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Microbiology Flashcards

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Dermatology Board Prep flashcards
1
Q

What is virulence?

A

The capacity of a microbe to cause damage to the host

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2
Q

What factors are responsible for the variation in virulence between different species?

A 
Adhesin
Invasin
Impedin
Aggressin
Modulin
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3
Q

How do Adhesins contribute to virulence?

A

Allows the organism to bind to host tissue

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4
Q

How do Invasins contribute to virulence?

A

Allows the organism to invade a host cell/tissue

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5
Q

How do Impedins contribute to virulence?

A

Lets the organism to avoid host defense mechanisms

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6
Q

How do aggressins contribute to virulence?

A

Cause damage to the host directly

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7
Q

What organisms make up the skin microbiota?

A
  • Staphylococci spp. (Coag -ve)
  •   Staphylococcus aureus
  •   Diptheroids (P.acnes)
  •   Streptococci spp.
  •   Bacillus spp
  •   Candida spp.
  •   Malassezia furfur

Mycobacterium (occasionally)

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8
Q

What superficial lesions can a staph aureus infection cause?

A 
Boil
Carbuncle 
Abscess
Folliculitis
Impetigo
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9
Q

What Toxinoses can be caused by a staph aureus infection?

A

Toxic Shock

Scalded Skin Syndrome

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10
Q

How does Fibrinogen binding protein contribute to virulence?

A

It is an Adhesin

=> allows Staph Aureus to bind to host cells and infect

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11
Q

How does Leukocidin (PVL) contribute to Virulence?

A

Kills leukocytes

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12
Q

What is Toxic Shock Syndrome Toxin (TSST-1) and how does it contribute to virulence?

A

superantigen secreted by Staph. aureus

CAUSES:

  • rash
  • shock.
  • desquamation
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13
Q

Give examples of adhesins found on Staph. Aureus

A
  • Fibrinogen-Binding (ClfA ClfB)

*   Collagen-Binding (CNA)

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14
Q

What is the Toxic Shock diagnostic criteria?

A
  •  Fever –  39˚C
  •  Diffuse Macular rash & desquamation (“sunburn”)
  •  Hypotension –  ≤ 90 mm Hg (adults)
  •  ≥ 3 Organ systems involved –  liver, blood, renal, mucous membranes, GI, muscular, CNS.
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15
Q

Panton-Valentine Leukocidin (PVL) gives rise to what severe skin diseases?

A
  • recurrent furunculosis

- sepsis/necrotising fasciitis

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16
Q

PVL & alpha-toxin associated with MRSA causes what?

A
  • necrotizing pnuemonia

- contagious severe skin infections

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17
Q

What skin conditions does Strep. Pyogenes cause?

A
  • Impetigo
  • Cellulitis (Erysipelas)
  • Necrotising Fasciitis
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18
Q

How do modulins contribute to virulence?

A

Causes damage to the host indirectly

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19
Q

How are Strep. Pyogenes classified?

A

Lancefield (Serotyping of Cell Wall Carbohydrate)

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20
Q

What are the Major classifications of Strep. Pyogenes?

A

Major serotypes A-H and K-V (20)

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21
Q

How is Group A Strep. Pyogenes further classified?

A

further subdivided according to M protein antigens

  • M1 and M3 major serotype
  • M3 and M18 severe invasive disease
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22
Q

Is intact skin more or less likely to become infected?

A

Less likely

infection is more common if skin is broken

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23
Q

How does dry skin protect from infection?

A

completely dries out the microorganisms

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24
Q

How does sebum contribute to protecting against infection?

A

The fatty acids found in sebum inhibit bacterial growth

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25
Q

Give an example of transient bacteria flora

A

MRSA

intermittent => doesn’t always show up in screening

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26
Q

What is the difference between pathogens and commensals?

