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medical microbiology > Skin and Soft Tissue Infections > Flashcards

Skin and Soft Tissue Infections Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

what is most common childhood skin condition?

A

impetigo

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2
Q

where is it found of the body?

A

site of minor trauma; often on the face or other exposed areas

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3
Q

what does the infection look like?

A

Red patch with central fluid (vesicle)
Vesicles burst leaving golden crust
Clusters of lesions at affected site
(cf chicken pox)

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4
Q

what organisms mainly causes it?

A

Staphylococcus aureus

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5
Q

which other bacteria is less common but still causative?

A

Streptococcus pyogenes (Gp A streptococcus

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6
Q

which is harder to treat?

A

when infection is combined; both bacteria

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7
Q

how is it usually diagnosed?

A

visually, as it is so common in children

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8
Q

how is it treat?

A

Flucloxacillin (erythromycin if penicillin allergic)
A topical antibiotic cream

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9
Q

what happens if not responding to treatment?

A

Swab lesion for culture and sensitivity testing
may be MRSA

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10
Q

what is the more serious form of impetigo?

A

Bullous impetigo

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11
Q

what are the more serious symptoms?

A

Larger vesicles
Whole sheets of skin lifted off – resembles a burn
Leaves skin exposed to further infection

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12
Q

why are the symptoms more serious?

A

Staphylococcus aureus strains (phage typeII) secreting epidermolytic toxins
SSSS

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13
Q

what are abscesses?

A

localized collection of pus

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14
Q

what is a furuncle?

A

common boil
Localised swelling with central pus collection

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15
Q

where do they form on body?

A

hair follicle

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16
Q

what bacteria is usually the cause?

A

S. aureus

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17
Q

what is a Carbuncle?

A

Furuncle involving many follicles or glands
Multiple discharging heads

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18
Q

what is the content of abscesses?

A

Pus
Mostly fluid + neutrophils + causative organisms

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19
Q

where else can abscesses form?

A

Sites of trauma (puncture wounds)

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20
Q

how do abscesses form in deep tissues?

A

“seeded” by pyogenic organisms in bloodstream
“seeded” by trauma

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21
Q

what bacteria causes abscesses?

A

Mainly S. aureus but
Often polymicrobial, with obligate anaerobes

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22
Q

what causes Buttock abscesses?

A

Obligate anaerobes + other gut flora (eg enterobacteriaceae, streptococci)

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23
Q

what causes deep tissue abscesses?

A

Obligate anaerobes +/- streptococci +/- S. aureus

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24
Q

what is the first treatment of abscesses?

A

Incision and drainage

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25
Q

what has a secondary but crusail treatment role?

A

Antibiotics (penicillin/flucloxacillin + metronidazole)

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26
Q

why must abscesses be drained?

A

Antibiotics cannot penetrate the pus;

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27
Q

what diagnostic benefit does the drain have?

A

the pus can be collected and tested -
Microscopy (deep tissues only)
Culture (including anaerobic)
Sensitivity testing

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28
Q

what is Cellulitis?

A

Acute spreading infection under skin surface

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29
Q

how does the infection begin?

A

Access from minor trauma or existing infection (eg boil)

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30
Q

what does it look like?

A

Hot, red, swollen, painful. Fever.

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31
Q

what complications are associated with cellulitis?

A

Spread to deeper soft tissues eg fat and muscle
Septicaemia

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32
Q

what are the two main Causative organisms?

A

S. aureus
Streptococcus pyogenes (Gp A streptococcus + other ß haemolytic streps eg B, C and G)

33
Q

what are the causative bacteria in buttock cellulitis?

A

Enterobacteriaceae and anaerobes

34
Q

what can cause cellulitis rarely in the immunosupressed?

A

Pseudomonas

35
Q

how is it diagnosed?

A

Clinical appearance

36
Q

what lab tests are done?

A

Blood culture
Biopsy (rarely – only done if treatment failure)
ASO (anti-streptolysin O) titres if culture negative

37
Q

what is used to treat?

A

Antistaphylococcal – flucloxacillin
+
Antistreptococcal – penicillin

38
Q

why does the disease look as it does?

A

due to variety of toxins

39
Q

what antibiotic should be used in severe disease?

A

use antibiotics that limit protein manufacture eg clindamycin

40
Q

what is Erysipelas?

A

A specific type of cellulitis

41
Q

how is the appearance different?

A

Generally head and neck only
Generally more superficial than cellulitis
Generally better defined edge

42
Q

how does the causative organisms differ?

