Dermatologie veterinara Curs 4 - Dermatitele bacteriene

Lecture 4 - Bacterial Skin Diseases

I. Normal skin environment

A. Resident microflora

Colonize normal skin and may be found in the superficial epidermis and hair follicles of normal skin. These commensal microflora play an important role in inhibiting colonization by pathogenic organisms.

B. Skin infection: Pathogenic bacteria are causing clinical signs in the host.

II. Overview of pyoderma

A. Pathogenic bacteria: Staphylococcus intermedius is most common

1.  Dog

a.  The primary skin pathogen is Staph. intermedius. In severe, complicated, or deep pyodermas, other organisms may also be causative (Pseudomonas, Proteus, etc.).

b.  Staphylococcus aureus and Staphylococcus schleiferi
An increasing prevalence of Staph aureus and the emergence of a new species (Staph schleiferi) has been noted in dogs. Both species are pathogenic, have the ability to develop multidrug resistance, and are of zoonotic concern.

2.  Cat
Whereas bacterial skin infections are quite common in the dog, Staph pyodermas are uncommon in the cat. The most common skin infection in the cat is the bite wound abscess.

B. Classification of pyoderma

1.  Primary pyoderma: skin infection that occurs in healthy skin with no apparent cause. Uncommon.

2.  Secondary pyoderma: skin infection that has an underlying cause or occurs in diseased skin.

a.  Most pyodermasare secondary in nature.

b.  Underlying causes: include allergies (approximately 80% of allergic dogs have a secondary pyoderma at time of diagnosis), mites, dermatophytes, seborrhea, and endocrine disorders.

c.  Diseased skin: trauma, moisture, immunocompromise, and altered normal flora predispose.

3.  Depth of infection: pyodermas are characterized as surface, superficial, or deep (see later).

C. Diagnosis

1.  History and physical exam
The diagnosis of pyoderma is made on exam based on clinical appearance of skin lesions. However, a meticulous history and complete physical exam is crucial in determining likely contributory causes (remember, most pyodermas are secondary!).

2.  Basic tests used in the evaluation of all patients with pyoderma

a.  Thorough dermatologic exam: to evaluate for contributory causes.

b.  Skin scrapings: to look for mites.

c.  DTM culture: to evaluate for dermatophytes.

d.  Cytology (Diff-Quik): needle aspirate (of pustule, papule, nodule), or imprint of exudate.
To evaluate for inflammatory cells (neutrophils, eosinophils) and microorganisms (bacteria, yeast, etc.). *Q: How can you differentiate between colonization and infection? Infection is associated with inflammatory cells and intracellular bacteria, colonization is not.

3.  Tests pursued in deep, non-responsive, or recurrent pyodermas
Skin biopsy: invaluable test in refractory, non-responsive pyoderma or dermatosis.

i.  Technique: obtain multiple skin biopsy samples (Baker biopsy punch often utilized). Collect intact primary lesions (ex: papule, vesicle) as well as samples with a border of normal:diseased skin.

ii.  Purpose: to obtain histopathologic diagnosis and look for causative etiology.

b.  Skin culture and sensitivity: to identify causative organism(s) and sensitivity pattern

i.  Biopsy: historically considered technique of choice (reduces likelihood of harvesting contaminants). The superficial skin is cleansed with an antiseptic and a punch biopsy is obtained and placed in a sterile vial containing transport media.

ii.  Skin swab: recent study (Evaluation of aerobic bacteriologic culture of epidermal collarette specimens in dogs with superficial pyoderma - JAVMA March 2005) indicates that swab technique was a simple and reliable method for identification of S. intermedius in dogs.

c.  Rule out contributory hypersensitivities *Q: How would you do this?

d.  Rule out underlying metabolic disease: CBC, profile, UA.

e.  Rule out underlying endocrine or immunologic disease: testing as indicated.

