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medical microbiology > Skin and Soft Tissue Infections > Flashcards

Skin and Soft Tissue Infections 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
what has a secondary but crusail treatment role?
Antibiotics (penicillin/flucloxacillin + metronidazole)
26
why must abscesses be drained?
Antibiotics cannot penetrate the pus;
27
what diagnostic benefit does the drain have?
the pus can be collected and tested - Microscopy (deep tissues only) Culture (including anaerobic) Sensitivity testing
28
what is Cellulitis?
Acute spreading infection under skin surface
29
how does the infection begin?
Access from minor trauma or existing infection (eg boil)
30
what does it look like?
Hot, red, swollen, painful. Fever.
31
what complications are associated with cellulitis?
Spread to deeper soft tissues eg fat and muscle Septicaemia
32
what are the two main Causative organisms?
S. aureus Streptococcus pyogenes (Gp A streptococcus + other ß haemolytic streps eg B, C and G)
33
what are the causative bacteria in buttock cellulitis?
Enterobacteriaceae and anaerobes
34
what can cause cellulitis rarely in the immunosupressed?
Pseudomonas
35
how is it diagnosed?
Clinical appearance
36
what lab tests are done?
Blood culture Biopsy (rarely – only done if treatment failure) ASO (anti-streptolysin O) titres if culture negative
37
what is used to treat?
Antistaphylococcal – flucloxacillin + Antistreptococcal – penicillin
38
why does the disease look as it does?
due to variety of toxins
39
what antibiotic should be used in severe disease?
use antibiotics that limit protein manufacture eg clindamycin
40
what is Erysipelas?
A specific type of cellulitis
41
how is the appearance different?
Generally head and neck only Generally more superficial than cellulitis Generally better defined edge
42
how does the causative organisms differ?
Almost always due to Group A Streptococci Rarely Group G
43
what is Necrotising Fasciitis?
Spreading infection of deeper tissues Destruction of connective tissue, fat, muscle
44
what are the associated side effects?
Extensive tissue destruction with loss of function Risk of overwhelming infection, septicaemia and death
45
what are the causative organisms?
Often polymicrobial Streptococci (Groups ABCGF) Staphylococcus aureus
46
which Obligate anaerobic gram positive organisms can cause the infection?
Clostridial species
47
which Obligate anaerobic gram negative organisms can cause the infection?
Bacteroides species
48
it is Rarely monomicrobial; but which species could cause the infection alone?
Gp A streptococci, Clostridial species
49
how do the bacteria cause NF?
Pathogens encounter ischaemic tissue Lytic toxins and toxins that promote spread
50
which toxins are produced?
(collagenases and hyaluronidases)
51
what predispositions you to NF?
Old age Diabetes Poor peripheral circulation – cardiovascular issues Immunosuppression
52
how is NF diagnosed?
Microscopy of fluids and tissue samples Aerobic and anaerobic culture of samples Blood culture
53
how is NF treated?
Wide surgical excision of affected tissue Antibiotics
54
what kind of antibiotics are used?
Cidal and Protein inhibitors
55
what are the Characteristics of puncture wounds?
Small or closed surface Deep
56
what environmental contamination do they often contain?
Soil Inorganic foreign body
57
what complications can be caused by these contaminates?
Cellulitis Abscess formation Osteomyelitis (location dependant)
58
what risk does soil contamination add in particular?
Tetanus (localised infection - systemic illness)
59
how are puncture wounds managed?
Clean Remove damaged tissue and foreign body
60
which medicines are necessary?
Vaccinate against tetanus (if required) Antibiotic cover Depends on nature of injury Often cover for anaerobic organisms
61
Uncomplicated puncture wound may not require any laboratory investigation. But why would Laboratory investigations ever be carried out?
depends on complications Eg as for abscess, cellulitis NB Tetanus is clinical diagnosis but: Anaerobic culture of tissue sample may confirm
62
name particular types of puncture wounds?
object speared into body animal bites
63
why do animal bites have more risk?
large bacterial inoculum from mouth commensals
64
what human pathogen bacteria is carried by dogs?
Capnocytophagia canimorsus
65
what human pathogen bacteria is carried by cats
Pasteurella multocida – only gram negative rod that is sensitive to penicillin
66
what can be carried from a human bite?
+ Streptococci, staphylococci and anaerobes
67
how are any pathogenic bacteria identified?
Culture (not microscopy) of swab of site Microscopy and culture of any subsequent abscess
68
what are pressure sores?
Skin ulcerates due to prolonged pressure
69
what are the risk factors for developing pressure sores?
Faecal/urinary incontinence Underlying fracture Malnutrition
70
what bacteria are involved?
Colonisation of moist surface S. aureus Group G streptococci Pseudomonas All are potential pathogens
71
when are lab tests performed?
only for Deeper infection Culture of swab from deep in lesion or if antibiotics have no effect
72
what can cause infection of surgical wounds?
Patient’s endogenous flora from operation site Normal flora of surgical team
73
what are the risk factors for infection of surgical wound
Length of operation Subsequent haematoma General health of patient “Wound classification
74
what is meant by the classification of a 'clean' surgical wound?
Planned operation on uninfected tissue
75
'clean / contaminated'
Planned procedure cutting mucous membranes Infection risk dependent on normal flora at that site
76
'contaminated'
Surgery on fresh trauma Surgery on gut - Infection certain if antibiotic prophylaxis not given
77
'infected'
Surgery on infected tissue Surgery on old trauma site
78
what lab investigations are carried out?
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
when is a blood culture done?
If systemically unwell patient

medical microbiology (29 decks)

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