Skin Pathogens Flashcards
What is the function of skin
Skin: barrier between the interior of our body and external environment
* Regulate body temperature
* Protection from UV light
* Protect from dehydration
* Protect from microorganisms
* Immune response
What are the main structures and layers of the skin
- Epidermis: 4-5 layers
- Dermis: 2 layers
- Hypodermis/SC
- Adnexa: follicles/nail/antler/claw/feather/sebaceous gland/sweat glands
What is the main function of the epidermis
- Epidermis: 4-5 layers = physical barrier (innate and acquired immune/microbiome)
List the 4 layers of the epidermis
o Stratum corneum: lipid enriched ECM
o Stratum granulosum
o Stratum spinosum
o Stratum basale (attached to basement membrane)
What 3 risk factors predispose to skin infection
- Predisposed by a thin stratum corneum, small amount of lipid, high skin pH
What is the primary way bacteria enter the skin
- Direct entry: epidermal damage
- wound
- chemical irritant
- burns
- moist/diry
- allergy
Define Blister
- Blister: serum or lymph filled lesion
Define Pustule
- Pustule: pus filled lesion
Define Furunculosis
- Furunculosis: deep infection of the hair follicle
Define Scab/crust
- Scab/crust: crust of coagulated blood/pus/skin debris
Define Scale
- Scale: dry/flaky exfoliation
Define Excoriation
- Excoriation: traumatic abrasion and scratches
Define Eczema
- Eczema: erythematous/itchy skin inflammation
Define Fissure
- Fissure: deep cracks
Define Hyperpigmentation
- Hyperpigmentation: increased deposits of melanin
Define Hyperkeratosis
- Hyperkeratosis: excessive overgrowth of kertatinized, epithelium like skin
Define Hypopigmentation
- Hypopigmentation: decreased deposits of melanin
Define Cellulitis
- Cellulitis: diffuse, deep and acute inflammation of the dermis and SC
Define Folliculitis
- Folliculitis: inflammation of hair follicles
Define urticaria
- Urticaria: raised, itchy rash on skin
Define seborrhea
- Seborrhea: excess secretion by sebaceous glands
Define Alopecia
- Alopecia: hair loss
List the 4 main commensals/opportunistic bacteria of the skin
o Staph/Strep/Cornybacterium/Entereococcus
List the 5 main commensals/opportunistic bacteria of the oral cavity
o Pasturella multocida (main)
o Staph/Strep/Neisseria/Cornybacterium
What are other considerations to have when administering antibiotics to treat skin infection
- Antibiotics will not remove the underlying cause of bacterial skin infection
o Treat pruritis: sedative/anesthetics/corticosteroids
o Treat fluid/electrolyte losses
o Address underlying factors
What are the things to consider when choosing an antibiotic to treat skin infections
- Topical vs systemic: superficial vs deep infection
- Antimicrobial choice: route of administration/duration/adverse effects
What are the main lesions of pyoderma? What are the lesions associated with the 2 forms?
- Presentations: pruritis (lead to excoriation)
o Superficial: pustular dermatitis
o Deep: furunculosis and cellulitis
o Puppy and kitten: impetigo
Where do the lesions of pyoderma occur? How does this vary between cats and dogs?
o Location
Kitten: on neck/shoulders (where mom grasps)
Dog: anywhere not covered by hair
What are the primary causative agents of pyoderma in dogs and also cats
o Dog: Staph pseudointermedius/intermedius
o Cat: Pasurella/Strep (oral)
o Staphylococcus (gram +)
What are the main features of Staph? What are the 3 primary virulence factors?
o Staphylococcus (gram +)
Pyogenic = suppurative lesions
Virulence factors:
* Capsular polysaccharides/teichoic acids/protein A (prevent phagocytosis)
Catalase (allow survival in phagocytes)
Coagulase (shield from phagocyte)
What are the 6 main risk factors of pyoderma infection
- Risk factors: skin damage or immune system failure
o Fleas/insect bites
o Food allergy
o Mange
o urine scald
o compromised immune system
o Weakened endocrine system
How is pyoderma treated? What antimicrobials are used?
- Tx: some can resolve
o Topical antiseptic shampoo
o Systemic antimicrobials: clindamycin/1st generation cephalosporins
o Long duration of treatment = use antimicrobials with minimal side effects
o MRSA more prevalent
What is another name for greasy pig disease
Exudative epidermitis (greasy pig disease)
Whaat is the causative agent of exudative epidermitis? Where does it come from?
- Agent: Staph hyicus
o Commensal in healthy sow vagina
What is the primary virulence factor of staph hyicus
o Virulence factors: exfoliative toxins (disrupt cell attachment causing clinical signs)
What animals are targeted by exudative epidermitis? What is the prognosis
- Target: up to 3 month old sucklers and piglets
o High mortality if untreated
o Extremely contagious
What are the main lesions of exudative epidermitis?
- Lesions: extensive, non-pruritis dermatitis
o Greasy exudate (excess sebaceous secretion, exfoliation, cellulitis, scab, blister, pustule)
What is the main risk factor of exudative epidermitis?
- Risk factors
o Stress (low immunity/bites)
How is exudative epidermitis treated? What antimicrobials are used?
- Tx: 5d of antimicrobials
o Systemic; amoxycillin/ceftiofur/cephalexin/gentimycin
o Topical: mix antimicrobial with mineral oil
o Maintain hydration
What is another name for diamond skin disease?
