Microbiology

Question 1

What is virulence?

Answer 1

The capacity of a microbe to cause damage to the host

Question 2

What is the pathogenesis of bacteria entering a host cell?

Answer 2

1) Host contact, colonisation, adheres and invades
2) Evade host defences
3) Multiply/ complete its life cycle
4) Exit host- host is undamaged

Question 3

Name some virulence factors

Answer 3

Adhesin, Invasin, Impedin, Aggresin, Modulin

Question 4

In relation to virulence factors, what is an adhesion?

Answer 4

• Enables binding of the organism to host tissue
• Specific adhesions determines differences in strains
• Contributes to the ability to colonise

Question 5

In relation to virulence factors, what is an invasin?

Answer 5

-Enables the organism to invade a host cell/tissue

Question 6

In relation to virulence factors, what is an impedin?

Answer 6

-Enables the organism to avoid host defence mechanisms

Question 7

In relation to virulence factors, what is an aggressin?

Answer 7

-Causes damage to the host directly

Question 8

In relation to virulence factors, what is a modulin?

Answer 8

-Induces damage to the host indirectly

Question 9

What percentage of people carry Staph Aureus permanently and what percentage transiently?

Answer 9

• 10-20% permenantly

- 40-60% transiently

Question 10

How specific are nosocomial strains of Staph Aureus?

Answer 10

They can be traced back to individual patients e.g. MRSA

Question 11

How does community acquired Staph Aureus tend to present?

Answer 11

-Abscess and rash

Question 12

How does nosocomial acquired Staph Aureus tend to present?

Answer 12

-Immunocompromised, more difficult to treat, very flexible organisms

Question 13

How does each organism cause a differing range of effects?

Answer 13

Not every strain carries every virulence factor

Question 14

What is Panton Valentine Leukocidin (PVL)?

Answer 14

• A cytotoxin, Beta pore forming toxins from Staph Aureus

- It has a specific toxicity for leukocytes and attacks WBCs

Question 15

What is toxic shock syndrome?

Answer 15

-One of the virulence factors of Staph Aureus, super antigens

Question 16

What is associated with Toxic Shock Syndrome?

Answer 16

Fever, hypotension, 3 organs involved

Question 17

What is Necrotising Pneumonia and what causes it?

Answer 17

• Rapid progression, multi-organ failure

- Caused by PVL and alpha exotoxin from Staph Aureus

Question 18

What are the virulence factors specific to Staph Aureus?

Answer 18

-Adhesins, PVL, Superantigens (TSST-1)

Question 19

What is the major of adhesins in Staph Aureus?

Answer 19

90% are joints, fibrinogen binding protein

Question 20

What 3 skin infections are associated with Strep pyrogenes?

Answer 20

Impetigo, Cellulitis (Erysipelas), Necrotising fasculitis

Question 21

What is cellulitis?

Answer 21

Deeper skin infection in the dermis that is not associated with necrosis

Question 22

What is erysipelas?

Answer 22

• Similar to cellulitis, infection of upper dermis and superficial lymphatics, usually caused by beta haemolytic group A strep
• More superficial than cellulitis, more raised and demarcated

Question 23

What is Impetigo?

Answer 23

• Highly contagious
• Through contact with discharge on the face
• Infection if below the surface

Question 24

What is Necrotising fasciitis?

Answer 24

• “Flesh-eating disease”
• Invasive Strep A strains penetrate mucus membrane and develop in lesions
• Rapidly destroys connective tissue

Question 25

What is the Lancefield System?

Answer 25

- Sereotyping of cell wall carbohydrate | - Major sereotypes are A-H and K-V

Question 26

What are the major M protein antigens in the Lancefield System?

Answer 26

M1+ M3= major sereotype | M3+ M18= severe invasive disease

Question 27

What are the differences in presentation of Toxic Shock Syndrome in Staph Aureus and Strep Pyrogenes?

Answer 27

Staph Aureus - Localised infection - No bacteremia - Menstral TSST-1 - Non menstral SEB or SEC - Pyrogenic Toxin - Virulence factor Strep Pyrogenes - Invasive disease - Spec A and Spec C (most common toxin) - Pyrogenic toxin - Virulence factor

Question 28

What antibiotic should be used in Staph Aureus infections?

Answer 28

Flucloxacillin

Question 29

Give 3 examples of toxins produced by Staph Aureus

Answer 29

Enterotoxin (food poisoning) SSSST (staph scalded skin syndrome toxin) PVL (panton Valentine Leukocidin)

Question 30

What is the organism which causes urinary tract infections in women of child-bearing age?

Answer 30

Staph saprophyticus

Question 31

Name a toxin produced by Beta Haemolytic Streptococci

Answer 31

Haemolysin

Question 32

What does group A and group B Beta haemolytic Streptococci cause?

Answer 32

Group A: throat, severe skin infections | Group B: meningitis in neonates

Question 33

What is the difference between resident bacterial flora and transient bacteria?

Answer 33

Resident: organism can be deep in hair follicles and hard to wash away Transient: can get rid of with hand washing

Question 34

Give examples of bacterial skin infections that Staph Aureus can cause

Answer 34

``` Boils and Carbuncles Cellulitis Infected eczema Impetigo Wound infection Staphylococcal scalded skin syndrome ```

Question 35

What is the difference between a boil and a carbuncle?

Answer 35

Boil: skin is traumatically pulled out of follicle Carbuncle: Deeper infection, ofter at the nape of the neck at the hair line. Requires oral flucloxacillin

Question 36

What is impetigo?

Answer 36

- Contagious superficial infection caused by Staph Aureus - Lesions well defined and start around nose and face with honey coloured crusts on erthyematous base - Usually seen in children aged 2-5 years

Question 37

What is cellulitis?

Answer 37

- Acute infection of skin and soft tissue - Caused by staph aureus and group A Beta haemolytic strep - Deeper and less well defined than Erysipelas

Question 38

What is Staphylococcal Scalded Skin?

Answer 38

- Widespread formation of fluid filled blisters that are thin walled and easily ruptured - Most common in neonates - Agressive antibiotics and rehydration due to loss of fluid due to weeping of skin - Mucous membranes are spared

Question 39

What is Erysipelas?

Answer 39

- Sharply defined superficial infection caused by Strep pyrogenes - Often affects the face, unilateral, with increased WBC and fever - Systemic Penicillin