Infections of the Skin Flashcards
Which features of the skin make it an ideal defense mechanism ?
- Hard horny layer of cells
- Mostly dry surface (not idea for pathogen breeding, but some areas moist)
- Constant sloughing
- Acidic pH (5.5)
- Sweat secretion (salt in it bad for pathogens)
- Rich vascular and lymphatic system
- Produced antimicrobial substances (sebum which lysozyme which catalyses destruction of cell wall of certain bacteria, defensins)
What is the advantage of normal microbiota? What are examples of normal microbiota found in the skin ? Where exactly in the skin ?
Prevents the harmful pathogens from colonising site (notably through secretions).
Staphylococcus aureus
Candida sp.
Streptococcus pyogenes
In superficial layer of epidermis and upper part of hair follicles.
Give examples of skin infections and where exactly in the skin they occur.
Ringworm - Keratinised epithelium Impetigo - Epidermis Folliculitis - Hair follicle Cellulitis - subcutaneous fat Necrotising Fasciitis - Fascia
What are the possible routes of infections through the skin ?
Skin (pores, hair follicles)
Wounds
Bites
What are examples of bacterial infections of the skin ?
Staphylococcus aureus
Streptococcus Pyogenes
Pseudomonas Aeruginosa
Myobacterium Tuberculosis
What are features of Streptococcus Pyrogenes ? What are features of its infections ?
Cocci morphology, Gram +, grow in chain.
Group A most clinically relevant:
Specific antigen on surface
Multiple virulence factors (M protein preventing opsonisation, capsule, beta-haemolytic so cause lysis of RBCs)
What are features of Staphylococcus Aureus ? What are features of its infections ?
Cocci morphology, Gram +, grow in clusters
Wide range of ilnesses, resistant strains (MRSA and VRSA), multiple virulence factors (may infect directly or through toxin)
What are features of Pseudomonas aeruginosa ? What are features of its infections ?
Coccobacillus morphology, Gram -.
Opportunistic pathogen
Multiple virulence factors (monotrichous flagellum, good at forming biofilm so may colonise catheters, produces endotoxin A which is kills host cell endocytosing it)
What are the different kinds of skin lesions ? Describe each briefly.
- Macule (flat, red, local inflammation)
- Papule (raised, red, more marked inflammation)
- Vesicle (small blister=bullae)
- Ulcer (disruption of epithelium)
Give examples of skin lesions.
Pyoderma Acnea vulgaris Impetigo Cellulitis Staphylococcal scalded skin syndrome Toxic shock syndrome Folliculitis Furuncle Carbuncle Wound dehiscence and superficial infection Ecthyoma Granulosum Necrotising Fasciitis
What is pyoderma ?
Pus-forming
cutaneous abscess
rubor due to subsequent inflammation
What is Acnea Vulgaris ?
Infection of sebaceous follicles blocked up with keratin (scaly red skin)
What is Impetigo ?
Two types: contagiosa/non-bullous (mostly in children)
Bullous (blistering, the vesicles are fluid filed)
(vesicles developing into rupturing pustules then forming dried crusts)
What is cellulitis ?
May be a result of septicaemia. Erythematous inflammation affecting deeper dermis and subcutaneous fat (superficial redening of skin + build up of fluid).
Why are Dibetics more vulnerable to infection ?
High glucose levels means good environment for pathogens to collect nutrients + cannot mobilise immune system as effectively + insulin shots easy access route
What is Staphylococcal scalded skin syndrome (Ritter’s disease) ?
Production of toxins by S. Aureus lead to acute exfoliation usually in newborn, which may lead to cellulitis.
What is toxic shock syndrome ?
Potentially fatal syndrome caused by toxins and superantigens leading to desquamation of skin cells. (high fever, low BP, confusion).
Often due to unhygienic use of tampon
What is folliculitis ?
Inflammation of hair follicles (fluid-filled vesicles)
What is a furuncle ?
Boil, pus-filled swelling on skin due to deep folliculitis.
folliculitis starts at hair follicle and goes deeper into dermis and subcutaneous layers
What is a carbuncle ?
Collection of boils
What is wound dehiscence ?
Wound rupture along surgical suture
What is Ecthyema Granulosum ?
Rupturing vesicles leading to erythematous lesions and dried crusts.
What is Necrotising Fasciitis ?
Cellulitis with necrosis affecting skin, deeper fascia and sometimes muscle, often due to toxin producing pathogens which have consequences of their own like toxic shock (pain, fever, infection, systemic toxicity)
How do bacteria undertake catheter-related infections?
Which specific bacteria usually causes these ?
Bacteria form biofilm, then use coagulase (causes blood cloths, fibrinogen to fibrin) to form protective coat against itself.
Coagulase (-) bacteria do not use coagulase as protective coat.
Coagulase (-) S. Aureus mainly causes these catheter-related infections.
