D values and endospores
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When does D value vary?
With temperature
How do organic molecules act?
As a heat sink to protect cells against thermal inactivation
What type of microbes are heat resistance?
Gram positive
Are bacterial endospores heat resistant?
Yes
What are the spore forming bacteria?
Bacillus and clostridium
Structure of spores
Exosporium Spore coat Cortex (outer membrane) Germ cell wall Inner membrane Core
What causes repression of sporulation?
Freely available C and low cell density
What causes activation of sporulation?
C, N, P starvation and high cell density
How does sporulation start?
Asymmetric division of the mother cell
What are spores activated by?
Elevated temperature and chemicals
How do chemicals mediate germination?
Bind to germinant receptors in the inner membrane
Where do signals go from the GR?
To the core
What causes repression of germination?
D-alanine
What causes activation of germination?
Heat shock and nutrients
What enters the core during germination?
H2O and germinant
What exits the core during germination?
Cations H, K, Na, Ca, DPA
What is the first step of germination?
Hydration activates lytic enzyme degrading outer layers
What is the second step of germination?
ATP synthesis begins and germination factors are packaged during sporulation
Clostridium botulinum
Spores are heat resistant and germinate in cooled food (meat)
Botulinum toxin (BT)
Most toxic substance on earth and used in cosmetic surgery
What is the ‘bot cook’?
12 D-value to kill 100% of bacteria
Bacillus cereus
Spores are heat resistant and germinate in cooled foods (rice)
Clostridium perfringens
Natural part of animal gut microflora (meat)
Clostridium tetani
Spores germinate and grow in the body through skin and lungs