Microbiology

Question 1

Are staphs generally coagulase negative or positive and which is the exception?

Answer 1

Generally coagulase negative however S. aureus is coagulase positive

Question 2

Which bacteria may be commensals of the skin?

Answer 2

Staph. aureus
Staphylococcus epidermidis
Corynebacterium sp. (diphtheroids)
Propionibacterium

Question 3

What is the antibiotic of choice for Staph aureus?

Answer 3

Flucloxacilin

Question 4

What drugs ill work against MRSA strains?

Answer 4

Doxycycline
Co-trimoxazole
Clindamycin
Vancomycin
Linezolid (toxic reserve antibiotic)

Question 5

Which kinds of toxins can different strains of S. aureus produce?

Answer 5

Enterotoxin = food poisoning
SSSST
PVL = panton valentine leukocidin

Question 6

Describe Staphylococcus sp.

Answer 6

Gram positive cocci in clusters
Aerobic and facultatively anaerobic
2 imp. types are Staph aureus and coagulase negative Staph

Question 7

Describe coagulase negative staphs

Answer 7

Skin commensals that are not usually pathogenic.

Example is Staph. epidermidis

Question 8

When may coagulase negative staphs cause infectoin

Answer 8

In association with implanted artificial material

Question 9

Describe Streptococcus sp.

Answer 9

Gram positive cocci in chains
Aerobic and facultatively anaerobic
Classified initially by haemolysis in blood

Question 10

Which toxin is produced by beta haemolytic streptococci?

Answer 10

Haemolysin

Question 11

Which serological group that beta haemolytic are further broken down into is important in skin?

Answer 11

Group A

Expample: Strep pyogenes

Question 12

What are the 2 important categories of alpha haemolytic streptococci?

Answer 12

Strep. pneumoniae

Strep. viridans group

Question 13

Non-haemolytic streptococci are commensals of where?

Answer 13

The bowel

Question 14

What bacterial skin infections can strep pyogenes cause?

Answer 14

Infected eczema
Impetigo
Cellulitis
Erysipelas
Necrotising fasciitis

Question 15

What will Strep. pyogenes be treated with?

Answer 15

Penicillin

Flucloxacillin will often be used as it also covers Staph. aureus

Question 16

What is necrotising fasciitis?

Answer 16

A bacterial infection spreading long fascial planes below the skin causing rapid tissue destruction

Question 17

What are the 2 types of necrotising fasciitis?

Answer 17

Type 1 - mixed anaerobes and coliforms

Type 2 - Group A Strep

Question 18

When should swabs of leg ulcers be taken?

Answer 18

Only if sign of cellulitis or infection are present

Skin has many commensals so treat the ulcer not the lab result

Question 19

What tissues do dermatophytes infect?

Answer 19

Keratinised tissues only

Skin, hair, nails

Question 20

Describe Dermatophyte pathogenesis

Answer 20

Fungus enters abraded soggy skin
Increases epidermal turnover and provokes inflammatory response in the dermis
grows outward and heals in centre giving ring-like appearance

Question 21

What are the sources of dermatophyte infection?

Answer 21

Other infected humans (most likely)
Animals
Soil (less common in UK)

Question 22

What are the man dermatophyte causal organisms?

Answer 22

Trichophyton rubrum (~70%)
Trichophyton mentagraphytes (~20%)
Microsporum canis

Question 23

How is diagnosis of dermatophyte infections made?

Answer 23

Clinical appearance
Woods light
Skin scraping for microscopy and culture

Question 24

How is dermatophyte infection treated?

Answer 24

Topical cream such as clotrimazole
Nail paint like amorolfine
Terbinafine or itraconazole orally for more extensive cases

Question 25

Where does candida cause infection?

Answer 25

In skin folds were it is warm and moist

Question 26

How is candida diagosed?

Answer 26

Swab for culture

Question 27

What is scabies caused by?

Answer 27

Sarcoptes scabiei

Question 28

How does scabies present?

Answer 28

Intensely itch rash affecting finger webs, wrist and genital area

Question 29

What is the incubation period of scabies?

Answer 29

Up to 6 weeks

Question 30

How is scabies treated?

