bacterial pathogenesis and infectious disease

Question 1

what are the different shapes of bacteria?

Answer 1

• cocci- round
• bacilli- rods
• spirals
• vibrio

Question 2

what do gram positive bacteria stain?

Answer 2

purple

Question 3

what do gram negative bacteria stain?

Answer 3

pink

Question 4

what is the cell wall of gram positive bacteria like?

Answer 4

• thick peptidoglycan layer

- lipoteichoic and teichoic acid layer

Question 5

what is the cell wall of gram negative bacteria like?

Answer 5

• thin peptidoglycan layer
• outer and inner membrane
• lipopolysacharides (lps)
• proteins ad pores

Question 6

What is an example of an obligate aerobe?

Answer 6

clostridium

Question 7

what is an example of an anaerobe?

Answer 7

s.aureus

Question 8

what are the different types of haemolytic streptococci?

Answer 8

• α haemolytic ‘viridans’ streptococci
  These cause partial haemolysis of blood agar and a greenish colour
• β haemolytic streptococci
  These cause complete haemolysis making the blood agar translucent
• γ (non)- haemolytic streptococci

Question 9

what are the different things that confer virulence of the s.aureus infection?

Answer 9

Coagulase
Stimulates clotting
Role in immune evasion
Not expressed by less virulent ‘coagulase negative’ staphs

Adhesins: bind host proteins
- elastin binding protein, collagen protein, fibronectin binding protein

cytotoxins- including cytotoxins, exfoliative toxins and super antigens

Question 10

what is an example of a facultative anaerobe?

Answer 10

e.coli

Question 11

what are the 4 different ways of describing bacteria?

Answer 11

1. staining
2. growth- aerobes vs anaerobes
3. morphology
   - microscopic
   - macroscopic- on agar
4. typing
   - related species
   primary serology
   - correlating genotypes

Question 12

what is a commensal bacteria?

Answer 12

• bacteria which is probably not causing disease when taken from a clinical sample

Question 13

what is a pathogen?

Answer 13

• a bacteria that is probably causing disease when identified from a clinical sample

Question 14

what are the 3 things that make bacteria pathogenic rather than commensal?

Answer 14

1. The immune status of the patient.
2. The site / sample in question.
3. The disease causing properties of the bacteria (virulence).

Question 15

what type of bacteria are streptococcus pyogenes and streptococcus aureus?

Answer 15

gram positive cocci

Question 16

what type of bacteria is e.coli?

Answer 16

gram negative rods

Question 17

when are surface proteins most responsible for virulence in s.aureus?

Answer 17

the exponential phase

Question 18

when are secreted proteins most responsible for virulence in s.aureus?

Answer 18

the stationary phase

- secreted proteins include toxins

Question 19

what does protein A do in s.aureus?

Answer 19

• binds the FC portion of IGg

- involved in immune cloaking

Question 20

what are the actions of adhesin in s.aures?

Answer 20

• tussle addrehence
• for colonisation
• allows deeper infections
• allows immune evasion by cloaking

Question 21

what are the 4 main types of staphylococcal toxin and what are they involved in?

Answer 21

1. cytotoxin
   - PVL lyses polymorphs and has a role in MRSA
2. exfoliative toxins
   - proteases
   - target epidermal structural proteins
3. exotoxins
   - superantigens
   - cause massive Tcell response in toxic shock syndrome
4. enterotoxin
   - ingestion leads to vomiting and diarrhoea

Question 22

what is ritter’s syndrome?

Answer 22

• caused by exfoliative toxin
• serine proteases specific fro desmoglein 1
• causes sheet-like desquamation

Question 23

what are the different ways that s. aureus infections can manifest?

Answer 23

• normal comensal
• soft tissue infection
• vascular line related infection
• bacteremia
• surgical site infections
• toxin mediated infections

Question 24

what are some s.aureus bacteraemia?

Answer 24

• endocarditis
• osteomyelitis
• septic arthritis

Question 25

what type of bacteria is s.epidermsis?

Answer 25

- coagulase negative gram poitive staph | - found normally on skin surface

Question 26

what things can s.epidermis cause when it becomes pathogenic?

Answer 26

- Central venous line infection - Endocarditis (prosthetic valve) - Orthopaedic surgical infections - Foreign material in a ‘sterile’ place grafts, implants etc

Question 27

where do streptococci colonise?

Answer 27

a huge family of Gram positive bacteria which colonise the GI tract and skin

Question 28

what are the 3 ways to classify streptococci?

Answer 28

1. Appearance on blood agar (haemolysis) e. g ‘beta haemolytic strep’ 2. Lancefield groups (A, B, C etc) Surface carbohydrate antigens e.g. ‘group A strep’ 3. True species names (S. pyogenes, S. pneumoniae etc) e.g.

Question 29

how is s.pyogenis classified?

Answer 29

S. pyogenes = group A strep and is a beta haemolytic strep

Question 30

what are superficial infections caused by strep. pyogenes?

Answer 30

Pharyngitis | Cellulitis

Question 31

what are deep infections caused by s.pyoges?

Answer 31

- myositis | - necrotising faciatis

Question 32

what are 2 common autoimmune sequelae of s.pyogenes?

Answer 32

Rheumatic fever – a major cause of heart disease | glomerulonephritis

Question 33

what are the virulence factors in s.pyogenes?

Answer 33

M PROTEIN - Fibronectin binding protein - collagen binding protein - c5a peptidase

Question 34

how is streptococcal M protein involved in pathogenesis of S.pyogenes?

Answer 34

1. Binds serum factor H – regulator of complement activation - Prevents opsonisation 2.Has an alpha-helical ‘coiled-coil’ protein Molecular mimickry

Question 35

how can molecular mimicry lead to post strep heart disease?

Answer 35

- M protein is a a helical coiled coil structure - has homology to cardiac myosin and tropomyosin - recurrent childhood infection can cause cross reactive anti self response which damages the heart occurs after rheumatic fever

Question 36

how can molecular mimicry lead to post strep glomerular nephritis?

Answer 36

- M protein has alpha helical coiled coil structure - which has homology with glomerular basement membrane - after recurrent childhood infection a cross reactive anti self response can occur

Question 37

what type of bacteria are enterococcus?

Answer 37

gram positive coccus

Question 38

what are examples of gram negative rods?

Answer 38

Klebsiella Enterobacter Citrobacter

Question 39

what can occur when opportunistic infections gain access to sterile sites?

Answer 39

- wound infections | - HAP

Question 40

what are 3 main diseases caused by E.coli?

Answer 40

UTI Enteric Meningitis (Neonatal, elderly, immunocompromised)

Question 41

what are 4 main virulence mechanisms of e.coli?

Answer 41

1. adhesins - p. fimbria= pyelonephritis associated - non fimrial= GI Adhesin causing diarrhoea 2. sidephores - enterobactin - powerful iron chelators - essential for survival in tissues 3. capsule - protects against complement - K1 serotype allows crossing the BBB to cause meningitis in neonates 4. toxins - enterotoxin- cause GI leak - verotoxin- disrupt ribosomal protein synthesis

Question 42

which pathogen is the biggest cause of urosepsis?

Answer 42

e. coli