4. CPE, TSST & SpeA Flashcards
Is Clostridium perfringens colonising?
No, but live organisms must be consumed. The bacteria sporulate in GIT & produce toxin (CPE)
What type of toxin does C. perfringens produce?
CPE (Clostridium perfringens enterotoxin) - pore-forming toxin
What disease is associated with Clostridium perfringens?
Food poisoning
Are most Clostridia harmless?
Yes
Common in gut
Describe C. perf
Gram positive, spore-forming, anaerobic rod
What are the symptoms of a C. perf infection?
Cramps, diarrhoea, onset 8-12 hrs, duration 24-36 hrs
What are common food sources of C. perf?
Large pieces of meat e.g. pork (pig roast), beef
(CPE is sensitive to proteases like trypsin. If you eat lots of protein (i.e. meat) you dilute out the trypsin & it is not longer there to degrade the CPE)
What may be the cause of >1 million cases of food poisoning in US annually?
Clostridium perfringens
Why isn’t C. perf a classic intoxication?
Since live cells are involved
C. perf can produce up to how many different toxins?
16
C. perf is classified into __ different toxinotypes based on the production of __ major toxins (alpha, beta, epsilon, iota)
5 different toxinotypes
4 major toxins
How does CPE work?
CPE binds to host cell → inserts into membrane → fluid loss (enterotoxin)
What percentage of C. perf strains produce CPE?
Only 5%
What strain of C. perf does not produce CPE?
Type B
What is alpha toxin (C. perf)?
membrane-damaging, hemolysin
What is beta toxin (C. perf)?
membrane-disrupting, pore-forming (halos of lysis form around colonies)
Discuss epsilon toxin (C. perf)?
- ETX is the 4th most potent toxin known
- Pore-forming
- Causes enterotoxaemia
- Produced by type B & D strains
- Highly lethal disease with major impacts on domestic ruminants
- LD50 = 100 ng/kg
What is special about the iota toxin (C. perf)?
It has ADP ribosylation activity
ADP ribosylates actin - will change actin cytoskeleton of target cell
What is a binary toxin?
- It looks like an A-B toxin but is different
- Has 2 components (A & B)
- B component involved in binding to host cell & delivering A component to host cell
- 2 components are produced separately & don’t interact until they find each other on the surface of the host cell
- They are not linked by a disulphide bridge
- They are not encoded by the same gene
What is Perfringolysin O, and what does it do?
It is a cholesterol-dependent cytolysin
It forms a pore, which leads to cell lysis
Where are most of the C. perf toxin genes found?
on plasmids
What is the binding domain?
C-terminus
What is the cytotoxic domain?
It carries the cytotoxic activity and inserts into the membrane of the target cell, creating a pore.
What is the function of complementation?
It controls for rare off-target genetic events that might account for phenotype
What protein does CPE appear to bind to?
Claudin (important in tight junctions)
Briefly explain the conformational change in claudin (protein) when CPE binds
Protein contracts, cytotoxin domain extends to form a needle-like structure & inserts into membrane of target cell. 6 of those proteins form a hexametric ring - D3 domain from all 6 proteins inserts into membrane - get a clear pore in the membrane through which fluid can leak out
What human disease is primarily associated with C. perf A toxinotype?
Human myonecrosis (gas gangrene) - characterised by its pungent smell of rotting flesh
What is the name for gut rot that is associated with C. perf?
Human enteritis necroticans - often fatal food poisoning
Does human enteritis necroticans most commonly occur in developed or developing countries?
Developing countries
Which toxinotype is gut rot associated with?
Toxinotype C (which has alpha and beta toxins)
What is an example of a food that contains protease inhibitors and increases susceptibility to intoxication by alpha and beta toxins?
Sweet potato
What bacterium is responsible for MRSA?
Staphylococcus aureus
Features of S. aureus & S. pyogenes
Gram positive cocci
Non-spore forming
Aerobic (require oxygen)
What bacterium produces the toxin that is responsible for Toxic Shock Syndrome?
Staphylococcus aureus
Is TSS exclusively a tampon-associated condition?
No - more recently associated with blisters due to football boots
What happens after colonisation by S. aureus in TSS?
Toxin is produced (TSST-1: toxic shock syndrome toxin)
What bacterium produces the superantigen that is responsible for Toxic Shock Like Syndrome?
Streptococcus pyogenes
Which has a higher death rate: TSS or TSLS?
TSLS
What is produced in TSLS?
A superantigen (SpeA: S. pyogenes erythrogenic toxin)
Differences between S. aureus & S. pyogenes?
S. aureus is non-invasive (bacteraemia is rare)
S. pyogenes is invasive (more severe than S. aureus, bacteraemia common)
S. aureus never gets into the body - do not get sepsis
TSLS - deep site of infection
TSS - superficial site of infection
How are TSST and SpeA functionally related?
They both interact with MHC and T cell receptors, but are not similar at the primary sequence level
What happens in TSS?
S. aureus grows in tampon or wound → TSST-1 enters the bloodstream → fever, rash, shock
TSS death rate?
3-6%
TSLS death rate?
> 30%
TSLS also termed severe invasive streptococcal disease
What happens in TSLS?
S. pyogenes grows in wound → bacteria enter bloodstream → produce SpeA → fever, rash, shock
What bacterium causes necrotising fasciitis (‘flesh eating disease’)?
Streptococcus pyogenes
What is necrotising fasciitis characterised by?
The rapid spread of inflammation (intoxication spreads v quickly)
What is the treatment for necrotising fasciitis?
Directly go in and clean the wound (scrape away all dead tissue) or amputate. Antibiotics are too slow
What are the 3 different types of necrotising fasciitis?
Type 1: polymicrobial
Type 2: GAS
Type 3: gas gangrene
What does acquired SlaA gene encode for?
A phospholipase (a membrane-disrupting toxin which allows pyogenes to become even more toxic)
How does S. pyogenes evade complement?
(i) by producing a C5a peptidase
(ii) surface covered with M protein degrades C3b
Where is SpeA gene located?
On a temperate bacteriophage
Staphylococcal food poisoning
- Common
- Vomiting, pain, rapid onset
- Foods which are handled, low water activity
- Classic intoxication (organism grows on food, produces toxin which is ingested)
- Superantigens can cause food poisoning independent of activating T cells - emetic properties, caused by SEs (Staphylococcus enterotoxins)
True or False: Most strains of S. aureus (food poisoning) produce multiple superantigens
True
What are superantigens?
A large family of pyrogenic (fever-inducing) toxins and their roles are variable. All have very similar shapes & interact with MHC & TCRs
What is missing in TSST-1 that is responsible for vomiting reaction?
Particular cysteine loop
Predominant symptoms associated with superantigens?
Vomiting (emesis)
Examples of intoxications (disease without colonisation)?
C. botulinum (A-B toxin), S. aureus (SAg)
Example of a toxicoinfection (disease without colonisation, toxin produced in GIT)?
C. perfringens - causes food poisoning, have to ingest the bacteria in order for the toxin to be delivered to gut
Example of opportunistic (defences breached) pathogens?
- TSS - S. aureus (SAg)
- TSLS - S. pyogenes (SAg)
- Tetanus - C. tetani (A-B toxin)
