa Stain: (+) multinucleated giant cells with intraNUCLEAR IB (cannot distinguish between herpetic lesions)
4. Culture with live cells
5. PCR Test

Diseases:
1. Chickenpox: GENERALIZED; “dew drops on top of a rose petal”
- vesicles appear in trunk and face then erupt in crops
- lesions are in varied stages
- infectious until ALL LESIONS SCAB OVER
2. Herpes Zoster: DERMATOMAL reactivation from dorsal ganglion
3. Cranial Nerve Palsies
4. Myositis
5. Encephalitis

Ocular Manifestation:
1. Blepharodermatitis (vesiculo-pustular and ulcerative dermatomal) –> Cicatricial En/Ectropion
2. Conjunctivitis
3. Keratitis (dendriform, punctate epithelial, nummular stromal, neurotrophic) and Corneal Melt
4. Epi/Scleritis
5. Iridocyclitis and Chorioretinitis
6. Necrotizing Herpetic Retinopathy
7. Optic Neuritis

Treatment:
1. Acyclovir/Valcyclovir/Famciclovir
2. Sorivudine/Brivudine
3. Zoster Immunoglobulin
4. Varicella Vaccine

59
Q

Describe Epstein-Barr Virus.

A

DNA virus
DOUBLE-stranded
ICOSAHEDRAL symmetry
Replicate in NUCLEUS
ENVELOPED

Diseases:
1. Infectious Mononucleosis: kissing disease
- transmission: saliva
2. Burkitt’s Lymphoma: infect B lymphocytes + oncogenic potential
- remains latent in B lymphocytes and mucosal cells

Ocular Manifestation:
1. Dacryoadenitis
2. Conjunctivitis (follicular or membranous)
3. Keratitis (epithelial, multifocal stromal)
4. Uveitis (multifocal choroiditis)
5. Optic Neuritis

DX:
1. Monospot Test: blood agglutination test which tests for heterophile antibodies, which when present, will cause clumping when exposed to equine RBCs
2. Antibody (IgM, IgG) titers to EBV capsid antigen; (+) at onset
3. Antibody to EBV nuclear antigen: (-) at onset; (+) for life
4. CBC: elevated WBCs with atypical lymphocytes
5. Culture in umbilical cord blood lymphocytes

TX:
1. Acyclovir
2. Corticosteroids
3. Supportive management: may spontaneously resolve

60
Q

Describe the Cytomegalovirus.

A

DNA virus
DOUBLE-stranded
ICOSAHEDRAL symmetry
Replicate in NUCLEUS
ENVELOPED
Ubiquitous; subclinical infection unless IMMUNOCOMPROMISED
Infected cells become swollen –> cytomegaly

Diseases:
1. Asymptomatic: 80%
2. TORCH syndrome: Toxoplasmosis, Others, Rubella, CMV, HSV
3. CMV Mononucleosis: but NEGATIVE monospot test

Ocular Manifestation:
1. Endotheliitis
2. Uveitis
3. Retinitis: common in AIDS pts but NOT transplant pts

DX:
1. Fluorescent Antibody Technique
2. Cytology: (+) multinucleated giant cells with intraNUCLEAR IB surrounded by OWL’S EYE HALO
3. Serology: Indirect Hemagglutination Test
4. Culture with live cells (embryonic lung and fibroblasts)
5. PCR Test

TX:
1. Foscarnet
2. Ganciclovir

61
Q

Describe the Adenoviruses.

A

DNA virus
DOUBLE-stranded
ICOSAHEDRAL symmetry
Replicate in NUCLEUS
NAKED: non-enveloped
Multiple serotypes

Disease:
1. URTI: rhinitis, pharyngitis, tonsillitis
2. Pharyngoconjunctival fever: fever, pharyngitis, acute follicular conjunctivitis, tender, enlarged preauricular adenopathy
3. Gastroenteritis

Ocular manifestation:
1. Acute follicular/pseudomembranous conjunctivitis
2. EPIDEMIC keratoconjunctivitis

DX:
1. Fluorescent Antibody Technique
2. Serology: (+) antibody titers
3. Culture with live cells: embryonic kidney cells

TX: Supportive (self-limited)

62
Q

Describe the Human Papilloma Virus.

