Microbiology of bacterial, fungal and parasite infections Flashcards
What are staphylococcus bacteria?
Gram POSITIVE (purple) cocci in clusters Aerobes and faculative anaerobes.
What are the 2 important types of staphylococcus?
1) Staph aureus which is coagulase positive and shows up golden on agar
2) coagulase negative staphs e.g. epidermidis
What does coagulase positive mean?
Clots plasma
What is SSSST?
Staph. scalded skin syndrome toxin
What is PVL?
A toxin called Panton Valentine Leukocidin
What kind of infections do coag. negative staphs (e.g. S. epidermidis) cause?
Infection in artificial materials e.g. valves, catheters, joints.
What kind of infections do Staph. saprophyticus cause?
UTIs in women of child bearing age
Describe streptococcus bacteria
Gram positive cocci in chains.
Aerobic and faculative anaerobes
How are streptococci classified?
Beta haemolytic - complete
Alpha haemolytic - partial
Gamma haemolytic- none
What are examples of beta haemolytic streps (dangerous!) ?
Group A strep causes throat and skin infections
Group B causes neonatal meningitis
Give two examples of alpha haemolytic strep
Strep pneumoniae which causes pneumonia
Strep viridans which cause endocarditis
What kind of gamma strep are commensals of bowels and cause UTIs?
Enterococcus faecalis
What kind of infections can strep. pyogenes (A) cause?
Infected eczema Impetigo Cellulitis Erysipelas necrotising fasciitis
How are infections diagnosed?
A swab of the lesion is taken if the surface is broken.
If it is a deeper lesion then pus or tissue can be taken.
Blood cultures if systemic
What is the treatment for staph aureus and strep. pyogenes infections?
Flucloxacillin
What is necrotising fasciitis?
Infection spreading along fascial planes below skin surface leading to rapid tissue destruction.
little to see on skin surface
How is necrotising fasciitis treated?
Medical emergency.
Immediate surgical debridement required as well as abx tx
What is the protocol for treating leg ulcers?
Only take swabs if signs of cellulitis or infection.
Treat if strep. pyognes, staph. aureus or other beta haemolytics.
Also treat if ? anaerobes espec in diabetic patients.
What is tinea?
Ringworm
Where does tinea capitis affect?
scalp
More common in children
Where does tinea unguiun affect?
nails
Where does tinea cruris affect?
Groin
What is tinea pedis also known as?
Athlete’s foot
What is the pathogenesis of fungal infections?
Fungus enters soggy skin
Hyphae is spread in stratum corneum and infects keratinised tissues only.
An increased epidermal turnover causes scaling.
Hair follicles are invaded.
Why do dermatophytes have a ringed appearance?
The lesion grows outwards and heals in the centre
How is a fungal infection diagnosed?
By clinical appearance
Woods light by fluorescence
Skin scrapings (scaly edge of lesion) or nail clippings are sent to lab in a dermapak.
Culture takes 2wks +
What is the treatment for small areas of fungal infected skin and nails?
Clotrimazole (Canestan cream)
What is the treatment for candida?
Clotrimazole cream with oral fluconazole
What organisms cause scabies?
Sarcoptes scabiei
What is the common presentation for scabies?
Intensely itchy rash affecting fingers, webs, wrists and genital areas
How are scabies transmitted?
Close skin to skin contact e.g.. sex and also sharing towels
What is the treatment for scabies?
Malathion lotion applied overnight to whole body and washed off the next day.
Benzyl benzoate can also be given but not in children!
How are lice (pediculus capitis) treated?
Malathion
What are the infection control issues with dermatology?
Patients who shed large amounts of skin give off bacteria into the environment.
Which patients need single room isolation and contact precaution?
Group A strep infections (Infected eczema Impetigo Cellulitis Erysipelas necrotising fasciitis) MRSA infected Scabies infected
