Microbiology of skin infections Flashcards
What are the skin’s defences against infection?
Intact skin is much less likely to become infected
Dry - dessication of microorganisms
Sebum - fatty acids inhibit bacterial growth
Competitive bacterial flora
Concept of resident and transient flora
What are common competitive bacterial flora on the skin?
Staphylococcus epidermis
Corynebacterium (diptheroids)
Propionibacterium
How are bacterial skin infections diagnosed?
Swab of lesions if surface broken
Pus or tissue if deeper lesion
+/- blood cultures if appropriate
How will staph auerus coagulase?
Golden
Positive coagulase
What are the different species of alpha haemolytic streptococcus chains?
Step pneumoniae
Strep viridans
What are the different species of beta haemolytic streptococcus chains?
Group A strep (throat, skin infection)
Group B strep (neonatal meningitis)
Group C, G strep
What are the different species of non haemolytic streptococcus chains?
Enterococcus (gut commensal, UTI)
What are the different species of coagulase positive staphylococcus clusters?
Staph aureus (wound, skin infection)
What are the different species of coagulase negative staphylococcus clusters?
Staph epidermis
In what air conditions will staphylococcus grow?
Aerobic and facultatively anaerobic
What are some virulence factors that staphylococcus aureus can produce?
Enterotoxin - food poisining
SSSST - staphylococcal scalded skin syndrome toxin
PVL - panton valentine leucocidin
What bacterial skin infections can staph aureus cause?
Boils and carbuncles Infected cuts Cellulitis Infected eczema Impetigo Wound infection Staphylococcal scalded skin syndrome
What are the treatment options for MRSA?
Skin or soft tissue - doxycycline, co-trimoxazole, clindamycin
Blood stream - vancomycin
What infections are staphylococcus epidermis bacteria associated with?
Implanted artifical material such as artifical joints, artifical heart valves, IV catheters
In what air conditions will streptococcus species grow?
Aerobic and faculatively anaerobic
What bacterial skin infections can strep pyogenes (group A strep) cause?
Infected eczema Impetigo Cellulitis Erysipeas Necrotizing fasciitis
How are strep. pyogenes infections treated?
Penicillin but can also be treated with flucoxacillin
How will necrotizing fasciitis present?
Patient in excrutiating pain disproportionate to the wound
Needs surgery ASAP
What is necrotizing fasciitis?
Bacterial infection spreading along fascial planes below the skin surface causing rapid tissue destruction - little to see on skin surface but severe pain
What are the different types of necrotising fasciitis?
Type 1 - mixed anaerobes and coliform, usually post-abdominal surgery
Type 2 - group A strep infection
What organisms are worth treating in regards to leg ulcers?
Strep pyogenes (group A), staph auerus
Other beta-haemolytic streptococci (B, C, G)
Anaerobes in diabetic patients
What would make a leg ulcer worrying?
If it has been there for more than 2 months and is over 2cm then you should be concerned about osteomyelitis
What is tinea?
Ringworm
How do dermatophytes enter the skin?
It enters abraded or soggy skin
How do the funal hyphae spread?
Via the stratum corneum
Infects keratinisied tissues only
How do fungal infections present?
Ring like structures
What fungus causes the most tinea infections?
Trichophyton rubrum THEN Trichophyton mentagraphytes THEN Microsporum canis
How are dermatophyte infections diagnosed?
Clinical appearance
Woods light
Skin scraping
How are small areas of fungally infected skin and nails treated?
Clotrimazole
How are funal scalp infections treated?
Terbinafine - need to monitor LFTs
Where does candida cause skin infections?
In the skin folds where the area is warm and moist - this is called candidia intertrigo
How is candidia intertrigo treated?
Clotrimazole cream
Oral fluconazole
What causes scabies?
Sarcoptes scabeiei
What is the most infectious form of scabies?
Chronic crusted scabies
What is the incubation period of scabies?
Up to 6 weeks
What are the symptoms of scabies?
Intensely itchy rash affecting finger webs, wristss and genital area
How are scabies treated?
Malathion lotion applied overnight to whole body and washed off next day
What patients need single room isolation?
Group A strep infection
MRSA
Scabies
