Microbiology of Skin Infections

Question 1

Name some competitive bacterial flora of the skin?

Answer 1

Staphylococcus epidermidis

Corynebacterium sp. (diptheroids)

Propionibacterium

Question 2

How is diagnosis made?

Answer 2

Swab of lesion if surface is broken

Pus or tissue if deeper lesion

+/- blood cultures if appropriate

Question 3

What is seen on the agar plate in staph aureus?

Answer 3

Golden colour (coagulase positive)

Question 4

What is seen on the agar plate in staph epidermidis?

Answer 4

White colour (coagulase negative)

Question 5

What are the alpha haemolytic strep ?

Answer 5

Strep pneumonia (pneumonia)

Strep viridians (commensals) (endocarditis)

Question 6

What are the beta haemolytic strep ?

Answer 6

Group A (throat, skin infection)

Group B (neonatal infections)

Group C, G etc

Question 7

What are the non-haemolytic strep?

Answer 7

Enterococcus sp (gut commensals, UTI)

Question 8

What is the result of latex agglutination?

Answer 8

Only staph Aureus is positive

Question 9

Where does staph aureus grow best?

Answer 9

Grow best in air but also can grow anaerobically

Question 10

What are the antibiotics of choice in staph aureus infection?

Answer 10

Flucloxacillin

Question 11

Name three toxins that staph aureus produce?

Answer 11

Enterotoxin- food poisoning

SSSST- staphylococcal scalded skin syndrome toxin

PVL- panton valentine leucocidin

Question 12

What presentations can staph aureus cause?

Answer 12

Boils and carbuncles

Other minor skin sepsis

Cellulitis

Infected eczema

Impetigo

Wound infection

SSSST

Question 13

What are the treatment options for MRSA?

Answer 13

Doxycycline 
Co-trimoxazole
Clindamycin
Vancomycin 
NOT FLUCLOXACILLIN

Question 14

why are coagulase negative staph not usually worrying?

Answer 14

Skin commensals

Question 15

When might coagulase negatives become problematic?

Answer 15

Implanted artificial material

UTI in women of child bearing age (step saprophyticus)

Question 16

What must you remember when prescribing topical antibiotics?

Answer 16

If there is pus it must go first

Question 17

Where do streptococcus species grow?

Answer 17

In air and facultatively anaerobic

Question 18

What classifies streptococcus species?

Answer 18

Haemolysis on blood agar;

B- complete haemolysis
A- partial haemolysis
Y- no haemolysis

Question 19

What toxin produced by beta haemolytic streptococci that damages tissues?

Answer 19

Haemolysin

Question 20

How can beta haemolytic step be further classified?

Answer 20

By antigenic structure on surface

• Group A
• Group B

Question 21

What infections are caused by Group A strep?

Answer 21

Infected eczema 
Impetigo
Cellulitis 
Erysipelas 
Necrotising fasciitis

Question 22

What can be used to treat strep pyogenes (group A strep)?

Answer 22

Penicillin, will also be treated by flucloxacillin

Question 23

What is the treatment for necrotising fasciitis?

Answer 23

Immediate surgical debridement as well as antibiotics

Question 24

What is necrotising fasciitis?

Answer 24

Bacterial infection spreading along fascial planes below skin surface -> rapid tissue destruction

Little to see but SEVERE pain

Question 25

What are the two types of necrotising fasciitis?

Answer 25

1- mixed anaerobes and coliform, usually post abdominal surgery 2- group A strep infection

Question 26

When do you take swabs of a leg ulcer and why?

Answer 26

Only if signs of clinical infection are present, you will grow lots of bacteria

Question 27

What organisms if found in leg ulcers would you treat?

Answer 27

Strep Pyogenes Staph aureus Strep B, C, G Anaerobes- esp in diabetic patients

Question 28

What does dermatophyte mean?

Answer 28

Fungal

Question 29

What is a dermatophyte infection called?

Answer 29

Ringworm

Question 30

What does tinea mean?

Answer 30

Ringworm

Question 31

What is the name for ringworm of the scalp?

Answer 31

Tinea capitis

Question 32

What is the name for ringworm of the beard?

Answer 32

Tinea barbae

Question 33

What is the name for ringworm of the body?

Answer 33

Tinea corporis

Question 34

What is the name for ringworm of the hand?

Answer 34

Tinea manuum

Question 35

What is the name for ringworm of the nails?

Answer 35

Tinea unguium

Question 36

What is the name for ringworm of the groin?

Answer 36

Tinea cruris

Question 37

What is the name for ringworm of the foot?

Answer 37

Tinea pedis

Question 38

What explains the shape of ringworm?

Answer 38

Lesion grows out and heals in centre

Question 39

What tissues do ringworm infect?

Answer 39

Ketatinised tissues (skin, hair, nails)

Question 40

What causes scaling?

Answer 40

Increased epidermal turnover

Question 41

What is the most likely source of ringworm infection ?

Answer 41

Other infected humans, anthropophilic fungi

Question 42

What is fungi from animals called?

Answer 42

Zoophilic fungi

Question 43

What is fungi from soil called?

Answer 43

geophilic fungi

Question 44

How is trichophyton rubrum transferred and how much of lab isolates is it responsible for?

Answer 44

Human- human transmission 70% lab isolates

Question 45

What is the next most common isolate to trichophyton rubrum and how is it transmitted?

Answer 45

Trichophyton mentagraphytes human-human

Question 46

What is an occasional dermatophyte isolate and how is this transmitted?

Answer 46

Microsporum canis cats, dogs-humans

Question 47

How do you diagnose a dermatophyte infection?

Answer 47

Clinical appearance Woods light Skin scraping (takes 2 weeks)

Question 48

What can you treat small areas of dermatophyte infection on skin, nails with?

Answer 48

Clotrimazole (Canestan) cream or similar Topical nail paint (amorolfine)

Question 49

What are extensive skin infections, nail and scalp infections treated with?

Answer 49

Terbinafine orally Itraconazole orally

Question 50

Where does candida infection infect?

Answer 50

In areas of skin where it is warm and moist 'candida intertrigo'

Question 51

How is candida diagnosed?

Answer 51

Swab for culture

Question 52

How is candida treated?

Answer 52

Clotrimazole cream, oral fluconazole

Question 53

What causes scabies?

Answer 53

Sarcoptes scabiei parasite

Question 54

What is the incubation period for scabies?

Answer 54

Up to 6 weeks

Question 55

Describe the symptoms and areas scabies affects?

Answer 55

Intensely itchy rash affecting finger webs, wrists and genital area

Question 56

What is the treatment for scabies?

Answer 56

Malathion lotion, applied overnight to whole body and washed off next day Benzyl benzoate

Question 57

What is the name for lice of the head, body and pubic area?

Answer 57

head- Pediculus capitis body- Pediculus corporis (vagabond disease) pubic-Phthirus pubis

Question 58

What is the treatment for lice?

Answer 58

Malthion

Question 59

Why are gram positive infections in patients with exfoliative skin conditions a risk for other patients?

Answer 59

Exfoliative skin conditions shed huge number of skin scales and associated bacteria into the environment; gram +ve bacteria can survive in environment because of their cell wall structure

Question 60

Who needs single room isolation?

Answer 60

Group A Step infected patients MRSA patients Scabies patients