practicals Flashcards
(18 cards)
what are the direct methods used to measure bacterial growth?
flow cytometry, microscopy counts and viable counting
how does flow cytometry measure bacterial growth and what does it show?
detects the individual bacterial particles by labelling them with fluorescent dye and passing them through laser beams and measuring scattered light
shows the size and shape of cells
how does microscopic counts measure bacterial growth?
directly visualising and counting the bacteria on a calibrated slide
how does viable counting measure bacterial growth?
counting the colony forming units on a plate of culture dilution
what are the advantages and disadvantages of flow cytometry?
can distinguish between live and dead cells
can distinguish between specific species
very sensitive
expensive equipment
what are the advantages and disadvantages of microscopic counts?
cheap
time consuming
what are the advantages and disadvantages of viable counting?
can distinguish between specific species
identifies live bacteria
time consuming
what are the indirect methods used to measure bacterial growth?
optical density, dry weight and metabolic activity
how does optical density measure bacterial growth?
measures cell density based on scattered light
how does dry weight measure bacterial growth?
measures the cell weight after freeze-drying
how does metabolic activity measure bacterial growth?
measures the production of specific metabolites
what are the advantages and disadvantages of optical density?
very quick
cheap
can’t distinguish between live and dead cell
only works with high cell density
what are the advantages and disadvantages of dry weight?
time consuming
expensive equipment
what are the advantages and disadvantages of metabolic activity?
can measure the activity of a specific group of bacteria
complicated
what is minimum inhibitory concentration (MIC)?
the lowest concentration of a drug that inhibits the visible growth of a test organism after overnight incubation
what is minimum bactericidal concentration (MBC)?
the lowest concentration of a drug that kills over 99.9% of a test organism after overnight incubation
how do you find the MIC?
use a serial dilution of the drug and inoculate the bacterial culture with it
leave it to incubate overnight and find the lowest concentration without any visible growth
how do you find the MBC?
use a serial dilution of the drug and inoculate it with the bacterial culture
leave it to incubate overnight and then find the lowest concentration where most of the bacteria have been killed