A

DNA virus
DOUBLE-stranded
ICOSAHEDRAL symmetry
Replicate in NUCLEUS
NAKED: non-enveloped
Prefers SQUAMOUS epithelial cells
Relapses are common because HPV DNA already found in normal tissues around the papilloma

Common serotypes:
6, 11: Papillomas
16, 18: Oncogenic potential (Cervical, Nasopharyngeal)

Ocular Manifestation: Verruca
- benign hyperproliferation of keratinized squamous epithelium
- lids, conjunctiva, punctum

DX: Clinical; PCR Test

TX:
1. Excision
2. Cryotherapy
3. Laser Ablation

63
Q

Describe the Poxviruses.

A

DNA virus
DOUBLE-stranded
ASYMMETRIC and BRICK-shaped (“pox in a box”)
Replicate in CYTOPLASM (little space in nucleus)
ENVELOPED
LARGEST and MOST COMPLEX virus
Common in IMMUNOCOMPROMISED
STI spread by skin-to-skin contact

Ocular Manifestation:
1. Molluscum Contagiosum: painless, round, waxy eyelid nodule with an UMBILICATED center
- benign hyperproliferation of epithelial cells
2. CHRONIC Follicular Conjunctivitis

DX: Clinical
1. Smear: (+) Henderson-Patterson bodies/Molluscum bodies
- large intraCYTOPLASMIC basophilic IB inside altered keratinocytes
2. Culture
3. PCR Test

TX: Excision

64
Q

Describe Picornaviridae.

A

Members:
1. Poliovirus: Polio
2. Coxsackievirus A and B: Hand-Foot-Mouth Disease
3. Hepatitis A virus
4. Common Cold

RNA virus
SINGLE-stranded
ICOSAHEDRAL symmetry
Replicate in CYTOPLASM
NAKED: non-enveloped
SMALLEST RNA virus

Ocular Manifestation: Acute Hemorrhagic Conjunctivitis
- red swollen eyes with subconjunctival hemorrhage

DX:
1. Serology
2. Immunofluorescence Tests
3. PCR Test
4. Culture Test

65
Q

Describe the Paramyxoviruses.

A

Members:
1. Parainfluenza Virus: Croup
2. Measles virus: Measles/Rubeola
3. Mumps virus: Mumps

RNA virus
SINGLE-stranded
HELICAL symmetry
Replicate in CYTOPLASM
ENVELOPED
(+) Fusion Protein: multinucleated giant cells like HERPES

Diseases:
1. Measles/Rubeola
- Replicates in conjunctival membranes
- (+) Koplik Spots: white spots in the buccal mucosa
- (+) Hirschberg’s Spots: Koplik spots on the caruncle and semilunar fold
- Acute catarrhal conjunctivitis (red eye with flu-like symptoms)
- Epithelial keratitis
- Chorioretinitis
- Pneumonia, Exanthem

  1. Mumps
    - Dacryoadenitis
    - Nummular keratitis
    - Epi/Scleritis
    - Iridocyclitis
    - Parotitis, Orchitis
66
Q

Describe the Orthomyxoviruses.

A

RNA virus
SINGLE-stranded
HELICAL symmetry
Replicate in NUCLEUS
ENVELOPED
Influenza Virus A, B, C: Flu virus

Ocular Manifestation:
1. SUBACUTE catarrhal conjunctivitis: vs. ACUTE in Measles
2. Dacryoadenitis: similar to Mumps

DX: Clinical
1. Serology: hemagglutination test
2. Culture with live cells: throat washing

TX:
1. Amantidine/Rimantidine
2. Zanamivir/Oseltamivir
3. Flu vaccine yearly

67
Q

Describe the HIV.

