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Flashcards in Microbiology Deck (72):
1

What are virulence factors

Proteins that contribute to an organisms virulence.

2

Which bacteria tend to survive on the skin

Usually gram positive as they can cope with the dryness
Gram negatives tend to be found in moister areas such as the armpit or perineum

3

What defences does the skin have against infection

The structure - should be impenetrable
Shedding layer prevents a biofilm forming
Sebaceous glands and sweat pores

4

What is MRSA

Methicillin resistant staph aureus
Defined by its resistance to flucloxacillin
Often seen in hospital patients, particularly elderly or immunosuppressed

5

What clinical presentations can be caused by a staph aureus infection

superficial lesions - boils to abscesses
Systemic effects - can be fatal
Toxinoses such as toxic shock, scalded skin syndrome

6

What virulence factor will all staph aureus strains carry

Coagulase
All are coagulase positive organisms

7

Do all strains of staph aureus carry the same virulence factors

NO
will have different combinations and lead to different presentations
Variety makes it an effective pathogen

8

Name some toxinoses that can be caused by staph aureus

TSST-1 can lead to fever, vomiting, diarrhoea, pain etc - toxic shock
Staph food poisoning caused by enterotoxin
Scaled skin syndrome

9

Describe scalded skin syndrome

Often occurs in neonates
exfoliatin toxins attack cross-bridges that hold the skin together
As a result the dermis and epidermis slide apart

10

What are the clinical signs of toxic shock syndrome

Fever
Defuse macular rash
Hypotension - <90mmHg
more than 3 organ system involved - life threatening

11

what is the cause of toxic shock syndrome

Particularly associated with TSST-1 (staph aureus toxin)
Tampon use
There is an overreaction of the immune system due to a massive release of cytokines

12

What is PVL

Panton-Valentine Leukocidin
Toxic to leukocytes
Associated with severe and recurrent skin infections

13

Describe necrotising pneumonia

Preceded by a flu like syndrome
rapidly progresses
Leads to acute respiratory distress, deterioration of lung function and organ failure
Organism destroys the respiratory tissue

14

What are the features of strep pyrogenes

Gram + cocci in chains
B haemolysis

15

Describe impetigo

Red/orange crusty rash, usually on face
Infection is just below skin surface
Common in nursery age children
Highly contagious - spread through direct contact with discharge

16

Describe necrotizing fasciitis

Caused by invasive Strep A strains
They penetrate the mucous membrane and develop
Rapidly destroys connective tissue
Irreversible

17

What type of virulence factor is responsible for toxic shock

Super antigens

Either in S. aureus or S. pyogenes

18

How can gene transfer occur in bacteria

Bacterial transformation - taking up DNA from another cell and incorporating it
Transduction -release of bacteriophage which transfer DNA
Conjugation - sex pili exchange plasmids

19

Where does staph aureus colonise

Multiple strains colonise the skin and mucous membranes

20

How does the skin act as an immune defence

It works if the skin is intact
Dry surface
Sebum - inhibits bacterial growth with fatty acid
Competitive bacterial flora

21

How do you diagnose a skin infection

Swab the lesion if the surface is broken
Bacterial and viral swabs used as appropriate
Take a pus or tissue sample if deeper
Blood cultures if necessary

22

How do you determine what type of staph is present

Best way is a coagulate test
Staph aureus is coagulase positive - gold appearance on plate
Other staphs are negative

23

Which strep strains are alpha haemolytic

Pneumoniae - cause of pneumonia
Viridans - commensal of mouth etc, can cause endocarditis

24

Which strep strains are beta haemolytic

Group A , B and C

25

Which strep strains are non haemolytic

Enterococcus - commensal of bowel
Can cause UTI

26

What is the choice of treatment for staph aureus

Flucloxacillin

27

What infections can staph aureus cause

Wound, skin and joint infections
Cellulitis
Infected eczema
Impetigo
SSS

28

What toxins can staph aureus produce

Enterotoxin - food poisoning
SSSST - causes scalded skin syndrome
PVL - caused multiple necrosing skin infections

29

What are the treatment options for MRSA

Doxycycline
Co-trimoxazole
Clindamycin - risk of c. Diff
Vancomycin

30

Where might staph epidermidis be found in the body

Common skin commensal
May cause infection in association with artificial material such as heart valves or joints

31

How do you treat necrotising fasciitis

Needs urgent surgical debridement
Back up with antibiotics

32

What is the key clinical sign for necrotising fasciitis

Pain that exceeds the visual presentation
Patient will be in excruciating pain

33

What is the underlying cause of leg ulcers

Vascular problems - venous or arterial

34

When do you need to swab a leg ulcer

ONLY when there is clinical signs of infection
There will always be commensals growing due to moist, warm nature of wound but not always requiring treatment

35

Name the different types of tinea infection (by location)

