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Dermatology > Microbiology > Flashcards

Microbiology Flashcards

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Dermatology Board Prep flashcards
1
Q

What are virulence factors

A

Proteins that contribute to an organisms virulence.

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2
Q

Which bacteria tend to survive on the skin

A

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

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3
Q

What defences does the skin have against infection

A

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

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4
Q

What is MRSA

A

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

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5
Q

What clinical presentations can be caused by a staph aureus infection

A

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

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6
Q

What virulence factor will all staph aureus strains carry

A

Coagulase

All are coagulase positive organisms

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7
Q

Do all strains of staph aureus carry the same virulence factors

A

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

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8
Q

Name some toxinoses that can be caused by staph aureus

A

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

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9
Q

Describe scalded skin syndrome

A

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

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10
Q

What are the clinical signs of toxic shock syndrome

A

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

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11
Q

what is the cause of toxic shock syndrome

A

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

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12
Q

What is PVL

A

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

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13
Q

Describe necrotising pneumonia

A

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

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14
Q

What are the features of strep pyrogenes

A

Gram + cocci in chains

B haemolysis

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15
Q

Describe impetigo

A

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

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16
Q

Describe necrotizing fasciitis

A

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

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17
Q

What type of virulence factor is responsible for toxic shock

A

Super antigens

Either in S. aureus or S. pyogenes

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18
Q

How can gene transfer occur in bacteria

A

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

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19
Q

Where does staph aureus colonise

A

Multiple strains colonise the skin and mucous membranes

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20
Q

How does the skin act as an immune defence

A

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

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21
Q

How do you diagnose a skin infection

A

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

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22
Q

How do you determine what type of staph is present

A

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

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23
Q

Which strep strains are alpha haemolytic

A

Pneumoniae - cause of pneumonia

Viridans - commensal of mouth etc, can cause endocarditis

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24
Q

Which strep strains are beta haemolytic

A

Group A , B and C

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25
Q

Which strep strains are non haemolytic

A

Enterococcus - commensal of bowel

Can cause UTI

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26
Q

What is the choice of treatment for staph aureus

A

Flucloxacillin

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27
Q

What infections can staph aureus cause

A 
Wound, skin and joint infections 
Cellulitis 
Infected eczema 
Impetigo 
SSS
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28
Q

What toxins can staph aureus produce

A

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

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29
Q

What are the treatment options for MRSA

A

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

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30
Q

Where might staph epidermidis be found in the body

A

Common skin commensal

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

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31
Q

How do you treat necrotising fasciitis

A

Needs urgent surgical debridement

Back up with antibiotics

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32
Q

What is the key clinical sign for necrotising fasciitis

A

Pain that exceeds the visual presentation

Patient will be in excruciating pain

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33
Q

What is the underlying cause of leg ulcers

A

Vascular problems - venous or arterial

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34
Q

When do you need to swab a leg ulcer

A

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
Q

Name the different types of tinea infection (by location)

A 
Tinea pedis - foot 
Tinea cruris - groin 
Tinea capris - scalp 
Tinea manum - hand 
Tinea corporis - body
36
Q

What is the medical name for ringworm

A

Tinea

Fungal infection

37
Q

Who is most commonly affected by ringworm

A

Men - particularly foot and groin

Children are the main group that get scalp ringworm

38
Q

What are some of the sources of dermatophyte infection

A

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

39
Q

How do you diagnose a dermatophyte

A

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

40
Q

Describe a candida infection

A

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

41
Q

How do you treat a candida infection

A

Clotrimazole cream

Oral fluconazole

42
Q

What is Norwegian scabies

A

A chronic crusted form of scabies - thick white crust
HIGHLY INFECTIOUS
Thousands of mites across the body
Common in elderly, debilitated or immunosuppressed patients

43
Q

What is the main symptom of a louse infection

A

Intense itching

Can affect head, lashes body (rare now) and pubic area (sexual contact)

44
Q

How do you treat lice

A

Malathion lotions

Physical removal with a fine tooth comb, repeated regularly to catch new lice as they emerge

