A sterile agar plate, I, is streaked with a pure culture of bacteria by means of aseptic techniques. Paper discs treated with the antibiotics Aureomycin (A) and penicillin (P) are placed at opposite sides of the plate, as shown in the diagram above. The plate is examined after a 24-hour incubation period, and a clear ring is discovered around disc A, but not around disc P. Within the clear ring around disc A, a single bacterial colony with physical characteristics like those of the pure culture is observed. A second sterile agar plate, II, is then streaked with this single colony and also incubated with antibiotics.

Which of the following would most likely be observed in plate II after 24 hours?

Question

A sterile agar plate, I, is streaked with a pure culture of bacteria by means of aseptic techniques. Paper discs treated with the antibiotics Aureomycin (A) and penicillin (P) are placed at opposite sides of the plate, as shown in the diagram above. The plate is examined after a 24-hour incubation period, and a clear ring is discovered around disc A, but not around disc P. Within the clear ring around disc A, a single bacterial colony with physical characteristics like those of the pure culture is observed. A second sterile agar plate, II, is then streaked with this single colony and also incubated with antibiotics.

Which of the following would most likely be observed in plate II after 24 hours?

BlackTom AI · Accepted Answer

To tackle this question, let’s break down what the observations on plate I imply and how they translate to plate II.
Option 1: There would be a clear ring around both disc A and disc P.
- A clear ring (zone of inhibition) around a disc indicates the bacteria are sensitive to that antibiotic. In plate I, a clear ring is seen only around disc A, not around disc P. This means the bacteria are susceptible to Aureomycin but not to penicillin. Therefore, predicting a clear ring around both discs on plate II would contradict the observed susceptibility pattern and the lineage of the colony used in plate II. This option is inconsistent with plate I data.
Option 2: There would not be a clear ring around either disc A or disc P.
- The colony used to inoculate plate II originates from a spot inside the Aureomycin inhibition zone on plate I, suggesting a possible Aureomycin-resistant variant (it survived within the A zone). If this colony is then tested again on plate II, it could be resistant to Aureomycin. Additionally, the initial plate showed no inhibition by penicillin, suggesting the isolate is also resistant to penicillin. Thus, no zones of inhibition around either disc on plate II would be consistent with a double-drug resistant phenotype and matches the inference from plate I to plate II. This option aligns with the described sequence of events.
Option 3: A clear ring larger than that around disc A in plate I would appear around disc P only.
- A larger inhibition zone around P than A would imply that the colony is more susceptible to penicillin than to Aureomycin, contradicting its origin from the Aureomycin-inhibition zone and the lack of a P zone on plate I. It also conflicts with the reasoning that the plate II colony could be Aureomycin resistant. This option is inconsistent with the observed data and the probable resistance profile.
Option 4: A clear ring smaller than that around disc A in plate I would appear around disc P only.
- A smaller P zone than A would suggest partial susceptibility to penicillin, yet plate I showed no ring around P at all, indicating strong resistance to penicillin in the original culture. Expecting a smaller but present P zone on plate II would not fit the initial lack of inhibition by P. This option misreads the plate I result and the lineage of the colony used for plate II.
Option 5: A clear ring larger than that around disc A in plate I would appear around disc A only.
- If plate II showed a larger A-zone but not a P-zone, that would imply increased Aureomycin sensitivity after passaging, which contradicts the premise that the colony came from within the Aureomycin inhibition zone and is likely resistant to Aureomycin. Moreover, the question’s setup expects the plate II result to reflect the resistance characteristics of the colony, not an increased susceptibility. This option is inconsistent with the expected behavior of a colony originating from within an inhibition zone of A.
In summary, considering that the plate I observation places the isolated colony inside Aureomycin’s inhibition zone (suggesting a resistant subpopulation) and absent P inhibition (penicillin resistance), the most coherent outcome on plate II is the absence of a clear zone around both discs A and P. This aligns with a resistant phenotype to both antibiotics and follows logically from the described experimental sequence.

APBIO142-030 with labs Unit 6 Test

View Explanation

Log in for full answers

Similar Questions

One of the major reasons for the increase in infectious diseases is antibiotic-resistant bacteria.

Question at position 57 Which is NOT a mechanism of bacteria antibiotic resistance?Overexpression of target proteinEnzymatic inactivation or modificationDecreased uptakeProtein misfoldingClear my selection

Question at position 38 Which of the following is FALSE regarding antibiotic resistance?It is naturally occurringIt is found in untouched habitatsIt is ancientIt is a new emerging trait in bacteriaClear my selection

Question at position 34 If the developed world eliminated agricultural antibiotic use…worldwide antibiotic resistance would disappearthere would be no effect on agricultureresistance would still be an issue due to misuse in the developing worldall of the aboveClear my selection

Question at position 5 Antibiotic resistant bacteria have been found in organic, antibiotic free farm animal products.FalseTrueClear my selection

More Practical Tools for Students Powered by AI Study Helper

Homework AI Solver

Stylized AI Paper Writer

Plagiarism Checker Assistant

Citation AI Academic Writing Tool

In-Class Translation Assistant

AI Note Generator

AI Quiz Answers

Past Exam Questions from University Test Bank

Smart Practice Assistant

Adaptive Practice

Making Your Study Simpler