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MCD Microbiology > Skin Infections > Flashcards

Skin Infections Flashcards

1
Q

what are the features of staphylococcus aureus?

A
  • gram +ve
  • commensal in 30% of humans in nose, axilla and groin
  • most common bacteria cause of skin infection
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2
Q

what are the 5 manifestations a skin staph aureus infection?

A 
- impetigo
 (and bullous (blistering) impetigo
- folliculitis
- ecthyma
- boils
- carbuncles
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3
Q

what is impetigo?

A

infection of subcorneal (strata corneum) layer of epidermis

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4
Q

what is folliculitis?

A

infection at the mouth of the hair follicle (at top)

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5
Q

what is ecthyma?

A

infection of full thickness the epidermis creating a thick adherent scar at necroses site

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6
Q

what is a boil?

A

abscess of the hair follicle spanning the epidermis and dermis

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7
Q

what is a carbuncle?

A

abscess of several adjacent hair follicles

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8
Q

what are the toxins (virulence factors) produced by staph aureus?

A
  • Panton Valentine Leuocidin
  • Exfoliative toxin
  • TSST-1 (Toxic Shock Syndrome Toxin 1)
  • Enterotoxin
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9
Q

what disease does the exfoliative toxin cause?

A

Staphylococcal Scalded Skin Syndrome (in children less than 5 yrs- version of bullous impetigo)

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10
Q

what disease does TSST-1 cause?

A

Toxic shock Syndrome

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11
Q

what disease does enterotoxin cause?

A

diarrhoea, food poisoning

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12
Q

what disease does Panton Valentine Leuocidin cause?

A

toxin of staph aureus:

Necrotising soft tissue infections

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13
Q

how are staph aureus infections of the skin normally treated?

A

antibiotics (no vaccine)

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14
Q

how does the exfoliative toxin lead to bullous impetigo?

A

splitting of the skin leads to pus filled blisters

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15
Q

describe how impetigo looks like on skin

A

golden and crusty
common in children
around the mouth and face

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16
Q

what type of bacteria is Treponema pallidum? what disease does it cause?

A

gram -ve
causes syphillis (STI)
- enhances HIV transmission

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17
Q

what are the stages of a syphillis infection? what are the features of disease at each stage?

A

1) Primary (3-8 weeks)
– painless ulcers (chancre) at site of inoculation.

2) Secondary (6-12 weeks)
– disseminated infection, rapid proliferation, with rash (maculopapular on palms and soles), condylomata lata and lymphadenopathy.

3) Latent
– asymptomatic period but still transmissible

4) Tertiary (years later)
– reactivated; gummatous skin lesions, bone lesions, , neurological and vascular manifestations e.g. thoracic aneurysm

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18
Q

What results in symphilis in an infant?

A

vertical transmission from the mother leads to congenital syphilis

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19
Q

what effect does syphilis have on a developing foetus?

A
  • stillbirth
  • miscarriage
  • prematurity
  • brain abnormalities
  • bone disease
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20
Q

how is syphilis treated?

A

antibiotics e.g. penicillin

no vaccine

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21
Q

what are some of the members of the herpes simplex virus family?

A

HHV1 –> HSV type 1
HHV2–> HSV type 2
HHV3–> VZV

HHV4–> EBV
HHV5–> CMV
HHV8–> Kaposi Sarcoma

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22
Q

what does Kaposi sarcoma affect?

A

endothelium of lymphatics

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23
Q

what does VZV cause?

A

chickenpox and shingles (herpes zoster)

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24
Q

what is common between HHV1 to 3?

A

are latent in nerves

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25
Q

what type of infections do HSV type 1 and HSV type 2 cause?

A

type 1 causes oral infections

type 2 causes genital infections

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26
Q

what type of infections does HSV type 1 cause?

A

oral

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27
Q

what type of infections does HSV type 2 cause?

A

genital

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28
Q

how is HSV transmitted?

A

direct contact

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29
Q

what are the clinical features of a HSV infection?

A
  • painful vesicular rash (heals over 2-4 weeks)
  • eczema herpeticum (eczema increases risk of herpes infection)
  • herpes encephalitis.
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30
Q

what causes the reactivation of HSV into the tertiary stage?

A

stress on the body e.g. infection

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31
Q

what is the treatment for HSV infection?

A

anti-viral medication such as acyclovir

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32
Q

what are the two stages of VZV infection?

A
  • primary infection causes chicken pox

- reactivation causes VZV causes shingles/herpes zoster

33
Q

what are the features of a primary infection with VZV?

A

chicken pox features:

  • prodrome of fever
  • malaise
  • followed by development of widespread vesicular rash concentrated on the face and trunk
  • oral lesions
  • mild in children, more serious in older children and adults
  • usually lasts ~2 weeks and then becomes latent.
34
Q

what is the hallmark feature of a reactivated VZV infection?

A

in shingles, and a painful vesicular rash appears along the course of a dermatome
e.g. CN V1 (ophthalmic division of trigeminal) on the top right of the face

– usually heals in 2-4 weeks.

35
Q

what is the treatment for VZV?

A

Vaccine is available and anti-viral medication can be given

36
Q

where does VZV lay latent?

A

dorsal root ganglia

37
Q

name two types fungi that cause superficial skin infections and give an example of the fungi

A

1) Dermatophytes (type of mould)
e. g. Trichophytum rubrum

2) yeasts
e. g. candida

38
Q

where do dermatophytes grow?

A

in parts of the body with keratin therefore hair, skin and nails
they grow as hyphae

39
Q

what are the infections that dermatophytes cause?