Tinea pedis - foot
Tinea cruris - groin
Tinea capris - scalp
Tinea manum - hand
Tinea corporis - body

36

What is the medical name for ringworm

Tinea
Fungal infection

37

Who is most commonly affected by ringworm

Men - particularly foot and groin
Children are the main group that get scalp ringworm

38

What are some of the sources of dermatophyte infection

Other infected humans
Animals - e.g. Cats and dogs
Soil - less common in the UK

39

How do you diagnose a dermatophyte

Clinical appearance
Woods light
Skin scraping, nail clippings - for microscopy and culture

40

Describe a candida infection

Fungal infection that infects skin folds
Looks for warm moist areas - under breasts, groin, ab skin folds
Diagnoses by swab

41

How do you treat a candida infection

Clotrimazole cream
Oral fluconazole

42

What is Norwegian scabies

A chronic crusted form of the disease
HIGHLY INFECTIOUS
Millions of mites across the body

43

What is the main symptom of a louse infection

Intense itching
Can affect head, body and pubic area

44

How do you treat lice

Malathion

45

Which skin infections need isolation

Group A strep
MRSA
Scabies - with extra PPE precaution if Norwegian

46

Describe the chickenpox virus

Varicella - clinical presentation of first exposure
Primary infection usually occurs in childhood
Presents with a generalised rash and fever
Usually only lasts a week or so - self-limiting
Virus can then become latent

47

Describe shingles

Caused by herpes zoster
Reactivation of the same virus as chickenpox
Often in old age
Affects the dermatome supplied by the nerve root it resided in

48

Describe the appearance of the chickenpox rash

Starts as macules, then to papules
Moves on to vesicles which then scab over and fade
Small chance of scarring
Skin looks inflames
comes with itch and fever

49

which groups are more likely to suffer severe consequences of chickenpox

The very young and very old
Immunosuppressed - e.g. leukaemia patients

50

What is neonatal varicella zoster virus

When a new-born develops the virus
Due to maternal infection in late pregnancy - if she has it within 5 days of delivery
Comes with higher mortality

51

How do you prevent neonatal VZV

If mother has never had chickenpox and has been exposed to someone with it you can give the VZ immunoglobulin to lessen the severity or prevent the case

52

How does the shingles rash present

Tingling and pain is the first sign
Then erythema to vesicles then crust

53

what is post-herpetic neuralgia

Zoster pain that continues for 4 weeks
Common in the elderly and in trigeminal shingles

54

what type of pain does shingles cause

sharp
neuralgic

55

What are the symptoms of ramsay hunt syndrome

Pain and vesicles in the ear canal and throat
Facial palsy
If CNVIII is irritated then deafness, vertigo and tinnitus

56

Is there a vaccine for chickenpox

Yes
A live attenuated vaccine is available
Not routine in the UK

57

Is there a vaccine for shingles

Same vaccine for chickenpox can be used in high titre
Can reduce chance and impact of shingles in the elderly
Routinely given to 70 year olds in the UK

58

What can HSV type 1 cause

Main cause of oral lesions - cold sores
Causes 1/2 of genital herpes
Encephalitis - very rare

59

What can HSV type 2 cause

Causes 1/2 of genital herpes
rare cause of oral lesions
Encephalitis

60

What is erythema multiforme

Triggered by drugs or infections
Target lesions with erythema appear
At worst can be life threatening

61

Describe molluscum contagiosum

Viral infection - common in kids
Fleshy, firm, umbilicated, pearlescent nodules
Usually self-limiting

62

how can you treat molluscum contagiosum

Usually self-limiting but can take months to fade
Can use local application of liquid nitrogen

63

What diseases can HPV cause

Warts/verrucas
Genital warts
Cervical cancer
head and neck cancer

64

what is herpangina

Blistering rash of back of mouth
Caused by enterovirus
Self-limiting

65

Describe hand, foot and mouth disease

caused by enteroviruses - particularly coxsackie
Can cause lesions on hand, foot and buttocks
Typically occurs in kids
Not common in UK

66

What is erythema infectiosum

Caused by erythrovirus
Red rash appears on cheek - known as slapped cheek disease
In adults it may present as arthritis in the small joints

67

What are some complications of erythema infectiosum

Spontaneous abortion
Aplastic crisis - drop in haemoglobin
Chronic anaemia

68

What is orf

Virus comes from sheep
Firm, fleshy nodule appears on hand
Common in farmers
Self-limiting

69

How does syphilis present

Priamry - painless ulcer at infection site
Secondary - red rash all over body
- prominent on soles and palms
Tertiary - CNS and cardio presentations

70

What causes lyme disease

Bacteria - borrelia burgdorferi
Passed to humans by tick - must be attached for around 24 hours

71

How does lyme disease present

Early - erythema migrans
Late - heart block, nerve palsy and arthritis

72

how do you treat lyme disease

doxycycline or amoxicillin