A

Pathogens have the potential to cause disease

Commensals don’t necessarily cause any illness

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27
Q

Give examples of competitive bacterial flora

A
  • Staphylococcus epidermidis
  • Corynebacterium sp. (diphtheroids)
  • Propionibacterium sp.
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28
Q

Give examples of alpha-haemolytic Streptococci

A

Strep. pneumonia

Strep. viridans (commensal/endocarditis)

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29
Q

Give examples of Beta-haemolytic streptococci

A 
Group A (throat, SKIN)
Group B (neonatal meningitis)
Groups C,G
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30
Q

GIve examples of non-haemolytic streptococci

A

Enterococcus (gut commensal, UTI)

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31
Q

Give an example of a coagulase positive and coagulase negative strain of Staphylococcus

A

Coag. Positive = Staph Aureus

Coag. Negative = Staph. epidermidis

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32
Q

Is staphylococcus an aerobe or an anaerobe?

A

Aerobic and facultatively anaerobic

=> grows best aerobically but can grow anaerobically

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33
Q

Name toxins that can be produced by some variations of staphylococcus

A
  • Enterotoxin –food poisoning
  • SSSST –staphylococcal scalded skin syndrome toxin
  • PVL –Panton Valentine Leucocidin
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34
Q

What antibiotic is used to treat staph. aureus infection?

A

FLUCLOXACILLIN

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35
Q

What can be used to treat MRSA?

A

Doxycycline
Co-trimoxazole
Clindamycin

if bloodstream involved = Vancomycin

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36
Q

If a patients blood cultures are consistently showing positive staph epidermidis, what must you consider?

A

Infection from an artificial material in the body

e.g. new heart valve, catheter, IV line

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37
Q

What skin problems can staph. aureus infection cause?

A
  • Boils and Carbuncles
  • Minor skin sepsis (infected cuts etc.)
  • Cellulitis
  • Infected eczema
  • Impetigo
  • Wound infection
  • Staphylococcal scalded skin syndrome
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38
Q

Is streptococcus aerobic or anaerobic?

A

Aerobic (and facultatively anaerobic)

=> grows best in air, but can grow without

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39
Q

What skin conditions can be caused by group A streptococcus?

A
  • Infected eczema
  • Impetigo
  • Cellulitis
  • Erysipelas
  • Necrotising fasciitis
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40
Q

What is necrotising fasciitis?

A

Bacterial infection spreading along fascial planes below skin surface →rapid tissue destruction

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41
Q

How do we differentiate between the two types of necrotising fasciitis?

A

Type 1 –mixed anaerobes and coliforms, usually postabdominal surgery

Type II –Group A Strep infection

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42
Q

How is necrotising fasciitis usually managed?

A

Surgical removal and antibiotics

Based on organisms isolated from tissue taken at operation

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43
Q

What is ‘Tinea’ the latin word for? And therefore what does ‘Tinea Pedis’ mean?

A

Tinea = ringworm (aka a FUNGAL infection)

Tinea pedis (athlete’s foot)

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44
Q

Describe the pathogenesis of a Dermatophyte (fungal infection)

A
  • Fungus enters soggy skin
  • Hyphae spread in keratin layer
  • Infects keratinised tissues only (skin, hair, nails)
  • Increased epidermal turnover => scaling
  • Inflammatory response
  • Hair follicles and shafts invaded
  • Lesion grows outwards/ heals in centre
    => “ring” appearance
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45
Q

Who is more commonly affected by ringworm infections and where?

A

Males more commonly affected (Foot and groin)

Scalp ringworm mainly affects children

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46
Q

What sources of fungal infection are there?

A

Other infected humans (anthropophilic)

Animals (cats, dogs, cattle) (zoophilic fungi)

Soil (geophilic fungi)

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47
Q

What organisms are most likely to cause a ringworm?

A

Trichophyton rubrum

Trichophyton mentagraphytes

48
Q

What investigations can be done to test for fungal infections?

A

Woods light (fluorescence)
Skin scrapings, nail clippings, hair
=> Send to lab for microscopy and culture (2 weeks)

49
Q

How should fungal infections be treated?

A

Small areas of infected skin, nails – Clotrimazole

Topical nail paint - amorolfine

Extensive skin/nail/scalp infections:

  • Terbinafine orally
  • Itraconazole orally
50
Q

Where does candida usually cause infection?

A

Candida causes infection in skin folds where area is warm and moist

Seen under the breasts in females, groin areas, abdominal skin folds etc, nappy area in babies

51
Q

What investigation can diagnose candida?

A

Skin swab for culture

52
Q

What is used to treat a candida skin infection?

