The number of DNA copies of the bacterium
Physicians are encountering difficulties in treating and managing patients with infectious diseases due to
antibiotic-resistant microorganisms. Determination of bacterial
susceptibility is usually performed using phenotypic methods. Those methods,
although quite specific, consist of lengthy analyses. Therefore, recently, a
rapid assay was suggested.
Bacterial growth kinetics is determined by
enumeration of DNA copies over time. This method is more specific than
bacterial culture and faster.
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- Why The number of DNA
copies of the bacterium can serve as a measure of the bacteria number?
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Streptococcus p obtained from a bacterial culture over time is given in Table 1.
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Table 2 gives the number of DNA copies of
Streptococcus p obtained over time when the bacteria were grown in the
presence of antibiotics (penicillin). |
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Table 3 gives the number of DNA copies of a
Streptococcus p strain which is resistant to antibiotics (penicillin),
obtained when the bacteria were grown in the presence of penicillin, over
time.
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2. Calculate the average mean number of
bacterial DNA copies over time (hours) for the replicated experiments in
Tables 1, 2 and 3. |
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3. Calculate the standard deviation of the
number of bacterial DNA copies over time (hours), for the replicated
experiments in Tables 1, 2 and 3. |
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4. Determine the uniformity of the
representative sample. Note that in this case, we assume that the sample is
uniform if the standard deviation from the mean is less than 10%. |
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5. Write up a summarizing table (Table 4) of the number of
bacterial (Streptococcus p) DNA copies obtained when the bacteria were
grown alone, and when antibiotic-resistant and susceptible strains of the
bacteria were grown in the presence of penicillin, over time (hours). |
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6. Draw a graph to show the kinetics of
bacterial growth and antibiotic (penicillin) susceptibility and resistance
over time (hours). |
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7. Describe the relationship between the
kinetics of bacterial growth and antibiotic susceptibility and resistance
over time (hours). |
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8. Explain how the antibiotic resistance of
the bacteria is shown in the graph that you drew. |
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9. Usually, we can divide the bacterial
growth curve into distinct segments over time. Divide the growth of
Streptococcus p over time. |
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10.If you failed to do so, what should be
done to allow you to divide the growth curve in a precise manner?
(Hint—format the x-axis scale to a
logarithmic one). |
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11. What should the number of DNA copies of
Streptococcus p be after 20 hours of culture?
Find the appropriate equation to calculate
the number of DNA copies of Streptococcus p after 20 hours. |
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12. When the scientists checked the number of
DNA copies of Streptococcus p after 20 hours, the number was significantly
low.
Try to explain this discrepancy. |
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13. Suggest some implementations based on the experiment's conclusions |
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