Microbiology Lecture 9: Bacterial Growth and Measurement Techniques

Which of the following equations would be used to solve this problem? (You may need a calculator for this.)

"How many bacteria would you need to start with in order to have as many cells as the Earth's population (6 billion) within 12 hours? The bacterium divides in 30 minutes."

(6 X 10 9 ) = x e (1.39)(12)

3 multiple choice options

A pharmaceutical technician wished to produce large quantities of a bacterial secondary metabolite from a chemolithoheterotroph. She grew the organism in a chemostat with glucose, H2S and oxygen, plus trace elements and growth factors. But she got very low yields of the secondary metabolite. What was her mistake?

she should not have used a chemostat

3 multiple choice options

Cells in a biofilm are very tightly adherent to one another, have variable metabolic activity, and many are dead. What technique would be best to enumerate (count) the cells in a biofilm?

most probably number method

3 multiple choice options

More than 99% of the organisms present in a soil sample do not grow in laboratory media. What would be the most appropriate way to count the organisms present in a soil sample?

Petroff-Hausser chamber

3 multiple choice options

One major difference between batch culture and continuous culture is that _____.

continuous culture allows the researcher to change the bacterial growth rate

3 multiple choice options

The Most Probable Number (MPN) method _____.

requires multiple culture tubes, but no petri dishes

3 multiple choice options

A new bacterial enumeration method has been developed that moves bacteria physically from one chamber of a microchip to another with a micromanipulator (sort of like an atomic force microscope probe tip). This would be an example of _____.

a direct cell count

3 multiple choice options

Compare the two cultures represented by the growth curves at right. Which of the following conclusions can you make?

Culture B has the higher growth rate

3 multiple choice options

One advantage of growing cells in continuous culture is that _____.

you can make the cells grow as fast or as slowly as you want

3 multiple choice options

Which of the following methods would give the lowest count for a population of bacteria in stationary phase?

Counting colonies on a pour plate

3 multiple choice options

At the right is a bacterial growth curve. What can you conclude about the culture from which the growth curve was measured?

it did not have to adapt to new growth conditions

3 multiple choice options

You have a bacterial culture with high turbidity. Which of the following would NOT be a reasonable way to quantify the number of bacteria in this sample?

membrane filtration and plating the filter

3 multiple choice options

Which of the following methods of enumerating bacterial growth could be most easily adapted to counting only motile bacterial cells in a culture?

Luciferase reaction

3 multiple choice options

Which of the following would typically be done in a chemostat?

Measuring the growth rate, μ, under a variety of nutrient concentrations

3 multiple choice options

You are using a fluorescence microscope and an antibody-based stain to examine a mixed culture from a patient's blood for the titer of Treponema pallidum, the bacterium that causes syphilis. What would be the best method to make this titer determination?

Petroff-Hausser chamber

3 multiple choice options

Which equation would you use to solve the following problem: You inoculate a single cell with a doubling time of 30 minutes into 50 ml of culture medium and allow it to grow for 7 days. How many cells will be in the culture after 7 days.

Binary fission will not continue for 7 days, so this cannot be solved with the growth equation

3 multiple choice options

The bacterium Streptomyces does not undergo binary fission, but rather each cell elongates and then divides to become from 6 to 10 identical daughter cells. What would be the best way to enumerate the cells in this culture?

Viable Cell Count

3 multiple choice options

Which equation could be used to solve the following problem? A sample of milk has been pasteurized (bacterial count reduced by 5 logs). If the bacteria are growing at the rate of 0.1 per hour, how long will it take until there are as many bacteria in the milk as there were before the pasteurization?

ln(100,000) = (0.1)(t)

3 multiple choice options

Why would a scientist want to grow a bacterial culture in a chemostat?

So she can adjust the bacterial growth rate

3 multiple choice options

Based on what you know about how the following methods for bacterial growth enumeration work, you should be able to classify one of them as a direct method. Which one?

Measurement of bacterial turbidity with a spectrophotometer

3 multiple choice options

In the United States, swimming beaches are periodically tested for bacterial counts. In Indiana, a beach is closed if the bacterial titer exceeds 125 bacteria per 100 mL. Which of the following would be the best way to determine this titer?

membrane filtration and plating

3 multiple choice options

Which of the following is NOT an example of a direct cell count?

Detecting acid production in the well of a biochip

3 multiple choice options

Salmonella is one of the important bacteria responsible for causing human diarrhea. It generally takes a million to ten million cells of Salmonella to make a person sick. You're running a medical clinic, and a patient comes to you with diarrhea. You want to count the titer of Salmonella in the fecal sample accurately, but as quickly as possible. Which of the following would be the best way to do it?

Dilute the fecal sample and plate it on selective media

3 multiple choice options

You are measuring turbidity as a surrogate for cell number to make a growth curve. What will happen during the death / decline phase?

turbidity will remain the same, since dead cells still reflect light

3 multiple choice options

Secondary metabolites, such as antibiotics, are produced most effectively _____.

by cells in crowded growth conditions

3 multiple choice options

You suspect a patient has a blood infection caused by a bacterium, and you need to get a titer of bacteria from the patient's blood. How would you do that most effectively?

Use a Petroff-Hausser chamber to estimate the titer

3 multiple choice options

You have developed a new way to enumerate the bacteria in a culture. It involves covalently adding a fluorescent label to peptidoglycan monomers so that newly synthesized peptidoglycan becomes fluorescent. Then a special device counts only fluorescent cells. This method _____.

is a type of viable cell count

3 multiple choice options

The luciferase reaction is not routinely used to obtain an accurate bacterial titer. Why not?

The amount of ATP produced per cell is not constant

3 multiple choice options