45
Q

Which skin infections need isolation

A

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

46
Q

Describe the chickenpox virus

A

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
Q

Describe shingles

A

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
Q

Describe the appearance of the chickenpox rash

A 
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
Q

which groups are more likely to suffer severe consequences of chickenpox

A

The very young and very old

Immunosuppressed - e.g. leukaemia patients

50
Q

What is neonatal varicella zoster virus

A

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
Q

How do you prevent neonatal VZV

A

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
Q

How does the shingles rash present

A

Tingling and pain is the first sign

Then erythema to vesicles then crust

53
Q

what is post-herpetic neuralgia

A

Zoster pain that continues for 4 weeks

Common in the elderly and in trigeminal shingles

54
Q

what type of pain does shingles cause

A

sharp

neuralgic

55
Q

What are the symptoms of ramsay hunt syndrome

A

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

56
Q

Is there a vaccine for chickenpox

A

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

57
Q

Is there a vaccine for shingles

A

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
Q

What can HSV type 1 cause

A

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

59
Q

What can HSV type 2 cause

A

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

60
Q

What is erythema multiforme

A

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

61
Q

Describe molluscum contagiosum

A

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

62
Q

how can you treat molluscum contagiosum

A

Usually self-limiting but can take months to fade

Can use local application of liquid nitrogen

63
Q

What diseases can HPV cause

A

Warts/verrucas
Genital warts
Cervical cancer
head and neck cancer

64
Q

what is herpangina

A

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

65
Q

Describe hand, foot and mouth disease

A

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

66
Q

What is erythema infectiosum

A

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
Q

What are some complications of erythema infectiosum

A

Spontaneous abortion
Aplastic crisis - drop in haemoglobin
Chronic anaemia

68
Q

What is orf

A

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

69
Q

How does syphilis present

A

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

70
Q

What causes lyme disease

A

Spirochete borrelia burgdorferi
Passed to humans by tick saliva when they bite - they get from infected host
Must be attached for around 24 hours to transmit

71
Q

How does lyme disease present

A

First stage - erythema migrans

2nd stage - lymphocytoma numbess, arthralgia and myalgia, , facial paralysis, meningitis, arrythmia

3rd stage - arthritis, chronic pain and neuro problems

72
Q

How do you treat lyme disease

A

Best is prevention! - tick repellent and early removal

Doxycycline or amoxicillin
2-3 weeks course

If more severe – IV penicillin / Ceftriaxone 14 – 21

73
Q

How do you treat shingles

A

Treat with Acyclovir 800mg 5 times daily for 7-10 days,
Tramadol 50mg 4 times daily
Advise local cooling agents

74
Q

How do insect bites typically present

A

Variable - small papules to bullae
Typically itchy
Often a linear pattern with grouped lesions
Asymmetrical

75
Q

How do you treat insect bites

A

Prevention with repellents
Symptomatic - antihistamine or topical steroid
Treat pets and environment if fleas

76
Q

Describe erythema migrans seen in Lyme disease

A

Occurs within a month of the bite and resolves in a month (days if treated)

Usually this is seen as a solitary macule, or annular (ring-shaped) lesion which can vary considerably in size - typical target appearance

77
Q

How does lymphocytoma present in lyme disease

A

Approximately 6 months after the initial bite
Firm, bluish red swelling on earlobes of children / nipple in adults
Associated with tender, local lymphadenopathy

78
Q

Describe Acrodermatitis Chronica Atrophicans seen in lyme disease

A

Late stage - 6/12 – 8yrs after initial infection
Characteristic blue/red discolouration progressing to atrophy
Treatable when in initial inflammatory stage

79
Q

What is the causative oragnism is scabies

A

The arthropod sarcoptes scabiei

80
Q

How is scabies spread

A

Direct skin-to-skin contact

It is a contagious disease and may spread extensively in residential establishments

81
Q

How does scabies present

A

Significant itch - particularly at night
Burrows are best seen on the sides of the fingers or flexor aspect of wrist, with the mite appearing as a small dark dot at the end of the burrow
Excoriations, vesicles, eczematous or urticated papules and rubbery nodules may be seen

82
Q

Describe the pathogenesis of scabies

A

Female mites burrow through the keratin layer of skin and lay eggs as they go
Affected individuals are asymptomatic for up to 6 weeks then delayed hypersensitivity reaction develops

83
Q

Which sites are commonly affected by scabies

A

Fingers and web spaces
Flexor wrists
Nipples + genitals
Feet - particularly in infants

84
Q

How do you treat scabies

A

Treat any secondary infection
Permethrin cream - top to toe , done twice, 1 week apart
Or malathion
Treat everyone in household and close contacts
Treat itch symptomatically with steroid or crotamiton cream - may take 1-4 weeks to settle

Dermatology (14 decks)

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