A

“tinea”:

e. g. Tinea capitis – Kerion is a type of tinea capitis; occurs on the scalp esp on prepubertal, black kids
e. g. Tinea manuum – dorsum of hand.
e. g. tinea cruris – inner thigh region (Jock itch)

40
Q

where do yeasts like candida grow?

A

grow in moist, humid places

41
Q

what is the clinical manifestation of yeast infection?

A

eryhthromatous scaly rash on skin/scalp, discoloured or crumbly nails.

42
Q

what is the treatment for superficial fungal skin infection?

A

topical or systemic anti-fungal medications such as Terbinafine

43
Q

what is scabies?

A

A skin infestation by the mite Sarcoptes scabei.

44
Q

how does the infestation of sarcoptes occur? what results after it has established itself in the skin?

A
  • The mite burrows into the surface of the skin (stratum corneum)
  • Asymptomatic for first 4 weeks
  • Exposure to the mite faeces and eggs cause a delayed-type allergic reaction
  • Results in widespread eczematous rash occurring ~4 weeks after first infestation
  • A secondary bacterial infection is common e.g. strept –> glomuronephritis
45
Q

where do sarcoptes mites burrow mostly?

A

genital regions, nipples, wrists, finger webs, instep of feet, axilla

46
Q

how do you spot a mite burrow?

A

a squiggle with a black dot (head of mite)

47
Q

how is scabies treated?

A

with topical systemic insecticides

48
Q

how is scabies transmitted?

A

by skin-skin contact over longer periods (minutes)

49
Q

what are the layers of the epdermis?

A

stratum corneum
granular layer
spinous layer
basal layer

then comes the dermis

50
Q

what is cellulitis and what can cause this?

A
  • staph aureus
  • acute, painful infection of deeper dermis and subcutaneous tissue
  • often due to break in skin from trauma or another infection
51
Q

what causes Scalded skin syndrome?

A
  • exotoxin of staph aureus
  • destroy keratinocyte attachments in stratum granulosum –> sloughing off of skin
  • seen in newborns and children
52
Q

what bacteria causes syphilis?

A

treponema pallidum

53
Q

what is the treatment for syphilis?

A

IM antibiotic : penicillin

54
Q

what are the types of syphilis?

A

primary: lone, painless ulcer on the genitals

secondary:
- Condylama lata (gray-white wart like lesions of mucous membranes
- Rash on palms/soles

tertiary:
- gummas (soft growths with necrotic centres)

55
Q

what part of the body is HSV1 usually confined to?

A

the upper body (oral)

56
Q

where does the HSV1 stay latent and then cause cold sores?

A

trigeminal ganglion

57
Q

what causes reactivation of the latent HSV?

58
Q

what are the effects of HSV 1 infection?

A
  • kertaoconjunctivitis
  • gingiviostomatitis (first sign)
  • erythema multiform (target lesion)
  • herpetic whitlow (painful hand vesicle)
59
Q

what is the most common cause of sporadic temporal lobe encephalitis?

60
Q

what does temporal lobe encephalitis present with?

A
  • seizures
  • aphasia
  • altered mental status
61
Q

what part of the body is HSV2 confined to usually?

A

lower and upper

sex associated (therefore STI)
urogenital

causes painful inguinal lymphadenopathy

62
Q

where does HSV2 remain latent?

A

sacral ganglion

63
Q

what are the diseases varicella zoster caused in children, adults and the elderly?

A

children and adults–> chicken pox

elderly–> shingles

64
Q

where does VZV in shingles remain latent?

A

dorsal root ganglia

65
Q

what effect does the location of VZV latency have on the presentation of infection?

A

as it stays latent in the dorsal root ganglia there is a dermatomal distribution to the infection

66
Q

what causes the reactivation of VZV in the elderly?

A

stress
ageing
immunocompromised state

67
Q

what effect does shingles have after the rash has cleared?

A

can be extremely painful (post herpetic neuralgia)

68
Q

why does shingles lead to involvement of the eye?

A

effect on trigeminal nerve

69
Q

what are some tinea manifestations of trichophytum rubrum?

A
  • rashes (tinea)
  • –> capitis (head)
  • –> corporis (body)
  • –> curries (groin)
  • -> pedis (foot)
70
Q

why may scabies be worse at night?

A

type 4 hypersensitivity reaction

71
Q

what layer of the skin does the sarcoptes scabei burrow into?

A

stratum cornium

into webspace of hands and feet

72
Q

skin disease epidemiology

A

In the UK:

  • approximately 15% of GP consultations are skin related
  • of those, 25% are due to a skin infections

Skin infections are much more common in hot humid climates and amongst poor populations.

73
Q

gram for Staph Aureus

A

+

colonisation in nose, axillae and groins.

74
Q

what are the common skin infections caused by staph aureus?

A 
impetigo
folliculitis
ecthyma
boils
carbuncles.
75
Q

gram for treponema pallidum

A

cause of syphillis

76
Q

what are the stages of syphillis?

A

Primary : painless ulcer (chancre) at site of inoculation

Secondary: disseminated infection with rash and lymphadenopathy

Latent (asymptomatic) period

Tertiary: skin, neurological and vascular manifestations

77
Q

what type of nucleic acid in HSV

78
Q

what disease does reactivation of VZV cause?

A

shingles (herpes zoster)

  • painful vesicular rash appears only along the course of a dermatome (sensory nerve)
  • serious eye consequences if the distribution of the Ophthalmic Division of the Trigeminal nerve is involved.

MCD Microbiology (6 decks)

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