Exam 4: Dynamics of Microbial Growth

A urine sample with more than 100,000 organisms is considered indicative of infection. A urine sample containing 5,000 bacteria, with a generation time of 30 minutes, sits for 3 hours before finally being assayed. How many bacteria will then be present within the sample?

Which of the statements about biofilms is True? 

One would expect most strict anaerobic organisms to have superoxide dismutase.

High concentrations of salt and sugar in foods

Peptone

Prokaryotes are the only organisms able to use atmospheric nitrogen as a nitrogen source.

A single bacterial cell may multiply to form a visible colony.

Mr. Jones comes to your clinic complaining of genital discharge. He admits that he recently had unprotected sex with an old friend with whom he reconnected after a school reunion. You suspect that he may have gonorrhea. You take a sample of the discharge and send it to the hospital lab for analysis. -The causative organism of gonorrhea is Neisseria gonorrhoeae, a fastidious, Gram-negative diplococcus. What does fastidious mean in this context?

Freezing is an effective means of destroying bacteria.

Which of the following is (are) obligate aerobes?

In nature, bacteria

You are culturing a new bacterium in the laboratory. You cannot find any glucose it the lab when you are making growth medium, so you decide to use honey instead. You add twice as much honey than is called for in the medium recipe, because you want to give the organism the best opportunity or growth. To your surprise, the organism does not grow on your modified medium. Select the most likely explanation.

A pure culture in exponential growth phase has a bacterial concentration of 6.4 × 10⁸ cells/ml. If the bacterium has a generation time of 1 h, how long ago was the cell concentration 8.0 × 10⁷ cells/ml?

The enzymes that deal with toxic oxygen-containing molecules is/are

Mrs. Thomas comes to the emergency department where you work, complaining of nausea and vomiting, bloody diarrhea, abdominal discomfort and fever. She tells you that she went out to a picnic the previous day, where barbecued chicken was served. Mrs. Thomas is a vegan, so she ate only salad. You think that she likely has salmonellosis, caused by the bacterium Salmonella enterica. However, the presence of blood in her stool causes you concern, and you want to rule out the possibility that patient has shigellosis, caused by Shigella bacterial species. -You take a stool sample from Mrs. Thomas, and send it to the lab for analysis. You tell her that the technicians will do a variety of tests to confirm the identity of the organism causing her illness. The first thing that will be done is to inoculate some of her stool sample onto a medium called hektoen enteric (HE) agar. On this medium, Shigella species produce blue-green colonies, while Salmonella produces blue-green colonies with a black center, and most Gram-positive bacteria do not grow at all. You explain to Mrs. Thomas that this type of medium is called a(n) ________ medium.

The colonies of interest in this case are the blue-green presumptive Shigella colonies. However, growth on hektoen enteric agar is not sufficient for definitive identification. Further tests are needed. First, the lab technicians need to prepare larger numbers of Shigella from your patient's stool sample, and then they need to ensure that they are culturing a single species. The methods used to do this are ________, followed by ________. 

You are a microbiologist working for a pharmaceutical company and discover a new secreted metabolite that can serve as a medication. Your company asks you to oversee the production of the metabolite. Which of the following does NOT need to be considered if you need to grow 5,000 liter cultures of bacteria for the purpose of harvesting the metabolite they secrete?

Generally the proteins of thermophiles

Small organic molecules that must be provided to bacteria in order for them to grow are called

You are determining the number of colony forming units (CFUs) for Susan, who has a urinary tract infection (UTI). You added 1 mL of Susan's urine sample to 99 mL of diluent, and spread 0.1 mL of that dilution on a culture medium. After appropriate incubation, you count 143 colonies on the plate. What was the concentration of bacteria in the original urine sample?