D. Treatment of skin infections

1.  Address underlying cause: key to successful treatment

2.  Antibacterial shampoos

a.  Purpose
Removes tissue debris and aids in eliminating bacteria in the more superficial layers of the skin (where antibiotic levels tend to be lower).

b.  Frequency of shampoo application:

i.  For active infections, provide shampoo therapy 2 - 3 times weekly.

ii.  For ongoing management, provide shampoo therapy 1 - 2 times weekly.
Work up good lather and allow minimum of 10 - 15 minutes contact time. Most effective if hair is clipped short and washed first.

c.  Antibacterial shampoo options (see table)

i.  Benzoyl peroxide
Most effective antibacterial shampoo. Also has keratolytic, antipruritic, degreasing and follicular flushing action. Can be irritating (drying) to the patient with inflamed or sensitive skin. Use of humectant spray or rinse after shampoo may be helpful.

ii.  Chlorhexidine
Also an effective antibacterial shampoo that is less irritating for the patient with dry skin. Chlorhexidine is a good antiseptic (kills microbes on tissues) as well as disinfectant (kills microbes on inanimate objects). No degreasing activity, not keratolytic.

iii.  Ethyl lactate
Similar to chlorhexidine in regards to efficacy. Antibacterial, rehydrating, keratoplastic, and has mild follicular flushing activity.

iv.  Other: sulfur containing shampoos (sulfur has both antibacterial and antifungal activity).

d.  Table of shampoos: adapted in part from: Practical Topical Therapy for Skin Infections Proceedings - WVC 2004 Karin M. Beale, DVM, DACVD

3.  Soaks and hydrotherapy (whirlpool bath)

a.  Purpose
Helpful in the initial management of deep pyoderma to remove crusts and decrease surface bacteria. Clip hair in affected area, and apply soaks or whirlpools until drainage abates.

b.  Agents: dilute solutions of chlorhexidine or povidone-iodine are good antiseptics.

4.  Topical antibacterial lotions, gels, wipes, spray: for localized lesions (table adapted from WVC 2004 Karin M. Beale DACVD)

5.  Oral antibiotics

a.  Role
Oral antibiotics are necessary to reach effective antibiotic levels in the skin in most pyodermas (as stratum corneum is a major barrier to effective topical penetration).

b.  Dose and duration of therapy

i.  Use maximal therapeutic dose
Antibiotic levels in skin are often much less than that in blood. Must insure complete surface (look at) as well as deep (palpate) healing before discontinuing antibiotics.

ii.  First-time pyoderma
Treat for minimum of 3 weeks (at least one week past clinical cure).

iii.  Complicated or deep pyoderma
Typically treated for minimum of 8 weeks (at least 2 weeks past clinical cure). Early relapses (< 7 days) are likely due to inadequate initial treatment. Later relapses (weeks to months) or likely due to unresolved underlying cause.

c.  Selection of appropriate antibiotics (see table)

i.  First line antibiotics: used initially in the treatment of most superficial pyodermas. These antibiotics are typically narrow spectrum, preserve endogenous flora, and are effective against Staph intermedius (B-lactamase producer).

ii.  Second line antibiotics: used in recurrent, deep, or non-responsive pyodermas. These antibiotics are often effective against resistant Staphylococcus and have an extended spectrum (to include gram negatives). Culture and sensitivity is best means by which to determine antibiotic selection.

6.  Immunostimulation therapy
May be helpful in the treatment of idiopathic recurrent pyoderma (no underlying causative factors identifiable). Staphage Lysate is a bacterial-derived product given by injection (on a longterm basis - detailed protocol) and may help boost CMI to resolve pyoderma. Controversial benefit.

III. Surface pyodermas

A. Definition

Bacterial colonization or overgrowth is present on the skin surface - but the skin is not infected.

B. Intertrigo (skinfold pyoderma)

1.  Etiology
Occurs in breeds with excess skin folds and is due to irritation (skin rubbing against skin). Bacterial multiplication is encouraged by moisture, obesity, and secretions (urine, saliva).

2.  Clinical signs

a.  Skin lesions occur in regions of the body with excessive folds and are characterized by local erythema, oozing, erosion, and odiferous discharge.

b.  Predisposed sites include lower lip (Spaniel, St Bernard), facial folds (brachycephalic breeds), vulvar fold (older obese female), tail fold (Pug, etc.) or body folds (Shar Pei). *Q: What may be another deleterious result of facial fold dermatitis?

3.  Treatment: reduce obesity, antibacterial shampoos, topical antimicrobial products (mupirocin, Malaseb wipes, benzoyl peroxide gels) and surgical excision of excessive skin folds (if possible).

