microbial growth lecture 2 Flashcards
why is agar a better substitute than gelatin 2
- agar is not destroyed by microbes
2. higher MP melts only at 100 degrees celcius
who produced evidence that bacteria could cause disease?
what bacteria did he inject into healthy mice
Robert Koch
-Bacillus anthracis
def of Koch’s postulates
criteria from providing the relationship between a microorganism and a specific disease
Koch’s postulates consists of 4 stages
- respective microorganism must be present in every sick individual but absent from healthy individuals
- isolate the suspected microorganism and grow into a pure culture
- inoculate healthy host with the isolated microorganism - same disease should occur
- re-isolate microorganism from diseased host
5 factors that influence microbial growth
- nutrients
- temperature
- pH
- oxygen requirements
- osmotic pressure
macronutrients
required in high amounts for cell components and metabolism e.g. carbon, oxygen and phosphate
micronutrients
and another name
trace elements
-required in lower amount for enzyme function and to maintain protein structure
heterotrophs
must obtain their carbon in an organic form e.g carbohydrates and proteins
autotrophs
- use inorganic carbon, CO2 and convert it into organic compounds
- form the base of food chains that support all other life forms
in the presence of oxygen respiration occurs what are the products
CO2 , NADH and FADH2
in the absence of oxygen fermentation takes place, what are the products
CO2 and ethanol
obligate anaerobes
- oxygen=toxic
- cannot grow in oxygen’s presence
- cultured in N2 or CO2
obligate aerobe
-dependent on O2
facultative anaerobes
- do not require oxygen
- but grow better in its presence
aerotolerant
not influenced by presence/absence of oxygen
microaerophiles
require 2%-10% O2
are fungi aerobic/anaerobic?
aerobic
are yeast aerobic/anaerobic? and specifically what kind
facultative anaerobes
water activity Aw
amount of water available to a cell for growth
pure water has the Aw of …
1
hypotonic solution
- low solute concentration and therefore high water potential
- water moves into cell and cell swells and may even burst =lyse
hypertonic solution
- soln has a high solute conc and low water potential
- water moves out of cell, cell shrinks and plasmolysis may occur
plasmolysis
plasma membrane pulls away from cell wall
osmotolerant
organisms that grow over a wide range of Aw
which grows at a lower Aw bacteria or fungi
fungi grow at a lower Aw than bacteria and cause spoilage of dry foods such as bread
osmophiles and an example
- grow only under high osmotic pressures
- e.g. halophiles which prefer high NaCl conc
how are halophiles adapted to a high NaCl conc (3)
1-plasma membranes and cell walls= stabilized by high Na+ ion con
2-accumulate K+ ions in their cytoplasm to balance ionic strength outside of the cell
3-cell walls lack peptidoglycan to allow for more cell wall flexibility
growth media can be divided into to main groups
- chemically defined (synthetic) media
2. complex media
chemically defined (synthetic) media
composed of known ingredients at known concentrations
complex media
- rich in vitamins and other nutrients, of which precise chemical composition of media is undefined
- can vary depending on the supplier
media can be prepared in 3 forms
- liquid
- semi-solid
- solid
what is liquid media used for
fermentation, to measure biomass
microbial growth in liquid media can be detected in 4 ways
- turbidity of liquid media
- pellicle formation where a mass of cells float on the surface of the liquid media
- sediment formation where cells deposit on the bottom of the tube
- slime production that binds cells together
solid media is used for
examination of colony properties, isolation and storage of pure cultures
semi-solid media used for
testing motility and oxygen requirements of organisms
microbial growth
- increase in cell numbers and not size
- its exponential
cell numbers can be expressed using 2
1-CFU in solid media
‘colony forming units’
2-turbidity in liquid media (less accurate)
4 stages of microbial growth in batch systems
- lag
- log/exponential
- stationary
- death
batch system
- closed system with limited nutrients
- follows a growth curve
3 characteristics of lag phase
- no/very little cell division
- cells may be under stress due to a change in environment
- essential enzymes, cofactors and ATP have to be produced before growth can commerce
exponential phase
microbes grow and divide at maximal rates
stationary phase
- growth plateau -level out
4 reasons for stationary phase
Due to:
1-depletion of nutrients
2-lack of oxygen (aerobes)
3-decrease in pH as a result of organic acids produced during growth
4-accumulation of toxic byproducts
death phase due to 2 things
- nutrient depletion
2. build up of toxic waste
death phase
decline in number of viable cells
4 ways to control microbial growth
- temperature
- irradiation
- desiccation
- filtration
4 types of heat treatments to sterilize stuff
- complete sterilization, temp in excess of 121 degrees celsius followed by autoclaving
- pasteurization
- tyndallisation
- extremely low temp to slow/prevent microbial growth = bacteristatic (cannot permanentally sterilize)
autoclaving uses a combination of
-it destroys bacterial spores
steam and pressure
pasteurization
- only reduces the number and/or types of microbes
- relatively short term solution, the remaining microbes will start growing again
3 types of pasteurization techniques include
- LTLT-low temp, long time
- HTST- high temp short time
- UHT-ultra high temp
tyndallisation
- breaks heat sensitive chemical bonds by flowing steam @ 100 degrees celsius for 30 min for 3 consecutive days
- does not destroy dormant spores but any spores that germinate during that time are destroyed
endospore vs spore
endospore=dormant, tough, non-reproductive structure
irradiation 3 characteristics
- permanently damages the nuclei acids of organisms
- bacterial endospores = resistant to irradiatio
- can use
1. UV light-kills cells but low penetrating ability, best to sterilize surfaces
2. ionizing radiation (gamma and X-rays)- high penetrating ability, breaks sugar phosphate backbone of DNA
desiccation
- inducing a hypertonic environment which inhibits microbes but dont completely eliminate them
e. g. biltong
filtration
temp-sensitive substances e.g. vitamins and antibiotics solutions have be sterilized by using a filter with a very small pore size that will retain most microbes
