Bacterial Causes of Skin Disease Flashcards
Where can bacteria come from for infections?
Already on skin
From environment
From other animals
Endogenous infections
Caused by bacteria already in microbiome of skin
Opportunistic pathogens
Which organisms are commonly involved in bacterial skin disease?
Endogenous
* Coagulase +ve Staphylococci
* Dermatophilus congolensis
* Gram -ve is less common unless already compromised
From environment
* Mycobacterium from soil
Reasons for bacterial skin disease
Occurs when skin’s normal protective mechanisms are compromised
Mechanical damage to skin
Immunocompromise
Defects in skin barrier function
Changes to microclimate
Dysbiosis
Mechanical damage to skin
Trauma from environment
Ectoparasites
Bites
Immunocompromise
Immature/naive immune system
Inadequate nutrition
Immunosuppressive medication/disease
Defects in skin barrier function
Inherent weakness
Disease effect
Changes to skin microclimate
Dermatophilosis - ‘rain scald’/’mud fever’/’lumpy wool’
□ Predisposed by wet skin
Pseudomonas infection
□ Growth predisposed by wet environment
Intertrigo - Skin fold pyoderma in dogs
□ Skin fold is a warm moist environment
Dysbiosis
The imbalance of normal microbiome
* Reduction in diversity
* Increase in population of staphylococci
How do microbes enter the skin?
- Via follicles
- Direct entry thought damaged skin
- Haematogenous spread - rare
Factors affecting disease manifestation
Organism and virulence factors
Predisposing/co-exisiting factors
Host immune response
What factors effect disease variation?
Depth on infection
Type of inflammatory response
Lesion distribution and severity
types of inflammatory response
Pyogenic - mainly neutrophils
Granulomatous - mainly macrophages
Necrotising - Vascular damage
Types of clinical manifestation of Bacterial Skin disease
- Surface problems
- Superficial pyodrma
- Deep pyoderma
- Bacterial granulomatous dermatitis
- Skin lesions secondary to systemic bacterial infection
- Surface problems
When bacteria multiply on skin surface only
Examples of surface problems
Canine intertrigo (‘skin fold pyoderma’)
Acute moist dermatitis
Bacterial overgrowth syndrome
Canine intertrigo (‘skin fold pyoderma’)
Mixed microbial overgrowth
+/- neutrophilic inflammation
Acute moist dermatitis
Pyotraumatic dermatiti / ‘hotspots’
Acute lesion caused by skin self-trauma
Bacterial Overgrowth syndrome
Bacterial multiplication with no/minimal inflammation
Often highly pruritic
2.Superficial pyoderma
Infections within epidermis +/- hair follicle
Primarily neutrophilic inflammation - acute
Clinical signs of superficial pydoderma
Papules/pustules
Crust
Epidermal collarettes/scale
Follicular plugs
Alopecia
Crust/scale caused by buildup/bursting of pustules
Examples of superficial pyoderma
Bacterial folliculitis
* Infection WITHIN follicle
Impetigo
* infection BETWEEN follicles
Exfoliative superficial pyoderma
* Infections between layers of stratum corneum
Dermatophilosis
Fleece rot - Pseudomonas
Greasy pig disease - staph hyicus
- Deep pyoderma
Infections outside epidermis or hair follicle
Caused by:
* Rupture of hair follicle wall (furunculosis)
* Penetrating wounds
* Haematogenous spread (sepsis)
Associated with
Thickening of skin/subcutaneous tissue
+/- nodules
+/- draining sinuses
Furunculosis
Extension of folliculitis - rupture of hair follicle wall
Deep infection of the hair follicle
Leading to abscess formation
Accumulation of pus and necrotic tissue - pyogranuloma
Microbes and keratin in dermis
Abscess
Commonly due to wound or foreign body
Wide range of organisms involved
Result from pooling of suppurative material in dermal or subcutaneous tissue
* Surrounded by granulation tissue/fibrosis
Rabbits have caseous pus - must remove surgically
Cellulitis
Poorly-delineated suppurative inflammation of deep cutaneous connective tissue
Skin may devitalise and slough
- Bacterial Granulomatous Dermatitis
Caused by traumatic implantation of saprophytic organisms
* Mycobacterial granulomas
* Non-filamentous bacterial granulomas
* Filamentous bacterial granulomas
Non-filamentous bacterial granulomas organisms
- Staphylococci
- Streptococcus
- Actionbacillus
AKA Botryomycosis
Small yellow granules (sulphur)
Filamentous bacterial granulomas organisms
- Nocardia
- Actinomyces - lumpy jaw
Nodular masses
May involve bone
- Skin lesions secondary to systemic bacterial infection
Systemic bacterial infections can cause vascular damage of skin
Leads to necrosis
* E.g. Erysipelas in pigs
Diagnostic tests for bacterial skin disease
Cytology
Culture
Histopathology (skin biopsy)
Cytology
○ Lesion surface, exudate, FNA
○ Visualise inflammatory cell type and often microorganism
○ May use special stains
E.g. Ziehl-Neelsen for mycobacteria
Culture
Pustules
Superficial tissue/exudate
Deep tissue - biopsy
Treatment principles of bacterial skin disease
Kill organism
Enhance body’s defences
Address underlying cause
Issues with killing organism
Antimicrobial Resistance (AMR)
* Avoid antibiotics
* Use topical antibacterials where possible
Base antibiotic choice on culture and sensitivity tests