IV. Superficial pyoderma

A. Overview

1.  Definition: bacterial infection of the skin that involves the epidermis and/or intact hair follicles.

2.  Clinical lesions: can be variable
Lesions often consist of papular to pustular eruptions (centered around the hair follicle), epidermal collarettes, and crusts. Many alternate clinical presentations also occur (see below).

B. Impetigo (puppy pyoderma)

1.  Clinical signs
Mild superficial pustular rash and crusts in hairless inguinal and axillary region of young puppies (< 1 year). May be idiopathic or associated with dirty environment, poor nutrition, or parasitism.

2.  Treatment
Most cases are self-limiting and respond to topical antimicrobial shampoo therapy, systemic antibiotics are rarely needed.

C. Bullous impetigo

1.  Clinical signs
Superficial pyoderma with large flaccid pus-filled bullae often noted in inguinal/axillary region. Occurs in adult dog and may be associated with underlying disease, immunosuppression (HAC, diabetes mellitus, etc).

2.  Treatment: antimicrobial shampoo therapy, systemic antibiotics, look for cause.

D. Superficial folliculitis: most common form of canine pyoderma (rare in cats)

1.  Predisposing factors: most pyodermas are secondary.
Staph intermedius is the primary cutaneous pathogen (other possible bacteria include E. coli , Proteus mirabilis, and Pseudomonas spp). Common predisposing conditions include demodicosis and dermatophytosis.

2.  Clinical signs: lesions are variable

a.  Lesions
Bacterial folliculitis = infection confined to hair follicle. The classic primary lesion is a tiny intact papule or pustule with a hair emanating from the center Lesions are often concentrated on the ventrum and trunk.

b.  Papulo-pustular rash
May note papules, pustules, crusts, epidermal collarettes, and hyperpigmented or erythematous macules.

c.  Moth-eaten alopecia
In other dogs, may note "surface bumps" covered by hair. Focal "moth-eaten" alopecia occurs as these hairs fall out.

3.  Diagnosis: pursue appropriate tests (see above) - must answer question: Why is infection present?

4.  Treatment

a.  Address underlying cause.

b.  Topical antibacterial (and sometimes anti-seborrheic) shampoo therapy (see table above).

c.  Oral antibiotics: institute therapy with a "first-line antibiotic." *Q: What is the minimum length of therapy? *Q: How do you determine when therapy is complete? Avoid concurrent use of glucocorticoids.

d.  Recurrence of disease: If pyoderma is pruritic and recurrent, consider underlying disease (*Q: Such as?). If pyoderma is recurrent and non-pruritic, consider other underlying diseases (*Q: Such as?)

E. Pyotraumatic folliculitis (hot spot)

1.  Etiology
Peracute skin lesion caused by self-trauma that is triggered by a painful or pruritic event.

2.  Clinical signs: most common in large breed, heavy coated dogs in warm humid climates.

a.  Initial lesions (pyotraumatic dermatitis) are well demarcated, painful, erythematous, moist, and have a yellowish center covered with a proteinaceous exuduate. Surface colonization of bacteria is present.

b.  Lesions rapidly progress to deeper involvement (pyotraumatic folliculitis) heralded by satellite papules and bacterial invasion of hair follicles.

3.  Treatment

a.  Eliminate trigger, clip hair (may require sedation, lesions can be painful), and remove exudate with antibacterial shampoo. Elizabethan collar may be necessary.

b.  Topical antibacterial ointment (such as mupirocin): acts as a wound barrier and helps to address bacterial infection.

c.  Systemic therapy: first-line oral antibiotics for folliculitis (see above) and oral glucocorticoids at anti-inflammatory doses for 3 to 5 days to alleviate associated inflammation and pruritis.

G. Juvenile cellulitis (juvenile pyoderma, puppy strangles)

1.  Pathogenesis
This is a sterile granulomatous and pustular disease of puppies that closely mimics superficial pyoderma. Cause unknown - may be heritable.

2.  Clinical signs
Acute swelling of the face and submandibular LN's followed by papules, pustules, oozing serum or pus, and crust formation. Systemic signs of illness are usually present.

3.  Diagnosis: biopsies reveal granulomas and cellulitis, skin cultures are usually negative.

4.  Treatment: immunosuppressive doses of glucocorticoids (most important), and oral antibiotics (to address secondary bacterial infection).

V. Deep pyoderma

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