A

RNA virus
SINGLE-stranded
HELICAL symmetry
Replicate in NUCLEUS
ENVELOPED

Diseases: Acquired Immunodeficiency Syndrome
- If CD4 < 200 or with AIDS-defining condition

Ocular manifestations:
1. HIV Retinopathy: cotton-wool spots with feathered edges
- Microangiopathy: most common ocular manifestation of HIV
2. CMV Retinitis
3. Ocular Toxoplasmosis
4. Herpes Zoster/Simplex
5. Neurosyphilis
6. Molluscum Contagiosum
7. Kaposi Sarcoma
8. Orbital Lymphoma

DX:
1. ELISA: screening
2. Western Blot Test: confirmatory
3. PCT Test for viral load: maintenance

TX: Antiretrovirals

68
Q

What are fungi?

A

EUKARYOTES with no chlorophyll
Obligate aerobes
RIGID cell wall
BILAYERED cell membrane made of ERGOSTEROL
- punches holes: Amphotericin B, Nystatin
- stops synthesis: Azoles, Echinocandin

Exist in 3 forms:
1. Yeast: UNIcellular growth form
- reproduce by BUDDING
- may not separate forming long chains: PSEUDOHYPHAE

  1. Mycelia: MULTIcellular colonies of clumped intertwined hyphae
    - Hyphae: threadlike branching tubules of fungal cells attached end to end
  2. Dimorphic: either as MOLD or YEAST depending on environment and temperature
    - Yeast: BODY temperature (in vivo)
    - Mycelia: ROOM temperature (in vitro)

DX:
1. Giemsa Stain
2. Gomori Methenamine Silver Stain
3. Potassium Hydroxide Mount
4. Culture: Saboraud’s Agar, Blood Agar

69
Q

What are the common fungi and their classification according to morphology?

A

Yeast
1. Candida

Mycelia (filamentous) - septated
1. Aspergillus
2. Fusarium

Mycelia (filamentous) - NON-septated
1. Mucor
2. Rhizopus
3. Rhizomucor

Dimorphic
1. Sporothrix schenckii
2. Blastomyces dermatitidis
3. Histoplasma capsulatum
4. Coccidioides immitis

70
Q

Difference between Periodic Acid Schiff stain VS Gomori Methenamine Silver stain.

A

Both stains anything with CARBOHYDRATES:
1. Glycogen
2. Mucin: glycolipids, glycosaminoglycans, glycoproteins
3. Basement membrane: connective tissues)
4. Fungal cell walls: high levels of carbohydrates

PAS Stain:
1. Periodic Acid
2. Schiff Reagent: gives purple/magenta color
3. Hematoxylin: blue counterstain
4. Appearance: red/purple fungi against blue background
5. Needs to be ALIVE

GMS Stain:
1. Chromic Acid
2. Methenamine Silver: gives it black color
3. Green Dye: counterstain
4. Appearance: black fungi against green background
5. May be DEAD or ALIVE

71
Q

How is a KOH Mount done?

A

Potassium Hydroxide
- Strong alkali
- Dissolves keratin in the tissues surrounding the fungi for better visualization

Steps:
1. Scrapings placed in slide and 10-20% KOH added
2. Slide left to stand for 5-15 minutes or until clear
3. View under microscope

72
Q

What is the Saboraud Dextrose Agar

A

pH 5.0 due to fermentation: inhibits bacterial growth

Ingredients;
1. Dextrose: fermentable nutrition
2. Peptones: provides nitrogen for growth
3. Chloramphenicol, Gentamycin, Tetracycline: inhibit bacterial growth

73
Q

Describe Candida spp.

A

Candida albicans

YEAST: UNIcellular
(+) PSEUDOHYPHAE: elongated budding cells
Normal flora of skin, mouth and GIT
NOT NORMAL in blood

Ocular manifestations:
1. Mucocutaneous Candidiasis: lids and conjunctiva
2. Ulcerative keratitis
3. Infectious Crystalline Keratopathy
4. Endophthalmitis
5. Chorioretinitis

DX:
1. KOH Mount
2. Gomori-Methenamine-Silver Stain
3. Saboraud Agar: white pasty colonies with FRUITY odor
4. Blood culture: candidemia

TX:
1. Azoles (keto, fluco, mico, itra)
2. Amphotericin B

74
Q

Describe Aspergillus spp.

