Day 3 (3): Ocular Microbiology Flashcards
Normal flora of the outer eye (conjunctiva and lid margin).
- Staphylococcus epidermidis
- Staphylococcus aureus
- Corynebacterium
- Micrococcus
- Propionibacterium acnes
Most common infectious cause of blepharitis?
- Staphylococcus
- Moraxella
Most common infectious cause of conjunctivitis?
- Staphylococcus aureus
- Streptococcus
- Chlamydia trachomatis
- Neisseria gonorrhoeae
- Haemophilus influenzae
- Moraxella
Most common infectious cause of keratitis?
- Staphylococcus (aureus and epidermidis)
- Streptococcus pneumoniae
- Pseudomonas aeruginosa
- Moraxella
- Fungal (Fusarium, Aspergillus, Candida albicans)
Most common infectious cause of canaliculitis?
Actinomycetes
Hordeolum vs Chalazion
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
Bacterial classification according to GRAM STAIN and SHAPE
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
Rationale behind Gram staining
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
What are the steps of Gram Staining?
- Primary Stain: Crystal Violet
- Mordant/Fixant: Iodine
- binds to crystal violet and traps and fixes it in the cell wall - 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 - Counterstain: Safranin
Culture media classification by function.
- Basic: simple media that supports growth of most NON-FASTIDIOUS bacteria
- okay for most bacteria but cannot isolate - Enriched: extra nutrients added for growth of FASTIDIOUS bacteria (choosy)
- for bacteria with special needs - Selective/Differential: inhibitory agents added to suppress growth of some microorganisms while allowing some to thrive
- antibiotics, dyes, chemicals, pH alteration
- for bacterial isolation
Most basic culture medium
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
What is Blood agar for?
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
Classification of bacteria based on hemolysis of RBCs on blood agar.
- 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)
- 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
What is Chocolate agar?
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
What is Thayer-Martin VPN agar?
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
What is the MacConkey and EMB agar?
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
- Weak - Strong fermenters: pink to dark red
- Non-fermenters: colorless
EMB Agar
- Inhibitors: Methylene Blue –> inhibit Gram (+)
- pH Indicator: Eosin Y –> differentiate lactose vs non-lactose fermenters
- Weak - Strong fermenters: brown-pink to deep purple to black
- Non-fermenters: colorless
Fermenters: Enterobacteriaceae, E. coli (with green metallic sheen)
Non-fermenters: P. aeruginosa, Salmonella, Shigella
What is the Thioglycolate Broth?
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
- Obligate aerobes: NEED oxygen
- topmost layer - Microaerophiles: anaerobes that can tolerate oxygen IN MODERATION
- upper part but not at top because too much oxygen is poison - Facultative anaerobe: aerobes that PREFER OXYGEN but can grow with no oxygen
- mostly at top but can be found everywhere - Aerotolerant: can tolerate any condition thus NO PREFERENCE
- everywhere - Obligate anaerobes: HATE oxygen
- bottommost layer
What is Brain Heart Infusion agar?
BHI Agar
- Enhanced: (+) boiled bovine/porcine heart and brain
- Non-selective
- Growth of FASTIDIOUS organisms
1. Streptococcus
2. Meningococcus/Neisseria meningitides
3. Fungi
What are the other culture media used and organisms that grow on them?
- Potassium Tellurite Agar: Corynebacterium
- Lowenstein-Jansen Agar: Mycobacterium
- Non-Nutrient Agar with E. coli overlay: Acanthamoeba
- alternative to corneal biopsy in keratitis - Saboraud Agar: Fungi
Common stains used.
- Gram Stain
- Gram (+): purple/blue
- Gram (-): red/pink - Giemsa/Wright-Giemsa Stain
- Nucleic acid stain: phosphate group of DNA
- Human cells: purple/blue
- Bacterial cells: red/pink - Acid Fast (Ziehl-Neelsen/Kinyoun) Stains
- Mycobacteria: red/pink
- Others: blue (ZN) or green (K) - Potassium Hydroxide (KOH) Stain
- Fungi (Dermatophytes, Candida) - Calcofluor-White Stain
- Acanthamoeba keratitis - Gomori-Methenamine Silver Stain
- Fungi (BOTH dead and alive)
- Cell wall: brown to black
- Background: green - Periodic Acid Schiff
- Fungi (ALIVE only)
- Cell wall: magenta
- Background: blue
When presented with a Gram (+) cocci, what test is used to determine if its Staphylococcus or Streptococcus?
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)
How to differentiate Staphylococcus species?
- Coagulase Test: coagulase activates prothrombin and causes fibrin in plasma to clot
- (+) if with clumps = clotting
Positive: S. aureus
Negative: Others
- Novobiocin Test: test for antibiotic resistance
Sensitive/(+) Zone of Inhibition: S. epidermidis
Resistant/(-) Inhibition: S. saprophyticus
How to differentiate Streptococcus species?
Growth pattern on BLOOD AGAR
- 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
- 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
- Gamma-hemolytic: no hemolysis = no change
Antibiotic resistance tests to determine Staphylococcus or Streptococcus species
Novobiocin: Staphylococcus (epidermis vs saprophyticus)
Bacitracin: Beta-hemolytic Streptococcus (pyogenes vs agalactiae)
Optochin: Alpha-hemolytic Streptococcus (pneumoniae vs viridans)
Describe Staphylococcus spp.
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)
Describe Staphylococcus aureus.
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
- Hemolysin: destroys RBCs, WBCs, platelets
- tested with blood agar - Leukocidin: destroys WBC
- Panton-Valentine-Leukocidin: in CA-MRSA, (+) recurrent abscess - Penicillinase: destroys B-lactam ring on penicillins
- Exfoliatin: causes skin to slough off (Scalded Skin Syndrome)
- Toxic Shock Syndrome Toxin (TSST-1): cytokine storm
- Enterotoxin: gastroenteritis
- Staphylokinase: thrombolytic to break up blood clots and spread from the initial site of infection
Describe Staphylococcus epidermidis.
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
Describe Staphylococcus saprophyticus.
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
Describe Streptococcus spp.
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:
- Hemolytic activity in blood agar
Beta = CLEAR zone = complete hemolysis = pyogenes, agalactiae
Alpha = GREEN zone = partial hemolysis = viridans, pneumoniae
Gamma = NO zone = non-hemolytic
- 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)
Describe Streptococcus pyogenes.
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:
- Pyogenes = Pus-producing = microaerophile = skin infections
- Streptolysin O: similar to hemolysin of S. aureus
- destroys RBCs, WBCs, and platelets
- test: Anti-Streptolysin O antibodies - Erythrogenic Toxin: similar to TSST-1 of S. aureus
- cytokine storm - Streptokinase: thrombolytic to break up blood clots and spread from the initial site of infection
- M protein: adherence, antigenicity and anti-phagocytic
Similarities in virulence factors of S. pyogenes and S. aureus
Thrombolytic: Staphylokinase :: Streptokinase
Cytokine Storm: Toxic Shock Syndrome Toxin - 1 :: Erythrogenic Toxin
Hemolysis: Hemolysin :: Streptolysin O
Describe Streptococcus agalactiae.
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)
Describe Streptococcus pneumoniae/Pneumococcus.
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)
Describe Viridans streptococcus group.
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
Describe Bacillus spp.
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.
Describe Corynebacterium diphtheriae
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
Describe Propionibacterium/Cutibacterium acnes.
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)
Describe the Gram POSITIVE filamentous bacteria.
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
Describe Neisseria spp.
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
Describe Neisseria meningitidis/Meningococcus.
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
Describe Neisseria gonorrhoeae/Gonococcus.
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
Describe Moraxella spp.
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
Describe Haemophilus influenzae.
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
What is the oxidase test?
Tests if organism used oxygen for energy production
Describe Pseudomonas aeruginosa.
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)
Describe the Enterobacteriaceae group.
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)
What are the Spirochetes?
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
Describe Treponema pallidum.
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
How is the Giemsa Stain performed?
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
Discuss Chlamydia trachomatis.
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)
- 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 - Keratitis (punctate or marginal)
- Reiter Syndrome: triad of CONJUNCTIVITIS + URETHRITIS + ARTHRITIS
- 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
What are the steps in Ziehl-Neelsen/Acid Fast Staining?
- Primary stain: CARBOLFUCHSIN (red)
- HEATING: for dye penetration
- Decolorizer: ACID ALCOHOL
- cell wall lipids of mycobacteria do not dissolve thus remaining red
- “hold FAST to the RED stain” - Counterstain: METHYLENE BLUE
- stains cell walls/membranes of non-mycobacteria
Remember:
Mycobacteria - lipid-rich walls that stain red/pink = ACID FAST
Describe Mycobacterium tuberculosis.
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)
Describe Mycobacterium leprae.
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
- Intermediate
- 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
What are the DNA viruses?
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
What are the RNA viruses?
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
What are the famous members of Herpesviridae?
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.
Describe the Herpes Simplex Virus.
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
Describe the Varicella Zoster Virus.
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
Describe Epstein-Barr Virus.
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
Describe the Cytomegalovirus.
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
Describe the Adenoviruses.
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)
Describe the Human Papilloma Virus.
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
Describe the Poxviruses.
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
Describe Picornaviridae.
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
Describe the Paramyxoviruses.
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
- Mumps
- Dacryoadenitis
- Nummular keratitis
- Epi/Scleritis
- Iridocyclitis
- Parotitis, Orchitis
Describe the Orthomyxoviruses.
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
Describe the HIV.
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
What are fungi?
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
- Mycelia: MULTIcellular colonies of clumped intertwined hyphae
- Hyphae: threadlike branching tubules of fungal cells attached end to end - 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
What are the common fungi and their classification according to morphology?
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
Difference between Periodic Acid Schiff stain VS Gomori Methenamine Silver stain.
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
How is a KOH Mount done?
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
What is the Saboraud Dextrose Agar
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
Describe Candida spp.
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
Describe Aspergillus spp.
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
Describe Fusarium spp.
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
Describe the Dimorphic fungi.
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
Describe the Mycelial - NON-septated fungi
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
Cause of River Blindness
Onchocerca volvulus: Onchocerciasis/River Blindness
- second-leading infectious cause of blindness after trachoma
- microfilariae migrate to the eye
TX: Ivermectin
Presents with bilateral palpebral edema, myalgias, and eosinophilia.
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
Intestinal roundworm of dogs
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
What are Calabar swellings?
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
What causes Cysticercosis?
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
Discuss Phthirus pubis.
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
What causes eyelash mites?
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)
What causes Amoebiasis?
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
Describe Microsporidia.
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)
What causes toxoplasmosis?
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
