You are in charge of water quality for your city's water treatment plant. Of the methods at your disposal, which will be the most efficient and cheapest method of determining the number of viable bacteria in the water coming out of your plant?
A. Direct counts using a microscope and a counting chamber.
B. Using a Coulter counter machine.
C. Performing serial dilutions of your samples and doing spread plate counts.
D. Using membrane filtration followed by placing the membrane in a growth medium for colony counts after incubation.
E. Biochemical analysis of secondary metabolites in the water that are given off by bacteria.
You take absorbance readings on a spectrophotometer across a 6-hour culture of E. coli cells growing in tryptic soy broth (TSB). Your absorbance readings clearly indicate a lag phase, a log phase, and a stationary phase.
You come back in and take readings at 8, 10, 12, 14, and 16 hours, but the absorbance number remains the same. Shouldn't it start coming down as the closed batch culture enters death phase? What's the most likely thing that is happening?
A. Clearly, something is wrong with the spectrophotometer and it isn't measuring the correct values. Perhaps something is on the detector, making it register falsely high absorbance numbers.
B. When we establish a growth curve, we should actually plot the log of the number of viable cells vs. time. However, a spectrophotometer can only measure absorbance. Absorbance is NOT the same as the number of viable cells. Many of the cells in the tube are most likely dead, but the machine can't discriminate between a live cell and a dead one. This keeps the absorbance high even into the death phase.
C. It'll happen-E. coli just grow slowly. We haven't gotten to the end of the stationary phase yet. Be patient
D. Perhaps there's a big smudge of something on the tube that is blocking some of the light. This would lead to an elevated reading for every timepoint after the smudge was placed on the tube.
Lister developed his ideas on prevention of infection during medical procedures after studying the work of
A. Koch.
B. Pasteur.
C. Jenner.
D. Fleming.
A physician sends a stool sample to your lab, and wants to know if there are lactose fermenting microbes in the sample. How might you determine if these microbes are present or not from this mixed-microbe specimen?
A. Streak the sample for isolation on Thayer-Martin agar (which contains lactose and particular antibiotics for selectivity).
B. Streak the sample for isolation on a blood agar plate (which contains lactose AND red blood cells that enrich the culture for iron).
C. Streak the sample for isolation on a MacConkey agar plate (which contains lactose and a pH indicator that turns pink when acid byproducts are present).
D. None of the above would work-there's no way to reliably determine this feature from the specimen given.
You are working in a clinical laboratory in a hospital setting. You're handed a throat swab from a patient. You are told specifically that the physician is only interested in the presence and type of Gram positive cells.
Identification isn't the main goal here-just a first step to work towards determining what Gram positive cells might be there.What might you do first to go about working towards this goal?
A. Perform a Gram stain.
B. Streak the sample for isolation on a tryptic soy agar general purpose medium plate.
C. Streak the sample for isolation on a medium that is selective for Gram positive cells while suppressing Gram negative cell growth.
D. Grow the microbes on the swab by inoculating a tryptic soy broth liquid medium tube.
E. Perform an acid-fast stain.
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