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Dermatology > Skin microbiology > Flashcards

Skin microbiology Flashcards

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Dermatology Board Prep flashcards
1
Q

How can staph. aureus be distinguished from other staphylococcal types and why?

A

Staph. aureus is coagulase positive - will coagulate at the bottom of a test tube

Also shows up golden on an agar plate

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2
Q

What property is unique to staph. aureus (compared to other staphylococcus)?

A

Produces enzymes including coagulase, an enzyme that causes clots to form

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3
Q

What are examples of toxins produced by staph. aureus?

A

Enterotoxin (food poisoning)

Staph. scalded skin syndrome toxin

Panton Valentine Leukocidin (MRSA)

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4
Q

Which bacteria is likely to stick to prosthetic materials in the body and why?

A

Staph. epidermidis

Produces a ‘slime’ that allows it to stick to these materials

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5
Q

Which species of staphylococcus causes UTIs in women of child-bearing age?

A

Staph. saprophyticus

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6
Q

What are the characteristics of beta-haemolytic streptococci?

A

Pathogenic

Produce toxins including haemolysin

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7
Q

What kind of infections are caused by group A beta-haemolytic bateria?

A

Throat infections

Severe skin infections

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8
Q

What kind of infections are caused by group B beta-haemolytic streptococci?

A

Meningitis in neonates

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9
Q

What are the characteristics of non-haemolytic streptococci?

A

Enterococcus species (E. faecalis, E. faecium)

Commensals of bowel

Common cause of urinary tract infection

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10
Q

What skin infections does staph. aureus cause?

A

Boils and Carbuncles

Other minor skin sepsis (infected cuts etc.)

Cellulitis

Infected eczema

Impetigo

Wound infection

Staphylococcal scalded skin syndrome

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11
Q

What skin infections does strep. pyogenes cause?

A

Infected eczema

Impetigo

Cellulitis

Erysipelas

Necrotising fasciitis – (N.B. may also be caused by mixed bacterial infection)

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12
Q

What does tinea mean?

A

Ringworm

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13
Q

How does tinea infection occur?

A

Fungus infection enters soggy/abraded skin

Hyphae spread in stratum corneum

Increased epidermal turnover causes scaling

Inflammatory response provoked (dermis)

Hair follicles and shafts invaded

Lesion grows outward and heals in centre, giving a “ring” appearance

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14
Q

Where does tinea infection occur?

A

Only occurs on keratinised surfaces e.g. nails, hair, body

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15
Q

Are males or females more commonly affected by ringworm?

A

Males

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16
Q

Which patients does scalp ringworm mainly affect?

A

Children

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17
Q

Which patients does foot and groin ringworm tend to affect?

A

Male patients

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18
Q

Which is the most common causal organism of dermatophytes?

A

Trichophyton rubrum

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19
Q

How is fungal infection of the skin diagnosed?

A

Clinical appearance

Woods light (fluorescence)

Skin scrapings, nail clippings, hair

Send to laboratory in a “Dermapak” for microscopy and culture (N.B. culture takes 2 weeks)

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20
Q

How should small areas of fungally infected skin/nails be treated?

A

Clotrimazole (Canestan) cream or similar

Topical nail paint (amorolfine)

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21
Q

How should extensive fungal skin nfection or scalp infection be treated?

A

Terbinafine orally

Itraconazole orally

22
Q

Which areas of the body are usually affected by scabies?

A

Finger webs

Wrists

Groin

23
Q

What is the treatment for scabies?

A

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

Benzyl benzoate (avoid in children)

24
Q

What is the treatment for lice?

A

Malathion

25
Q

What are some of the complications of chickenpox?

A

Secondary bacterial

Pneumonitis

Haemorrhagic

Scarring

Encephalitis

26
Q

Which skin diseases are due to varicella zoster virus?

