skin infections Flashcards
(14 cards)
Staphylococcal infections - Folliculitis
Folliculitis – inflammation of hair follicles (Sty for eyelashes)
Aetiology:
Staphylococcus aureus – the most common cause; non-contagious.
Yeast infection - Malassezia spp. can contribute
Non-infectious causes – Irritation from shaving, friction
Clinical Manifestations:
Small, red, pus-filled pimples around hair follicles (face, neck, thighs).
Itching & tenderness in the area
Bacteria can spread into the dermis and cause deep folliculitis
About deep folliculitis
Furuncles or boils (deep folliculitis)
Infection spreads in the dermis attracting neutrophils pus
Pus is sealed by an abscess limiting infection
Painful, larger, swollen nodule with a central core
Carbuncles (deeper folliculitis)
Cluster of connected furuncles or one furuncle not walled off
Larger areas of inflammation, deeper in the dermis or hypodermis.
Often with fever. Slow healing and risk of scarring
Streptococcal skin infections - Erysipelas
Clinical manifestations
Well-defined, raised, and shiny bright red rash
Sharp borders, often with raised margins
Common on face (“butterfly pattern”) and/or lower limbs
Fever, chills and nausea
bacterial toxins can spread infection -> risk of cellulitis, sepsis
Cellulitis
Infection in the deep dermis - subcutaneous tissue
Clinical manifestations
Commonly in one extremity of lower limbs, or face/trunk
Dark-red/purplish, swollen, warm, tense skin (with fluid)
The redness is less clearly defined than in erysipelas
The infection can spread along tendons and muscles -> risk of sepsis
Necrotizing fasciitis (flesh-eating disease)
severe infection in subcutaneous tissues and below (deep fascia)
Clinical manifestations & pathogenesis
Bacteria release proteolytic enzymes to penetrate deeper
Severe pain, swelling, and erythema. Rapid progression.
Skin changes, including blistering, necrosis. Fever & malaise
It may completely destroy the tissue, requiring amputation/surgery
treatment options for bacterial skin infections
Superficial localised impetigo:
Topical Hydrogen peroxide (H₂O₂) 1% cream (not suitable for open skin)
aspecific biocide -> Generating free radicals -> destroy bacterial cell components
Superficial widespread impetigo:
Topical antibiotics - fusidic acid or mupirocin (if fusidic acid resistance)
treatments for mild and severe bacterial infections?
Bullous impetigo or Non-bullous at risk of complications
Mild deeper infections (cellulitis/erysipelas)
Oral antibiotics
1st line - Flucloxacillin (500mg to 1g QDS – 5/7 days). Co‑amoxiclav if near the eyes
In penicillin allergy - Clarithromycin or erythromycin (macrolides)
Severe skin infections
Intravenous antibiotics
Intravenous Cefuroxime or Ceftriaxone (cephalosporins)
Or oral Co‑amoxiclav or oral clindamycin (lincosamine)
Methicillin-resistant Staphylococcus aureus (MRSA)
Display higher MIC values to β-lactams compared to MSSA
MRSA have mecA gene, encoding an altered transpeptidase (PBP2a) prevents β-lactam binding/activity, making them infective
Treatment for severe MRSA (or suspected):
IV vancomycin or IV teicoplanin (glycopeptide cell wall inhibitors)
or linezolid (protein synthesis inhibitor)
Human papilloma viruses (HPV)
Cervical screening smear test to detect the HPV genotype and precancerous cells
HPV vaccines are available to prevent infections from high-risk genotypes
Cutaneous warts
Benign skin growths from cutaneous HPV
Grainy (“cauliflower-like”), slightly raised lesions
Common warts (on hands), plantar warts or verruca (on soles).
Self-limiting but may cause discomfort
Ano-genital warts are caused by low-risk mucosal HPV
Transmission:
Cutaneous -> Direct skin contact or indirectly via contaminated surfaces.
HPV can survive for a long time on surfaces (swimming pool)
Genital warts are sexually transmitted (STI)
reatment options for warts
Cutaneous warts (affected area only)
Topical salicylic acid - long treatment
Cryotherapy using liquid nitrogen (−196°C)
Thermal injury to induce HPV-infected tissue death
Ablative therapy (e.g. laser treatment)
to destroys wart tissue with focused light
Antiviral Chemotherapy for Herpesvirus infections
Acyclovir 5% Cream: OTC for cold sores/genital herpes
Reduce outbreak duration if applied within 24h of first symptoms
Oral Acyclovir/Prodrugs: severe infections, shingles, or patients at risk complications (immunocompromised/neonatal/elderly)
To be effective start within 48-72 hours of rash onset
Dermatomycoses (fungal)
Trunk, arms and legs – ringworm
Feet – athlete’s foot
Groin area - jock itch
Nails - onychomycosis
Transmission: Direct contact or sharing contaminated objects (spores).
Subcutaneous mycoses: rare; involve dermis invasion
treatment for dermatomycoses
1st choice - Imidazole cream for ringworm/athlete’s foot
2% miconazole, 1% clotrimazole, 1% ketoconazole
Mechanism: Inhibit ergosterol synthesis (unique cell membrane component)
Alternatives - allylamines (e.g. terbinafine cream)
