Microbiology of skin infections

Question 1

What are the skin’s defences against infection?

Answer 1

Intact skin is much less likely to become infected
Dry - dessication of microorganisms
Sebum - fatty acids inhibit bacterial growth
Competitive bacterial flora
Concept of resident and transient flora

Question 2

What are common competitive bacterial flora on the skin?

Answer 2

Staphylococcus epidermis
Corynebacterium (diptheroids)
Propionibacterium

Question 3

How are bacterial skin infections diagnosed?

Answer 3

Swab of lesions if surface broken
Pus or tissue if deeper lesion
+/- blood cultures if appropriate

Question 4

How will staph auerus coagulase?

Answer 4

Golden

Positive coagulase

Question 5

What are the different species of alpha haemolytic streptococcus chains?

Answer 5

Step pneumoniae

Strep viridans

Question 6

What are the different species of beta haemolytic streptococcus chains?

Answer 6

Group A strep (throat, skin infection)
Group B strep (neonatal meningitis)
Group C, G strep

Question 7

What are the different species of non haemolytic streptococcus chains?

Answer 7

Enterococcus (gut commensal, UTI)

Question 8

What are the different species of coagulase positive staphylococcus clusters?

Answer 8

Staph aureus (wound, skin infection)

Question 9

What are the different species of coagulase negative staphylococcus clusters?

Answer 9

Staph epidermis

Question 10

In what air conditions will staphylococcus grow?

Answer 10

Aerobic and facultatively anaerobic

Question 11

What are some virulence factors that staphylococcus aureus can produce?

Answer 11

Enterotoxin - food poisining
SSSST - staphylococcal scalded skin syndrome toxin
PVL - panton valentine leucocidin

Question 12

What bacterial skin infections can staph aureus cause?

Answer 12

Boils and carbuncles 
Infected cuts 
Cellulitis
Infected eczema
Impetigo
Wound infection 
Staphylococcal scalded skin syndrome

Question 13

What are the treatment options for MRSA?

Answer 13

Skin or soft tissue - doxycycline, co-trimoxazole, clindamycin
Blood stream - vancomycin

Question 14

What infections are staphylococcus epidermis bacteria associated with?

Answer 14

Implanted artifical material such as artifical joints, artifical heart valves, IV catheters

Question 15

In what air conditions will streptococcus species grow?

Answer 15

Aerobic and faculatively anaerobic

Question 16

What bacterial skin infections can strep pyogenes (group A strep) cause?

Answer 16

Infected eczema
Impetigo
Cellulitis
Erysipeas
Necrotizing fasciitis

Question 17

How are strep. pyogenes infections treated?

Answer 17

Penicillin but can also be treated with flucoxacillin

Question 18

How will necrotizing fasciitis present?

Answer 18

Patient in excrutiating pain disproportionate to the wound

Needs surgery ASAP

Question 19

What is necrotizing fasciitis?

Answer 19

Bacterial infection spreading along fascial planes below the skin surface causing rapid tissue destruction - little to see on skin surface but severe pain

Question 20

What are the different types of necrotising fasciitis?

Answer 20

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

Question 21

What organisms are worth treating in regards to leg ulcers?

Answer 21

Strep pyogenes (group A), staph auerus
Other beta-haemolytic streptococci (B, C, G)
Anaerobes in diabetic patients

Question 22

What would make a leg ulcer worrying?

Answer 22

If it has been there for more than 2 months and is over 2cm then you should be concerned about osteomyelitis

Question 23

What is tinea?

Answer 23

Ringworm

Question 24

How do dermatophytes enter the skin?

Answer 24

It enters abraded or soggy skin

Question 25

How do the funal hyphae spread?

Answer 25

Via the stratum corneum | Infects keratinisied tissues only

Question 26

How do fungal infections present?

Answer 26

Ring like structures

Question 27

What fungus causes the most tinea infections?

Answer 27

``` Trichophyton rubrum THEN Trichophyton mentagraphytes THEN Microsporum canis ```

Question 28

How are dermatophyte infections diagnosed?

Answer 28

Clinical appearance Woods light Skin scraping

Question 29

How are small areas of fungally infected skin and nails treated?

Answer 29

Clotrimazole

Question 30

How are funal scalp infections treated?

Answer 30

Terbinafine - need to monitor LFTs

Question 31

Where does candida cause skin infections?

Answer 31

In the skin folds where the area is warm and moist - this is called candidia intertrigo

Question 32

How is candidia intertrigo treated?

Answer 32

Clotrimazole cream | Oral fluconazole

Question 33

What causes scabies?

Answer 33

Sarcoptes scabeiei

Question 34

What is the most infectious form of scabies?

Answer 34

Chronic crusted scabies

Question 35

What is the incubation period of scabies?

Answer 35

Up to 6 weeks

Question 36

What are the symptoms of scabies?

Answer 36

Intensely itchy rash affecting finger webs, wristss and genital area

Question 37

How are scabies treated?

Answer 37

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

Question 38

What patients need single room isolation?

Answer 38

Group A strep infection MRSA Scabies