Anaerobic Spore Forming Gram Positive Rods Flashcards
(31 cards)
State the classificationand characteristics of Anaerobic Spore Forming Gram-Positive Rods
- Kingdom: Bacteria / Family: Clostridiaceae / genus Clostridium
- Main Characteristics:
(a) Gram-positive rods; motile with peritrious flagellum (extends aaround the whole bacterial cell; 1µm (width) X 20µm (length)
(b) Ubiquitous saprophytes (lives on dead or decaying organic matter)/ mammalian intestine
(c) Low G/C content in their DNA
(d) Produce endospores (spore-forming bacteria)
(e) Strictly anaerobic metabolism (anaerobic respiration and fermentation; reduce sulfate to sulfite, as the final electron acceptor to obtain energy, produce ATP)
Tend to be found in the soil or in the gut
Explain the anaerobic respiration in Clostridia
Anaerobic Respiration: electron acceptor is EXOGENOUS to the cell, it is not oxygen)
- Organic energy source e.g. gluoce
- Glycolysis occurs which produces pyruvate as an intermediate
- As a result hydrogen and electrons are generated from this metabolism
- The final electron acceptor is sulphate (SO42-) which is reduced to sulphite
- Less ATP is produced in anaerobic metabolism, as a result anaerobic bacteria grow more slowly
Explain fermentation in clostridia
Fermentation: electron acceptor is an ENDOGENOUS (within the cell)organic molecule; No electron transport chain (ETC) or oxygen is involved
- Organic energy and electron source e.g. glucose is oxidised and produced pyruvate
- Pyruvate acts as the electron acceptor in fermentation
- This produces enough energy for substrate level phosphorylation where ADP is phosphorylated to ATP
- Pyruvate is reduced further via the butyric fermentation pathway to produce butyric acid
What are endospores?
- Dormant, dehydrated, highly resistant ‘survival’ structures carrying allt the bacterial genetic material (DNA)
- Produced in unfavourable conditions
- They can be terminal (produced by C. tetani); subterminal (produced by C.difficile and C. botulinum); central (produced by C. novyi )(oval; round; rectangular) depending on the species of clostridia
State the distinct components of endospore
(a) Exosporium (aids adhesion)
(b) Spore Coat (protein)
(c) Cortex (peptidoglycan)
(d) Core (low H2O- they are dehydrated structures, they also contain small acid soluble spore proteins –SASP that coat protect the DNA and contain dipicolinic acid (DPA)
→DPA-Ca2+ ccomplex in the core “mops up” any free water
What is the function of the DPA-Ca2+ complex?
It binds free H2O to promote dehydration (protection against wet heat)
What are the function of the small acid soluble spore proteins –(SASPs)
saturates DNA (protection from wet/dry heat)
Describe the process of sporulation
- Upon unfavourable conditions, spore formation is initiated
- DNA condenses and aligns itself in the centre of the cell, the vegetative cell is now referred to as the mother cell
- The DNA divides into 2 copies and the mother cell membrane invaginates to form the developing forespore
- The mother cell membrane contines to grow and engulfs the developing spore
- The developing spore is now surrounded by two membrane layers
- Peptidoglycan is layed down between the two membranes of the developing spore to form the cortex
- Dipicolinic acid is formed inside the developing spore and Ca2+ enters from the outside
- As Ca2+ enters H2O is removed
- A protein coat forms exterior to the cortex and the spore becomes mature
- Some spores form an additional layer called the exosporium
- Lytic enzymes destroy the mother cell and the mature spore is released
Explain the process of germination (becoming a metabolically active bacterial cell)
- Stage 1: Exposure to specific germinant and activation (IRREVERSIBLE)
-
Stage 2:
1. Partial rehydration
2. DPA-Ca2+release
3. Loss of some resistance to environmental extremes - Stage 3:
- Cortex hydrolysis
- Full core rehydration and expansion
- Loss of resistance and dormancy
-
Stage 4 (Outgrowth):
1. SASP degradation
2. Metabolic activity is initiated
3. Escape from spore coat and division
State the following for Clostridium botulinum:
- Historical Derivation
- Spore Structure
- Disease
- Frequency of Disease
Organism and Spore Structure: Clostridium botulinum
Historical Derivation: botulus= sausage
Spore Structure: Oval, subterminal