A

Almost always due to Group A Streptococci
Rarely Group G

43
Q

what is Necrotising Fasciitis?

A

Spreading infection of deeper tissues
Destruction of connective tissue, fat, muscle

44
Q

what are the associated side effects?

A

Extensive tissue destruction with loss of function
Risk of overwhelming infection, septicaemia and death

45
Q

what are the causative organisms?

A

Often polymicrobial
Streptococci (Groups ABCGF)
Staphylococcus aureus

46
Q

which Obligate anaerobic gram positive organisms can cause the infection?

A

Clostridial species

47
Q

which Obligate anaerobic gram negative organisms can cause the infection?

A

Bacteroides species

48
Q

it is Rarely monomicrobial; but which species could cause the infection alone?

A

Gp A streptococci, Clostridial species

49
Q

how do the bacteria cause NF?

A

Pathogens encounter ischaemic tissue
Lytic toxins and toxins that promote spread

50
Q

which toxins are produced?

A

(collagenases and hyaluronidases)

51
Q

what predispositions you to NF?

A

Old age
Diabetes
Poor peripheral circulation – cardiovascular issues
Immunosuppression

52
Q

how is NF diagnosed?

A

Microscopy of fluids and tissue samples
Aerobic and anaerobic culture of samples
Blood culture

53
Q

how is NF treated?

A

Wide surgical excision of affected tissue
Antibiotics

54
Q

what kind of antibiotics are used?

A

Cidal and Protein inhibitors

55
Q

what are the Characteristics of puncture wounds?

A

Small or closed surface
Deep

56
Q

what environmental contamination do they often contain?

A

Soil
Inorganic foreign body

57
Q

what complications can be caused by these contaminates?

A

Cellulitis
Abscess formation
Osteomyelitis (location dependant)

58
Q

what risk does soil contamination add in particular?

A

Tetanus (localised infection - systemic illness)

59
Q

how are puncture wounds managed?

A

Clean
Remove damaged tissue and foreign body

60
Q

which medicines are necessary?

A

Vaccinate against tetanus (if required)
Antibiotic cover
Depends on nature of injury
Often cover for anaerobic organisms

61
Q

Uncomplicated puncture wound may not require any laboratory investigation. But why would Laboratory investigations ever be carried out?

A

depends on complications
Eg as for abscess, cellulitis
NB Tetanus is clinical diagnosis but:
Anaerobic culture of tissue sample may confirm

62
Q

name particular types of puncture wounds?

A

object speared into body
animal bites

63
Q

why do animal bites have more risk?

A

large bacterial inoculum from mouth commensals

64
Q

what human pathogen bacteria is carried by dogs?

A

Capnocytophagia canimorsus

65
Q

what human pathogen bacteria is carried by cats

A

Pasteurella multocida – only gram negative rod that is sensitive to penicillin

66
Q

what can be carried from a human bite?

A

+ Streptococci, staphylococci and anaerobes

67
Q

how are any pathogenic bacteria identified?

A

Culture (not microscopy) of swab of site
Microscopy and culture of any subsequent abscess

68
Q

what are pressure sores?

A

Skin ulcerates due to prolonged pressure

69
Q

what are the risk factors for developing pressure sores?

A

Faecal/urinary incontinence
Underlying fracture
Malnutrition

70
Q

what bacteria are involved?

A

Colonisation of moist surface
S. aureus
Group G streptococci
Pseudomonas
All are potential pathogens

71
Q

when are lab tests performed?

A

only for Deeper infection
Culture of swab from deep in lesion
or if antibiotics have no effect

72
Q

what can cause infection of surgical wounds?

A

Patient’s endogenous flora from operation site
Normal flora of surgical team

73
Q

what are the risk factors for infection of surgical wound

A

Length of operation
Subsequent haematoma
General health of patient
“Wound classification

74
Q

what is meant by the classification of a ‘clean’ surgical wound?

A

Planned operation on uninfected tissue

75
Q

‘clean / contaminated’

A

Planned procedure cutting mucous membranes
Infection risk dependent on normal flora at that site

76
Q

‘contaminated’

A

Surgery on fresh trauma
Surgery on gut - Infection certain if antibiotic prophylaxis not given

77
Q

‘infected’

A

Surgery on infected tissue
Surgery on old trauma site

78
Q

what lab investigations are carried out?

A

Microscopy + culture: pus, infected tissues and infected fluids
Likely pathogens will vary with surgical site
Therefore culture methods will vary
But in most instances will include anaerobic culture

79
Q

when is a blood culture done?

A

If systemically unwell patient

medical microbiology (29 decks)

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