A

Chickenpox
Shingles

27
Q

A 26-year-old man presented with a 5-day history of cough, fever, and mild dyspnea

He had an exanthematous vesicular rash that had started 3 days before the respiratory symptoms began

He smoked cigarettes (30 per day for the previous 14 years)

His daughter had recently had chickenpox; he had not been vaccinated against the disease nor did he have a history of it

A skin examination revealed a polymorphic rash with vesicles, pustules, and crusty lesions

On Xray: multiple small nodules in both lungs

On CT: no liver or CNS involvement

What is the diagnosis?

A

Varicella pneumonia/chickenpox

This diagnosis was made on the basis of the rash, pulmonary symptoms, and contact with a child with chickenpox

28
Q

How is development of chickenpox in the neonate prevented?

A

Prevention with Varicella Zoster Immune Globulin in susceptible women in contact

29
Q

How does shingles present?

A

Dermatomal distribution

Tingling pain

Erythema

Vesicles

Crust

30
Q

In which patients is the incidence of shingles highest?

A

Elderly

Immunocompromised

31
Q

What is the diagnosis here and the management?

A

Opthalmic shingles/zoster (see involvement of tip of nose)

Requires urgent referral to opthalmology

32
Q

Which nerve is involved in opthalmic zoster?

A

Opthalmic division of trigeminal nerve

33
Q

What are the features of Ramsay-Hunt syndrome?

A

Facial nerve palsy

Vestibulocochlear nerve irritation - deafness, vertigo, tinnitus

Vesicles and pain in auditory canal and throat

34
Q

What is Ramsay-Hunt syndrome?

A

Geniculate or otic herpes zoster

35
Q

What is the diagnosis here?

A

Primary gingivostomatisis - herpes simplex infection

36
Q

Which patients are affected by primary gingivostomatitis and how long does it last?

A

Pre-school children

Ulceration lasts around a week

37
Q

What are the characteristics of type 1 herpes simplex virus?

A

Main cause of oral lesions
Causes half of genital herpes
Causes encephalitis

38
Q

What are the characteristics of type 2 herpes simplex virus?

A

Rare cause of oral lesions
Causes half of genital lesions
Encephalitis / disseminated infection (particularly in neonates)

39
Q

What is the treatment for herpes simplex virus and varicella zoster virus?

A

Aciclovir

40
Q

Does aciclovir affect latent viruses?

A

No

41
Q

How does aciclovir work?

A

It is selectively incorporated into viral DNA, inhibiting replication

42
Q

What are the nodules in molluscum contagiosum like?

A

Fleshy, firm, umbilicated, pearlescent nodules

1 to 2 mm diameter

43
Q

How can molluscum contagiosum be treated?

A

Usually self-limiting but can take months to disappear

Local application of liquid nitrogen

44
Q

What is herpangina?

A

A blistering rash of the back of the mouth

45
Q

What organism causes herpangina?

A

Enterovirus:
Coxsackie virus
Echovirus

46
Q

What is slapped cheek disease and what causes it?

A

Erythema infectiosum

Caused by parovirus B19

47
Q

What does slapped cheek disease look like?

A

Erythematous rash on the cheeks

As the rash on the face fades a lacy macular rash on the body appears

In adults rash may be absent and an acute polyarthritis of the small joints eg of the hands may be more prominent

48
Q

How is parovirus confirmed in the lab?

A

Parvovirus B19 IgM test

49
Q

. A 23-year-old woman presented to the emergency department after 1 day of fever, sore throat, arthralgia, and rash

Diffuse erythema (Panel A) that blanched on pressure was noted over the face, neck, trunk, and arms, along with posterior cervical lymphadenopathy

The next day, the fever and rash subsided, but she reported pain in the oral cavity

Examination revealed petechial hemorrhages on the soft palate (Panel B) that disappeared spontaneously in 2 days

She had no history of rubella vaccination

What is the diagnosis and what would show up on lab tests?

A

Testing for rubella IgG antibody was negative, and testing for rubella IgM antibody was positive, which confirmed the clinical diagnosis of rubella

50
Q

What is the causal organism in syphilis?

A

Treponema pallidum

Dermatology (8 decks)

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