Week 7 Flashcards
Is bacterial reproduction sexual or asexual?
Asexual
How many stages does binary fission have?
4
By what process do bacteria grow?
Binary fission
What are the 4 stages of binary fission?
- The cell elongates and the DNA is duplicated.
- Cell and plasma membrane begin to divide.
- Septum completes.
- Daughter cells separate
What is the approximate generation time of E.Coli?
20 minutes
What is the generation time for most bacterial species?
1-3 hours
What is the generation time of Mycobacterium Tuberculosis?
24 hours
What are the 4 phases of bacterial growth (as part of a graph)?
Lag
Log
Stationary
Death
What happens in the lag phase of bacterial growth.
There is no overall increase in cells but there is intense metabolic activity.
What happens during the log phase of bacterial growth?
The maximum possible growth rate for that given environment is maintained.
During what phase of bacterial growth should rate of growth be measured?
The exponential log phase.
What happens during the stationary phase of bacterial growth?
There is a balance between cellular division and cellular deaths.
The cells still remain metabolically active.
What are the possible causes of the stationary phase of bacterial growth?
Exhaustion of nutrients, accumulation of waster, harmful changes in pH, oxygen depletion, spore formation.
What device is used for bacterial continuous culture
Chemostat
What is bacterial continuous culture ?
A device called a chemostat is used to maintain bacterial population at a constant density which is similar to bacterial growth in a natural environment.
What are the advantages of using continuous culture to grow bacteria?
Continuous log phase of growth.
Not limited by nutrient availability.
Closed system makes it easy to control conditions for maximum growth.
Define sterilisation
The killing or removal of all living organisms and their viruses
Define disinfection
Elimination of microorganisms from inanimate objects
Define antibiotic
A chemical substance produced by a microorganism that kills or inhibits the growth of another microorganism
What are the features of a good microbial growth control agent?
Inexpensive
Fast acting
Stable during storage
Control all microbial growth whilst being harmless to humans, animals and objects.
What are the substances needed for bacterial growth?
Water Optimum temperature Food source Oxygen Correct pH
What is the overall purpose of food preservation?
To prevent microbial growth on foods to avoid spoilage and increase food shelf life.
How does keeping food in low temperature areas help preservation?
It reduces metabolic activity and enzyme catalysed reactions which microbes carry out.
How does refrigeration alter the effects of microbes on foods?
It reduce enzymic and metabolic activity.
How does freeing alter the effects of microbes on foods?
Decreases water activity, slows microbial activity
What is pasteurisation of a food or drink?
The partial sterilisation of a product to make it safe for consumption.
Describe the relative strengths of pasteurisation and and sterilisation
Pasteurisation is weaker
What type of substances is pasteurisation usually used to preserve?
Heat sensitive liquids
What method is frequently used to preserve heat sensitive liquids?
Pasteurisation
How does pasteurisation prevent food/ liquid spoilage?
It retards the growth of spoilage microorganisms.
What type of food is easiest to can?
Acidic
What is ‘canning’ of food?
Sealed food is heated to kill or inhibit microbial growth.
What type of microorganisms can spoil canned food?
Anaerobes
What are the issues that can occur with canned food?
Anaerobic molecules can spoil the food, releasing gases as they do so. This increases pressure in the can and can often lead to bursting.
What is asepsis in terms of food preparation?
Avoidance of contamination
What methods can be used to remove water from foods?
Lyophiliation
Spray Drying
What methods can be used to reduce water availability of foods?
Adding solutes
Is gamma radiation ionising or not?
Yes
Is U.V. radiation ionising or not?
No
What is water activity ?
The measurement of availability of water that a microorganism can use.
How do you calculate water availability to a microorganism?
(Relative humidity of the product)/ (Relative humidity of pure water)
What water availability can most bacteria not grow below?
0.85
What water availability can most yeast and mould not grow below?
0.65
How can water become unavailable for microorganisms?
If it becomes bound to food.
By what methods can water be removed from foods?
Evaporation
Sublimation
Adding solutes to the food
What are the effects of reduced water activity in microbes?
Reduced metabolism and growth
What is fermentation?
A process used to presence and enhance foods.
What factors can affect the process of fermentation?
Water availability
pH
Presence of fermentative organisms
What is irradiation?
The use of gamma rays to kill organisms within a food
What is the term used to describe the use of gamma rays to kill organisms in food?
Irradiation
What are autoclaves and what do they do?
Sealed chambers which use a high temperature to create a higher temperature than boiling water. This is used to kill microorganisms.
On average, how long do autoclaves take to achieve sterility?
60 minutes
How does ‘dry heat’ kill microorganisms?
Incinerates them
Describe the relative Times taken to kill microorganisms using autoclave and dry heat methods.
Autoclave is quicker
What type of substances is filtration used to remove microbes from?
Liquids that heating would damage
What method can be used to sterilise liquids that would be damaged by heating?
Filtratin
Describe the wavelength used when radiating microbes and why this is used
Short wavelength use to give greater energy and penetrative force
What type of substances are disinfectants used to disinfect?
Non-living
What type of substances are antiseptics used to disinfect?
Living tissues
What are the uses of ‘phenols’ as controllers of microbial growth?
Surgical antiseptics
Used in health care and in labs
What type of microbes can alcohols kill?
Bacteria and fungi but not spores or viruses
How do alcohols kill bacteria and fungi overall?
Protein denaturation or membrane disruption.
Give a use of alcohol as a microbial killer
Used on the skin before injections
How is chlorine halogen used as a microbial killer?
To treat drinking water and swimming pools
How is Hypochlorite halogen used as a microbial killer?
Used for cleaning babies bottles and surfaces
How is iodine halogen used as a microbial killer?
Antiseptic for wounds
How is hydrogen peroxide used as a microbial killer?
Disinfect and sterilise surfaces of objects
How do surfactants have biocidal action?
They assist in the removal of microorganisms by scrubbing.
