Microbiology 2 - Skin infections

Question 1

S. aureus infections. Describe the bacteria

Answer 1

Gram positive, commensal.

Has cell wall and membrane –> susceptible to treatment with penicillin

Question 2

High skin infection rates occur in?

Answer 2

Hot humid countries

Question 3

What are the medical considerations of S. aureus

Answer 3

MRSA

Toxins produced by S. aureus:

1. Panton valentine leuocidin
2. Exfoliative toxin - causes splitting of epidermis
3. TSST-1
4. Enterotoxin

Can also cause bone, joint, lung infections and sepsis

Question 4

Describe the manifestations of s. aureus skin infections

Answer 4

Impetigo - infection of sub corneal layer of epidermis (i.e. v superficial)

Folliculitis - infection of mouth of hair follicle

Ecthyma - infection of full thickness of epidermis (and maybe some superficial dermis)

Boil - abscess of hair follicle (try and let pus out)

Carbuncle - abscess of several adjacent hair follicles

Question 5

What is one of the classic features of a s. aureus infection?

Answer 5

Golden crust

Question 6

Describe staphylococcal scalded skin syndrome

Answer 6

Exfoliative skin toxin enters blood - becomes systemic and causes cleavage of epidermis away from initial infection site

Question 7

Describe treponema pallidum

Answer 7

Gram negative spirochaete

• cause of syphilis (STD)
• 12 million new cases per year worldwide - increases transmission of HIV

Question 8

Describe the phases of syphilis

Answer 8

Primary (3-8 weeks) - painless ulcer at inoculation site (chancre)

Secondary (6-12 weeks) - disseminated infection, generalised rash and lymphadenopathy

Latent syphilis - no clinical signs

Tertiary syphilis (usually years later) - skin, neurological and vascular manifestations/lesions - can cause thoracic aneurysms

Congenital syphilis —> acquired perinatally if mother has latent syphilis –> crosses placenta

Question 9

What is congenital syphilis associated with

Answer 9

Miscarriage
Stillbirth
Prematurity
Rashes
Brain and neurological problems
Bone disease

Question 10

How many herpes viruses are there?

Answer 10

8 (we only need to know 3 though)

HHV-1/2/3

NB - HHV3 = varicella zoster virus

All 3 target mucoepithelial cells

HHV1/2 cause oro-genital herpes

HHV 3 causes chickenpox and shingles

All 3 HHV latent in neurones

Question 11

What are the 2 types of herpes and what are their clinical presentations

Answer 11

Type 1 - oral herpes
Type 2 - genital herpes

Clinical presentations - vesicular rash (2 weeks)

• eczema herpeticum
• herpes encephalitis

Question 12

What do HSV1, HSV2 and VZV all have in common

Answer 12

They have latency

Initial infection subsides - virus lives on in body in dormant state –> e.g. neurones (DRG). Upon reactivation, occurs in same place as initial activation

Question 13

How do you treat eczema herpeticum

Answer 13

Acyclovir

Question 14

How is VZV (chickenpox) spread?

Answer 14

Inhalation or close contact

Face most dense area of vesicles

Question 15

If VZV comes back after dormancy what do you get?

Answer 15

Herpes zoster –> comes when patient immunocompromised

aka shingles —> follows one dermatome usually one one side

IF it gets the back of the eye –> it can cause blindness

Question 16

There are 2 types of superficial skin fungal infections

Answer 16

1. Dermatophytes - e.g. trichophyton rubrum. Grow in keratin. Long hyphae, grow from tip
2. Yeasts - e.g. candida. Grow on warm, wet surfaces. Single cell and bud

Question 17

What is tinea unguium

Answer 17

Fungal infection of the nails - usually dermatophytes (but can be yeasts)

Treated by taking anti-fungals

Question 18

What is tinea capitis

Answer 18

Fungal infection of the head, doesn’t affect adults

May be a kerion (looks like an abscess type lesion - it is a type of tinea capitis)

Question 19

What other tineas are there

Answer 19

1. Tinea magnum - hands
2. Tinea pedis - feet
3. Tinea cruris - affects schema of scrotum
4. Tinea facei - face

Question 20

What fungal skin infection may yeasts cause

Answer 20

Candida intertrigo

Wet, eczema like red rashes. May occur in mouth, genital area, under breast, etc

treated with topical antifungals

Question 21

How are fungal infections of the hair and nails treatedd

Answer 21

With a systemic antifungal (can’t use topically as infection is too deep)

Question 22

What is scabies (sarcoptes scabei) caused by

Answer 22

Mites
Transmitted from human to human via skin to skin contact

Mites burrowing in the surface of epidermis - just below stratum corneum

Commonly occurs in hands, wrists, toes, etc

No initial symptoms in first few weeks –> then get type 4 hypersensitivity to mite –> widespread itchy eczematous rash

Treat with insecticide