Bacterial growth Flashcards
What is bacterial growth?
An increase in cellular constituents and may result in an increase in a microorganisms size, population numbers, or both. (Prescott 5th edition)
Organism may gain additional skills or become more complex (eg MRSA resistance).
What is generation time?
Generation time is the time it takes for a population of bacteria to double in number.
For many bacteria the generation time ranges from minutes to hours.
Depending on species and conditions, some bacteria can divide as quickly as every 20 minutes.
What is exponential growth (or log growth)?
Exponential growth is when bacteria divides very quickly.
1 → 2
2 → 4
4 → 8
8 → 16
16 → 32
32 → 64
64 → 128
128 → 256
What happens every generation time?
Population doubles every generation time (each bacterium splits in two.).
How do bacteria reproduce?
Prokaryotic fission (Binary fission) → asexual
reproduction → cells genetically identical
Describe the process of binary fission.
1) Cell elongates and DNA is replicated
2) Cell wall and plasma membrane begin to divide
3) Cross-wall forms completely around divided DNA
4) Cells separate
How fast can e.coli grow under optimum conditions?
at 37 oC and in optimal growth medium; E. coli
will divide roughly every 20 minutes
What are the four main factors that affect bacterial growth?
warmth, moisture, pH
levels and oxygen levels
What else is needed for growth?
- Nutrients – Culture medium (food)
- Time – To allow for division
- Osmotic concentration (Solutes and Water)
- Oxygen – aerobe / anaerobe (20%)
- Space – to expand
- Temperature – unicellular
- Ph (Acidophiles pH 0-5.5), Neutrophiles
pH5.5-8.0 and alkalophiles pH 8.5- 11.5 - Absence of predators
What is growth like in natural envionments?
In a natural environment growth is often severely
limited by availability of nutrients, supplies and other
environmental factors
WHat are the four phases of growth in a closed environment?
1) Lag phase
2) Log (exponential) phase
3) Stationary phase
4) Death phase.
What happens in the lag phase?
Introduction to fresh medium (from dormant to actively
growing). Time depends on species and other environmental
factors.
What happens in the log (exponential) phase?
Binary fission, with no limiting factors (log for
numbers used as exponential expansion)
What happens in the stationary phase?
Cell begin to die as well as being produced. Due to less nutrients, toxins being released and critical density.
What happens in the Death phase?
Limited nutrients and build-up of toxins. Death becomes exponential. Cells revert to dormant stage or spore stage
What effect does temperature have on microorganisms?
Temperature (High and Low) has a profound effect on micro-organisms –
What does a microorganisms temperature depend on?
Most microorganisms are unicellular, hence their temperature varies
depending upon the environment they are in – directly reflects surroundings.
What are enzyme catalysed reactions defined as?
Enzyme catalysed reactions are temperature sensitive (enzyme reactions will
double for every 10 rise)
How does temperature effect microbial growth?
Metabolism increases / more active resulting in faster growth.
However, with continued heating, growth is
inhibited – Membrane lipid bilayer
disintegrates.
Damage and halted growth
What happens if microbes are at too high a temperature?
Cell bursts
Why does higher temp increase growth?
Increasing enzyme
catalysed reactions
What is the relationship between temperature and growth?
Increasing temperature = faster growth
Decreasing temperature = slower growth
What is the ideal temperature of psychrophiles?
Psychrophiles (cryophiles) (optimal 15° C or lower, max 20° C
What is the ideal temperature of Mesophiles?
(optima around 20 - 45° C, max 45° C or lower) - most micro-organism
What is the ideal temperature of Thermophiles?
(45° C minimum, optima between 55 - 65° C)
What is the ideal temperature of Hyperthermophile?
(90 ° C or above, max of 100 ° C) - prokaryotes
What is the ideal temperature of Psychrotrophs?
Psychrotrophs thrive between 4°C and 25 °C
Where is optimum temp located on a graph?
Around the peak of the graph
What microorganism are part of the group Psychrophiles / Psychrotrophs?
Pseudomonas, Bacillus,
Arthrobacter
What microorganism are part of the group mesophiles?
Listeria monocytogenes,
Staphylococcus aureus, and
Escherichia coli
What microorganism are part of the group Thermophile?
Clostridium, Thiobacillus
What microorganism are part of the group Hyperthermophile?
