3: Microbiology - bacterial and fungal skin infections Flashcards
What does sebum contain which lends towards its antibacterial properties?
Fatty acids
Name three species of bacteria which live on the skin.
Staph. epidermidis
Corynebacterium spp.
Propionibacterium spp.
What is a boil / furuncle?
A deep folliculitis - infection of the hair follicle
What can be used to identify the organism responsible for a skin infection?
Swab
Blood cultures if appropriate
Which test is used to differentiate different species of Staphylococcus?
Coagulase test
How do Staph. aureus appear on a coagulase test?
Golden
How does Staph. epidermidis appear on a coagulase test?
White
(Coagulase negative)
Which species of Staphylococcus appear white on a coagulase plate?
More than 20, including epidermidis, all referred to as “Coagulase negative Staph.”
How do Staphylococci appear under the microscope?
Gram positive clusters of round cocci
Which organism is usually responsible for cellulitis (i.e skin infections)?
Staph. aureus
Why aren’t coagulase negative organisms (e.g Staph. epidermidis) considered more seriously if found on a swab?
Commensals found on the skin
Sometimes they cause infection (e.g infective endocarditis in prosthetic valves) but usually not
Are Staphylococci Gram positive or Gram negative?
Gram positive (appear dark purple when Gram stained)
The coagulase test is used to differentiate different species of Staphylococci. Which test is used for Streptococci?
Haemolysis
Streptococci appear in (chains / clusters) and are Gram (positive / negative).
chains
Gram positive
Which species of Streptococci are alpha haemolytic?
Which colour do they turn on the plate?
Strep. pneumoniae
Strep. “viridans”
Green
Which cardio condition are Strep. viridans often involved in?
Endocarditis
Alpha haemolysis is also known as ___ haemolysis.
partial
Which species of Streptococci are beta haemolytic?
What colour do they turn on the plate?
Group A and B Strep.
Yellow
What is beta haemolysis also known as?
Complete haemolysis
Which species of Strep. is the one synonymous with Group A Strep?
Streptococcus pyogenes
Gamma haemolysis is also known as __ haemolysis.
no
Which species of Streptococci are non-haemolytic?
Enterococci - bowel commensals
Give 1) the type of haemolysis and 2) the colour change on the plate for each of these bacteria:
Strep. pyogenes
Strep. pneumoniae
Strep. agalactiae (Group B)
Strep. viridans
Enterococcus spp.
Strep. pyogenes (A) - Beta haemolytic - Yellow
Strep. pneumoniae - Alpha haemolytic - Green
Strep. agalactiae (B) - Beta haemolytic - Yellow
Strep. viridans - Alpha haemolytic - Green
Enterococcus - Non-haemolytic - No change
What is another species of Coagulase negative Staph., excluding epidermidis?
Staph. saprophyticus
Which species of Staph. is responsible for wound, skin, bone and joint infections?
Staph. aureus
Why is Staph. aureus so virulent?
Produces loads of enzymes
What is the drug of choice for treating Staph. aureus infections?
What is the exception?
Flucloxacillin
If it’s methicillin resistant i.e MRSA
What are some toxins produced by Staph. aureus?
Enterotoxin - food poisoning
SSSST - Staphylococcal scalded skin syndrome toxin
PVL - Pantol Valentine Leucocidin (comes up in exams)
Name some skin infections Staph. aureus is commonly responsible for.
Boils and carbuncles (clusters of boils)
Cellulitis
Infected eczema
Impetigo
SSST
What drugs can be used instead of fluxcloxacillin to treat MRSA?
Doxycycline
Co-trimoxazole
Clindamycin
Vancomycin
Coagulase negative organisms like Staph. epidermidis are usually (commensal / pathogenic).
commensal
When may Staph. epidermidis cause infection?
Artificially implanted stuff like pacemakers, joints, heart valves, catheters…
What kind of infection does Staph. saprophyticus tend to cause?
UTIs in women
Streptococci are Gram positive organisms commonly found in (clusters / chains).
chains
Name an enzyme produced by beta-haemolytic Strep. which damages tissues.
Haemolysin
What are some skin infections caused by Strep. pyogenes i.e Group A Strep.?
Infected eczema
Impetigo
Cellulitis
Erysipelas (superficial dermatitis on face, upper & lower limbs)
NECROTISING FASCIITIS
What life-threatening condition is caused by Group A Strep**.?
Necrotising fasciitis
What is the antibiotic of choice for treating Staph. aureus infections?
Flucloxacillin
What is the antibiotic of choice for treating Strep. pyogenes (Group A) infections?
Penicillin / Flucloxacillin
In addition to giving penicillin, what needs to be done for a patient with necrotising fasciititis?
Immediate removal of affected tissue
Although there is little to see on the skin itself, what is the main symptom of necrotising fasciitis?
Why?
Severe pain
Infection is spreading along the fascia, destroying all the tissue
A leg ulcer tends to be a ___ problem only.
vascular
i.e you don’t need to give antibiotics
What investigation should be carried out if a leg ulcer looks infected?
Swabs
What drug should you add to fluclox/penicillin if you suspect that there are anaerobes in a diabetic foot ulcer?
Metronidazole
What kind of infection is ringworm?
Fungal infection
What does tinea mean?
Ringworm
Where is tinea capitis found?
Scalp
Where is tinea barbae found?
Beard
Where is tinea corporis found?
Body
Where is tinea manuum found?
Hands
Where is tinea unguium found?
Nails
Where is tinea cruris found?
Groin
Where is tinea pedis found?
What is this infection also known as?
Feet
Athlete’s foot
What is the fungus responsible for 70% of ringworm infections?
Trichophyton rubrum
How is ringworm infection diagnosed?
By examination +/- Wood’s lamp
Nail/hair/skin shavings sent for microscopy and culture
What is used to treat small fungal infections on the hair or nails?
Clotrimazole cream (Candesan)
Amorolfine nail paint
What is used to treat fungal scalp infections?
Terbinafine orally
Itraconazole orally
Where do Candida. infections tend to be seen?
Warm, moist areas - breasts, groin areas, skin folds, nappy area
How is Candida. infection diagnosed?
Swabs > Culture
What is given to treat Candida infections?
Clotrimazole cream (Cantesan)
Oral fluconazole i.e antifungals
What is scabies?
Itchy rash on fingers, wrists and genitals
What is the chronic, crusty form of scabies called?
Norwegian scabies
What is the organism causing scabies?
Sarcoptes scabiei
What are some treatment options for scabies?
Malathion lotion
Benzyl benzoate
What else is treated with malathion lotion?
Lice
