Microbiology 1

Question 1

name a main competitive bacterial flora in the skin

Answer 1

staph epidermidis

Question 2

how is a bacterial skin infection diagnosed?

Answer 2

swab of lesion if broken surface
pus or tissue if its a deeper lesion
blood cultures if needed

Question 3

how is staph aureus diagnosed?

Answer 3

coagulase +ve

Question 4

what is the most common coagulase -ve organism and what usually causes this result on a culture?

Answer 4

staph epidermidis

usually a contaminant in the sample as epidermidis is a skin commensal

Question 5

describe staph

Answer 5

gram +ve cocci in clusters

best growth aerobically but can be anaerobic

Question 6

what gives staph aureus its effectiveness as a pathogen?

Answer 6

produces enzymes (coagulase)
produces toxins:
- enterotoxin = food poisoning
- SSSST = staphylococcal scalded skin syndrome toxin
PVL = panton valentine leucocodin (difficult to treat)

Question 7

what is first and second line for staph aureus?

Answer 7

flucloxacillin

vancomycin if penicillin allergic etc but not as effective

Question 8

is staph aureus always a dangerous pathogen?

Answer 8

no, 30% carry it without problems

but can cause minor skin sepsis, cellulitis, impetigo and infected eczema etc

Question 9

why does pus have to be removed from a lesion?

Answer 9

as antibiotics don’t work on pus

Question 10

how is MRSA treated?

Answer 10

if skin/soft tissue:
- doxycycline
- co-trimoxazole
- clindamycin
- linezoid
If blood - vancomycin

Question 11

coagulase negative staph are usually not pathogenic as they are skin commensals, when might they be pathogenic?

Answer 11

when associated with artificial joints, valves, catheters etc

Question 12

describe strep

Answer 12

gram +ve cocci in chains
aerobic
classified by haemolysis

Question 13

what are the categories of haemolysis?

Answer 13

beta = complete (gold on blood agar)
alpha = partial (green on blood agar)
gamma = non haemolytic

Question 14

what infections are associated with strep pyogenes (group A strep)?

Answer 14

infected eczema
impetigo
cellulitis
necrotising fasciitis
erysipelas

Question 15

how are beta haemolytic strep further classified?

Answer 15

group A and group B

differentiated by antigenic structure on surface

Question 16

what are the 2 main groups of alpha haemolytic strep?

Answer 16

strep pneumoniae

strep viridans - common endocarditis

Question 17

what is the main non-haemolytic strep group?

Answer 17

enterococcus

common cause of UTI

Question 18

how is skin sepsis treated?

Answer 18

no antibiotics if minor
general first line = flucloxacillin as it covers staph aureus and group A strep
If known group A strep = penicillin

Question 19

how is necrotising fasciitis treated?

Answer 19

immediate surgery is only cure

antibiotics wont cure but used alongside surgery

Question 20

what are some signs of necrotising fasciitis?

Answer 20

massive pain with not much to see on the skin
makes crepitus sound when you press on it
air on imaging

Question 21

what is necrotising fasciitis and what are the 2 types?

Answer 21

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

Question 22

how are leg ulcers investigated?

Answer 22

only take swabs if evidence of active infection as underlying cause is actually vascular

Question 23

how are leg ulcers treated?

Answer 23

only treat if following organisms found?

• strep pyogenes, staph aureus
• beta haemolytic strep (B,C,G)

Question 24

what indicates osteomyelitis with a leg ulcer?

Answer 24

if the ulcer is more than 2cm and has been there more than 2 months

Question 25

what is a tinea infection?

Answer 25

ringworm
different types depending on site
i.e - tinea capitis = scalp etc

Question 26

how do fungal infections (dermatophyte infections) occur?

Answer 26

fungus enters abraded/soggy skin
spreads in stratum corneum and only infects keratinised tissues
increased epidermal turnover causes scaling
provokes inflammatory response

Question 27

what is the classical presentation of a dermatophyte infection?

Answer 27

ring appearance

more common in men

Question 28

what is the most common source of fungal infection?

Answer 28

from other infected humans

Question 29

what is the most common cause of dermatophyte infection?

Answer 29

trichophyton rubrum

Question 30

how are dermatophyte infections diagnosed?

Answer 30

clinical appearance
woods light
skin scrapings (from edge of lesion), nail clippings, hair etc

Question 31

how are dermatophyte infections treated?

Answer 31

if small areas = clotrimazole cream or topical nail paint (amorolfine)
If scalp = terbinafine or itraconazole

Question 32

where is candida infection commonly found?

Answer 32

skin folds, warm moist areas (under breasts etc)

Question 33

how is candida diagnosed and treated?

Answer 33

diagnosis = swab for culture
treatment = clotrimazole/oral fluconazole

Question 34

what is the bad form of scbies?

Answer 34

norweigian scabies

chronic, crusted and highly infectious

Question 35

what are the features of a scabies infection?

Answer 35

intensely itchy rash in finger webs, wrists and genitals

visible burrows in skin

Question 36

how are scabies treated?

Answer 36

malathion lotion overnight
benzyl benzoate (not in children)

Question 37

how are lice treated?

Answer 37

malathion

Question 38

what is the proper term for lice?

Answer 38

pediculus

Question 39

which type of bacteria can survive in the environment the best and why?

Answer 39

gram +ve

because of thicker cell wall

Question 40

which infections require single room isolation?

Answer 40

group A strep
MRSA
scabies