Passage II

Samples of Species C bacteria must often be transported from the areas in which they are collected. During transport, the samples are typically packed in ice to keep them alive. However, ice is not always available where the samples are collected.

Scientists studied how lyophilization (a freeze-drying process that doesn't require ice) followed by incubation affects the survival of 2 strains (Strain E and Strain V2) of species C bacteria.

Experiment 1

The scientists placed a 100 uL (1 μL=10-3 mL) sample of a nutrient medium containing 4 × 106 Strain E elementary bodies into each of 8 sterile test tubes. An elementary body is the infective form of Species C. The sample in each of the tubes was then lyophilized, and each tube was sealed. Two of the tubes were incubated at 4°C, 2 were incubated at 20°C, 2 were incubated. at 30°C, and 2 were incubated at 37°C.

One week after the start of incubation, the percent survival (the percent of the elementary bodies that survived) was determined for the sample in 1 of the 2 tubes at each temperature. Then, 1 month after the start of incubation, the percent survival was determined for the sample in the remaining tube at each temperature. The results are shown in Table 1.

Experiment 2

The scientists repeated Experiment 1, except with Strain V2 instead of Strain E. The results are shown in Table 2.

11. One week after the start of incubation, which of the 4 samples of Strain V2 elementary bodies would have been least likely to infect another organism that came into contact with the samples?

Answer and Explanation

Your Answer is

Correct Answer is D

Explanation

least likely infect another organism means that the bacteria has the least number and therefore the least infectivity. See Table 2, at 37°C, the survival rate of Strain V2 is 0%, so it is the least likely to infect other organisms.