Skin microbiology

Question 1

Which microbe is seen in higher numbers in Bassets?

Answer 1

• Mallassezia (yeast)

- It is also high in WHW, Cockers, Daschunds

Question 2

Define a resident organism

Answer 2

-Can replicate on the skin and can persist

Question 3

Define a nomadic organism

Answer 3

-Can colonise and reproduce on skin for a short time

Question 4

Define a transient organism

Answer 4

-Can NOT replicate so stay for short time

Question 5

List some resident microbes found on dogs

Answer 5

-Skin
Micrococcus spp
Clostridium
Acinetobacter
-Hair
Micrococcus spp
Staphylococcus pseudintermedius 
-Hair follicle
Staphylococcus pseudointermedius
Micrococcus spp

Question 6

List dome transient microbes found on the skin of dogs

Answer 6

• S.aureus
• E.coli
• Staphylococcus pseudinetmedius

Question 7

List some examples of bacteria found on dogs and state is gram positive or negative

Answer 7

• Clostridium= Gram +
• Staphyloococcus= Gram +
• Micrococcus spp= Gram +

Question 8

What would you not expect to find on skin?

Answer 8

-Gram negative bacteria or rods

Question 9

Describe staphylococcus

Answer 9

• Gram positive
• Facultative anaerobes
• Catalase +/ Oxidase -
• S.pseudointermedius CANNOT ferment maltose but s.aureus can

Question 10

Describe penicillin resistance and methicillin

Answer 10

• Penicillin (B-lactam) uses PBP (penicillin binding protein) to work.
• In penicillin resistant bacteria they make B-lactamas which destroys the antibiotics
• People switched to using methicillin which aren’t affected by B lactamases.
• Bcateria then expressed MecA or PBP2 channels which the methicillin cannot bind to therefore it s also resistant to methicillin.

Question 11

With which bacteria is it common to have concurrent infections with malassezia?

Answer 11

S. pseudintermedius

Question 12

Which bacteria causes greasy pig disease?

Answer 12

-Staphylococcus hyicus

Question 13

What effect do superantigens have?

Answer 13

The over activate T lymphocyte and thus bypass the normal process (don’t need the peptide to be presented)
-cause massive cytokine release

Question 14

What are the primary causes that can lead to proliferation of commensal microbes?

Answer 14

• Hypersensitivity
• Systemic disease
• Damage leading to compromise of defences

Question 15

Define a secondary infection

Answer 15

-When defences are compromised by an existing condition allowing further organisms that wouldn’t normally cause a problem cause infection.

Question 16

List a common infection found in the following species dog, cattle, pig, sheep, horse

Answer 16

• Dog= Staphylococcus intermedius
• Cattle= Dermatophysis (ringworm)
• Pig= greasy pig disease Staphylococcus hyicus
• Horse= Mud fever, dermatophilus

Question 17

Discuss the pathogenicity of staphylococcus

Answer 17

• Pyogenic (pus forming)

- Virulence factors: coagulase, lipases, protein A (inhibits opsonisation)

Question 18

Describe dermatophysis

Answer 18

• AKA ringworm
• Grows ONLY in kertinised non living tissue of skin and nails
• Causes inflammation and irritation
• Most common in cattle= Trichopyton verrucosum
• Commonly affects young stock

Question 19

Name a dimorphic yeast species that produces a capsule

Answer 19

Cryptococcus

Question 20

What medium is normally used in fungal cultures of dermatophytes?

Answer 20

Dermatophyte test medium

Question 21

What is wood’s lamp?

Answer 21

Some dermatophytes produce metabolites which fluoresce green when immulinated by the lamp.

Question 22

What is a trichogram?

Answer 22

A microscopic exam of a plucked hair

Question 23

How do you take a skin scrape?

Answer 23

Use a scalpel blade coated with mineral oil and scrape along skin

Question 24

What is a common fungal stain?

Answer 24

Lactophenol cotton blue