Infection 3) Bacterial pathogenesis

Question 1

Describe the envelope structure of gram positive bacteria

Answer 1

Thick peptidoglycan layer

Lipoteichoic and trichroic acid

Question 2

Describe the envelope structure of gram negative bacteria

Answer 2

Outer membrane of lipopolysaccharide, proteins and pores
Thin peptidoglycans
Inner membrane

Question 3

Give an example of bacteria that need an aerobic environment

Answer 3

Staph.aureus

Question 4

Give an example of a bacteria that needs an anaerobic environment

Answer 4

Clostridium species

Question 5

Give an example of a facultative anaerobe bacteria

Answer 5

E.coli

Question 6

What is a facultative anaerobe bacteria?

Answer 6

Bacteria that can switch between aerobic and anaerobic metabolsim

Question 7

Describe the consequence of alpha haemolytic streptococci on agar

Answer 7

Cause partial haemolytic of blood agar and produce a greenish colour

Question 8

Describe the consequence of beta haemolytic streptococci on agar

Answer 8

Complete haemolysis so agar becomes transparent

Question 9

What is serological typing?

Answer 9

Type of cell-surface antigens present, antibodies to expressed antigens

Question 10

What is genotyping

Answer 10

Genes encoding those antigens

Replacing serotyping

Question 11

What is a commensal?

Answer 11

Something which is probably not causing disease when identified from clinical sample
Living in a relationship in which one organism derives food or other benefits from another organism without hurting or helping it

Question 12

What is a pathogen?

Answer 12

Something that causes disease

Question 13

What 3 things determine an organism’s pathogenicity?

Answer 13

Organism’s virulence
Site
Immune state of patient

Question 14

Describe the 2 types of site

Answer 14

Sterile - blood and urine

Unsterile - stool and throat

Question 15

Give examples of gram positive cocci

Answer 15

Staphylococci
 - s.aureus
 - coagulase negative staphylococci 
Streptococci
 - group A streptococcus (S.pyogenes)
 - group B, C, G
 - group D (enterococcus)
 - S.pneumoniae
 - viridans type streptococci
Peptococcus / peptostreptococcus

Question 16

Give examples of gram positive rods (bacilli)

Answer 16

Bacillus e.g. B.cerus and B.anthracis
Corynebacterium
Propionibacterium
Listeria monocytogenes
Clostridium e.g. C.difficle

Question 17

Give examples of gram negative cocci

Answer 17

Neisseria
- n.meningitis
- N.gonorrhoea
Moraxella (branhamella) catarrhalis

Question 18

Give examples of gram negative rods

Answer 18

Haemphilus influenza
Enterobacteriaceae
 - salmonella and shigella
 - eschericia coli
 - klebsiella and enterobacter
 - proteus
Pseudomonoas e.g. P.aeruginosa
Bacteroides e.g. B.fragilis
Campylobacter and helicobacter
Vibrio cholera
Bordatella pertussis
Legionella

Question 19

What infections does S.aureus cause?

Answer 19

Furunculosis
Staph abscess
Impetigo
Sepsis - line, splenic abscess, lung abscess
Toxin mediated - toxic shock, scalded skin, food poisoning
Bacteraemia - endocarditis, osteomyelitis, septic arthritis

Question 20

Describe S.aureus virulence

Answer 20

Coagulase enzyme
Adhesions
Protein A
Toxins

Question 21

What toxins does S.aureus have?

Answer 21

Cytotoxins
Exfoliative toxins
Enterotoxins

Question 22

What cytotoxin does S.aureus have?

Answer 22

PVL (pantun-valentine leukocidin)

Question 23

Describe scalded skin syndrome

Answer 23

Exfoliative toxins
Outbreaks in nurseries
Local infection
Distant bullae
Sheet-like desquamation

Question 24

Why is coagulase negative staphylococci less virulent?

Answer 24

Doesn’t make coagulase

Question 25

Give examples of alpha haemolytic streptococci

Answer 25

S.milleri S.mitis S.anguis S.pneumoniae

Question 26

Give examples of beta haemolytic streptococci

Answer 26

S.pyogenes | S.equi, S.canis

Question 27

What superficial infections can streptococci cause?

Answer 27

Pharyngitis | Cellulitis

Question 28

What deep infections can streptococci cause?

Answer 28

Severe soft tissue infection Myositis Necrotising fasciitis

Question 29

Describe the clinical signs of necrotising fasciitis

Answer 29

``` Pain out of proportion to physical signs Bruising and blistering Generalised toxaemia Renal impairment Very high inflammatory response (CRP) Raised creatine kinase ```

Question 30

Describe the structure and virulence of streptococci

Answer 30

``` Fibronectin-binding proteins Collagen binding proteins C5a peptidase M protein Capsule, wall, membrane Exotoxins ```

Question 31

What is M protein?

Answer 31

Major antigenic determinant of S.pyogenes Binds serum factor H to prevent opsonisation Alpha-helical coiled coil protein

Question 32

What is molecular mimicry?

Answer 32

Structural similarity of microbial antigenic determinant and host proteins resulting in cross creativity of antibody and T-cell responses to microbial antigens with self antigens

Question 33

What exotoxins does streptococci produce?

Answer 33

``` Superantigens Streptococcal inhibitor of complement Haemolysis DNAses Hyaluronidase Streptokinase ```

Question 34

Give examples of non-bacterial pathogens

Answer 34

Fungal organisms Yeasts, moulds, dimorphic fungi Candida species Aspergillus species

Question 35

What infections can enterobacter cause?

Answer 35

``` Klebsiella Enterobacter Citrobacter Wound infections, biliary infections Hospital acquired pneumonia Meningitis ```

Question 36

What are the 4 main virulence mechanisms of E.coli?

Answer 36

Adhesions Siderophores Capsule Toxins

Question 37

Describe the adhesions of E.coli

Answer 37

P fimbria - binds uroepithelial antigens | Non-fimbral GI adhesions causing diarrhoeal diseases

Question 38

Describe the siderophores of E.coli

Answer 38

Enterobactin | Powerful iron chelators

Question 39

Describe the toxins produced by E.coli

Answer 39

Endotoxin Exotoxin Verotoxins