L18 - Infections of the Skin, Soft Tissues, Bones & Joints Flashcards
Define colonisation
The presence of bacteria on the skin, a mucous membrane or a wound without any symptoms or signs of infection
Describe the microbiology of normal skin - permanent residents
Staphylococci
Corynebacteria (diptheroids)
Propionibacteria (acne)
Acinetobacter
What bacterium can be described as a temporary resident on normal skin?
S. aureus
What comprises the transient flora of skin?
Coliforms
Pseudomonas
What effect does damaged skin have on colonisation?
Makes skin prone to colonisation with more pathogenic bacteria
Give three examples of pathogenic bacteria that colonise damaged skin
S. aureus
Streptococci
Pseudomonas
What must happen for colonisation to become infection?
Breaching of the normal skin barrier
What are the two main pathogens of skin/soft tissue?
Staph. aureus
Strep. pyogenes
Give examples of pathogens affecting the skin/soft tissue - Bacterial
Haemolytic streptococci
Pseudomonas
Coliforms
Anaerobes
Give examples of pathogens affecting the skin/soft tissue - Viral
Herpes (HSV, VZV)
Give examples of pathogens affecting the skin/soft tissue - Fungal
Dermatophytosis (Tinea)
Describe the skin/soft tissue infections caused by S. aureus
Pustular lesions Impetigo Cellulitis Infected wounds Cannula infections Toxin-mediated (scalded skin syndrome)
Describe the skin/soft tissue infections caused by S. pyogenes
Impetigo Erysipelas Cellulitis Necrotising fasciitis Toxin-mediated (scarlet fever)
Describe a carbuncle
A cluster of boils draining pus onto the skin
How are carbuncles treated?
Draining of pus and antibiotic therapy
Describe cellulitis
Infection of the upper layers of skin
Erythrema, swelling, painful
Often turns white on pressure
Can cause blisters/ulcers
Describe erysipelas
Infection of the upper skin and lymphatics that causes a skin rash on the face/limbs
How is erysipelas different from cellulitis?
More superficial
More raised/demarcated
Describe impetigo
Yellow, crusting lesions present on the skin
Often heals w/o scarring
Often a mix of S. aureus/S. pyogenes
Very contagious
Describe scalded skin syndrome
Due to S. aureus infection (often at distant site) releasing scalded skin syndrome toxin
Layers of skin split, can slough off easily
Describe Herpes Simplex - Whitlow
An abscess in the soft tissue near fingernails/toenails
V. painful
Describe Shingles (VZV)
Reactivation of dormant Varicella Zozter Virus
Characterised by painful skin rash w/ blisters in a localised area
Describe Thrush
Infection w/ Candida
Itching, burning, white discharge
Describe Tinea Pedis (Dermatophyte)
Athletes Foot
Fungal infection causing itching, redness and scaling
Describe Anthrax
Infection caused by bacillus anthracis
Skin form presents as a small blister w/ surrounding swelling that develops into an ulcer w/ black centre
Relatively painless
Describe necrotising fasciitis
Infection resulting in soft tissue death
Sudden onset and rapid spread
Red/purple skin, fever, vomiting
SEVERE PAIN
What is the surgical treatment for necrotising fasciitis?
Debridement, cutting away of soft tissue
Describe a central line infection
Infection of inserted central line
Can give rise to soft tissue infection
Can be v. serious
What is the antibiotic therapy for S. aureus?
Flucloxacillin
Co-amoxiclav
Define MRSA
Methicillin Resistant Staph Aureus
What is the antibiotic therapy for S. pyogenes?
Penicillins
Flucloxacillin
What antibiotics are available for treating MRSA/resistant S. pyogenes?
Erythromycin
Clindamycin
Cefuroxime
Vancomycin
By what mechanism does resistance arise in MRSA?
PBP2 is the main target site for penicillins in S. aureus
MRSA has a mutated PBP2a
Cross-resistant to all Beta-lactams
Usually resistant to macrolides
What proportion of hospital-acquired skin/soft tissue infections are caused by MRSA?
1-2%
Define disinfectant
Chemical w/ ability to destroy or inactivate potentially pathogenic micro-organisms
Define antiseptic
Disinfectant that can be applied to skin or mucous membranes
Define topical antibiotic
Natural/synthetic drug w/ antimicrobial activity applied directly to the skin
What are the advantages of topical antibiotics?
High conc at site of infection
Can use agents too toxic for systemic use
Cheap
Combination preparations w/ steroids available
What are the disadvantages of topical antibiotics?
May not penetrate to site of infection
Can get systemic absorption
Resistance
Where are topical antibiotics most commonly used?
Skin Mucous membranes Mouth Eyes Nose Skin Vagina
What topical antibiotics are used around the mouth? - What are they treating?
Nystatin (candida)
What topical antibiotics are used around the eyes? - What are they treating?
Chloramphenicol/Tetracycline (conjunctivitis)
What topical antibiotics are used around the nose? - What are they treating?
Mupirocin (S. aureus/MRSA)
What topical antibiotics are used on the skin? - What are they treating?
Fucidin (impetigo)
Aciclovir (cold sores)
Azoles (fungal infections)
Describe septic arthritis
Acute bacterial infection of a joint, often metastatic
What are the principle pathogens for SA?
S. aureus
S. pyogenes
Pneumococcus
What are the clinical features of SA?
Pain, inflammation Joint effusion Restricted movement Pyrexia Systemic sepsis
How is SA diagnosed?
Mc&C on Joint aspirate
Blood culture
What is the treatment for Septic Arthritis?
High dose of i.v. antibiotics >2wks
Followed by 4wks oral antibiotics
Define osteomyelitis
Acute/chronic infection of bone, usually metastatic spread
What are the principle pathogens for osteomyelitis?
S. aureus
Streptococci
M. tuberculosis
What are the clinical features of osteomyelitis?
Pain, swelling, fever
Systemic sepssis
Deformity, collapse (vertebra), fracture
How is osteomyelitis diagnosed?
X-ray, bone scan, MRI
Blood cultures
Bone biopsy
What is the treatment for osteomyelitis - Acute
High dose i.v. antibiotics >6wks
+/- surgical drainage
What is the treatment for osteomyelitis - Chronic
Formation of sequestrum (dead bone w/i tissue)
Months of antibiotics + surgery
Often relapses
