lecture 5 Flashcards
Q. What are the consequences for this graph not being symmetrical?
the death of a bacteria. therefore you will report a false negative result because bacteria die at 38*c
Each bacterial species grows at a particular minimum, optimum and maximum temperature.
The minimum growth temperature is the lowest temperature the organism will grow at
The optimum growth temperature is the temperature at which the organism grows the best
Note that the optimum growth temperature is towards the top of the range ie curve not symmetrical. Above that temperature the growth rate drops off dramatically (probably inactivates necessary enzyme reactions)
explain the growth of different microbes
Would psychrophiles grow in a warm room like a laboratory? No
Grow mostly in the ocean depths or in certain polar regions,
Psychrotrophs more likely to grow in foods improperly stored as they are more common in the environment wheras psychrophiles are not generally outside of cold seas
Examples of psychrophiles include mould and some slime producing bacteria that spoil food
Mesophiles are the disease producing bacteria
Thermophiles prefer temperatures of hot water, sun lit soils and thermal springs. Also important in compost heaps were temps can get to 50 – 60
Endospores of thermophilic bacteria may survive canning processes.
Hyperthermophiles are the extremophiles
what limits the growth at different temperatures?
At low temperatures
the cell membrane loses fluidity
enzymes stop working
transport in/out goes very slowly
Growth cannot occur
At temperatures above the optimum
proteins denature
ribosomal RNA denatures
cell membrane becomes too fluid
Cells cannot continue to grow
what is the acidophile bacteria in yoghurt?
lactobacillus
why do bacteria have a wide range of tolerance?
bacteria produce acid when they grow
Most bacteria grow best in a narrow pH between 6.5 and 7.5
Q. So how can this be used in food preservation?
we use this in food preservation when we do fermentation which has acid and the acid can slow down other organisms from growing
When bacteria are grown they often produce acids that interfere with their growth
Q. So what can we add to growth media to help prevent this?
we add a buffer to help prevent that acid slowing down growth to maximise production if you work in a pharmaceutical company
a buffer is a chemical that tends to bring the pH back to neutral (7)
What microbes grow over a larger pH range and have a optimum of pH 5 – 6?
the fungal family such as yeast and mould
Moulds and yeasts will grow over a larger pH range than bacteria, an optimum in lower (pH 5 – 6)
Buffers, phosphate salts have the advantage of exhibiting their buffering effect in the pH growth range of most bacteria, they are non toxic and they provide phosphorus and essential nutrient
Microbes made up of 80 – 90% water
Internal environment of cell has high osmotic pressure but hypertonic solutions will stop growth
Some bacteria have adapted to growth in hypertonic solutions – called halophiles
Some bacteria have become obligate halophiles
Q. Why might you have to add extra salt to isolate a food poisoning microbe derived from sea food?
you have to add extra salt to say sushi and its causing food poisoning so the salt to the agar will grow the food poisoning bacteria from the sushi
Q. What would you say the difference is between a halophile and a non-halophile?
non-halophiles can grow without salt. but halophiles need salt to grow
what is water activity aW
the amountof water free to react (water availability so this bigger the number the more available to be)
Q. Which group of microbes grows first on salty or sugary foods?
fungi grows well in low water availability like on bread
what are aerobes?
Some microbes require oxygen for energy extraction from organic chemicals – aerobes
what are anaerobes?
Some microbes can extract energy from organic chemicals only in the absence of oxygen – anaerobes
what are facultative anaerobes?
Some microbes can extract energy from organic chemicals with and without oxygen – facultative anaerobes like e coli.
think of facility/ability to grow - e coli prefers to grow in air.
Pseudomonas spp. requires what for growth?
it requires oxygen to grow
strict aerobes like Pseudomonas is used to test?
anaerobiosis
the strict anaerobes Clostridium spp. and
Bacteroides spp. require what to grow?
they require a reducing environment. may be killed or poisoned by oxygen
what are aerotolerant anaerobes?
no difference O2 or AnO2
Lactobacillus spp. goes with yoghurt
what are facultative anaerobes?
Utilise oxygen if it is present
grow better O2 than AnO2
Escherichia coli
microaerophilic organisms like Campylobacter spp. require what to grow?
they require some O2 to grow
Most prokaryotes replicate by?
binary fission – cell continues to grow until it divides. every 20 min they divide
state the prokaryote growth phases and explain them
3 phases of prokaryote growth:
Exponential growth phase: Cell numbers double at a constant rate: e.g. one E.coli cell after 20 minutes = 2 cells, after 1 hour = 8 cells, after 2 hours = 64 cells, after 6 hours = 262,144 cells, after 10 hours = 51,073,741,824 cells
Stationary phase: If nutrients are limited, cells cannot continue exponential growth indefinitely, also a buildup of waste products will inhibit growth - cells growing = cells dying, no increase or decrease in total cell number
(WRONG ANSWER: ORGANISMS HAVE STOPPED GROWING) so what is actually happening in the stationary phase? the number of organisms dying equal the number of organisms multiplying. the numbers remain stationary but the bacteria dont.
Death phase: No cell growth, cells die and may lyse, due to lack of nutrients/toxic waste products
