4. Explain how you could use pour plates to calculate the number of bacteria in
ID: 272265 • Letter: 4
Question
4. Explain how you could use pour plates to calculate the number of bacteria in the original liquid culture. 5. Classify each of the media used according to its functional type (i.e. defined, undefined, selective, differential). a. MSA: b. Blood Agar: c. TSA: d. M9 minimal media: 6. How does MSA allow Staphylococci to grow and inhibits the growth of other microbes, and how do pathogenic forms of Staphylococci differ from non-pathogenic forms when grown on MSA? Blood agar is used to determine if a species has the ability to do what? What does a positive result for this ability look like on blood agar? 7. Why might a microbiologist grow a bacterial species on a medium that contains the minimal nutrients necessary for its growth, such as M9 minimal media? 8. 9. How can you improve your aseptic technique?Explanation / Answer
Answer=4] pour plate method is used to calculate the number of colonies in the original liquid samples:
In this method a fixed amount of inoculum generally 1 ml from a broth or sample is placed in the center of sterile petri dish.molten cooled agar then poured into that dish& mix well.
After solidification of the agar,the plate is inverted at 37 degree for 24-48 hours.
each colony is carefully counted using colony counter.
Colony forming unit (CFU) is a measure of viable bacterial cells.In direct microscope counts (cell counting using haemocytometer) where all cells,dead and living ,are counted ,but cfu measures only viable cells.
the results are given as CFU/ml for liquids.
the number of bacteria per mililiter of sample by dividing the number of colonies by the dilution factor.
The CFU/ml can be calculated using formula ,
cfu/ml = (no.of colonies X dilution factor) /volume of culture plate.
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