Ch. 8 - Controlling Microbial Growth in Vitro Flashcards
Factors that affect microbial growth (6)
- availability of nutrients
- moisture
- temperature
- pH
- osmotic pressure
- barometric pressure
- gaseous atmosphere
Optimum temperature/pH at which an organism functions is largely determined by ____
optimum temp/pH ranges of the enzymes
Thermophiles
microorganisms that grow best at higher temps
Mesophiles
microorganisms that grow best at moderate temps (37degrees)
- most likely the bacteria we see as pathogenic
Why does our body trigger a fever to fight infection?
High temp= low rate microbial growth because they are no longer at their ideal temperature for reproduction
Psychrophiles
Prefer cold temperatures
Psychrotrophs
group of psychrophiles that prefer fridge temperature
Psychroduric organisms
prefer warm temperatures but can endure cold to freezing
Acidophiles
prefer pH 2-5
Alkaliphiles
prefer pH greater than 8.5
DF Osmotic pressure
Pressure exerted on a cell membrane by solutions both inside and outside the cell
DF Osmossis
movement of a solvent through a permeable membrane from low solute concentration to high solute concentration
solvent vs solute
solvent: liquid
solute: the thing that dissolves in it
Hypertonic
concentration external solutes > concentration internal solutes
- water rushes out of cell
- cell shrinkage
Plasmolysis
Cell membrane and cytoplasm shrink away from the cell wall.
Occurs when bacteria with rigid cell walls are placed in hypertonic solution.
Crenation
Eukaryotic cell shrinking without cell wall, leading to weird cell shape
Occurs in hypertonic situations
Hypotonic
concentraion external solutes < concentration internal solutes
- water rushes into cell
- cell swelling/bursting
Plasmoptysis
process of cell bursting and cytoplasm escaping
- happens in hypotonic situations
Isotonic
concentration external solutes = concentration internal solutes
Explain IV fluids in regards to hypertonic/hypotonic concentrations
IV fluids are isotonic, meaning the concentration or solutes in the solution matches the concentration of solutes in your cells.
If IV bags were just water, we would be creating a hypotonic solution
Halophilic
prefer to live in salty environments
Haloduric
Do not prefer salty but could live there
ex: staphylococcus aureus
Piezophiles
microbes that can survive at high atmospheric pressures
> 14.7 PSI
Microaerophiles
prefer reduced O2 (~5%)
Chemically defined media
All ingredients are known
Enriched medium
contains special nutrients that promote growth of fastidious organisms
ex: chocolate agar
Selective medium
contains added inhibitors that discourage the growth of certain organisms while allowed the growth of a desired organism
ex: PEA agar
Differential medium
Permits the differentiation of organisms that grow on that medium.
We see colour changes depending on what kind of bacteria are there. As the bacteria grow, they lyse the cells of medium, leading to a release of colour
ex: MacConkey agar
What type(s) of medium is blood agar?
enriched - allows certain bacteria to grow
differential - certain bacterial will lyse the medium cells leading to a colour change
Aseptic technique
Using practices and procedures to prevent contamination from pathogens
Biologic safety cabinets
- Air flow that prevents any air binding bacteria from getting down to the agar. Minimize contamination and protect lab/person.
Innoculation
Introducing microorganisms into a culture where they can grow and reproduce
Incubation
the maintenance of microbiological cultures at specific temperatures for a given time.
Done using incubator which maintains appropriate atmosphere, temp, and moisture level
3 Types of Incubators
1) CO2 incubator - 5-10% CO2
2) Non CO2 incubator - room air
3) Anaerobic incubator (0% O2)
Spectrophotometer
Determines bacterial growth by measuring the turbidity (transparency) of the medium
Viable Plate Count
Determines number of viable bacteria in liquid sample after making serial dilutions of the liquid and inoculating onto a nutrient agar. After overnight incubation, count the number of colonies
2 Methods for bacterial population count
1) Spectrophotometer
2) Viable plate count
Population growth curve
- How is it determined?
- (Y) vs (X) axis
Determined by growing a pure culture of the organism in a liquid medium at constant temp and collecting samples at fixed intervals
Graph: (Y) # viable organisms ; (X) incubation time
Population growth curve: stages
Lag phase - bacteria adapt to growth conditions . Maturing and not yet able to divide
Log phase - exponential growth
Stationary phase - no growth, just using up resources
Death phase - Once resources are used up, number of cells die
3 Obligate intracellular pathogens
viruses
Rickettsias
Chlamydias
These microbes can only live and multiply within living cells
How do you culture obligate intracellular pathogens?
In embryonated chicken eggs, lab animals, or cell cultures
Which agar is selective for fungi and why?
Sabouraud dextrose agar (SDA)
Selective for fungi because of its low pH , which is fungi like
Sterilization
The complete destruction of all microbes, including cells, spores, and viruses.
Accomplished by dry heat, autoclaving, gas, radiation, chemicals
Disinfection
Destruction/removal of pathogens from nonliving objects by physical or chemical methods
Disinfectant vs antiseptic
disinfectant: chemical substances that eliminate pathogens on inanimate stuff
antiseptic: solutions used to disinfect skin and other living tissues
Microbistatic agent
drug/chemical that inhibits growth and reproduction of microbes
Lyophilization
Process combining dehydration and freezing.
Used to preserve foods, antibiotics, etc.
Sepsis vs Asepsis
Sepsis: presence of pathogens in blood/tissues
Asepsis: absence of pathogens
Antisepsis
prevention of infection
Physical methods to Inhibit Microbial growth
1) Heat
2) Cold
3) Desiccation
4) Radiation
5) Ultrasonic waves
6) Filters
7) Gaseous atmosphere
Thermal death point (TDP)
Lowest temperature that will kill all of the organisms in a standardized pure culture within a specified time
Autoclave
large metal pressure cooker that uses steam under pressure to completely destroy all microbial life.
High pressure = high temperature >100degrees— forces steam into materials being sterilized
How does cold temp affect microbial life?
Most microbials don’t die, but their metabolic activities are slowed
How does desiccation affect microbial life?
Dries them out. Many remain viable, but they cant reproduce
How does radiation affect microbial life?
reduces the number of microorganisms in the air
What type of physical method is used on hospital equipment to inhibit microbial growth?
ultrasonic waves
Chemical disinfection
use of chemical agents to inhibit the growth of pathogens, either temporarily or permanently
Characteristics of an ideal chemical antimicrobial agent (3)
1) nontoxic to human tissue, non corrosive, no allergic reaction
2) Fast acting -kill pathogen before it mutates and becomes resistant
3) Should leave a residual antimicrobial film on surface to prevent further infection
Asthma Cleanliness Hypothesis
Hypothesis: Childhood exposure to germs and certain infections help the immune system develop.
Our immune system is stimulated differently in a clean environment vs a farm etc.
