Bacterial Causes of Skin Disease

Question 1

Where can bacteria come from for infections?

Answer 1

Already on skin
From environment
From other animals

Question 2

Endogenous infections

Answer 2

Caused by bacteria already in microbiome of skin
Opportunistic pathogens

Question 3

Which organisms are commonly involved in bacterial skin disease?

Answer 3

Endogenous
* Coagulase +ve Staphylococci
* Dermatophilus congolensis
* Gram -ve is less common unless already compromised
From environment
* Mycobacterium from soil

Question 4

Reasons for bacterial skin disease

Answer 4

Occurs when skin’s normal protective mechanisms are compromised
Mechanical damage to skin
Immunocompromise
Defects in skin barrier function
Changes to microclimate
Dysbiosis

Question 5

Mechanical damage to skin

Answer 5

Trauma from environment
Ectoparasites
Bites

Question 6

Immunocompromise

Answer 6

Immature/naive immune system
Inadequate nutrition
Immunosuppressive medication/disease

Question 7

Defects in skin barrier function

Answer 7

Inherent weakness
Disease effect

Question 8

Changes to skin microclimate

Answer 8

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

Question 9

Dysbiosis

Answer 9

The imbalance of normal microbiome
* Reduction in diversity
* Increase in population of staphylococci

Question 10

How do microbes enter the skin?

Answer 10

1. Via follicles
2. Direct entry thought damaged skin
3. Haematogenous spread - rare

Question 11

Factors affecting disease manifestation

Answer 11

Organism and virulence factors
Predisposing/co-exisiting factors
Host immune response

Question 12

What factors effect disease variation?

Answer 12

Depth on infection
Type of inflammatory response
Lesion distribution and severity

Question 13

types of inflammatory response

Answer 13

Pyogenic - mainly neutrophils
Granulomatous - mainly macrophages
Necrotising - Vascular damage

Question 14

Types of clinical manifestation of Bacterial Skin disease

Answer 14

1. Surface problems
2. Superficial pyodrma
3. Deep pyoderma
4. Bacterial granulomatous dermatitis
5. Skin lesions secondary to systemic bacterial infection

Question 15

1. Surface problems

Answer 15

When bacteria multiply on skin surface only

Question 16

Examples of surface problems

Answer 16

Canine intertrigo (‘skin fold pyoderma’)
Acute moist dermatitis
Bacterial overgrowth syndrome

Question 17

Canine intertrigo (‘skin fold pyoderma’)

Answer 17

Mixed microbial overgrowth
+/- neutrophilic inflammation

Question 18

Acute moist dermatitis

Answer 18

Pyotraumatic dermatiti / ‘hotspots’
Acute lesion caused by skin self-trauma

Question 19

Bacterial Overgrowth syndrome

Answer 19

Bacterial multiplication with no/minimal inflammation
Often highly pruritic

Question 20

2.Superficial pyoderma

Answer 20

Infections within epidermis +/- hair follicle
Primarily neutrophilic inflammation - acute

Question 21

Clinical signs of superficial pydoderma

Answer 21

Papules/pustules
Crust
Epidermal collarettes/scale
Follicular plugs
Alopecia

Crust/scale caused by buildup/bursting of pustules

Question 22

Examples of superficial pyoderma

Answer 22

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

Question 23

3. Deep pyoderma

Answer 23

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

Question 24

Furunculosis

Answer 24

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

Question 25

Abscess

Answer 25

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

Question 26

Cellulitis

Answer 26

Poorly-delineated suppurative inflammation of deep cutaneous connective tissue Skin may devitalise and slough

Question 27

4. Bacterial Granulomatous Dermatitis

Answer 27

Caused by traumatic implantation of saprophytic organisms * Mycobacterial granulomas * Non-filamentous bacterial granulomas * Filamentous bacterial granulomas

Question 28

Non-filamentous bacterial granulomas organisms

Answer 28

* Staphylococci * Streptococcus * Actionbacillus AKA Botryomycosis Small yellow granules (sulphur)

Question 29

Filamentous bacterial granulomas organisms

Answer 29

* Nocardia * Actinomyces - lumpy jaw Nodular masses May involve bone

Question 30

5. Skin lesions secondary to systemic bacterial infection

Answer 30

Systemic bacterial infections can cause vascular damage of skin Leads to necrosis * E.g. Erysipelas in pigs

Question 31

Diagnostic tests for bacterial skin disease

Answer 31

Cytology Culture Histopathology (skin biopsy)

Question 32

Cytology

Answer 32

○ Lesion surface, exudate, FNA ○ Visualise inflammatory cell type and often microorganism ○ May use special stains E.g. Ziehl-Neelsen for mycobacteria

Question 33

Culture

Answer 33

Pustules Superficial tissue/exudate Deep tissue - biopsy

Question 34

Treatment principles of bacterial skin disease

Answer 34

Kill organism Enhance body's defences Address underlying cause

Question 35

Issues with killing organism

Answer 35

Antimicrobial Resistance (AMR) * Avoid antibiotics * Use topical antibacterials where possible Base antibiotic choice on culture and sensitivity tests