Answer 30

``` Malthion lotion applied over night to whole body, washed off next day Benzyl benzoate (avoid in children) ```

Question 31

What causes chicken pox and shingles?

Answer 31

Varicella zoster virus

Question 32

Explain the progression of chickenpox

Answer 32

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

Question 33

What can cause chicken pox to be denser?

Answer 33

Already inflamed skin

Question 34

What can pre-dispose to serious chickenpox?

Answer 34

Extremes of age | Immunosuppression

Question 35

What causes neonatal VZV

Answer 35

Maternal chickenpox late in pregnancy

Question 36

How does shingles present?

Answer 36

The reactivation of VZV in a dermatomal distribution | Stars with tingling pain

Question 37

What is the nature of zoster related pain?

Answer 37

Neuralgic

Question 38

Which dermatomes is shingles typical in in adults?

Answer 38

T or L dermatomes

Question 39

Which dermatomes is shingles typical in in children?

Answer 39

Face of S dermatome

Question 40

What is Ramsay Hunt syndrome?

Answer 40

Shingles infection affecting the facial nerve, can result in facial palsy

Question 41

How can shingles be prevented?

Answer 41

Higher titre of chickenpox vaccine can reduce the impact | Routinely given to 70 year olds

Question 42

What does HSV type 1 cause?

Answer 42

Recurrent cold sores typically at the vermilion border

Question 43

What is herpetic whitlow?

Answer 43

Cold sore where nail meets finger

Question 44

What is used as VZV and HSV therapy?

Answer 44

Aciclovir

Question 45

Does aciclovir eliminate latent virus?

Answer 45

It does not eliminate latent virus

Question 46

How does erythema multiforme present?

Answer 46

As target lesions with erythema shown

Question 47

How does molluscum contagiosum present?

Answer 47

Fleshy, firm, umbilicated, pearlescent nodules

Question 48

Erythema infectiosum is also known as what?

Answer 48

Slapped cheek disease

Question 49

What causes Erythema infectiosum?

Answer 49

Parovirus B19

Question 50

What are the complications of Erythema infectiosum?

Answer 50

Spontaneous abortion Aplastic crisis Chronic anaemia in immunosuppressed patients

Question 51

How is erythema infectiosum confirmed?

Answer 51

Antibody testing | Parovirus B19 IgM

Question 52

What is Orf?

Answer 52

Virus of sheep Firm fleshy nodules in hands Self-limiting

Question 53

Is lab confimation necessary for Orf?

Answer 53

No, clinical diagnosis is made

Question 54

How does primary infection of syphilis manifest?

Answer 54

Chancre | Painless ulcer at site of entry

Question 55

How does secondary infection of syphilis manifest?

Answer 55

Red rash over body, prominent on soles of feet and palms | "Snail track" ulcers on mucous membranes

Question 56

What is the vector for Lyme disease?

Answer 56

Ticks

Question 57

What pathogen causes Lyme disease?

Answer 57

Borrellia burgdorfi | Bacterial

Question 58

What is the early presentation of Lyme disease?

Answer 58

Erythema migrans

Question 59

What is the late presentation of Lyme disease?

Answer 59

Heart block Nerve palsies Arthritis

Question 60

What is the therapy for Lyme disease?

Answer 60

Doxycycline or Amoxicillin

Question 61

How many people infected with Zika virus become ill

Answer 61

~ 1 in 5

Question 62

What are the symptoms of Zika virus?

Answer 62

``` Fever Mild rash Headaches Arthralgia Conjunctivitis Presentation similar to dengue ```

Question 63

What are complications of Zika virus?

Answer 63

Microcephaly | Guillain Barre Syndrome

Question 64

What causes Toxic Shock Syndrome?

Answer 64

TSS toxin producing Staph aureus

Question 65

How does toxic shock syndrome present?

Answer 65

Fever Hypotension Diffuse macular erythematous rash followed by desquamation of the skin

Question 66

What is a super-antigen of S. aureus?

Answer 66

TSST-1

Question 67

What are important virulence factors of group A streptococci?

Answer 67

M surface proteins

Question 68

Why are M surface proteins important virulence factors in group A streptococci?

Answer 68

They inhibit opsonisation

Question 69

What is a super antigen of Strep. pyogenes?

Answer 69

Pyrogenic exotoxins | Produced by lysogenic strains