A

Aspergillus

MYCELIAL (multicellular) - SEPTATED
Ubiquitous (damp, decaying vegetation)
Members:
1. Fumigatus
2. Flavus: (+) aflatoxin in peanuts, grains and rice
3. Niger

Disease: Aspergillosis +/- Aspergilloma

Ocular manifestation:
1. Ulcerative Keratitis
2. Scleritis
3. Endophthalmitis
4. Dacryocystitis
5. Orbital Cellulitis

DX:
1. Sputum culture
2. CBC: eosinophilia
3. Chest X-ray/CT Scan: aspergilloma
4. KOH Mount: (+) conidiophore with sterigmata and long chains of radiating conidia

TX:
1. Steroids: to limit inflammatory response
2. Surgery: for aspergilloma
3. Voriconazole
4. Amphotericin B
5. Caspofungin

75
Q

Describe Fusarium spp.

A

Fusarium solani

MYCELIAL (multicellular) - SEPTATED
Ubiquitous saprophytic
Seen in people working in the fields during harvest season

Ocular manifestation:
1. Keratomycosis (ulcerative keratitis): most common cause
2. Endophthalmitis
3. Disseminated if immunocompromised

DX:
1. Saboraud Agar: white and violet cottony colonies with REVERSE PIGMENTATION
2. KOH Mount: SICKLE/BANANA-shaped macroconidia

TX: largely resistant to most anti-fungals
1. Natamycin
2. Amphotericin B

76
Q

Describe the Dimorphic fungi.

A

Histoplasma capsulatum
Blastomyces dermatitidis
Coccidioides immitis: Chorioretinitis
Sporothrix schenckii: Sporotrichosis/Granulomatous Blepharoconjunctivitis

DIMORPHIC:
- mycelia at room temperature/Saboraud (25 degrees)
- yeast at body temperature/Blood Agar (37 degrees)
SS: subcutaneous nodules which necrose and ulcerate
Others: systemic manifestation

DX: Biopsy of affected tissue
1. Gomori-Methenamine-Silver Stain
2. Saboraud/Blood Agar Culture

TX:
SS: Potassium iodide, Itraconazole, Fluconazole
Others: Amphotericin B, Itraconazole

77
Q

Describe the Mycelial - NON-septated fungi

A

Rhizopus
Rhizomucor
Mucor

MYCELIAL - NON-septated
Saprophytic

Disease: Rhinocerebral/Orbital MUCORMYCOSIS

DX: (+) black nasal discharge and biopsy

TX:
1. Aggressive debridement
2. Amphotericin B, Posaconazole

78
Q

Cause of River Blindness

A

Onchocerca volvulus: Onchocerciasis/River Blindness
- second-leading infectious cause of blindness after trachoma
- microfilariae migrate to the eye

TX: Ivermectin

79
Q

Presents with bilateral palpebral edema, myalgias, and eosinophilia.

A

Trichinella spiralis/Trichinellosis
- larvae in raw pork is ingested and migrates to skeletal muscles

DX:
1. Muscle biopsy
2. Increase muscle enzymes
3. CBC: eosinophilia

TX: Albendazole

80
Q

Intestinal roundworm of dogs

A

Toxocara canis/Toxocariasis
- ingestion of ova from dog feces
- larval migration to the eyes

Manifestation: Ocular Toxocariasis
1. Chronic endophthalmitis
2. Posterior pole or peripheral granuloma
3. Chorioretinitis

DX:
1. ELISA
2. Biopsy
3. CBC: eosinophilia

TX: Albendazole

81
Q

What are Calabar swellings?

A

Loaloa/Loiasis
- may localize to the conjunctiva
- (+) Calabar swellings: allergic reaction to the metabolic products of the worms or to dead worms; can occur anywhere, but frequently on the forearms

TX:
1. Diethylcarbamazine
2. Extraction of worm from the eye

82
Q

What causes Cysticercosis?

A

Taenia solium/saginata
- due to ingestion of undercooked pork/beef
- travels to the CNS or eye and form calcified cysts with surrounding inflammatory reaction

DX:
1. CT Scan –> biopsy
2. CBC: eosinophilia

TX:
1. Praziquantel
2. Albendazole

83
Q

Discuss Phthirus pubis.

