Microbiology of skin infection Flashcards
Gram positive in clusters
Staphylococcus sp
Staph saprophyticus
Coagnulase negative
Test for staph aureus
Latex agglutination
Does coagulase plasma clot in the bottom of the tube?
Yes it does (only staph aureus)
Novobicin resistant
Staph saprophyticus
Neonatal meningitis
Group B strep
Throat, skin infections
Group A strep
Commensals, endocarditis
Strep viridans
Which staph produces coagulase
Staph aureus
Some strains produce:
• Enterotoxin – food poisoning
• SSSST – staph. scalded skin syndrome toxin
• PVL – Panton Valentine Leukocidin
Staph aureus
Toxins produced by staph aureus
Enterotoxin
SSSST
PVL
causes urinary tract infection in women of child-bearing age
Staph saprophyticus
May cause infection in association with implanted artificial material, such as artificial joints, artificial heart valves, intravenous catheters (produces “slime” that allows it to stick to prosthetic material)
Staph epidermis
Beta-haemolytic
Complete haemolysis
Alpha-haemolytic
Partial haemolysis
Gamma haemolytic
No haemolysis
Toxin produced by beta-haemolytic streptococci
Haemolysin
Throat, severe skin infections
Group A Beta-haemolytic streptococci
How do you further classify beta-haemolytic streptococci?
Classify by antigenic structure on surface (SEROLOGICAL GROUPING)
e.g.
– Group A (throat, severe skin infections)
– Group B (meningitis in neonates)
Name 2 alpha haemolytic strep
Strep pneumonia
Strep viridans
Name a non-haemolytic streptococci and where you would find it
Enterococcus
- commensals of bowel
- common cause of UTI
What does sebum (fatty acids) do?
Inhibits bacterial growth
Competitive bacterial flora of the skin
Staphylococcus erpidermidis
Corynebacterium (“diptheroids”)
Proprionbacterium
Boils and carbuncles
Staph aureus
Infected eczema
Staph aureus
Erysipelas
Strep pyogenes (GROUP A STREP)
Necrotising fasciitis
Strep pyogenes (GROUP A STREP)
is a bacterial skin infection involving the upper dermis that characteristically extends into the superficial cutaneous lymphatics. It is a tender, intensely erythematous, indurated plaque with a sharply demarcated border. Its well-defined margin can help differentiate it from other skin infections (eg, cellulitis).
Erysipelas
Diagnosis of skin infection
- Swab of lesion if surface is broken
- Pus or tissue if deeper lesion
- +/- blood cultures, if appropriate
Green vial
Aerobic culture bottle
Red/pink vial
Anaerobic culture bottle
Yellow vial
Paediatric culture bottle
Antibiotic for strep pyogenes (Group A strep)
Penicillin (will also be treated by flucloxacillin)
Tinea capitis
Scalp
Tinea barbae
Beard
Tinea corporis
Body
Tinea manuum
Hand
Tinea unguium
Nails
Tinea cruris
Groin
Tinea pedis
Foot
How do dermatophytes enter the skin?
Enter abraded or soggy skin
In which layer do hyphae spread?
Spread in stratum corneum
Which type of tissue do dermatophytes infect?
Infects keratinised tissues only (skin,hair,nails)
•Increased epidermal turnover causes scaling
• Inflammatory response provoked (dermis)
• Hair follicles and shafts invaded
Lesion grows outward and heals in centre, giving a “ring” appearance
Dermatophyte
Males or females more commonly affected in dermatophyte infections?
Males
Who are more commonly affected by scalp ringworm?
Children
Foot and groin ringworm mainly affects who?
Men
Anthropophilic fungi
Other infected humans
MOST LIKELY
Zoophilic fungi
Animals (cats, dogs, cattle)
Geophilic fungi
Soil (less common in UK)
Dermatophyte infections, sources of infection
Other infected humans (MOST LIKELY)
Animals
Soil
How is trichophyton rubrum spread?
Human-human transmission
How is trichophyton mentagraphytes spread?
Human-human transmission
How is microsporum canis spread?
Cats, dogs-humans
Dermatophyte infection diagnosis
Clinical appearance • Woods light (fluorescence) • Skin scrapings, nail clippings, hair – Send to laboratory in a “Dermapak” for microscopy and culture – N.B. Culture takes 2 weeks +
Where should skin scrapings be taken from?
Taken from the edge of the scaly lesion
Treatment for small areas of infected skin, nails
Clotrimazole (canestan) cream or similar
Topical nail paint (amorolfine)
Treatment for scalp dermatophyte infections
Terbinafine ORALLY
Itraconazole ORALLY
Diagnosis of candida?
Swab for culture
Where would you get candida infection?
Candida causes infection in skin folds where area is warm and moist “candida intertrigo”
Seen under the breasts in females, groin areas, abdominal skin folds etc, nappy area in babies
Treatment for candida?
Clotrimazole cream
Oral fluconazole
What type of skin infection is scabies?
Parasitic
Infection caused by Sarcoptes scabiei
Scabies
Scabies incubation period?
6 weeks
Intensely itchy rash affecting finger webs, wrists, genital area
Scabies
Treatment for scabies
malathion lotion, applied overnight to whole body and washed off next day
– benzyl benzoate (avoid in children)
Where would you get scabies?
Finger webs, wrists, genital areas
This parasitic infection burrows in your skin and makes “tracts”
Scabies
Pediculus capitis
Head louse
Pediculus corporis
Body louse
Vagabond’s disease
Pediculus corporis (body louse)
Plithirus pubis
Pubic louse
Treatment for lice (pediculosis)
Malathion lotion
Which type of bacteria can survive in the environment because of their cell wall structure?
Gram positive
-these may become a source of infection for other patients
WHO NEEDS SINGLE ROOM ISOLATION
Group A strep
MRSA
Scabies (also need long sleeved gown)
