Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

LR Dermatology > Microbiology > Flashcards

Microbiology Flashcards

1
Q

What is meant by virulence?

A

The ability of a microorganism to cause disease in a host

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is meant by a virulence factor?

A

A component of a pathogen that contributes to its ability to cause disease

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How do the following virulence factors help a pathogen cause disease?

  • adhesin
  • invasin
  • impedin
  • aggressin
  • modulin
A

Adhesin - enables binding of organism to host tissue

Invasin - enables organism to invade host cell/tissue

Impedin - enables organism to avoid host defence

Aggressin - damages host directly

Modulin - damages host indirectly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Skin infections tend to be gram +ve/-ve

A

Gram +ve staph and strep infections are most common

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the 2 most common staphylococcus skin infections?

A
  • S. aureus

- S. epidermis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

S. epidermis has a ?% colonisation

A

100%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

In what individuals is S. epidermis infection most commonly seen?

A

In immunocompromised/ hospital patients, particularly in association with foreign devices e.g., catheters

Everyone carries S. epidermis on their skin (100% colonisation), it doesn’t usually cause infection

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

S. aureus has a ?% colonisation

A

20% (-60%)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

In what individuals is S. aureus infection seen in?

A

In the community and in the hospital (nosocomial) setting

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Which surfaces are most commonly colonised by…
- S. aureus
- S. epidermis
…?

A

S. aureus -> anterior nostrils and perineum

S. epidermis -> skin and mucous membranes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How can you distinguish between staph aureus and staph epidermis?

A

Coagulase testing

Staph aureus is coagulase +ve and staph epidermis is coagulase -ve

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is MRSA?

Where is it seen?

A

Methicillin resistant staph aureus -> a strain of staph aureus which is resistant to flucloxacillin

It is mainly seen in the hospital (nosocomial) setting in elderly and immunocompromised patients

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the various presentations of staph aureus skin infection?

A
  • Rash
  • Abscess
  • Folliculitis
  • Carbuncle
  • Impetigo
  • Scalded skin syndrome
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are the important virulence factors that make staph aureus a highly effective pathogen?

A

Fibrinogen binding protein ->
allows staph aureus to create a fibrinogen shield around itself to avoid the immune response

Superantigens -> bacterial proteins that massively overstimulate the T cell immune response

Protein A ->
binds antibodies the wrong way round so they are not activated and the pathogen is not cleared

Panton-Valentine Leukocidin (PVL) ->
a toxin that destroys leukocytes, associated with severe infections

Toxic shock syndrome toxin (TSST-1) ->
a toxin that acts as a superantigen to cause toxic shock syndrome

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are toxinoses? Where do they affect an individual?

A

Syndromes caused by a bacterial toxin

They affect the host away from the site of colonisation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Give 2 examples of pathogenesis caused by staph aureus toxins

A

Toxic shock syndrome

Scalded skin syndrome

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the diagnostic criteria for toxic shock syndrome?

A
  • Fever
  • Diffuse macular rash
  • Hypotension
  • > = 3 organ systems involved
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Why is toxic shock syndrome associated with the use of tampons?

A

Staph aureus often colonises the perineum which is in close proximity with a tampon

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

PVL is a toxin produced by some strains of staph aureus.

What severe skin infection is this strain associated with?

A

Necrotising pneumonia

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Describe the progression of necrotising pneumonia

A
  • Flu like syndrome
  • Necrotising haemorrhagic pneumonia
  • Rapid progression
  • Acute respiratory distress
  • Deterioration of pulmonary function
  • Refractory hypoxaemia
  • Multi-organ failure despite antibiotic therapy
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is the most common streptococcus skin infection?

A

Streptococcus pyogenes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What are the most common presentations of strep pyogenes?

A
  • Streptococcal sore throat

- Scarlet fever

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

According to the Lancefield system, strep pyogenes is a group A/B streptococcus

A

Group A strep (GAS)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Strep pyogenes is…

  • catalase +ve/-ve
  • alpha/beta/gamma haemolytic
A
  • Catalase -ve

- Beta haemolytic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

The ? system groups gram +ve streptococci depending on their cell wall antigens

A

Lancefield

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

How are Group A Strep (GAS) further subdivided?

