Microbiology 6: Skin Disease

Question 1

Compare the presentation on infectious skin disease in GP vs hospital setting

Answer 1

GP- 25%

Hospital- 5%

Question 2

Name the bacteria that causes the most common skin infection and give some of its key features

Answer 2

Staph Aureus
Gram +ve; has a capsule; commensal
Infections: bone, joints, lungs and sepsis
Swab diagnosis

Question 3

Name some of the toxins produced by Staph aureus

Answer 3

1. Panto Valentine Leucocidin
2. Exfoliative toxin
3. Toxic shock syndrome toxin-1 (TSST-1)
   Enterotoxin- skin infection –> food handling –> diarrhoea

Question 4

Describe the manifestation of S. Aureus skin infections

Answer 4

1. Impetigo- subcorneal layer (epidermis)
   *often impetiginised eczema
2. Folliculitis- mouth of hair follicle
3. Ecthyma- full epidermal thickness
   // Below epidermis
4. Boil- abscess of hair follicle
5. Carbuncle- several adjacent hair follicles

Question 5

Describe the presentation of staph aureus

Answer 5

Golden crust

Question 6

What can the expholiative toxin cause?

Answer 6

Puss filled blisters (due to splitting of the skin in the higher levels of the dermis)

Question 7

Describe presentation of ecthyma and an abscess

Answer 7

1. Looks like the surface of the skin dies –> thick adherence scar.
   Potentially caused by an infected insect bite or immunosuppression
2. Collection of puss under the skin

Question 8

Explain staphylococcal scaled skin syndrome

Answer 8

SA infection somewhere on the body. Normally occurs under 5 y/o before the toxin immune reaction is removed. Recovery takes 2-3 days with correct antibiotics treatment.
Acute exfoliation of the skin typically following an erythematous cellulitis. Caused by the exfoliative toxin.

Question 9

Name the bacterial cause of syphilis and give some of its features

Answer 9

Treponema pallidum
Gran -ve spirochete
12 million cases/ year worldwide
Increases transmission of HIV

Question 10

Primary stage of syphilis:

Answer 10

3-8 weeks
Painless ulcer at inoculation site (genital or oral)= CHANCRE which gets better and disappears.
At this stage serology is -ve but swab +ve.

Question 11

Secondary stage of syphilis:

Answer 11

6-12 weeks
Disseminated infection and rapid proliferation.
Generalised maculopapular (red and blotchy on palms and soles especially) rash and lymphadenopathy (feeling unwell). Condyloma lata (perianal region (these are not warts they are filled with spirochetes).
Serology at this stage is +ve. A biopsy of the rash will be teeming with plasma cells= indication.

Question 12

Stage of latent syphilis:

Answer 12

No clinical signs

Question 13

Tertiary stage of syphilis:

Answer 13

usually years later

Skin (gummatous skin lesions), neurological and vascular manifestations (thoracic aneurysm)

Question 14

Describe congenital syphilis

Answer 14

Acquired perinatally. Miscarriage; still birth; premature delivery; rashes; bone disease and neurological problems
Early and late manifestations

Question 15

Differentiate between T1 and T2 herpes

Answer 15

T1: Oral
T2: Genital

Question 16

Clinical presentations of herpes simplex

Answer 16

Itchy and painful vesicular rash- 2 weeks
Eczema herpecticum
Herpes encephalitis

Vermilion border of the lip= crops appear.

Question 17

What is herpes simple stomatitis?

Answer 17

Herpes simplex 1 (HSV-1) virus causes herpes stomatitis. It is more common in young children between the ages of 6 months and 5 years.

Question 18

What is eczema herpecticum? How is it diagnosed and treated?

Answer 18

Defective barrier function with super added herpes simplex virsus. Results in punched out skin ulcers.
Dx: PCR
Tx: iv Acyclovir

Question 19

Describe a typical Varicella zoster infection

Answer 19

1. Feeling unwell: malaise, fever, sore throat

2. Specific rash- Vesicular with erythematous base. Centripetal but also in mouth (no insect bites in mouth!)

Question 20

What condition arises when varicella zoster reactivation occurs from the dorsal root ganglia?

Answer 20

Herpez Zoster (shingles)
If in the trigeminal –> ophthalmic shingles and can lead to blindness/ chronic pain.
This is why patients should have the shingles vaccine post 70 y/o.

Question 21

Two types of superficial skin fungal infection and an example of each

Answer 21

1. Dermatophytes (type of mould)- Trichophyton rubrum

2. Yeasts- Candida

Question 22

Summarise dermatophyte infections

Answer 22

Grow in keratin (skin, hair and nails)
Long hyphae, grow from tip.
Examples: Tinea unguium (yellow and crumbly); capitis*; kerion (type of tinea capitis); magnum; pedis; cruis (x effect scrotum); facei

• Sebum prepubertally increases susceptibility.
• • crusty lesion on scalp with widespread/ boggy mass- kerion . Possible occipital lymphadenopathy.

Question 23

Who is susceptible to tinea infections?

Answer 23

Afro-Caribbean’s

People with pets

Question 24

Describe a typical candida infection

Answer 24

Grow on warm wet surfaces
Single cell and bud
Satalite lesions around infection site. (look like additional red dots).

Question 25

Treatment of dermatophytes and candida infections

Answer 25

1. Cream temidine
2. Camizole cream

Nail/scalp= deep so oral Terbinafine.

Question 26

Summarise the infection by scabies mite

Answer 26

Mite known as known as Sarcoptes scabiei. The female burrows into the 1st epidermal layer (corneum). Transmission requires long contact time.

Initially: asymptomatic.
4 weeks: widespread eczema secondary to immune response.
Coinfection with streptococcus can cause post infectious glomerulonephritis (PIGN)- most common cause of renal failure in 3rd world

Question 27

Diagnosis of scabies

Answer 27

Find burrows- 4mm squiggle line with a black dot at the end (look in groin, axillary, cubital fossa, wrist, insteps, in-between fingers and dorsal hard).
Possible look at with a dermatoscope

Question 28

Describe the treatment of scabies

Answer 28

Insecticide cream all over and leave for 12 hours. Repeat 5 days later. Alongside washing all bedding ect.

Alternatively Ivermectin tablet available.