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Dermatology > Microbiology > Flashcards

Microbiology Flashcards

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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
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 scabies - thick white crust HIGHLY INFECTIOUS Thousands of mites across the body Common in elderly, debilitated or immunosuppressed patients
43
What is the main symptom of a louse infection
Intense itching | Can affect head, lashes body (rare now) and pubic area (sexual contact)
44
How do you treat lice
Malathion lotions | Physical removal with a fine tooth comb, repeated regularly to catch new lice as they emerge
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
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
How does lyme disease present
First stage - erythema migrans 2nd stage - lymphocytoma numbess, arthralgia and myalgia, , facial paralysis, meningitis, arrythmia 3rd stage - arthritis, chronic pain and neuro problems
72
How do you treat lyme disease
Best is prevention! - tick repellent and early removal Doxycycline or amoxicillin 2-3 weeks course If more severe – IV penicillin / Ceftriaxone 14 – 21
73
How do you treat shingles
Treat with Acyclovir 800mg 5 times daily for 7-10 days, Tramadol 50mg 4 times daily Advise local cooling agents
74
How do insect bites typically present
Variable - small papules to bullae Typically itchy Often a linear pattern with grouped lesions Asymmetrical
75
How do you treat insect bites
Prevention with repellents Symptomatic - antihistamine or topical steroid Treat pets and environment if fleas
76
Describe erythema migrans seen in Lyme disease
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
How does lymphocytoma present in lyme disease
Approximately 6 months after the initial bite Firm, bluish red swelling on earlobes of children / nipple in adults Associated with tender, local lymphadenopathy
78
Describe Acrodermatitis Chronica Atrophicans seen in lyme disease
Late stage - 6/12 – 8yrs after initial infection Characteristic blue/red discolouration progressing to atrophy Treatable when in initial inflammatory stage
79
What is the causative oragnism is scabies
The arthropod sarcoptes scabiei
80
How is scabies spread
Direct skin-to-skin contact | It is a contagious disease and may spread extensively in residential establishments
81
How does scabies present
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
Describe the pathogenesis of scabies
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
Which sites are commonly affected by scabies
Fingers and web spaces Flexor wrists Nipples + genitals Feet - particularly in infants
84
How do you treat scabies
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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