Swine Erysipelas (diamond skin disease)
What is the causative agent of Swine Erysipelas? What are the main features?
- Agent: Erysipelothric rhusiopathiae (gram + rod, catalase -)
o Zoonotic
What are the virulence factors of Swine Erysipelas?
o Virulence factors
Capsule (protect from phagocytosis)
Neuraminidase (adhere to endothelial cells)
Where is Erysipelothric rhusiopathiae found?
o Commensal in tonsils (in 50% pigs) – excrete in feces/urine/saliva/nasal discharge
What are the 4 main presentations of Swine Erysipelas? What is a pathognumonic sign?
- Lesions
o Cutaneous (diamond shaped erythema = pathognomonic)
o Septicemia
o Arthritis
o Endocarditis
How is Swine Erysipelas treated and prevented?
- Tx; 3-6d antimicrobials
o Penicillin (main)/tetracycline) - Prevent with vaccine
What is the features of Dermatophilus congolensis?
- Agent: Dermatophilus congolensis (gram +, filamentous branching cocci)
o Class: actinobacteria
o Has coccal zoospores that germinate into hyphae
Form tram track/rail road on cytology
Where is Dermatophilus congolensis found
o Commensal on skin (trauma or persistant wetting allows entry = acute inflame)
Transmitted by direct contact with infective animals or blood sucking insects
What are the 2 main virulence factors of Dermatophilus congolensis
o Virulence:
phospholipase
proteolytic enzymes
What animals does Dermatophilus congolensis target? What are the clinical presentations in the main animal species?
- Target: wide host range
o Cattle/goat/horse: cutaneous streptothrichosis
o Sheep: lumpy wool/strawberry foot rot
o Horse/cow: rain rot
o Rare in companion animals
What are the main lesions of Dermatophilus congolensis
- Lesion: raised scab-like lesions (full of branching filament containing zoospores)
o Sticky matted hair with multiple crusts containing purulent exudate (paintbrush lesions)
How to treat Dermatophilus congolensis
- Tx: spontaneously resolve
o Systemic oxytetracycline: long lasting
o Penicillin (streptomycin) for 3-5d
o Topical antimicrobials = not effective
What is the main species targeted by cornybacterium pseudootuberculosis and what are the disease manifestations in each?
- Target: horse/cow
- Lesions
o Small ruminants: caseous lymphadenitis
o Horse: ulcerative lymphangitis (pigeon fever/false strangles)
o Cattle: cutaneous granuloma (skin trauma associated
What are the specific Cornybacterium tuberculosis supsp that cause disease? What species do they cause disease in?
- Agent: Cornybacterium pseudotuberculosis (gram =, rod)
o C. pseudotuberculosis equi = horse and cow
o C. pseudotuberculosis ovis = small urminants
What are the 2 virulence factors of Cornybacterium tuberculosis
o Virulence factors
Phospholipase D (ability to invade)
Mycolic acid (protect from immune system)
How to diagnose Cornybacterium tuberculosis
- Diagnosis: culture abscess pus
How to treat Cornybacterium tuberculosis in cow and horses
o Cattle: don’t need +/- topical shampoo
o Horse: lance and drain abscess
Penicillin G (for 1mo)
If internal abscess = 50% die
Fly control
What are the features of nocardia bacteria and where is it located
- Agent: nocardia (gram +, rod, filamentous)
o Found in the soil and decaying vegetation
o Opportunistic (require immunosuppression)
What are the 2 virulence factors of nocardia
o Virulence factors: allow intracellular survival
Superoxide dismutase
Catalase
What are the disease presentations and related lesions of nocardia
- Lesions: thoracic, cutaneous, disseminated forms
o Indolent ulcers or pyogranulomatous lesions with draining tracts
o Firm nodules
o Abscess
o Fistulous tracts and extensive fibrosis
How is nocardia infection treated
- Tx: surgical removal
o Antimicrobial use depends on bacterial susceptibility
Amikacin/TMS/sulfamethoxazole (min for 6 weeks)
What are the main features of P. multocida bacteria
- Agent: Pasturella multocida (gram =, coccobacilli)
What is the main virulence factor of P. multocida
adhesins
What type of injury is p. multocida associated with
- Target: cat (cat bite- especially intact males)
What lesion is common in P. multocida related cat bites
- Lesion: cellulitis
How to treat P. multocida related cat bites
- Tx: drain purulent fluid
o Ampicillin/cefazolin/amoxicillin/clavulanate/cefvecin
What are 4 common agents found in cat bite infections
o Cat bite: stapy/P. multocida/C. pseudotuberculosis/Clostridium) = cellulitis
What are the 4 common agents causing post surgical wound infections in dogs
o Staph pseudointermedius
o Staph aureus
o Step
o Coliforms
What are the 3 common agents causing post surgical wound infections in dogs
o Staph and Strep
o Coliforms
o P. multocida
How are post surgical wound infections treated
- Tx: broad spectrum abx (clavamox/ampicillin sulbactam)
What is the most likely causative agent of deep cellulitis
- Agent: staph
What animals ar commonly affected by deep cellulitis
- Target; horse and companion animals
How to treat deep cellulitis
- Tx; aggressive systemic abx (cephalosporins)
What animal does mycobacterial dermatitis affect
- Target: cat
What are the common lesions associated with mycobacterial dermatitis
- Lesion: nodular dermatitis with draining tracts and panniculitis (not systemic)
How to treat mycobacterial dermatitis
- Tx: based on abx susceptibility
