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Clinical Microbio > Skin & Ear Pathogens > Flashcards

Skin & Ear Pathogens Flashcards

1
Q

Name some antimicrobial defense mechanisms of the skin

A
  • Epithelial barrier
  • continuous desquamation of keratinocytes
  • acidic environment
  • intercellular “shield” - stratum corneum, emulsion
  • compounds produced by sebaceous and sweat glands
  • antimicrobial peptides (e.g. defensins)
  • resident phagocytes
  • interferon, lysozyme, immunoglobulins
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2
Q

Name some resident flora of the skin

A
  • Mostly Gram positives
    • ​Micrococcus spp.
    • alpha-hemolytic Strep
  • Gram negatives: Actinobacter spp.
  • Anaerobes:
    • Clostridium perf
    • Propionibacterium acnes
  • Fungi: liphophilc yeasts in small #s
    • ​Malassezia & Pityrosporum spp.
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3
Q

What are some of the transient flora of the skin?

A

Facultative pathogens

  • Gram +: Staph pseudintermedius
  • Gram -: E. Coli, Proteus mirabilis, Enterococcus, Pseudomonas aeruginosa
  • Anaerobes: Fusobacterium necrophorum, Bacteroides spp.

*associated with pus

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4
Q

What causes a bacterial pyoderma?

A

overgrowth/overcolonization of normal resident or transient flora

  • *second most common skin dz in dogs - 1st = FAD
  • uncommon in cats (abscesses)
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5
Q

What bacteria is the most common cause of bacterial pyoderma and where do you find this most often?

A
  • Staph pseudintermedius
  • found in warm, moist areas and pressure points
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6
Q

How do you differentiate superficial vs. deep pyoderma in dogs?

A
  • Superficial:
    • multifocal areas of alopecia, follicular papules/pustules, epidermal collarettes/crusts
  • Deep:
    • Pain, crusting, odor​, exudation of blood and pus
    • Affects a large region of skin
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7
Q

How do you differentiate superficial vs. deep pyoderma in cats?

A
  • Superficial
    • overlooked and under diagnosed
    • scaling, miliary dermatitis, intact pustules rare
  • Deep
    • alopecia, ulcerations, hemorrhagic crusts, draining tracts
  • Recurrent nonhealing
    • consider systemic dz (FIV, FeLV, atypical mycobacteria)
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8
Q

What microbes cause draining tracts and subcutaneous abscesses in dogs?

A

Actinomyces viscosus or A. Hordeovulneris

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9
Q

What microbes cause scrotal dermatitis in dogs?

A

Brucella canis

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10
Q

What microbes cause cellulitis, folliculitis, furunculosis, and impetigo (skin fold dermatitis) in dogs?

A

Staph pseudintermedius, S. Aureus, other coag-positive Staph

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11
Q

What microbes cause subcutaneous abscesses in cats?

A
  • Pasteurella multocida
  • obligate anaerobes
    • peptostreptococcus
    • fusobacterium
    • porphyromonas
    • clostridium
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12
Q

What microbes cause chronic nodular dermatitis, draining ducts, and inflammation of the fat tissue layer in cats?

A
  • Mycobacterium sp.
    • M. Fortuitum
    • M. Chelonei
    • M. Xeonopi
    • M. Smegmatis
    • M. Phlei
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13
Q

What microbes cause nodular ulcerative skin lesions with lymphadenopathy in cats?

A

Mycobacterium lepraemurium

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14
Q

What are some differentials for pyoderma?

A
  • Demodicosis
  • Neoplasia (sweat gland adenocarcinoma, cutaneous metastasis, histiocytosis)
  • drug eruption
  • other dermatitides: fungal, oomycetes, sterile
  • autoimmune dz (pemphigus foliaceous)
  • hypersensitivity
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15
Q

How do you diagnose pyoderma?

A
  • Direct impression smears (intact pustules/crusts/collarettes)
  • Skin scrapes (r/o demodex)
  • Swabs
  • Tape preps
  • Biopsy
  • Culture/Sensitivity
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16
Q

What are some common causes of recurrent bacterial pyoderma?

A
  • Failure to ID underlying trigger
  • antibiotic undertreatment (dose too low/short)
  • concurrent use of glucocorticoids
  • wrong abx choice/dose
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17
Q

How do you treat superficial pyodermas?

A

Topical therapy

  • bathing with shampoos containing:
    • 2-4% chlorhexidin​e
    • ethyl lactate
    • Ticolsan
    • benzoyl peroxide
  • 2x per wk, 10 min contact
  • sprays and mousses if cannot bathe
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18
Q

What are the specifications for antibiotic treatment of skin infections?

A
  • Duration post clinical signs: 1 wk superficial, 2 wks deep
  • Poor efficacy = penicillin, ampicillin, amoxicillin, tetracycline
  • Preferred narrow spectrum: Erythromycin, lincomycin, oxacillin
  • For deep pyodermas: Cephalexin, trimethprim, quinolones
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19
Q

Which antimicrobial is not recommended for canine pyoderma treatment?

