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Flashcards in Microbiology 2 Deck (68)
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1
Q

What are three features of skin that prevent against infection?

A
  • Dryness: dries out the organism
  • Sebum: inhibits bacterial growth
  • Competitive flora
2
Q

What are some protective bacterial flora?

A

Staph. Epidermidis, Corynebacterium, Propionibacterium

3
Q

How do you investigate a skin lesion where the surface is broken but is relatively superficial?

A

Swabs

4
Q

How do you investigate a skin lesion where the surface is broken but is relatively deep?

A

Pus or tissue sample +/- blood cultures

5
Q

How will staph aureus show on blood agar?

A

Golden

6
Q

How will coagulase - staph show on blood agar?

A

White

7
Q

Which variants of Staph are coagulase +?

A

Staph aureus only

8
Q

Which variants of Staph are coagulase -?

A

All types except staph aureus, a good example is staph epidermidis

9
Q

What will staph and strep be on a gram stain?

A

Positive

10
Q

An organism is gram + cocci in clusters, what is this likely to be?

A

Staphylococcus

11
Q

An organism is gram + cocci in chains, what is this most likely to be?

A

Streptococcus

12
Q

Once you have decided an organism is staph, what test will decipher if it is staph aureus?

A

Coagulase test will be positive

13
Q

Once you have decided an organism is strep, what test will decipher if it is Group A strep?

A

Haemolysis- will be B (complete) haemolysis

14
Q

In what conditions will staph aureus grow?

A

Aerobic and facultatively anaerobic

15
Q

Does staph aureus produce enzymes?

A

Yes (coagulase is an enzyme)

16
Q

Where does staph aureus usually cause infections?

A

Bone, skin, joint and wounds

17
Q

What is the antibiotic of choice for staph aureus?

A

Flucloxacillin

18
Q

Can MRSA be treated with flucloxacillin?

A

No

19
Q

What are some antibiotic options for MRSA?

A

Doxycycline, co-trimoxazole, clindamycin, vancomycin

20
Q

What is the enterotoxin produced by staph aureus associated with?

A

Food poisoning

21
Q

What are some skin infections which staph aureus can cause?

A
Minor skin sepsis
Cellulitis
Infected eczema
Impetigo
Wound infections
22
Q

Where are most other staph organisms found?

A

As skin commensals, not usually pathogenic

23
Q

When do coagulase - staph cause infections?

A

In association with foreign devices

24
Q

What can staph saprophyticus cause?

A

UTIs in women of child bearing age

25
Q

What conditions does strep grow in?

A

Aerobic and facultatively anaerobic

26
Q

How is streptococci classified?

A

Haemolysis on blood agar

27
Q

What does beta haemolytic strep mean?

A

Complete haemolysis- always pathogenic

28
Q

What does alpha haemolytic strep mean? Give examples.

A

Partial haemolysis e.g. Strep pneumoniae, strep viridans

29
Q

Where is strep viridans usually found? What can it cause?

A

Commensal of the mouth, throat, vagina

May cause infective endocarditis

30
Q

In terms of skin infection, which type of strep is the most important?

A

Group A beta haemolytic strep

31
Q

How is beta haemolytic strep further classified?

A

Based on antigenic surface structure

32
Q

What can group A strep cause?

A

Throat and severe skin infections

33
Q

What does group B strep cause?

A

Meningitis in neonates

34
Q

What are some skin infections that group A beta haemolytic strep can cause?

A

Infected eczema
Impetigo
Cellulitis
Necrotising fasciitis

35
Q

What is an example of a group A beta haemolytic strep which can cause impetigo, cellulitis and necrotising fasciitis?

A

Strep pyogenes

36
Q

Group A strep are further divided into M protein groups. What are M1 and M3?

A

The major serotypes

37
Q

Group A strep are further divided into M protein groups. What are M18 and M3?

A

Severe invasive disease

38
Q

Describe impetigo?

A

This is a skin infection under the surface in the stratum corneum. It usually affects the face and may be linked with the lymphatic system.

39
Q

Is impetigo infectious?

A

Highly contagious through contact with discharge from the face

40
Q

Describe cellulitis?

A

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

41
Q

Describe necrotising fasciitis?

A

Group A strep penetrates the mucus membranes and develops in lesions which rapidly destroys connective tissue

42
Q

Do all skin infections require antibiotics?

A

Minor ones may not

43
Q

What antibiotics target Group A strep?

A

Mainly penicillin, though flucloxacillin may also work

44
Q

What is the treatment for necrotising fasciitis?

A

Immediate surgical debridement or amputation and antibiotics

45
Q

How will necrotising fasciitis present?

A

Little to see on the skin but will cause severe pain

46
Q

What are group 1 and 2 types of necrotising fasciitis?

A

1- mixed coliforms and anaerobes (usually post-abdominal surgery)
2- group A strep

47
Q

When should you take swabs of leg ulcers?

A

If signs of infection/cellulitis are present

48
Q

What antibiotic treats anaerobes?

A

Metronidazole

49
Q

What is the main fungal infection of skin?

A

Tinea (ringworm)

50
Q

What are TINEA:

a) capitus
b) barbae
c) corporis
d) manuum
e) unguium
f) cruris
g) pedis

A

a) head
b) beard
c) body
d) hand
e) nail
f) groin
g) foot

51
Q

What is the common name for tine pedis?

A

Athlete’s foot

52
Q

Where do fungi enter the skin?

A

Abraded or soggy skin

53
Q

Where do fungi only infect?

A

Keratinised surfaces

54
Q

Which sex is more likely to be affected by tinea infections? Which age group are they most common in?

A
  • Males

- Children

55
Q

Where do tinea infections come from?

A

Mainly from other humans, though can be from animals or soil

56
Q

How do the lesions of tinea appear?

A

The lesions grow outwards and heal in the middle, giving a ring appearance

57
Q

What are some diagnostic tests for tinea infection?

A
  • Fluorescence (Wood’s lamp)

- Skin scrapings for microscopy and culture

58
Q

How do you treat small tinea infected areas?

A

Clotrimazole cream or topical nail paint

59
Q

What do you treat tinea corporis with?

A

Terbinafine

60
Q

What is the most common organism causing tinea infections?

A

Trichophyton Rubrum

61
Q

Where does microsporum canis come from?

A

Cats and dogs (cause of tinea infection)

62
Q

Where do candida infections occur?

A

Skin folds where the area is warm and moist e.g. under breasts, groin areas, under abdominal skin folds

63
Q

How do you treat candida infections?

A

Clometrizole cream or oral fluconazole

64
Q

What is Norwegian scabies?

A

A chronic, crusted form of scabies which is highly infectious

65
Q

What will scabies present with?

A

Intensely itchy rash affecting finger webs, wrists and genital areas

66
Q

How do you treat scabies?

A
  • Malathion lotion applied overnight and then washed off

- Benzyl benzoate

67
Q

Who should benzyl benzoate not be used in?

A

Children

68
Q

Who are some examples of infectious patients who would need in a separate room?

A
  • MRSA
  • Group A strep
  • Scabies