A

According to M protein antigens on their surface

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Name 3 skin infections caused by strep pyogenes/GAS

A
  • Impetigo
  • Cellulitis
  • Necrotising fasciitis

(progressively deeper infections)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is impetigo?

A

A red rash, usually on the face, with the infection immediately below the skins surface

It is highly contagious through contact with discharge on the face

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is the most common presentation of GAS in young children?

A

Impetigo

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is cellulitis?

What other symptoms may accompany it?

A

A deeper skin infection in the dermis but that is not associated with necrosis

Can be accompanied by fever, rigours and nausea

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What is necrotising fasciitis?

A

An invasive GAS disease (iGAS) known as ‘the flesh eating bug’ that rapidly destroys connective tissue of the fascia below the skin

32
Q

Describe the rapid progression of necrotising fasciitis from day 0 (insult) to day 4

A

Day 0 - discomfort around area of trauma, pain in area of infection

Day 1 - flu-like symptoms, vomiting, fever, diarrhoea

Day 2 - swelling/sunburn in the area of trauma

Day 3 - boil-like blisters and smelly pus

Day 4 - gangrene

33
Q

How can bacteria pass on the ability to express virulence factors and toxins?

A

Via horizontal gene transfer

34
Q

What is the treatment of choice for staph aureus?

A

Flucloxacillin

35
Q

What is the treatment of choice for strep pyogenes?

A

Penicillin

36
Q

What defences does the skin have against infection?

A
  • Intact keratin layer
  • Dry surface dries out microorganisms
  • Sebum inhibits bacterial growth
  • Commensal bacteria
  • Competition between bacterial flora
37
Q

In what ways can a bacterial infection be diagnosed?

A
  • Clinical diagnosis (no test required)
  • Swap of lesion if the surface is broken
  • Pus or tissue culture if deeper lesion
  • Blood cultures
38
Q

What is the most common skin infector?

A

Staph aureus

39
Q

Coagulase negative staph (e.g., s epidermis) are usually pathogenic/commensal bacteria

A

Commensal

40
Q

Name 3 bacteria that may be commensal skin bacteria

A

Staph epidermis
Corynebacterium sp (aka diphtheroids)
Propionibacterium sp

41
Q

List 8 skin presentations of a staph aureus infection

A
  • Boils
  • Carbuncles
  • Minor skin infection e.g., infected cut
  • Cellulitis
  • Infected eczema
  • Impetigo
  • Wound infection
  • Staphylococcal scalded skin syndrome
42
Q

What are the treatment options for MRSA infection?

A
  • Oral doxycycline
  • Vancomycin
  • Co-trimoxazole
  • Clindamycin (beware of C. diff)
43
Q

Staph and strep are both aerobic and facultatively anaerobic. True/false

A

True

44
Q

Name a toxin produced by beta-haemolytic strep sp that causes damage to tissues

A

Haemolysin

=blood lysis

45
Q

List 5 skin presentations of strep pyogenes (GAS) skin infection

A 
Infected eczema
Impetigo
Cellulitis 
Erysipelas
Necrotising fasciitis
46
Q

Alpha-haemolytic strep don’t cause skin infections as commonly as beta-haemolytic. Which 2 alpha-haemolytic strep are most common if they do infect the skin?

A

Strep pneumoniae (pathogen, most common cause of pneumonia)

Strep viridans (commensals of mouth, throat & vagina, cause infective endocarditis)

47
Q

What are erysipelas?

What do they look like?

A

Bacterial infection of the superficial layers of the skin (most often caused by GAS/strep pyogenes)

They appear as a fiery red rash with raised edges

48
Q

What is the treatment of choice for necrotising fasciitis?

A

Immediate surgical debridement and antibiotics

49
Q

What is a common presentation of necrotising fasciitis? Why is this the case?

