T4L3 - Professional Pathogen

Question 1

Infection

Answer 1

Organism enters body and multiples -> damage host in process (invasion, replication and damage)

Question 2

Colonisation

Answer 2

Organism lies on body (outside) - NO infection

Question 3

Pathogen

Answer 3

Organism which causes infection (evade immune defences)

Question 4

Commensal

Answer 4

Organism lives on us/in gut - NO infection

Question 5

Symbiosis

Answer 5

Mutual benefit

Question 6

Parasite

Answer 6

Unequal

Question 7

Professional Pathogen vs Opportunistic pathogen

Answer 7

Professional pathogens: almost always cause disease

Opportunistic pathogens: only cause disease in immunocompromised patients

Question 8

Pathogenicity depends on

Answer 8

Probability of organism causing disease once isolated
Virulence - fundamental property
Immune state of patient
Location

Question 9

Pathogen vs commensal

Answer 9

Immune status of patient
Site/sample in question
Disease causing properties of bacteria

Question 10

Sterile??

Answer 10

Blood, urine (normally sterile)

Stool, throat (not normally sterile)

Question 11

Staphylococcus aureus overview [3]

Answer 11

Commensal of anterior nares
20-60%
Highly adapted: species & nose

Question 12

Staphylococcus aureus virulence

Answer 12

Adhesins - bind host proteins
Tissue adherence and immune evasion

Protein A - Binds Fc portion of immunoglobulins

Question 13

Staphylococcus aureus binding proteins

Answer 13

Elastin
Collagen
Fibronectin

Clumping factor
Coagulase
Protein A
Enterotoxin B

Question 14

Coagulase [3]

Answer 14

Stimulate clotting
Role in immune evasion
Bacteria added to sheep serum

Question 15

Staphyloccocal toxins

Answer 15

Cytotoxins
Exfoliative toxins
Enterotoxins

Question 16

Cytotoxins

Answer 16

Pore forming toxins, lyse host cells

Panton-valentine leukocidin (PVL) – lyses polymorphs

Question 17

Exfoliative toxins

Answer 17

Proteases

Target epidermal structural proteins

Question 18

Enterotoxins (superantigens)

Answer 18

Stimulate massive T cell activation ?immune evasion

Ingestion → vomiting

Question 19

Staphylococcal capsule

Answer 19

Antibodies can’t bind to antigens - peptidoglycans etc

Binding of cell wall opsonins to complement receptors and FcRs is prevented by capsule

Question 20

S. aureus skin infections

Answer 20

Furunculosis
Staph abscess
Impetigo

Question 21

S.aureus infection

Answer 21

• Normal commensal
	• Pathogen in skin / soft tissue infections
	• Surgical site infections
	• Vascular line related infections
	• Bacteraemia – commonest cause
		• Endocarditis
		• Osteomyelitis
		• Septic arthritis
Almost anywhere else

Question 22

Food poisoning

Answer 22

S. aureus enterotoxins
Ingestion →
Rapid brief illness, Vomiting +++ & Minimal diarrhoea

Contamination of food

• Manufacture
• Preparation

Question 23

Gram positive and Gram negative virulence

Answer 23

Gram positive
Thick peptidoglycans layer
Lipoteichoic and teichoic acid

Gram negative
Outer membrane
Lipopolysaccharide
Proteins and pores
Thin peptidoglycans
Inner membrane

Question 24

Lipopolysaccharide recognition

Answer 24

Innate immune system VERY SENSITIVE to LPS

LPS interact with TLRs (TLR4) on monocyte/macrophage/endothelium)

Question 25

Lipopolysaccharide results in activation of

Answer 25

Results in activation of
Inflammatory pathways
Coagulation and clotting pathways
Changes in endothelial integrity

Question 26

Lipoteichoic acid / Peptidoglycans recognition

Answer 26

Gram positive bacteria don’t have endotoxin

Cell wall components: Lipoteichoic acid
and Peptidoglycans

Can stimulate immune responses just like LPS
Different Toll-like receptors

Question 27

Meningococcal pathogenicity

Answer 27

Adhesins: Respiratory epithelium& Meninges

Lipopolysaccharide
Capsule