A

Ciprofloxacin (not super effective vs. Gram positives)

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20
Q

Which fungus/fungi causes exfoliative dermatitis in dogs?

A
  • Malassezia pacydermatis
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21
Q

What fungi cause circular, scaly, crusty, allopecic skin lesions in dogs?

A
  • Microsporum canis, M. Gypseum
  • Trichophyton mentagrophytes
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22
Q

Which fungi cause papules, nodules, abscesses, and draining tracts in dogs?

A

Think systemic mycoses

  • Blastomyces dermatidis
  • Cocciodes immitis
  • Cryptococcus neoformans
  • Histoplasma capsulatium
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23
Q

Describe Malassezia dermatitis

A
  • Moderate to severe pruritus
  • regional or generalized alopecia, excoriation, erythema, seborrhea
  • chronicity —> lichenified, hyperpigmented, hyperkeratotic
  • unpleasant odor
  • lesions occur in interdigital spaces, ventral neck, axillae, perineal region, leg folds
  • concurrent yeast otitis externa
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24
Q

How does a Malassezia infection differ in cats?

A
  • C/S: blacky, waxy otitis externa, chronic chin acne, alopecia, multifocal to generalized erythema and seborrhea
  • less common than in dogs
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25
Q

True or False: Malassezia infections in dogs are almost never associated with underlying predisposing conditions, such as atopy or food allergy

A

False, they are almost always associated with these underlying conditions

26
Q

How do you diagnose Malassezia infections?

A
  • R/o for DDx (demodex, superficial pyoderma, dermatophytosis, ectoparasites, allergies)
  • Cytology (tape prep/impression smear)
  • Dermatohistopath
  • Fungal culture
  • Allergy test
27
Q

Describe dermatophytosis (ringworm)

A
  • ZOONOTIC
  • infection of keratinized tissue (skin, hair, claws)
  • dermatophytes
    • Epidermophyton, Microsporum, Trichophyton
    • In dogs - M. Canis = 70%, M. Gypseum = 20%, T. Mentogrophytes = 10%
    • In cats - M. Canis = 98%
  • usually self-limiting, common
  • higher risk = kittens/puppies, immunocompromised animals, long haired cats, Persians, Yorkies, JRT
28
Q

What are the clinical signs seen with dermatophytosis?

A
  • Pruritus (mild)
  • circular, irregular, or diffuse alopecia with scaling
  • remaining hairs are stubbled or broken off
  • can have asymptomatic carriers
29
Q

How do you diagnose dermatophytosis?

A
  • UV (Wood’s lamp)
  • Trichogram
  • Dermatohistopath
  • Fungal culture (DTM media) - Microsporum or Trichophyton spp.
  • IDEXX PCR
30
Q

How do you treat dermatophytosis in dogs?

A
  • Clip wide margin around lesion
  • Topical antifungals applied q12h until lesion resolves
    • Terbinafine, Enilconazole, or Ketoconazole cream
    • Clotrimazole
    • Miconazole
  • Bathe w/ chlorhexidine and miconazole or ketoconazole then topical antifungal rinse/dip 1–2x per wk for 4-6 wk until follow-up culture is negative
  • Decontaminate environment
31
Q

How do you treat dermatophytosis in cats?

A

Cats almost always require concurrent systemic therapy

  • Topical: Eniconazole 0.2% solution or Lime sulfur 2-4% solution
  • Systemic: Terbinafine, Ketoconazole, Fluconazole, Itraconazole
    • Treat until 3-4wks beyond neg follow up culture (avg 8–12 wks)
32
Q

What virus is associated with nasal and footpad hyperkeratosis in dogs?

A

Canine distemper virus

33
Q

What virus causes cutaneous papillomas in dogs?

A

Canine papillomavirus

34
Q

What virus causes cutaneous and subcutaneous nodules?

A

Feline sarcoma virus

35
Q

What fungal agents cause draining tracts, ulcers, and nodules in cats?

A

Cryptococcus neoformans, Sporothrix schneckii

36
Q

What fungus can cause alopecic angular skin lesions and pseudomycetomas in cats?

A

Microsporum canis

37
Q

What are the clinical signs of canine distemper virus-induced dermatitis?

A
  • Mild to severe nasal and digital hyperkeratosis (hard pad dz)
  • pustular dermatitis that resembles impetigo, upper resp signs, fever, cough, dyspnea, diarrhea, enamel hypoplasia
38
Q

How do you diagnose canine distemper virus?

A
  • Immunocytology or PCR - detection of distemper Ag
  • Dermatohistopath (affected footpads)
  • Immunohistochem
39
Q

How did you treat canine distemper virus?

A
  • No specific antiviral tx exists
  • supportive care - broad spectrum abx
  • Prognosis is poor for dogs w/ nasodigital hyperkeratosis
  • Preventable by vaccination
40
Q

How do you diagnose canine papilloma virus?

