Lecture 2 Flashcards
What are the 2 types of media and describe them
Defined and Complex. defined is super accurately measured and called chemically pure. complex uses complex sources of nutrients but is actually the more simple culture media to make, and is not classified as chemically pure
What are the 5 types of specialised complex media
Transport media, enriched media, enrichment media, selective media and differential media
Describe transport media
Lacks growth factors, carbon and nitrogen. Liquid broth. Contains only buffers and salts. Prevents growth of the culture, purpose is too maintain in its current state.
Describe enriched media
“generally encouraging”. Liquid or solid. Contains general nutrients supplements such as yeast extract or serum.
Good for fussy microbes that rely on supplied amino acids and growth factors
Describe enrichment media
“specifically encouraging”. Liquid. Encourages the growth of one specific type of microbe and gives it a competitive edge to allow it to become the dominant species. therefore drawing it out for study better. Holds the microbes not of interest in the lag phase.
Describe selective media
“specifically inhibiting” Solid. Encourages the growth of some microbes but specifically inhibits growth of others. Composed of general nutrients for growth and one specific chemical that will inhibit most microbes. Eg. Mannitol salt agar with salt- inhibits all but staphylococci. Hektoen with bile salts- inhibits all gram-positive and some non-enteric gram-negative
Describe differential media
“visually distinguishable” solid. contains indicators to have a visual difference in the agar depending on the organism growing. Has carbohydrates that are fermented into acids, to see this in the agar REQUIRES you have a pH indicator. These parts are differentials so you can see the difference.
Give an example of differential media
Mannitol salt agar is both selective and differential. The mannitol is the carbs and one of the differential elements, the mannitol gets fermented into an acid from the microbe of interest. The phenol red(pH indicator) differential allows for us to see this as the change in pH towards acidic will change agar from pink to yellow
Describe blood agar
Both enriched and differential media. The blood creates haemolysins which are enzymes that act on animal cytoplasmic membranes. During growth the haemolysins lyse the red blood cells creating zones of haemolysis.
What are the 3 types of haemolysis. Describe differences
Alpha, beta and gamma. Alpha is areas of partial lysis, leaving green discolouration. Beta is complete lysis leaving a clear zone(indicating pathogen). Gamma is non-haemolytic meaning it can’t break down the red blood cells
Name the stages in the bacterial growth curve observed in ideal conditions
Lag phase, exponential phase, death phase and long term stationary stage
What is the lag phase
The time spent building up precursors of growth to increase growth. The length depends on how much the microbe already has
What is the equation to calculate the number of cells in a culture after a specific time period
initial number x 2^n where n is the number of generations.
if you dont know number of generations find it by ‘total time elapsed in mins/mean generation time in mins’
What are primary metabolites and when are they produced.
They are products essential for growth of the microbe such as nucleotides and amino acids. They are produced during the “primary” growth phase/logarithmic phase
What are secondary metabolites and when are they produced.
They are products non essential for growth such as antibiotics. Secondary metabolites are produced in the Stationary phase. The 2 s’s
What are the 2 ways of measuring microbial growth and the 3 methods involved
Direct and viable. However direct includes the count of dead cells as we can’t tell the difference and viable takes a long incubation time but CAN tell the difference.
The 3 methods are Microscopic observation, Turbidity (both direct) and Plate count (viable)
