lecture 3: the two sides of bacterial endospores Flashcards
why do cells change to endospores
- may change to endospores when under stress because they are more resistant
- however this process is long and the cell could die before it completes the cycle
process of going from a cell to endospore
- vegetative cell dividing by binary fission
- DNA becomes more dense
- larger compartment engulfs the smaller compartment
- forming the forespore
- cortex and coat formed, dehydration
- lysis of cell and release of endospore
endospore structure (from inside to outside)
- core
- inner membrane
- germ cell wall
- cortex
- outer membrane
- coat
- exosporium
core, inner membrane and cell wall
contains normal cell structures (DNA, ribosomes etc) but these are metabolically inactive
cortex, outer membrane
layered structure that surrounds the core, peptidoglycan (less cross linked)
coat
surrounds the cortex, made up of 7 protein layers, quite thick = impermeable, responsible for endospores resistance to physical factors like chemicals or uv light
exosporium
thin layer, coat around the whole thing
what determines resistance?
- physical
- coat (thick layers)
- inner membrane (impermeable) - chemical (core)
- low water content (15%, compared to >80% in vegetative cells)
- lower pH
- high content of dipicolinic acid and Ca2+ - chemical (cortex)
- decreased peptidoglycan cross linking index = 2.9% in endospore (33% in vegetative cells)
why does cross linking idex of endospore cortex peptidoglycan occur at only 2.9% of the peptidoglycan residues compared to 33% in actively growing bacterial cells
because this modified peptidoglycan is required for the maintenance of the dehydration in the endospore core, and the accompanying metabolic dormancy and heat resistance
endospore germination
- activation = where the cell prepares to germinate
- germination = endospore swelling (more water), rupture of the spore coat, so the cell is now exposed to the environment, increase in metabolic activity
- growth = binary fission, population growth happens again
death of microorganisms
loss of ability to multiply under any known conditions
sterilisation
complete removal or destruction of all microorganisms from inanimate objects. it is brought about by the use of physical or chemical methods. non selective
physical control methods using moist heat
- autoclave
- boiling water
- pasteurisation
autoclave
- increasing the boiling point, increases the temperature you can get to
- pure steam is crucial
temp: 121
time: 15mins
kills all cells: yes
kills all endospores: yes
how does mosit heat work as a physical control method
kills by denaturing vital molecules in the DNA cell, involves the application of heat over time
examples of items that can be sterilised by autoclaving
- most culture media for bacteria
- glassware
- surgical dressings, cotton wool
- some surgical instruments
items that cannot be autoclaved
- toxic chemicals
- heat labile compounds
- heat sensitive equipment
- some types of plastics
boiling water
temp: 100
time: 15mins
kills all cells: yes
kills all endospores: no
pasteurisation
63 degrees for 30mins or 71 degrees for 15sec
quality control = less than 5 x 10^5 cells/ml
kills all cells: no
kills all endospores: no
dry heat as a physical control method
- flaming and incineration
- hot air oven
- freezing
flaming and incineration
- reaches 1000 degrees
- kills all endospores
hot air oven
temp: 160
time: 2hrs
kills all cells: yes
kills all endospores: yes
freezing
- not sterilisation process, it is used for storage
