Lecture 1-3 Flashcards
Agar
-complex polysaccharide from marine red algae
-used in petri dishes
Chemically defined media
Exact chemical composition is known
Complex media
Extracts and digests of yeast, meat, or plants
-composition not known
Streak plate method
used to isolate pure colonies
What is TSA plate
Tryptic Soy Agar
-isolate microbes from surfaces
-not differential
What is differential media
-differentiate microbes based on ability to metabolize specific nutrients
-produce visible colors
-can sometimes be selective
What is selective media
Suppress unwanted microbes and encourage desired ones
What kind of media is MacConkey agar and how does it work
Selective and differential
-Gram (-) bacteria grow, (+) does not grow–>differential (contains bile salts and crystal violet)
-Differentiates between lactose fermenters and non fermenters–>turns red if lactose (+), turns yellow if lactose (-)
What kind of medium is Kings B medium, what is used for and how does it work)
-Enriched differential medium
-anything can grow but differentiates if pseudomonas fluorescens grows b/c it turns blue-green due to pyoverdine
-Has magnesium sulphate
True or false: King’s B is a selective medium?
False
-It is a differential medium that will turn blue-green if it is P.fluorescens
-anything can grow on it
What is pyoverdine?
A type of siderphore that Pseudomonas uses to scavenge iron from environment
What is a siderophore?
Used to sequester iron (Fe3+)
Why does bacteria need iron
Iron is used in the electron transport chain
What are biofilms and why are they important?
Microorganism form communities as a way for microbes to survive–>stay stuck to a surface while environment changes
-share nutrients
-shelter from harmful factors
-from slime/hydrogels
How does biofilm help with resistance?
The biofilms protect the cells, and the cells may not be actively dividing
-antibiotics only work when cells are actively dividing
-exopolysaccharide protects bacteria and antibiotics cannot enter
What are some biofilms in eukaryotes?
-Candidia albicans cause vaginitis, diaper rash, oral thrush
-S. cerevisiae form biofilms on plastic surfaces and soft agar
True or false: P. fluorescens in a shaking environment always forms a biofilm
False
-P. fluorescens in shaking environment will NEVER form a biofilm
-The shaking does not disrupt the biofilm, the reason why it does not form is b/c in shaking oxygen is distributed throughout the tube
-in static oxygen will only be at the top forcing the bacteria to form a biofilm to survive
Where do you expect to see the biofilm for P. fluorescens in static conditions?
Interface between air & medium (top)
-b/c P.fluorescens is strictly aerobe and it needs oxygen so it will go to the top
What dictates the metabolic pathway for bacteria?
Oxygen
Obligate aerobes
Needs oxygen
-cells found at top of tube
-Ex: P.fluorescens
Obligate anaerobes
-Hates oxygen
-found at the bottom of tube
-Ex: Clostridium botulinum
Facultative anaerobe
Prefers. oxygen, but can live without
-Mostly at top of tube with cells throughout the rest
-Ex: Salmonella, E.coli, S. cerevisae
Microaerophiles
-Uses 2-10% oxygen (little amount)
-Found near the top, with a little underneath
-Ex: Helyobacter pylori
Aerotolerant anaerobes
Ignores oxygen, do not use oxygen only live in the presence of oxygen
-Found at top (oxic zone)
-Found in rest tube (anoxic zone)
-Ex: Lactobacillus acidophilus
What kind of oxygen does P.fluorescens need
-Obligate aerobe
-NEEDS oxygen
Why do we use Kings B medium for P. fluorescens
-Does not contain thioglycolate or agar, most bacteria would sink
-Biofilm allows them to float and use oxygen effectively
What do wrinkly cells from biofilm mean
Have mutations from biofilm formation
What is the standard plate count
A serial dilution and spread plate
-used to estimate the number of cells from the original sample
How to calculate the dilution factor?
FINAL VOLUME/INITIAL VOLUME
True or false: the dilution factor is always less than 1
False
-Dilution factor is always more than 1
True or false: DF is the reciprocal of dilution
True
True or false: The dilution is always less than 1
True
How to calculate culture density (CFU/ml)
number of colonies/(dilution factor) x (volume plated in mL)
How many colonies need to be on a plate to be countable?
30-300
What is the difference between a serial dilution and a dilution series?
-A serial dilution has the same dilution factor for ALL tubes
-A dilution series has at least 1 tube that has a DIFFERENT dilution factor
What is quorum sensing?
How microbes communicate
-needs enough bacteria to produce a signal/communicate
What are biofilms associated with?
-Catheters
-Pacemakers
-Aortic valves