A

clotrimazole cream

oral fluconazole

53
Q

What is the scabies incubation period?

A

Incubation period up to 6 weeks

54
Q

How does scabies usually present?

A

Intensely itchy rash affecting finger webs, wrists, genital area

55
Q

What treatments are used in scabies?

A

malathion lotion, applied overnight to whole body and washed off next day

benzyl benzoate (avoid in children)

56
Q

What is a pediculosis and therefore what is Pediculus capitis?

A

Pediculosis = louse

=>Pediculus capitis = head louse

57
Q

What is used to treat lice?

A

Malathion lotion (due to extreme itch)

58
Q

If a patient with exfoliative skin conditions sheds huge numbers of scales and bacteria into the environment, why is this issue?

A

Infection control

Gm positive bacteria in the shedding can survive in the environment due to its cell wall structure
=> can infect other patients

59
Q

What conditions does Varicella Zoster Virus cause?

A

Chickenpox (varicella) singles (zoster/ Herpes Zoster)

60
Q

Describe the morphology of the lesions in chickenpox and how they change over time

A

Macules -> papules -> vesicles -> scabs -> recovery

61
Q

Where are chickenpox lesions usually found on the body?

A

centripetal (more dense in the centre of body i.e. trunk)

62
Q

What other symptoms can occur with a chickenpox rash?

A

inflamed skin
Fever
Itch

63
Q

What are the secondary complications of chickenpox infection?

A
  • secondary bacterial infection
  • pneumonitis
  • haemorrhagic rash
  • scarring
  • encephalitis
64
Q

What can predispose to a more severe chickenpox infection?

A
  • extremes of age

- immunosuppression

65
Q

What is the cause of neonatal chickenpox?

A

secondary to chickenpox in pregnant mother developed roughly 5 days before delivery

if mother hasn’t had it before delivery, an injection to prevent it can be given

66
Q

Describe the difference in distribution between chickenpox and shingles

A

Chickenpox = widespread

Shingles = in a specific dermatome

67
Q

Who is most likely to reactivate the varicella zoster virus in order to develop shingles?

A

Elderly and immunocompromised

68
Q

Describe the morphology of the lesions in shingles

A

Tingling/pain -> erythema -> vesicles -> crusts

69
Q

If neuralgic pain due to shingles lasts more than 4 weeks, what is this called?

A

Post Herpetic Neuralgia

70
Q

Who does post hepatic neuralgia most commonly affect?

A
  • elderly patients

- patients who get shingles in the trigeminal dermatome

71
Q

Is scarring of the skin common in shingles?

A

No

72
Q

How is ophthalmic zoster usually managed?

A

Ophthalmic division of trigeminal nerve = affected => affects eye and surrounding area

Tx = Urgent ophthalmic referral indicated

73
Q

What other trigeminal distributions can shingles present in?

A

Ophthalmic division
Maxillary division
Mandibular division

74
Q

When is it possible for ophthalmic zoster to occur in children?

A
  • if chickenpox is caught in utero

- if child becomes immunocompromised

75
Q

What is Ramsay-Hunt syndrome?

A
  • Vesicles and pain in ear canal and throat
  • Facial palsy (7th nerve palsy)
  • Irritation of the 8th cranial nerve
    => Deafness
    => Vertigo
    => Tinnitus (ringing/buzzing)
76
Q

What type of vaccine is available for chickenpox?

A

Live attenuated vaccine

77
Q

Who is the chickenpox vaccine used for?

A

Children in some countries (NOT UK)

Used in susceptible health care workers

Used in high titre to reduce impact of shingles in elderly
UK: routinely in 70 year olds

78
Q

Describe the appearance of herpes simplex virus

A

Blistering rash at vermillion border

Can be spread:

  • herpetic whitlow (finger)
  • eczema herpeticum (this can be life threatening)
79
Q

What Type of Herpes Virus causes oral and genital lesions?

A

Type 1

80
Q

What Type of Herpes Virus causes only genital herpes?

A

Type 2

81
Q

What antiviral can be used to treat herpes?

A

Aciclovir

incorporated into viral DNA inhibiting replication

Does not eliminate latent virus

82
Q

When are antibody tests used as opposed to swabbing the site of viral infection?

