Microbiology 1 Flashcards
name a main competitive bacterial flora in the skin
staph epidermidis
how is a bacterial skin infection diagnosed?
swab of lesion if broken surface
pus or tissue if its a deeper lesion
blood cultures if needed
how is staph aureus diagnosed?
coagulase +ve
what is the most common coagulase -ve organism and what usually causes this result on a culture?
staph epidermidis
usually a contaminant in the sample as epidermidis is a skin commensal
describe staph
gram +ve cocci in clusters
best growth aerobically but can be anaerobic
what gives staph aureus its effectiveness as a pathogen?
produces enzymes (coagulase) produces toxins: - enterotoxin = food poisoning - SSSST = staphylococcal scalded skin syndrome toxin PVL = panton valentine leucocodin (difficult to treat)
what is first and second line for staph aureus?
flucloxacillin
vancomycin if penicillin allergic etc but not as effective
is staph aureus always a dangerous pathogen?
no, 30% carry it without problems
but can cause minor skin sepsis, cellulitis, impetigo and infected eczema etc
why does pus have to be removed from a lesion?
as antibiotics don’t work on pus
how is MRSA treated?
if skin/soft tissue: - doxycycline - co-trimoxazole - clindamycin - linezoid If blood - vancomycin
coagulase negative staph are usually not pathogenic as they are skin commensals, when might they be pathogenic?
when associated with artificial joints, valves, catheters etc
describe strep
gram +ve cocci in chains
aerobic
classified by haemolysis
what are the categories of haemolysis?
beta = complete (gold on blood agar) alpha = partial (green on blood agar) gamma = non haemolytic
what infections are associated with strep pyogenes (group A strep)?
infected eczema impetigo cellulitis necrotising fasciitis erysipelas
how are beta haemolytic strep further classified?
group A and group B
differentiated by antigenic structure on surface
what are the 2 main groups of alpha haemolytic strep?
strep pneumoniae
strep viridans - common endocarditis
what is the main non-haemolytic strep group?
enterococcus
common cause of UTI
how is skin sepsis treated?
no antibiotics if minor
general first line = flucloxacillin as it covers staph aureus and group A strep
If known group A strep = penicillin
how is necrotising fasciitis treated?
immediate surgery is only cure
antibiotics wont cure but used alongside surgery
what are some signs of necrotising fasciitis?
massive pain with not much to see on the skin
makes crepitus sound when you press on it
air on imaging
what is necrotising fasciitis and what are the 2 types?
bacterial infection spreading along fascial planes below skin surface causing rapid tissue destruction
type 1 = mixed anaerobes and coliforms, usually post abdo surgery
type 2 = group A strep infection
how are leg ulcers investigated?
only take swabs if evidence of active infection as underlying cause is actually vascular
how are leg ulcers treated?
only treat if following organisms found?
- strep pyogenes, staph aureus
- beta haemolytic strep (B,C,G)
what indicates osteomyelitis with a leg ulcer?
if the ulcer is more than 2cm and has been there more than 2 months
what is a tinea infection?
ringworm
different types depending on site
i.e - tinea capitis = scalp etc
how do fungal infections (dermatophyte infections) occur?
fungus enters abraded/soggy skin
spreads in stratum corneum and only infects keratinised tissues
increased epidermal turnover causes scaling
provokes inflammatory response
what is the classical presentation of a dermatophyte infection?
ring appearance
more common in men
what is the most common source of fungal infection?
from other infected humans
what is the most common cause of dermatophyte infection?
trichophyton rubrum
how are dermatophyte infections diagnosed?
clinical appearance
woods light
skin scrapings (from edge of lesion), nail clippings, hair etc
how are dermatophyte infections treated?
if small areas = clotrimazole cream or topical nail paint (amorolfine)
If scalp = terbinafine or itraconazole
where is candida infection commonly found?
skin folds, warm moist areas (under breasts etc)
how is candida diagnosed and treated?
diagnosis = swab for culture treatment = clotrimazole/oral fluconazole
what is the bad form of scbies?
norweigian scabies
chronic, crusted and highly infectious
what are the features of a scabies infection?
intensely itchy rash in finger webs, wrists and genitals
visible burrows in skin
how are scabies treated?
malathion lotion overnight benzyl benzoate (not in children)
how are lice treated?
malathion
what is the proper term for lice?
pediculus
which type of bacteria can survive in the environment the best and why?
gram +ve
because of thicker cell wall
which infections require single room isolation?
group A strep
MRSA
scabies