Disease: Botulism (foodborne, infant, wound)
Frequency of Disease: Uncommon
State the following for Clostridium difficile:
- Historical Derivation
- Spore Structure
- Disease
- Frequency of Disease
Historical Derivation: difficile=difficult
Spore Structure: Oval, subterminal
Disease: antibiotic associated diarrhoeai (AAD) in hospitalised patients; PMC One of the leading causes of Healthcare associated infections (HAI)
Frequency of Disease: Very common
State the following for Clostridium perfringens:
- Historical Derivation
- Spore Structure
- Disease
- Frequency of Disease
Historical Derivation: perfringens=‘breaking through’
Spore structure: Large rectangular
Disease: GI infection
Frequency of Disease: Common
State the following for Clostridium tetani:
- Historical Derivation
- Spore Structure
- Disease
- Frequency of Disease
Historical Derivation: tetani=tension
Spore Structure: Round, terminal (‘drumstick’)
Disease: tetanus
Frequency of Disease: Uncommon
Give a brief history of Clostridium tetani
- 1500BC: Edwin Smith Papyrus- an association between wound infections and spastic paralysis; 500BC: Hippocrates wrote about a patient with a dart wound in his neck then ended up with spastic paralysis in the face
- 1832: Sir Charles Bell (Anatomy and Philosophy of Expression) noticed that wounded soldiers often ended up with spastic paralysis
- 1884: Discovered by Arthur Nicolaier- He noticed that when mice were injected with soil, they contracted spastic paralysis
- 1889: Isolated by Shibasaburo Kitasato from soil samples
What are the characteristics of Clostridium tetani?
- Large ram positve spore forming rods-GPSFR (0.5-1.7µm X 2.0-18µm); obligate anaerobe; motile; ubiquitous (soil, intestinal tracts and faeces of various animals)
- Round terminal spores (‘drumstick’ morphology)
Virulence factors:
(a) Spore Former (easily contaminates wounds)
(b) Exotoxins: TETANOLYSIN→causes cell lysin and TETANOSPASMIN→causes spastic paralysis in humans and mammals
Explain the 21st Century Epidemiology of Clostridium tetani
Incidence and Mortality:
- Rare in developed nations; high prevalence in India, China, Africa (Ghana, Egypt, Zaire, Mali)
- 50 million cases worldwide
- ½ million deaths worldwide (60,000 in neonates)
- 80% occurring in Africa / SE Asia
- USA: 50-100 cases PA
- UK: 3-5 cases PA
What are the risk factors associated with Clostridium tetani?
•Lack of immunisation;
aging immune system >60 years
- Open wounds contaminated with soil /manure
- Skin/tissue puncture: rusty metals, thorns, ear piercing
- Childbirth (esp in Africa and India)
Explain the pathogenesis of Clostridium tetani
- Germination of spores (following entry into wound)
- Adhere to host cells: Fibronectin binding proteins;
- S-Layer surface proteins that aid adhesion and help the organism evade phagocytosis; peritrichous flagella helping it move toward favourable conditions
- Haemolysin III,Tetanolysin (pore forming/type II toxin), Collagenase (helps the organism spread throughout our deeper tissues)
The main virulence factor is Tetanospasmin (TeTx):
- Type III toxin; A/B subunits (150 KDa)
- Potenet neurotoxin (lethal dose of 2.5ng/kg; 175ng can kill a 70 kg human)
Describe Tetanospasmin’s (TeTx) mode of action
- Produced in stationary phase of growth; transported to peripheral nerves and CNS
- Prevents inhibitory neurotransmitters: gamma-aminobutyric acid (GABA) and glycine from being released:
SPASTIC PARALYSIS (continuous muscle contraction)
Draw a diagram of tetanospasmin
- Heavy chain (100kDa) responsible for neuronal binding
- Light chain (50 kDa) acts on synaptobrevin
Explain normal muscle contraction
- Neuron: Vesicles ‘dock’ via SNARE (synaptobrevin) protein complexes (v-SNARE / t-SNARE) and release acetylcholine →muscle contraction
- Inhibitory interneuron: Vesicles containing GABA/glycine ‘dock’ via SNARE protein complex and release inhibitory neurotransmitters by exocytosis
- Inhibitors bind to specific neuron receptors →muscle relaxation
How is muscle contraction altered in the presence of tetanospasmin?
A subunit (light chain) cleaves synpatobrevin (V SNARE) and prevents DOCKING of the inhibitory neurotransmitters vesicle to the presynaptic membrane.
The V SNARE forms a SNARE COMPLEX with the T SNARE on the presynaptic terminal.
The muscle exists in a permanently contracted state