A

where virus infected site is inaccessible

83
Q

What infections can cause erythema multiforme?

A

Herpes simplex virus

Mycoplasma pneumoniae bacterium

84
Q

Describe the morphology of the lesions seen in Molluscum contagiosum

A

Fleshy, firm, umbilicated, pearlescent nodules

1 to 2 mm diameter

85
Q

How long does it usually take for Molluscum Contagiosum to disappear?

A

Self limiting but take months to disappear

86
Q

Is Molluscum Contagiosum more common in adults or children?

A

Children

87
Q

How is Molluscum Contagiosum sometimes transmitted?

A

Sexual transmission

88
Q

What can be used to treat Molluscum Contagiosum?

A

local application of liquid nitrogen

89
Q

What skin manifestations are caused by Human papilloma virus (HPV)?

A

Warts and verrucas

90
Q

What is used to treat warts and verrucas?

A

Topical salicylic acid

91
Q

What other illnesses can be caused by HPV?

A

Genital warts
Cervical cancer
Head and neck cancer

92
Q

What types of HPV usually cause genital warts?

A

HPV Types 6 and 11

93
Q

What types of HPV usually cause cervical cancer?

A

HPV types 16 and 18

94
Q

What is herpangina?

A

Blistering rash at back of mouth

Caused by enterovirus not herpes virus

  • coxsackie virus
  • echovirus
95
Q

How is herpangina diagnosed?

A

Swab of lesion

sample of stool for enterovirus PCR

96
Q

What viruses usually cause family outbreaks of hand, foot and mouth disease?

A

Enteroviruses (especially coxsackie viruses)

97
Q

What virus causes “slapped cheek” syndrome?

A

erythrovirus (parvovirus B19)

98
Q

What type of rash develops after “slapped cheek” disappears?

A

lacy macular rash on the body appears

In adults:
rash may be absent
acute polyarthritis of the small joints eg hands

99
Q

What other complications does Parvovirus B19 cause?

A
  • spontaneous abortion
  • Aplastic crises
    • sudden drop in haemoglobin (important in patients
      with RBC disorders eg. Leukaemia)
  • Chronic anaemia
    (in immunosuppressed patients)
100
Q

How is parvovirus B19 diagnosed?

A

parvovirus B19 IgM test

Not skin swab!

101
Q

What is Orf and how is it diagnosed?

A

Virus of sheep “scabby mouth”

Firm, fleshy nodule on hands of farmers

Clinical diagnosis, lab confirmation not used

102
Q

Describe the appearance of a primary syphilis infection

A

Painless ulcers at site of entry

103
Q

Describe what occurs in a secondary syphilis infection

A
  • Red rash over body
  • especially soles of feet and palms of hands
  • Mucous membrane “snail track” ulcers
104
Q

What body systems become involved in a tertiary syphilis infection?

A

CNS, cardiovascular, gummatous

105
Q

What bacteria is sexually transmitted in order to cause syphilis?

A

Treponema pallidum

106
Q

How is syphilis diagnosed?

A

Diagnosis by blood test or swab of ulcer for PCR

107
Q

What is used to treat syphilis?

A

injections of penicillin

108
Q

Is syphilis a bacterial, fungal or viral infection?

A

Bacterial

109
Q

What is known to cause Lyme’s disease?

A

Ticks

Bacteria = Borrelia burgdorferi

110
Q

How does Lyme’s disease present?

A

Early: erythema migrans
Late: heart block, nerve palsies, arthritis

111
Q

What antibiotics are used to treat lyme’s disease?

A

doxycycline or amoxicillin

112
Q

Out of everyone who becomes infected by the Zika virus, how many actually become ill?

A

1 in 5 people

113
Q

When do symptoms of Zika infection usually start and subside?

A

Symptom onset: 3–12 days after exposure

Symptoms resolution: 2–7 days after onset

114
Q

What are the symptoms of Zika virus?

A 
Mild fever
Rash (mostly maculopapular)
Headaches
Arthralgia
Myalgia
Non-purulent conjunctivitis
115
Q

What helps to spread Zika virus?

A

Mosquito

Sexual transmission also seen person to person

116
Q

Name 2 severe complications of Zika virus

A

Microcephaly

Guillain Barré syndrome

Dermatology (18 decks)

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