A

Excruciating pain out of proportion to the redness of the skin

This is because the infection is spreading along the fascia below the skin

50
Q

Swabs should only be taken from leg ulcers (caused by vascular problems) if there are signs of…

A

Cellulitis or infection

51
Q

What are the main fungal skin pathogens?

A
  • Candidiasis
  • Tinea (dermatophytoses)
  • Pityriasis versicolor
  • Emboli
52
Q

Candida is an intertrigo. What does this mean?

A

It causes infection in skin folds where the area is warm and moist

53
Q

How is candida infection diagnosed and treated?

A

Diagnosis: swab for culture

Treatment: clotrimazole cream, oral fluconazole

54
Q

Tinea infections are dermatophytoses. What does this mean?

A

Ringworms

55
Q

Describe how dermatophytes infect a person

A
  • Fungus enters abraded/soggy skin
  • Hyphae spread in stratum corneum, infecting keratinised tissues only (skin, hair, nails)
  • Increased epidermal turnover causes scaling
  • Inflammation occurs
  • Hair follicles are invaded
  • Lesion grows outwards and heals in the centre, giving it a ringed appearance
56
Q

State which part of the body is infected in the following fungal infections:

Tinea capitis 
Tinea barbae
Tinea corporis
Tinea manuum
Tinea unguium
Tinea cruris
Tinea pedis
A

Tinea capitis = scalp

Tinea barbae = beard

Tinea corporis = body

Tinea manuum = hand

Tinea unguium = nails

Tinea cruris = groin

Tinea pedis = foot (athletes foot)

57
Q

The most likely source of dermatophyte infection is…

A

Other infected humans e.g., swimming pool

58
Q

What is the most common dermatophyte causal organism?

A

Trichophyton rubrum

59
Q

How can a dermatophyte infection be diagnosed?

A
  • clinical appearance
  • Wood’s light
  • microscopy and culture of skin scrapings, nail clippings and hair
60
Q

How can dermatophyte infections be treated?

A

Skin and nails:

  • Clotrimazole cream
  • Topical nail paint

Scalp:

  • Oral terbinafine
  • Oral itraconazole
61
Q

Name 2 common skin parasites

A
  • Scabies

- Lice

62
Q

What is Scabies?

A

An intensely itchy rash caused by the parasite Sarcoptes scabiei

It affects the finger webs, wrists and the genital area where the scabies burrow

63
Q

What is the incubation period for scabies?

A

Up to 6 weeks

64
Q

What is the first-line treatment for Scabies?

A

Malathion lotion

Applied overnight to the whole body and washed off the next day

65
Q

Malathion lotion is used to treat Scabies and…

A

Lice

66
Q

The main symptom of lice is usually…

A

Intense itching in the head/body/pubic area

67
Q

Patients with the following infections need single room isolation and contact precautions…?

A
  • Group A Strep
  • MRSA
  • Scabies
68
Q

List the most common viral skin infections

A
  • Herpes simplex virus
  • Human papillomavirus
  • Poxvirus
  • Varicella-zoster virus
  • Viral exanthems
69
Q

Why are viral infections spread so rapidly?

A

They are associated with an incubation period so affected individuals are infectious before they are symptomatic

70
Q

List 3 erythematous exanthems that tend to start on the face

A

Measles
Rubella
Erythema infectiosum

71
Q

Why should you isolate a patient who reports a rash that started on the face?

A

It could be measles

The patient can come out of isolation if their results are negative upon testing

72
Q

List 2 erythematous exanthems that tend to start on the trunk

A

Roseola

Scarlet fever

73
Q

List 2 papulo-vesicular exanthems

A

Chickenpox (varicella)

Gianotti-Crosti syndrome

74
Q

Name an exanthem of the extremities

A

Hand, foot and mouth disease

75
Q

List 6 possible skin manifestations of COVID-19

A
  • Morbilliform (measle-like, starts in the face then spreads)
  • “COVID toe” (chillblain-like)
  • Lace-like purpura
  • Urticaria
  • Vesicular blisters
  • Multisystem inflammation in children

LR Dermatology (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions