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Bacteriology and Mycology > Mycology Part 1A > Flashcards

Mycology Part 1A Flashcards

1
Q

How are specimen collected for Cutaneous Mycoses? (I.e. Ringworm)

A
  1. Clean area with alcohol
  2. Collect hair by plucking from periphery of lesions
  3. Use edge of scalpel for skin scrapings
  4. Place in envelope or sterile petri dish
  • Do not use tightly sealed containers
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2
Q

How are specimen collected for systemic and subcutaneous Mycoses?

A
  1. Collect exudate or material from edge of lesion
  2. Place in sterile, leak proof test tube for direct examination and culture
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3
Q

What is a Woods Lamp?

A
  • Diagnostic method in mycology
  • UV light - 366nm
  • Yellow-green fluorescence of infected hairs or skin
  • False positive with some medications
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4
Q

Which dermatophytes fluoresce under Wood’s Lamp?

A
  • Microsporum canis - animals
    • 80% of ringworm in dogs and cats
  • M. distortum - humans
  • M. ferrugineum - humans
  • M. audouinii - humans
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5
Q

How is Direct Examination of Mycoses work?

A
  1. Place sample on a slide with a few drops 10% NaOH or KOH
  2. Incubate for 15-30 minutes in a moist chamber
  3. Look for hyphae, arthrospores - Endothrix or Ectothrix spores
  • False positives: oil or grease droplets
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6
Q

How are wet preparations (pus, exudates, etc) directly examined?

A
  1. Wet mount with New Methylene Blue or Lacto-Phenol Cotton Blue
  2. Stain with Gram, Geimsa, or other special stains
    1. Cryptococcus- India Ink preparations of CSF - thick capsule
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7
Q

What media should be used for the isolation of fungus?

A
  • Dependent on the suspected fungus
    • Sabouraud Dextrose Agar: pH 5.6
      • Inhibits many species of bacteria
    • Sabouraud/Cycloheximide/Chloramphenicol
      • Inhibits many bacteria and contaminating fungi
    • Dermatophyte Test Medium (DTM)
      • Dermatophytes - Red - Alkaline
      • Other Fungi - Yellow - Acid
    • Potato Dextrose Agar
      • Sporothrix schenkii - Black Colonies
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8
Q

How should fungi be incubated?

A
  • Moist atmosphere to prevent drying of plates
  • Incubate at room temperature or 25C
    • 30 C for Candida spp
    • T. verrucosum (bovine ringworm) 37C
    • Diphasic fungi
      • yeast or tissue form 37C
      • Mycelial form 25C
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9
Q

What Biochemical Tests are available for Candida species?

A
  • Sugar fermentation
  • Sugar assimilation
  • Commercial test kits - API system
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10
Q

What Immunologic Test are available for fungi?

A
  • CMI response
    • usually done by skin testing (Type IV hypersensitivity)
  • Humoral response
  • Histoplasmosis -AGID
  • Blastomycosis - AGID
  • Coccidioidomycosis -AGID
  • Cryptococcosis - Latex Agglutination
  • Aspergillosis - AGID
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11
Q

What are fungi Opportunists?

A
  • May be primary or secondary pathogens under appropriate conditions
    • Old, young, immunocompromised
    • Individuals of low resistance
    • Individuals on long term hormone, antibiotic, or steroid therapy
    • Individuals who are debilitated
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12
Q

What are the significant Fungi Species?

A
  • Mucor spp.
  • Rhizopus spp.
  • Absidia spp
  • Aspergillus spp.
  • Alternaria spp.
  • Penicillium spp.
  • Geotrichum spp.
  • Fusarium spp.
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13
Q

What is Dermatomycosis?

A
  • Cutaneous Mycoses
  • Live on superficial parts of the host
  • Non-Invasive
  • Usually will not survive long in living tissue
  • Will NOT survive in areas of intense inflammation
  • Have Keratolytic activity
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14
Q

What is the Geographic Distribution of Dermatomycosis?

A
  • World Wide
  • More prevalent in tropical and sub-tropical climates
  • Particularly prevalent in hot humid areas
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15
Q

What is the Prevalence of Dermatomycosis?

A
  • Microsporum canis associated with:
    • >90% of all Feline Ringworm
    • >70% of all Canine Ringworm
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16
Q

What is the pathogenesis of Dermatomycosis?

A
  • Dermatophyte contacts skin of animal:
    • Brushed off
    • Competes with bacterial flora
    • Set up residence and produce carrier state - cats
    • Set up residence, multiply, and produce disease
    • Excretes toxins or irritants which are generally protein in nature
    • Elastase, Collagenase, Keratinase
    • Survival dependent upon mutual existence
    • Local inflammation is due to galactomannan glycopeptides
    • Excessive inflammation results in:
      • Peripheral movement of the fungus
      • Typical ring lesion
17
Q

What are the Clinical Manifestations of Dermatomycosis?

A
  • Extremely variable:
    • Eruptive lesion (Kerion)
    • May be mixed with Staphylococcus spp.
    • Ringed lesions in animals not common
18
Q

How does Dermatomycosis affect Dogs and Cats?

A
  • M. canis most common
  • Dogs:
    • Face, extremities, lower abdominal wall
    • Crusty alopecic lesions
  • Cats:
    • Ears, face, extremities
    • Crusty alopecic lesions, a minimum of erythema
19
Q

How does Dermatomycosis affect cattle?

A
  • T. verrucosum - 99+%
  • Crusty, plaque-like lesions on face and neck
20
Q

How does Dermatomyosis affect sheep?

A
  • Trichophyton spp. - most common
  • Crusty lesions on shoulders, neck, and chest
21
Q

How does Dermatomycosis affect Horses?

A
  • T. equinum and T. mentogrophytes - Most common
  • Deep scaly ulcerating lesions
22
Q

How does Dermatomycosis affect swine?

A
  • M. namum most common
  • Reddish-brown, ringed lesion on lower abdominal wall
23
Q

How does Dermatomycosis affect Poultry?

A
  • T. gallinae - most common
  • Crusty, scaly lesions most evident on comb and wattles
24
Q

How is Dermatomycosis Diagnosed?

A
  • Clinical Diagnosis:
    • Wood’s Lamp Examination - 366 nm
      • Limited value
      • False positive - medication
      • False negative
        • Not all M. canis fluoresce
        • spores may be subcutaneous
  • Laboratory Diagnosis:
    • Direct Microscopic examination
      • Observe arthrospores
    • Cultural examination
      • Incubate at room temp (25C) for 2-4 weeks
25
Q

Is Dermatomycosis Zoonotic?

A
  • Animal ringworm rarely spreads to humans
  • Route of infection:
    • Direct, indirect or airborne rare
    • Spores viable for years on fomites
26
Q

How is Dermatomycosis treated?

A
  • 5 Mechanisms of action
    • Irritants - invoke inflammatory response
    • Keratolytics - remove stratum corneum
    • Fungicidal agents
    • Fungistatic agents
    • Vaccine for T. verrucosum - Live
      • attenuated - Europe
27
Q

What are the important Antifungal Agents?

A
  • Amphotericin B
  • Nystatin, Natamycin
    • Affects permeability
    • Hemolytic anemia
    • Renal toxicity
  • 5-Fluorocytosine
    • Fungal RNA - Errors
  • Imidazoles / Triazoles
    • Cell wall
    • Cell membrane
    • Nutrient uptake
  • Griseofulvin
    • Chitin wall
    • Inhibits nucleic acid synthesis
  • Sulfur compounds
  • Salicylic acids
  • Fatty acids
  • Benzoic acid
  • Phenoll
  • Tincture of Iodine
  • Organic Iodine compounds as soaprs

Bacteriology and Mycology (35 decks)

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