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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
True or False: Malassezia infections in dogs are almost never associated with underlying predisposing conditions, such as atopy or food allergy
False, they are almost always associated with these underlying conditions
26
How do you diagnose Malassezia infections?
* R/o for DDx (demodex, superficial pyoderma, dermatophytosis, ectoparasites, allergies) * Cytology (tape prep/impression smear) * Dermatohistopath * Fungal culture * Allergy test
27
Describe dermatophytosis (ringworm)
* 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
What are the clinical signs seen with dermatophytosis?
* Pruritus (mild) * circular, irregular, or diffuse alopecia with scaling * remaining hairs are stubbled or broken off * can have **asymptomatic carriers**
29
How do you diagnose dermatophytosis?
* UV (Wood’s lamp) * Trichogram * Dermatohistopath * Fungal culture (DTM media) - Microsporum or Trichophyton spp. * IDEXX PCR
30
How do you treat dermatophytosis in dogs?
* 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
How do you treat dermatophytosis in cats?
**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
What virus is associated with nasal and footpad hyperkeratosis in dogs?
Canine distemper virus
33
What virus causes cutaneous papillomas in dogs?
Canine papillomavirus
34
What virus causes cutaneous and subcutaneous nodules?
Feline sarcoma virus
35
What fungal agents cause draining tracts, ulcers, and nodules in cats?
Cryptococcus neoformans, Sporothrix schneckii
36
What fungus can cause alopecic angular skin lesions and pseudomycetomas in cats?
Microsporum canis
37
What are the clinical signs of canine distemper virus-induced dermatitis?
* 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
How do you diagnose canine distemper virus?
* Immunocytology or PCR - detection of distemper Ag * Dermatohistopath (affected footpads) * Immunohistochem
39
How did you treat canine distemper virus?
* No specific antiviral tx exists * supportive care - broad spectrum abx * **Prognosis is poor for dogs w/ nasodigital hyperkeratosis** * **Preventable by vaccination**
40
How do you diagnose canine papilloma virus?
* Dermatohistopath * PCR or immunohistochem
41
How do you treat canine papillomavirus?
* **Most infections regress spontaneously after development of host cell-mediated immune response** * cryotherapy and laser ablation * surgery for persistent solitary lesions * Azithromycin
42
Describe feline rhinotracheitis virus
* Herpesvirus upper resp dz * **Oral or superficial skin ulcers on face, trunk, and footpads may occur** * ​may be mistaken for allergic dermatitis
43
How to you diagnose feline rhinotracheitis virus?
* Hx and C/S and response to empiric therapy with famciclovir * viral isolation (oropharyngeal swabs) * fluorescent Ab or PCR techniques (conjunctival smears) * Dermatohistopath
44
How do you treat feline rhinotracheitis virus?
* 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
Describe otitis externa
* Acute or chronic inflammatory dz of external ear canal * **Almost always an underlying primary disease**
46
What are some primary factors that directly cause otitis externa?
* Parasites (e.g. Otodectes, Demodex) * FB * Tumors * Hypersenstivity (Atopy, food, contact dermatitis) * Disorders of keratinization, hypoT4, autoimmune dz, juvenile cellulitis, irritants
47
How do acute and chronic otitis externa differ?
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
What should be suspected if otitis externa has been present for 2 months or longer?
Concurrent otitis media EVEN if tympanic membrane appears to be intact and no clinical signs of otitis
49
How do you diagnose otitis externa?
* Otoscopic exam * Mineral oil prep (ear swab) * Cytology (ear swab) * Bacterial culture * Fungal culture * Radiography (bulla series), CT, MRI * Dermatohistopath
50
Name three synergistic agents used to treat otitis externa
* Tris-EDTA * Polymixin * Miconazole
51
What are the clinical signs of otitis media?
* Facial nerve paralysis * Horner’s syndrome
52
Where should you sample for a bacterial/fungal ear culture?
* Horizontal canal (region where most infections arise) * middle ear in cases of tympanic rupture
53
Which agent is safe to use in the middle ear?
Tris EDTA
54
What is the issue with use of systemic antimicrobials to treat otitis media?
* 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
How long should treatment be continued for otitis media?
4-6 weeks
56
What are some systemic agents used to treat otitis media?
* Cephalexin * Clavamox * Marbo/Enrofloxacin * Itraconazole (fungal infections)
57
When should systemic therapy be used in treating otitis?
* 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
What are the clinical signs of otitis interna?
* More pronounced head tilt towards affected side * may circle/fall towards affected side * generalized incoordination * spontaenous horizontal/rotary nystagmus
59
What are some perpetuating factors that prevent resolution of otitis?
Bacteria * Staph pseudintermedius * B-hemolytic Strep sp. * Pseudomonas * Proteus Yeasts * Malassezia * Candida * Microsporum canis
60
What is the treatment outcome of otitis treatment?
* 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
How does Pseudomonas otitis differ from other agents?
* 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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