A

Crab Louse

  • Six-legged ectoparasite
  • Adapted only to THICK hair
  • (+) Pruritus: hypersensitivity to saliva of louse
  • (+) Macula Ceruleae: bluish-brown macules from hemosiderin deposition secondary to louse bite marks

Disease: Phthiriasis
1. Phthiriasis pubis: pubic hair
2. Phthiriasis palpebrarum/ciliaris: eyelashes/lid margin
- Chronic Blepharoconjunctivitis
- Eyelid Infestation
- Follicular Conjunctivitis

DX: Slit-Lamp Exam for nits and adult lice

TX:
1. Mechanical removal
2. Petroleum jelly over eyelids

84
Q

What causes eyelash mites?

A

Demodex folliculorum/brevis

  • Normal commensal parasite of hair, eyelash follicles, sebaceous and Meibomian glands
  • Common in elderly
  • Appearance: worm-like CIGAR-shaped body with 8 stumpy legs anteriorly
  • Feeds on skin cells and oils in the hair follicle

Manifestations:
1. Demodectic blepharitis
2. Lid hyperemia
3. Meibomitis –> Chalazion

DX: Slit-Lamp Examination
- (+) Sleeves :around the base of eyelashes; cuffs of hypertrophic follicular epithelium
- (+) Epilated eyelashes

TX: Lid Scrubs (ether, tea tree oil)

85
Q

What causes Amoebiasis?

A

Acanthamoeba

Ubiquitous free-living protozoa found mostly in fresh water
2 Forms:
1. Active Trophozoite
2. Dormant Cyst

Diseases:
1. Immunocompetent: keratitis esp. in contact lens wearers
2. Immunocompromised: chronic granulomatous brain infection
- both stages present

Ocular manifestions:
1. Epithelial or Stromal Keratitis with ring infiltrates
2. Perineural infiltrates
3. Nodular Scleritis

DX: Corneal scraping
1. Calcofluor White: visualize CYSTS
- binds to cellulose (acanthamoeba cyst) and chitin (fungi) –> (+) fluorescence
2. Non-nutrient Agar with E. coli overlay: visualize TROPHOZOITES
- selective media; alternative to corneal biopsy for keratitis
- (+) trails or tracks

TX:
1. Polihexanide/PHMB 0.02%
2. Chlorhexidine
3. Propamidine isethionate 0.1% (Brolene)
4. Corneal transplant: for severe corneal damage

86
Q

Describe Microsporidia.

A

Obligate INTRACELLULAR fungi
Opportunistic infection in IMMUNOCOMPROMISED
2 stages:
1. Schizogenic stage
2. Sporogenic stage
Transmission:
1. Fecal-oral route
2. Direct inoculation into cornea: trauma (mud)

Ocular manifestations:
1. Immunocompetent: focal stromal keratitis
2. Immunocompromised: punctate epithelial keratitis
- course punctate keratitis with minimal stromal inflammation
3. Mixed follicular-papillary conjunctivitis

DX: Calcofluor White - (+) intraepithelial PELLET-like spores

TX:
1. Bicyclohexylammonium fumagillin (Fumidil B)
2. Propamidine isethionate (Brolene)

87
Q

What causes toxoplasmosis?

A

Toxoplasma gondii

Obligate INTRACELLULAR protozoan
Hosts:
Definitive: Cat
Intermediate: Humans, Mice
2 forms:
1. Sporocysts (infectious)
2. Bradyzoites
3. Tachyzoites (proliferative)
Transmission:
1. Inhalation: cysts in cat feces
2. Ingestion: cysts in raw pork

Ocular manifestation:
1. Anterior Uveitis
2. Chorioretinitis: congenital or reactivation
3. Papillitis: specific type of optical neuritis

DX:
1. Blood agglutination
2. Antibody immunofluorescence
3. ELISA

TX:
1. Sulfadiazine or Pyrimethamine
2. Clindamycin: if sulfadiazine

Ophthalmology (44 decks)

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