Clostridium

Question 1

Characteristics of clostridium

Answer 1

Gram-positive
Forms endospores
Anaerobes
Part of enteric flora of humans and animals

Question 2

Life cycle of clostridium

Answer 2

Germination: dormant spore to germinated spore
Emergence: germinated spores become emerged cell
Division
Sporulation and toxin formation

Question 3

Species of clostridium

Answer 3

Perfringens
Difficile
Botulinum

Question 4

Sources of perfringen spores

Answer 4

Soils, lakes, air, dust
Gut and faeces of animals and birds
Raw and processed foods

Question 5

Characteristics of perfringens

Answer 5

Aerotolerant
40-47C ideal
7.1 mins to double
D-value of spores: up to 123 mins
Aw of 0.95-0.97
Optimum pH is 6-7

Question 6

How does perfringens cause disease in humans?

Answer 6

Gas gangrene, gastroenteritis or necrotic enteritis

Question 7

How does perfringens cause disease in animals?

Answer 7

Necrotic diseases of the GI tract

Question 8

What is lecithinase?

Answer 8

Toxin that splits lecithin

Question 9

What does lecithinase cause?

Answer 9

Edema

Question 10

How does lecithinase cause edema?

Answer 10

It has a C-terminal domain which enters the phospholipid bilayer and a N-terminal domain which hydrolyses phosphatidyl choline to increase vascular permeability

Question 11

What does gas gangrene do?

Answer 11

Produce gas for fermentation

Question 12

What toxins are used by gas gangrene?

Answer 12

α-toxin, γ-toxin, δ-toxin (haemolysins), κ-toxin (collagenase) λ-toxin (protease)

Question 13

Characteristics of gastrointestinal disease

Answer 13

Germination of spores in raw or unchilled foods
10^6-10^8 CFU/g
Low mortality rate unless elderly

Question 14

Symptoms of gastrointestinal disease

Answer 14

8-24h after consumption
Diarrhoea, vomiting, fever
Clears within 12-24h

Question 15

What does CFE stand for?

Answer 15

Perfringens enterotoxin

Question 16

Structure of CFE

Answer 16

Gene (cpe) is chromosomally, or plasmid located
Chromosomal cpe associated with foodborne illness
Plasmid cpe in GI disease causing diarrhoea

Question 17

Where is CFE common?

Answer 17

Hospitals and nursing homes

Question 18

Characteristics of CFE

Answer 18

Produced in foods
Heat sensitive (60C for 10mins)
pH sensitive and proteolytic enzyme sensitive

Question 19

How does CPE cause infections?

Answer 19

Survives stomach acid causing sporulation in small intestine
Then released into rumen where mature spore is released

Question 20

Site of action of CPE

Answer 20

Intestine lined with 1000s of villi
Villi contain region where new epithelial cells are born which move up to replace cells
Neighbour cells adhere tightly to form barrier through ZO-1 proteins
CPE then binds to tight junction protein

Question 21

Mode of action of CPS

Answer 21

Ileum is target organ
CPE forms pores in cell membrane of intestinal epithelial cells
CPE binds to claudin proteins of tight junctions
Leads to cell permeability and villus shortening
Damage occurs within 30mins

Question 22

Symptoms of CPE

Answer 22

Electrolyte losses
Diarrhoea and cramps
Self-limiting
Rarely fatal

Question 23

Sources of CPE

Answer 23

Meat and poultry products kept warm for too long

Question 24

Necrotic enteritis symptoms

Answer 24

Protein malnutrition
Low intestinal trypsin protease
High mortality if untreated

Question 25

How does necrotic enteritis cause damage?

Answer 25

Beta toxin damages mucosa, necrosis of jejunum and ileum

Question 26

Characteristics of clostridium difficile

Answer 26

Pseudomembranous colitis and antibiotic-associated diarrhoea Gut flora altered High prevalence in hospital patients Antibiotic resistance

Question 27

Symptoms of clostridium difficile

Answer 27

Watery stools Diarrhoea containing blood Abnormal heart rhythm

Question 28

How does difficile cause infection?

Answer 28

Toxin A and B Covalently modify cell protein Rho Toxins bind to colon, disrupt epithelial mucosal surface

Question 29

How do toxins A and B work for difficile?

Answer 29

Binds to cell surface receptors and are endoctosed Toxins insert into vesicle membranes, translocate to cytosol at low pH Inositol hexakisphosphate activates cysteine protease, causing release of catalytic domain Catalytic domains modifies and inactivates Rho proteins

Question 30

What are the consequences of Rho inactivation?

Answer 30

Fluid accumulation, inflammatory responses and mucosal destruction

Question 31

What are RhoGTPases?

Answer 31

Cell signalling switches which mediate regulation of cell functions

Question 32

Where can difficile be found?

Answer 32

Meat and vegetables

Question 33

Structure of botulinum neurotoxins

Answer 33

150kDa protein Binding domain allows toxin to attach to nerve Translocation domain Catalytic domain with zinc-endopeptidase activity

Question 34

Role of 150kDa protein

Answer 34

Blocks transmission message from nerve to muscle with three domains

Question 35

Role of catalytic domain

Answer 35

Give potency and duration

Question 36

How does the botulinum toxin bind?

Answer 36

Binding of heavy chain to receptors on neurone membrane Internalisation into vesicles Acidification of vesicle lumen, translocation of light chain into cytosol Reduction of interchain disulphide bond

Question 37

How can botulism be prevented?

Answer 37

Botulism immune globulin

Question 38

Lethality of botulism

Answer 38

Highly fatal 30ng neurotoxin

Question 39

Treatment of botulism

Answer 39

Anti-toxin given in bloodstream If disease becomes severe then respiratory support given Complete recovery may take months or years

Question 40

Growth conditions for proteolytic botulinum

Answer 40

10-12C min 37-43C ideal >4.6 pH 121C for 0.2 mins

Question 41

Growth conditions for non-proteolytic botulinum

Answer 41

2.5-3C min 25-30C ideal >5 pH 90C for 10 mins