A
  • Dermatohistopath
  • PCR or immunohistochem
41
Q

How do you treat canine papillomavirus?

A
  • Most infections regress spontaneously after development of host cell-mediated immune response
  • cryotherapy and laser ablation
  • surgery for persistent solitary lesions
  • Azithromycin
42
Q

Describe feline rhinotracheitis virus

A
  • Herpesvirus upper resp dz
  • Oral or superficial skin ulcers on face, trunk, and footpads may occur
    • ​may be mistaken for allergic dermatitis
43
Q

How to you diagnose feline rhinotracheitis virus?

A
  • Hx and C/S and response to empiric therapy with famciclovir
  • viral isolation (oropharyngeal swabs)
  • fluorescent Ab or PCR techniques (conjunctival smears)
  • Dermatohistopath
44
Q

How do you treat feline rhinotracheitis virus?

A
  • No specific tx
  • good nursing care and broad spec systemic or ophthalmic abx
  • antiviral eyedrops
  • antiviral meds
    • famciclovir
    • alpha-interferon
    • lysine
  • prognosis usually good, recovery in 10-20d
  • Some cats harbor latent infection - recrudescence w/ stress/immunosuppression
45
Q

Describe otitis externa

A
  • Acute or chronic inflammatory dz of external ear canal
  • Almost always an underlying primary disease
46
Q

What are some primary factors that directly cause otitis externa?

A
  • Parasites (e.g. Otodectes, Demodex)
  • FB
  • Tumors
  • Hypersenstivity (Atopy, food, contact dermatitis)
  • Disorders of keratinization, hypoT4, autoimmune dz, juvenile cellulitis, irritants
47
Q

How do acute and chronic otitis externa differ?

A

Acute

  • inner ear pinna & the ear canal are erythematous and swollen (can also be eroded/ulcerated)
  • Pinnal alopecia, excoriation, crusts

Chronic

  • Pinnal hyperkeratosis, hyperpigmentation, lichenification
  • ear canal stenosis from fibrosis/ossification
48
Q

What should be suspected if otitis externa has been present for 2 months or longer?

A

Concurrent otitis media EVEN if tympanic membrane appears to be intact and no clinical signs of otitis

49
Q

How do you diagnose otitis externa?

A
  • Otoscopic exam
  • Mineral oil prep (ear swab)
  • Cytology (ear swab)
  • Bacterial culture
  • Fungal culture
  • Radiography (bulla series), CT, MRI
  • Dermatohistopath
50
Q

Name three synergistic agents used to treat otitis externa

A
  • Tris-EDTA
  • Polymixin
  • Miconazole
51
Q

What are the clinical signs of otitis media?

A
  • Facial nerve paralysis
  • Horner’s syndrome
52
Q

Where should you sample for a bacterial/fungal ear culture?

A
  • Horizontal canal (region where most infections arise)
  • middle ear in cases of tympanic rupture
53
Q

Which agent is safe to use in the middle ear?

A

Tris EDTA

54
Q

What is the issue with use of systemic antimicrobials to treat otitis media?

A
  • The external ear canal and middle ear have a poor blood supply, so there’s limited diffusion of parenteral antimicrobials into the middle ear
55
Q

How long should treatment be continued for otitis media?

A

4-6 weeks

56
Q

What are some systemic agents used to treat otitis media?

A
  • Cephalexin
  • Clavamox
  • Marbo/Enrofloxacin
  • Itraconazole (fungal infections)
57
Q

When should systemic therapy be used in treating otitis?

A
  • Most cases of chronic otitis
  • if neutrophils or rod-type bacteria seen on cytology
  • therapeutic failure with topical antimicrobials
  • chronic recurring ear infections
  • All cases of otitis media
58
Q

What are the clinical signs of otitis interna?

A
  • More pronounced head tilt towards affected side
  • may circle/fall towards affected side
  • generalized incoordination
  • spontaenous horizontal/rotary nystagmus
59
Q

What are some perpetuating factors that prevent resolution of otitis?

A

Bacteria

  • Staph pseudintermedius
  • B-hemolytic Strep sp.
  • Pseudomonas
  • Proteus

Yeasts

  • Malassezia
  • Candida
  • Microsporum canis
60
Q

What is the treatment outcome of otitis treatment?

A
  • Otitis media with intact tympanum - usually responds well to systemic antibiotic therapy
  • if chronic otitis externa exists and tympanum is ruptured - chances of successful treatment are reduced
61
Q

How does Pseudomonas otitis differ from other agents?

A
  • Frustrating and difficult perpetuating cause
  • Development of resistance to most common antibiotics
  • often chronic in course (>2mo)
  • marked suppurative exudation
  • severe epithelial ulceration, pain, edema of the canal

Tx is multifaceted

Clinical Microbio (11 decks)

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