Pyrococcus abyssi, Pyrodictium
occultum
What kind of membranes do bacteria have?
selectively permeable membranes
Details about bacteria and moisture?
Bacteria need water to grow – ‘like moisture’
▪ Bacteria have selectively permeable membranes and
therefore can be strongly affected by the environment.
▪ If the area around bacteria is pure water then water can
flow into the cell causing it to burst.
▪ If there is no water present then the bacteria can die.
What happens if there is no water present?
If there is no water present then the bacteria can die.
How is water needed by bacteria to live calculated?
How much water bacteria need to live is calculated using water activity (aw)
What is water activity?
the ratio of water vapour
pressure of the substance to the water vapour pressure of pure
water.
What is water activity affected by?
Water activity (aw) is affected by temperature, pressure,
and chemical environment
Define hypertonic solution.
- external solution with a higher solute conc and low water
conc compared to (in this case) inside the cell.
Define Hypotonic solution.
external solution that has a lower solute concentration and higher water concentration compared to inside the cell.
What is the typical water activity of food? How do this relate to bacterial growth?
The water activity (Aw) of most foods is greater than 0.95 and supports growth, typical bacteria require 0.91 or above.
Why cant microbes grow in jam?
The sugar and pectin in jams bind the water making it unavailable for microbial
growth
How does microbial growth depend on water activity limits?
Water Activity limits for
microbial growth
WHats the water activity of distilled water?
Aw= 1.0 Distilled water
What does pH represent?
pH represents the amount of H ions presents.
As with temperature every microorganism has a…
As with temperature every microorganism has a minimum, an
optimum and a maximum pH for growth.
What pH do most microorganisms grow best at?
Most microorganisms grow best at pH values around 7.0
Are yeasts and molds more or less acid tolerant than bacteria?
Yeasts and molds are generally more acid tolerant than bacteria and can grow at lower pH values.
What food pH values are not easily spoiled by bacteria?
Foods with pH values below 4.5 are usually not easily spoiled
by bacteria but are more susceptible to spoilage by yeasts
and molds
What affect does extreme pH have on bacteria?
Extreme PH can effect the membranes
* Disrupts the membrane
* Inhibits enzyme activity
What is the optimum pH for acidophiles?
Acidophiles – pH 0-5.5 (growth optimum)
What is the optimum pH for neutrophiles?
pH 5.5 and 8.0
What is the optimum pH for Alkalophiles?
Alkalophiles – pH 8.5-11.5 (extreme alkalophiles pH 10 <)
Whats an example of a microbe which thrives in acidic pH environments (less than 7)?
Dunaliella
acidophila
Whats an environmental example of something with an acidic pH (less than 7)
Gastric contents,
acid thermal
springs
Whats an environmental example of something which thrives in neurtal pH environments (7)?
Beef, Chicken, Milk, Blood, pure water
Whats an example of a microbe which thrives in neutral pH environments?
E.coli, lactobacillus, Staphylococcus
aureus
Whats an example of a microbe which thrives in basic/alkaline pH environments?
Bacillus, Micrococcus, Pseudomonas
Whats an environmental example of something which is alkaline/basic (pH 7-14)?
Bleach, soap
What are aerobic bacteria?
Aerobic - need oxygen for growth as need for chemical pathways etc (superoxide dismutase and catalase protect the microbe by converting toxic oxygen products) – E.coli, Salmonella
What are anaerobic bacteria?
Anaerobic – Do not have the correct proteins to deal with toxic oxygen products and therefore cannot survive in oxygen rich environments - Fusobacterium, Prevotella, and Bacteroides.
How is bacteria cultured in anaerobic conditions?
Using a GasPak Anaerobic system.
How does a GasPak Anaerobic system work?
Hydrogen and carbon dioxide gas generated via GasPak envelope
Palladium catalyst – catalyzes formation of water from Hydrogen and Oxygen (removes oxygen from sealed container)
What do bacteria need to successfully grow?
- Correct nutrients (food)
- Correct temperature
- Right amount of oxygen
- Correct pH
- Space and time (flasks /plates)
Define culture medium.
Culture medium - composed of water, nutrients / growth factors specific to each bacterium and
necessary for their growth.
Define growth factor?
Growth factors - ‘Substances that are needed for growth but cannot be manufactured by the microorganism’.
What are the three main and most common methods of culturing bacteria?
Poured plates, Stab tubes and Streak plates
