Bacterial causes of skin disease Flashcards
What is an endogenous infection?
Skin disease caused by organisms that are present on normal skin
Give examples of common bacteria found on the normal skin that are involved in skin disease
Coagulase +ve Staphylococci
Dermatophilus congolensis (horses, sheep, cattle)
Gram -ve bacteria
What are the possible sources of bacteria causing skin disease?
Present on normal skin
From the environment e.g., mycobacteria in soil
From other animals e.g., Treponema cuniculi infection in rabbits
Give examples of how the skin’s normal protective mechanisms can be compromised
Mechanical damage to skin e.g., bumblefoot
Immunocompromise e.g., greasy pig disease
Defects in skin barrier function
Changes in skin microclimate e.g., moisture, warmth etc.
Dysbiosis
Give examples of how an animals immune system can be compromised leading to disease?
Immature/naïve immune system
Inadequate nutrition
Immunosuppressive medication/disease
Give examples of defects in skin barrier function leading to skin disease
Inherent weakness in dogs:
- thin stratum corneum
- lack of lipid seal at opening to hair follicles
- relatively high pH
=> high incidence bacterial skin disease
Disease effect –
e.g. skin barrier changes in canine atopic dermatitis predispose to secondary infections
Give examples of diseases that occur when there are changes to the skins microclimate
Dermatophilosis (‘rain scald’, ‘mud fever’, ‘lumpy wool’) - predisposed by wet skin
Pseudomonas infection – growth predisposed by wet environment
Intertrigo (skin fold pyoderma) – dogs – skin fold => warm moist environment
Describe the effect of dysbiosis in skin disease
allergic skin disease in dogs
=> reduce diversity of microbiome
=> increase population of staphylococci/Malassezia
=> development of lesions
What are the portals of entry for microbes entering the skin?
What factors influence the manifestation of skin disease?
Organism and its virulence factors
predisposing/coexisting factors
host immune response
Depth of infection e.g., epidermis, -> subcutis
type of inflammatory response
Lesion distribution and severity
What are the different types of inflammatory response seen in skin disease?
Pyogenic - ‘pus-producing’ - mainly neutrophils – ‘pyoderma’
Granulomatous - mainly macrophages
Necrotising - involve vascular damage => ischaemia
What are the possible clinical manifestations of bacterial skin disease?
Surface pyoderma
Superficial pyoderma
Deep pyoderma
Bacterial granulomatous dermatitis
Skin lesions secondary to systemic bacterial infection or infection with toxin-producing bacteria
What is surface pyoderma?
bacteria multiplying on the skin surface only
Give examples of diseases that manifest as a surface pyoderma
Canine intertrigo (‘skin fold pyoderma’):
- mixed microbial overgrowth +/- neutrophilic inflammation
Acute moist dermatitis (pyotraumatic dermatitis, ‘hotspots’):
- acute lesion caused by skin self-trauma
Bacterial overgrowth syndrome:
- bacterial multiplication with no/minimal inflammation
- often highly pruritic
What is a superficial pyoderma?
Infection within epidermis +/or hair follicle
=> papules/pustules => crust, epidermal collarettes/scale, follicular plugs, alopecia
Primarily neutrophilic inflammation
Give examples of skin diseases that manifest as a superficial pyoderma
Bacterial folliculitis - infection within hair follicle
Impetigo - interfollicular infection of epidermis
Exfoliative superficial pyoderma - infection between layers of stratum corneum (exfoliative toxins => intraepidermal splitting => scale)
Dermatophilosis – esp horse, cattle, sheep
Fleece rot – Pseudomonas - sheep
Greasy pig disease (exudative epidermitis) - Staph hyicus
What is a deep pyoderma?
Infection outside epidermis or hair follicle epithelium due to:
- rupture of hair follicle wall (furunculosis)
- penetrating wounds
- haematogenous spread (sepsis)
Usually associated with thickening of skin/subcutaneous tissue, +/- nodules, +/- draining sinuses
Give examples of skin diseases that manifest as a deep pyoderma
Furunculosis
Abscess (esp large animals, cats)
Cellulitis
Describe the features of furunculosis as a manifestation of deep pyoderma
Extension of folliculitis => rupture of hair follicle wall => microbes + free keratin in dermis
Often associated with pyogranulomatous inflammation
Describe abscesses as a manifestation of deep pyoderma
Commonly due to wounds, foreign bodies
Wide range of organisms involved
Result from pooling of suppurative material in dermal or subcutaneous tissue - surrounded by granulation tissue/ fibrous connective tissue.
Well-defined
Frequently rupture and drain spontaneously.
Describe cellulitis as a manifestation of deep pyoderma
Poorly-delineated suppurative inflammation of deep subcutaneous connective tissue.
Range of organisms potentially involved
Some organisms => malodour/gas production (e.g. Clostridia - sheep/cattle)
Skin may devitalise and slough
Describe bacterial granulomatous dermatitis
Caused by traumatic implantation of saprophytic organisms
Give examples of bacterial granulomatous dermatitis
Mycobacterial granulomas/ pyogranulomas
Non-filamentous bacterial granulomas:
e.g. Staphylococci, Streptococci, Actinobacillus
Also called botryomycosis
Lesions contain small yellow granules (‘sulphur’ granules)
Filamentous bacterial granulomas:
e.g. Nocardia, Actinomyces
=> nodular masses which may involve bone
Give examples of Skin lesions secondary to systemic bacterial infections / infections with toxin-producing bacteria
systemic bacterial infections
=> vascular damage of skin => necrosis
e.g. erysipelas of pigs
infection with toxin-producing bacteria (rare):
- Acute febrile illness with shock, visceral disease, cutaneous lesions – caused by bacterial toxins
